% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %
%                                                                         %
% The Project Gutenberg EBook of Matter, Ether, and Motion, Rev. ed., enl., by 
% Amos Emerson Dolbear                                                    %
%                                                                         %
% This eBook is for the use of anyone anywhere at no cost and with        %
% almost no restrictions whatsoever.  You may copy it, give it away or    %
% re-use it under the terms of the Project Gutenberg License included     %
% with this eBook or online at www.gutenberg.org                          %
%                                                                         %
%                                                                         %
% Title: Matter, Ether, and Motion, Rev. ed., enl.                        %
%        The Factors and Relations of Physical Science                    %
%                                                                         %
% Author: Amos Emerson Dolbear                                            %
%                                                                         %
% Release Date: February 27, 2010 [EBook #31428]                          %
% Most recently updated: June 11, 2021                         %
%                                                                         %
% Language: English                                                       %
%                                                                         %
% Character set encoding: UTF-8                                           %
%                                                                         %
% *** START OF THIS PROJECT GUTENBERG EBOOK MATTER, ETHER, AND MOTION *** %
%                                                                         %
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\begin{PGtext}
The Project Gutenberg EBook of Matter, Ether, and Motion, Rev. ed., enl., by 
Amos Emerson Dolbear

This eBook is for the use of anyone anywhere at no cost and with
almost no restrictions whatsoever.  You may copy it, give it away or
re-use it under the terms of the Project Gutenberg License included
with this eBook or online at www.gutenberg.org


Title: Matter, Ether, and Motion, Rev. ed., enl.
       The Factors and Relations of Physical Science

Author: Amos Emerson Dolbear

Release Date: February 27, 2010 [EBook #31428]
Most recently updated: June 11, 2021

Language: English

Character set encoding: UTF-8     

*** START OF THIS PROJECT GUTENBERG EBOOK MATTER, ETHER, AND MOTION ***
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Produced by Andrew D. Hwang, Peter Vachuska, Chuck Greif
and the Online Distributed Proofreading Team at
http://www.pgdp.net
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%%%%%%%%%%%%%%%%%%%%%%%%%%% FRONT MATTER %%%%%%%%%%%%%%%%%%%%%%%%%%

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\textit{\footnotesize MATTER, ETHER AND MOTION}
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The Factors and Relations of Physical Science \\
Enlarged Edition\quad Cloth\quad Illustrated\quad  \$2.00
\end{minipage}

\medskip
\textit{\footnotesize THE TELEPHONE}
\smallskip

\hspace*{\QUAD}
\begin{minipage}{\linewidth-2\QUAD}
\scriptsize
With directions for making a Speaking Telephone \\
Illustrated\quad 50~cents
\end{minipage}

\medskip
\textit{\footnotesize THE ART OF PROJECTING}
\smallskip

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\begin{minipage}{\linewidth-2\QUAD}
\scriptsize
A Manual of Experimentation in Physics, Chemistry,
and Natural History, with the Porte Lumière
and Magic Lantern \\
New Edition\quad Revised\quad Illustrated\quad \$2.00
\end{minipage}

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\textgoth{\footnotesize Lee and Shepard Publishers Boston}
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{\LARGE \scshape Matter, Ether, and Motion} \\[\Titleskip{4}]
{\itshape THE FACTORS AND RELATIONS \\[\Titleskip{1}]
OF\\[\Titleskip{1}]
PHYSICAL SCIENCE}\\[\Titleskip{4}]
{\scriptsize\upshape BY} \\[\Titleskip{1}]
{\scshape A.~E. DOLBEAR Ph.D.}
\medskip

\tiny\upshape PROFESSOR OF PHYSICS TUFTS COLLEGE \\
AUTHOR OF ``THE TELEPHONE'' ``THE ART OF PROJECTING'' ETC.

\vspace*{4\TmpLen}
{\scriptsize\itshape REVISED EDITION, ENLARGED}
\vspace*{4\TmpLen}

\small B\,O\,S\,T\,O\,N %[** PP: One-off gesperrt]

LEE\quad AND\quad SHEPARD\quad PUBLISHERS
\smallskip

\scriptsize 10 MILK STREET

\small 1894
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\null\vfill
\scshape Copyright, 1892, 1894, by Lee and Shepard \\[\Titleskip{1}]
\itshape All Rights Reserved \\[\Titleskip{1}]
\scshape Matter, Ether, and Motion
\vfill
C.~J. Peters \& Son, \\
Type-Setters and Electrotypers, \\
145 High Street, Boston.
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\Preface{PREFACE TO THE SECOND EDITION}
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\First{The} issue of a new edition of this book gives me an
opportunity to make some needed corrections, and enlarge
it by the addition of three new chapters, which
I hope will make it more useful to such as have a taste
for fundamental physical problems. The first of these,
Properties of Matter as Modes of Motion, presents
the evidence that all the characteristic properties of
matter are due to energy embodied in various forms
of motion. The second, on The Implications of
Physical Phenomena, points out what assumptions
are made in explaining phenomena. It is the substance
of a series of articles published in the \textit{Psychical
Review} in 1892 and~1893. The third, on The Relations
between Physical and Psychical Phenomena,
was read as a paper before the Psychical Congress at
the World's Fair in August,~1893.

Judging from some of the comments made about my
statements as to Modern Geometry on \Pageref{page}{57}, and
as to Vital Force, \Pageref{p.}{279}, I have thought it would be
useful to some to see corroboratory statements; and I
have therefore added, in an appendix, a few pages of
\DPPageSep{005.png}{iv}%
quotations from some of the most eminent mathematicians
and biologists on these subjects, and from them
one may judge whether or not my statements are
correct.

As the work is a treatise on Physics, there is no
special reason for going beyond it; but if this presentation
of the subject is any approach to the truth, there
is an important conclusion to be drawn from it. If the
ether be the homogeneous and uniform medium it is
believed with reason to be, then, in the absence of
what we call matter, no physical change which we call
a phenomenon could possibly arise in it; for every such
phenomenon is a product, and in the absence of one of
the essential factors, viz., matter, it could not be. If
matter itself be a form of motion of the ether, the ether
must have existed prior to matter; also, if the atom be a
form of energy, then must energy have existed before
matter existed. Hence there must have been some
other agency radically different from any physical
energy we know, and independent of everything we
know, which was capable of producing orderly physical
phenomena, by acting upon the ether; for a homogeneous
medium could not originate it. Some philosophers
call this antecedent power The Unknowable; others call
it God. If energy \emph{as we know it} implies antecedent
energy as we do not know it, so, likewise, mind as we
know it implies antecedent mind under totally different
conditions from those in which we find it embodied.

In whatever direction one pursues physical science,
\DPPageSep{006.png}{v}%
he is at last confronted with a physical phenomenon
with a superphysical antecedent where all physical
methods of investigation are impotent. Such considerations
raise the theistic hypothesis of creation to the
rank of such physical theories as the nebula theory
of the origin of the solar system, and the undulatory
theory of light.
\DPPageSep{007.png}{unnumbered}% vi
% [Blank Page]


\Preface{PREFACE}
\DPPageSep{008.png}{vii}%

\First{Within} the past fifty years the advance in physical
knowledge has not only been rapid, but it has been
well-nigh revolutionary. Not that knowledge that was
felt to be well grounded before has been set aside,---for
it has not been,---but the fundamental principles
of natural philosophy that were applied by Sir Isaac
Newton and others to masses of visible magnitude
have been applied to molecules; and it has thus been
discovered that all kinds of phenomena are subject to
the same mechanical laws. It was thought before that
physics embraced several distinct provinces of knowledge
which were not necessarily related to each other,
such as mechanics, heat, electricity, etc. Such terms
as imponderable matter, latent heat, electric fluid,
forces of nature, and others in common use in text-books
and elsewhere, served to maintain the distinctions;
and even to-day some of these obsolete physical
agencies are to be met in books and places where one
would hope not to find them. As all physical phenomena
are reducible to the principles of mechanics, atoms
and molecules are subject to them as much as masses
\DPPageSep{009.png}{viii}%
of visible magnitude; and it has become apparent that
however different one phenomenon is from another, the
factors of both are the same,---matter, ether, and
motion; so that all the so-called forces of nature,
considered as objective things controlling phenomena,
are seen to have no existence; that all phenomena are
reducible to nothing more mysterious than a push or
a pull.

Some say that science is simply classified knowledge.
To the author it is more than that, it is a consistent
body of knowledge; and a true explanation of any
phenomenon cannot be inconsistent with the best
established body of knowledge we have. If physical
factors are fundamental, then theorizers must square
their theories to them.

The text-books have not kept pace with the advance
of knowledge; and there is a large body of persons
desirous of knowing more of natural philosophy, and
especially of its trend, who have neither time nor
opportunity to read and digest monographs on a thousand
topics. To meet the wants of such, this book has
been written. It undertakes to present in a systematic
way the mechanical principles that underlie the phenomena
in each of the different departments of the
science, in a readable form, and in an untechnical
manner. The aim has been to simplify and reduce
to mechanical conceptions wherever it was possible
to do so.

One may often hear the question asked, What is
\DPPageSep{010.png}{ix}%
electricity? but a similar question as to the nature of
heat or light or chemism is just as pertinent, although
there chances now to be less popular interest in these
than in the former; not, however, because they are in
themselves better understood, or less interesting.

It is hoped that some of those whose interests lie
along such special lines as chemistry, electricity, and
even biology, will find something helpful in the chapters
dealing with those subjects.

In covering so much ground in so small a treatise, it
was necessary to select such facts as give prominence
to fundamental principles. Doubtless others might
have selected different materials, even with the same
end in view, for otherwise competent persons are
generally more familiar with certain details of a given
science than with others; and I have used what was
closest at hand.

Aside from the topics usually treated upon in a book
of physics, the reader will find a chapter on Physical
Fields, which is unique, as it extends the principle of
sympathetic action---recognized in acoustics---to the
whole range of phenomena, including living things.

The chapter on Life, in a treatise on physics, must
justify itself; while the one on Machines points out
their functions in a more complete way than has been
done before.

Lastly, however large the physical universe may be,
and however exact such relations as we have established
may be, it is daily becoming more certain that
\DPPageSep{011.png}{x}%
even in the physical universe we have to do with a
factor,---the ether,---the properties of which we vainly
strive to interpret in terms of matter, the undiscovered
properties of which ought to warn every one against
the danger of strongly asserting what is possible and
what impossible in the nature of things. With the
electro-magnetic theory of light now just established,
and the vortex ring theory of matter still \textit{sub~judice},
but with daily increasing evidence in its favor, one may
now be sure that matter itself is more wonderful than
any philosopher ever thought. Its possibilities may
have been vastly underrated.

In the book called ``The Unseen Universe,'' it is
pointed out that possibly the ether may be the medium
through which mind and matter re-act. What fifteen
years ago was deemed \emph{possible}, is to-day deemed \emph{probable},
and to-morrow may be demonstrated; and a perusal
of that book is recommended to persons who are
interested in questions of that kind.
\DPPageSep{012.png}{unnumbered}%
% table of contents

\pagestyle{empty}
\tableofcontents
\phantomsection
\pdfbookmark[0]{Contents}{Contents}%


\iffalse

CONTENTS

CHAPTER   PAGE

I. MATTER AND ITS PROPERTIES    1

II. THE ETHER   26

III. MOTION   44

IV. ENERGY   59

V. GRAVITATION   83

VI. HEAT   99

VII. ETHER WAVES   134

VIII. ELECTRICITY   173

IX. CHEMISM   238

X.  SOUND   256

XI. LIFE  277

XII. PHYSICAL FIELDS   298

XIII. ON MACHINES.--MECHANISM   312

XIV. PROPERTIES OF MATTER AS MODES OF MOTION  331

XV. IMPLICATIONS OF PHYSICAL PHENOMENA    354

XVI. RELATIONS OF PHYSICAL AND PSYCHICAL PHENOMENA  384

APPENDIX  397

INDEX   403

\fi

%\DPPageSep{013.png}{1}%

\mainmatter
\pagestyle{fancy}
\phantomsection
\pdfbookmark[-1]{Main Matter}{Main Matter}

% MATTER, ETHER, AND MOTION


\Chapter{I}{Matter and Its Properties}{1}

\First{All} kinds of phenomena that we can become conscious
of through any of our senses are traceable
directly or indirectly to what we call matter. The
sense of feeling implies contact with a body of some
kind; the sense of hearing depends upon movements
of the air, which is a body of matter having certain
properties; and the sense of sight, also due to vibratory
motion, implies that matter exists, however distant,
which has given rise to the vibratory motions that are
perceived as light. So of taste and smell, actual contact
of material particles endowed with particular
properties are the conditions for exciting these sense
perceptions. Some philosophers have added a sixth
sense to the five senses we have recognized for so long
a time---the sense of weight, as distinguished from the
sense of touch; and still others have thought to distinguish
a sense of temperature---relative perceptions of
heat and cold, from the sense of touch; and if these
truly represent distinct senses, they illustrate still
further the truth that it is through the reactions of
\DPPageSep{014.png}{2}%
matter upon the nervous organizations of living things
that all of our knowledge of things about us and of
the universe as a whole is obtained.

It might seem to one as if our knowledge of matter
should be tolerably good, accurate, and complete, seeing
that it is thrust upon us everywhere, and affects us
for good or evil continuously from the dawn of sensation
till death; yet it may truly be said that the knowledge
of matter, its properties, and the wonderful complexity
of phenomena that are due to them, which we
possess to-day was wholly unknown to all mankind
until the time of Sir~Isaac Newton, whose discovery
of the law of gravitation was the first discovery of
a universal property of matter; and by far the larger
part of the knowledge we have, has been acquired in
this century and mostly within the last half of it. The
mass of mankind is, as it always has been, without
any knowledge at all and without any desire for it.
Whatever we have is due to the work of a small number
of persons in Western Europe and America. Probably
the large majority of mankind are quite unable
to understand phenomena and their significance, yet
among the brighter and more competent individuals in
every country there is an apathy and indifference to the
subject, due, of course, to the estimate they have of its
degree of importance; and this estimate is in a good
measure due to the philosophy of things in general
held by the individual thinkers.

When Mr.\ Emerson was told by a Millenarian that
the world was coming to an end the next day, he
declared that he could get along without it, and so it
\DPPageSep{015.png}{3}%
probably has seemed to the majority of philosophers
that the material world was a condition of things to be
endured, rather than to be understood and utilized:
that they were in it but were not a part of it.

Knowledge has, however, increased, and the wise
ones are growing wiser; and some of the modern questions
of philosophy and psychology are now so woven
in with physical details that a knowledge of matter and
its possibilities has become to them imperative.

There have been many attempts to define matter,
such as, whatever occupies space, or whatever affects
our senses, and so on; and there is no brief definition
that has been generally adopted. In the ordinary
affairs of life one rarely needs to make such distinctions
as are necessary in philosophical and scientific affairs,
where accuracy and clearness are of the utmost importance.
There seems to be no way to define matter
except by means of some of its properties. If we say
that it is whatever occupies space, there is implied in
the statement that the term is properly applicable to
everything that exists in space; but so far as we know
there may be any number of things in illimitable space
that are not subject to any of the physical laws, such as
a piece of wood or an air particle are known to be controlled
by. If we say whatever affects our senses, we
again are going beyond our warrant; for electricity is
capable of affecting several of our senses,---sight, taste,
feeling,---and yet there is no good reason for thinking
electricity to be matter.

There is one property of matter that may seem to
differentiate it from everything else, and hence, if
\DPPageSep{016.png}{4}%
\index{Matter, characteristic property}%
\index{Matter, its definition}%
adopted, will enable one to be precise about his use of
the term. One part of the law of universal gravitation
is---\emph{every particle of matter in the universe attracts every
other particle}. This makes gravitation a universal property
of matter. The astronomers have observed the
movements of exceedingly distant stars to be in accordance
with this law, and there are no exceptions to it
that have been discovered.

If, then, one adopts as the definition of matter, \emph{whatever
possesses the property of gravitative attraction}, he
will have a definition that is in accordance with everything
we know, and with the added advantage that if
there be anything else in the universe that involves
observable phenomena he will not need to confuse it
with the phenomena of gravitative matter. This is the
sense in which that term is used throughout this book.
\TBskip

Matter presents itself to our senses in a scale of
magnitude from particles in the neighborhood of the
hundred-thousandth part of an inch in diameter, and
requiring the highest powers of the microscope to see,
to such huge masses as that of the earth, eight thousand
miles in diameter, the planet Jupiter, nearly eighty
thousand miles, and the sun, eight hundred thousand
miles in diameter, while some of the more distant stars
are probably ten times larger than the sun. The large
masses, however, are but collections of smaller ones,
each particle bringing its own properties of whatever
kinds they may be; and it does not appear that new
qualities are developed by simply changing the distance
between bodies. So the properties of matter may be
\DPPageSep{017.png}{5}%
studied exhaustively without employing specimens
inconveniently large.

The thin stratum of gold spread upon cheap jewelry
has all the characteristics and qualities of any specimen
of gold however large; and a small test tube of
hydrogen will exhibit all the kinds of phenomena that
any larger quantity would show. For such reasons the
study of the universe of matter can be carried on in
the laboratory. The universe may be in the crucible
one holds in the tongs; whatever difference there may
seem to be, it will really be one of bigness only.

In treatises on physics one will generally find the
properties of matter arranged in two divisions, called
essential properties and non-essential ones. Of the
former are (1)~extension, or space occupying; (2)~inertia,
or passiveness under conditions of rest or motion;
(3)~impenetrability, or total and exclusive occupancy of
its own space; (4)~elasticity, or ability to recover its
form after distortion, this, however, varying in degree
in different bodies; (5)~attraction, of which there are
several varieties,---gravitation, acting at all distances;
chemism, acting at close distances and selective in its
operation, and apparently not existing at all between
some kinds of matter, as, for instance, between oxygen
and fluorine. Chemism is also capable of complete
neutralization, and is thus in marked contrast with
gravitative attraction, which is not affected in the slightest
degree discoverable by contiguity; and lastly, cohesion,
which is not apparent except bodies are in contact,
but is the agency that holds the particles of bodies together
so they form liquids and solids of any and all sorts.
\DPPageSep{018.png}{6}%

The so-called non-essential properties are color, hardness,
malleability, ductility, and the like, which vary very
much in different substances. Among the metals silver
is white, copper is red, gold is yellow. Diamond is the
hardest substance known, while graphite is one of the
softest, though both are composed of the same ultimate
substance---carbon. Iron is malleable, and may be
forged into any shape. Gold may be hammered out into
leaves no more than one three-hundred-thousandth of
an inch thick, but zinc is wholly unmanageable in that
way. Platinum, one of the heaviest metals we have,
can be drawn out into a wire finer than a spider's web,---a
single grain may be drawn into a mile of wire; while
bismuth, also a metal, cannot be drawn at all.

There are other conditions of matter that offer
opportunities for convenient grouping sometimes, such
as the solid, the liquid, and the gaseous: the solid
being the one where the parts strongly cohere; the
liquid, where the parts have but slight cohesion; and
the gaseous, where the individual particles do not
cohere at all, but, being elastic, bump against each
other and rebound continually.

Farther on it will be shown how all substances may
assume either of these conditions, inasmuch as it is
temperature that determines whether a given substance
be a solid, a liquid, or a gas.

Density signifies compactness of matter, or the relative
\index{Density}%
number of particles in a given unit volume. If compression
be applied to two cubic feet of common air until
it occupies but one cubic foot, there is twice as much
matter in that cubic foot as there was at the outset, and
\DPPageSep{019.png}{7}%
we express that fact by saying that the density is
doubled. If twice the amount of matter is in the unit
space, evidently the weight of the matter in that space
must be twice what it was at first. So one may measure
the density of matter by the weight of a unit
volume of it compared with the weight of the same
volume of some other substance taken as unity. Thus,
if a cubic foot of water weighs $62.5$~pounds, and a cubic
foot of rock weighs $155$~pounds, the density of the rock
is~$2\frac{1}{2}$, which means that it is $2\frac{1}{2}$~times heavier than
water, and that the amount of matter in the rock
is $2\frac{1}{2}$~times greater than that of the water. Such
determinations have been made of all the different
materials that could be found, and extensive tables
have thus been constructed; but it is seen that the
appeal is to gravitation, and presumes that every particle
obeys that law, and that degrees of compactness of
matter do not affect the law. Such comparative tables,
based upon gravitation measure, are frequently called
tables of \emph{Specific Gravity}, so that density and specific
\index{Gravity, specific}%
\index{Specific gravity}%
gravity mean substantially the same thing. The following
examples of the relative densities of bodies may be
of interest:---
\begin{center}
\TableFont%
\begin{tabular} {ll<{\qquad} ll<{\qquad} ll}
Gold,   & $19$   & Diamond,        & $4$    & Alcohol,   & $\Z.8$ \\
Silver, & $10.5$ & Common Stone,   & $2.5$  & Ether,     & $1.1$  \\
Copper, & $8.8$  & Wood,           & $\Z.8$ & Water,     & $1$    \\
Iron,   & $7.8$  & Sulphuric Acid, & $1.8$  & The Earth, & $5.6$
\end{tabular}
\end{center}
Such numbers are to be understood as signifying that
if a given volume of water weighs one pound, an equal
volume of gold weighs nineteen pounds, an equal volume
of iron seven and eight-tenths pounds, and so on.
\DPPageSep{020.png}{8}%

Sometimes, however, it is convenient to choose for a
standard of density some body, a small unit volume of
which is much lighter than water, such as air, or more
frequently hydrogen gas, a hundred cubic inches of which
weigh $2.2$~grains. In the metric system, a litre, which
is nearly two pints is the standard of volume; and a
litre of hydrogen weighs $.0896$~of a gram.

In chemical work this is the common standard for
gases; while for solids and liquids a cubic centimetre of
water is taken, which weighs one gram.

\Section{DIVISIBILITY OF MATTER.}
\index{Matter, divisibility of}%

Particles of matter as small as the hundred-thousandth
of an inch may be seen with a good microscope
as the smallest visible thing, but there is no reason for
thinking that such a degree of fineness is any approach
to the ultimate fineness of the parts into which it is
possible to divide matter. For a long time philosophers
have considered whether or not there could, in
the nature of things, be an actual limit to the divisibility
of matter, so that the smallest fragment could
not be again divided into two or more parts by the
application of appropriate means, thus making matter
infinitely divisible, at any rate ideally.

In Mr.\ Spencer's ``First Principles'' this subject is
considered at length, and the conclusion reached that it
is impossible to conceive the existence of real atoms---bodies
that cannot be divided into halves; nevertheless,
we shall see presently that it is possible to
conceive precisely that thing. It will be best here to
\DPPageSep{021.png}{9}%
note how far division has been carried and the means
employed to effect it.

If a bit of phosphorus be put into a solution of gold,
the gold will be set free in such a finely divided state
that the particles remain suspended in the solution,
giving to it a blue, green, or ruby color, depending
upon the degree of fineness into which it has been
broken up. Faraday estimated that the particles of
gold in the ruby-colored liquid did not exceed the five-hundred
thousandth part of the volume of the liquid.
One-eighth of a grain of indigo dissolved in sulphuric
acid will give a distinctly blue color to two and a half
gallons of water, which would be about the millionth
part of a grain to a drop of the water.

A grain of musk will keep a room scented for many
years. During the whole of the time it must be slowly
evaporating, giving out its particles to the currents of
air to be wafted presently out of doors; yet in all this
time the musk seems to lose but little in weight.

The acute sense of smell of the dog is well known;
for he can detect the track of his master long after the
tracks have been made, which shows that some slight
characteristic matter is left at each footfall.

A spider's web is sometimes so delicate that an
ounce of it would reach three thousand miles, or from
New York to London. No one would think it likely
that such a web would be made up of a single row of
atoms, like a string of beads; for it would not seem
probable that such a string could have such a degree
of cohesion as spiders' webs are known to possess.

Chemists have concluded from their experience with
\DPPageSep{022.png}{10}%
matter in its various forms and conditions that it is
really reducible to ultimate particles which have never
broken up, no matter what conditions they have been
subject to; and these ultimate particles are called \emph{atoms}.
\index{Atoms}%
The term is not now understood to signify what is
implied in its derivation, as something that cannot be
divided, only something that has not yet been broken
up into smaller parts. Thus hydrogen, oxygen, iron,
silver, are reducible to such ultimate atoms; and there
are now known about seventy different kinds of
atoms, and these are often spoken of as the elements.
Though they are excessively minute when compared
with ordinary objects of sight, yet they have a real
magnitude which the physicist has measured in several
different ways. Most of these methods are complicated,
and, in order to be understood, require a pretty
thorough knowledge of molecular physics; but the following
one may probably serve to give one an idea of
the degree of smallness which atoms must have.

When a soap-bubble is blown, the material of the
\index{Soap-bubbles}%
film slides down the sides, making the bubble thinnest
on top. When a certain degree of thinness has been
reached at the top, colors begin to appear in concentric
rings, and these colors appear to move towards the
equatorial regions, new rings being formed at the top
as fast as room is made for them by the displacement
of the earlier ones. These colors always appear in the
same order as they are in the rainbow, namely, beginning
with the red and ending with the violet, then
another set with the same order, until there have been
ten or more such sets of rainbow tints. They are
\DPPageSep{023.png}{11}%
explained as being due to what is called interference
in the light waves that fall upon the film. Light is
reflected more or less from every surface it reaches.
Some light is reflected from the first or outer surface
of the film; some goes through the film to the inner
surface, and is there reflected back to the outer surface,
and then takes the direction that the light has which
is reflected from the first surface, so that the light that
reaches the eye from a point on a bubble comes from
both outer and inner surfaces. That coming from the
inner surface has had to travel farther than that coming
from the outer surface by a distance of twice the
thickness of the film. As light consists of waves, if
one set of waves all of a length be made to move in the
same direction as another set having the same length,
their crests may coincide and produce a single higher
wave; or the crest of one may be behind the crest of
the other at any distance up to one-half the length of
the wave itself, in which case the crest of one will
coincide with the trough of the other, and the two
waves will cancel each other, and this process is called
interference. Now, in the case of the bubble, when the
thickness is such that the distance through the film
and back again is such as to equal half a wave length
of a given kind of light, that particular wave is extinguished;
and when one of the constituents of white
light is wanting, that which is left is seen as colored
light, and the color seen must depend upon the kind
of color that has been cancelled. Red light has the
longest wave length, about one forty-thousandth of an
inch, and violet, the shortest of the waves we see, about
\DPPageSep{024.png}{12}%
one sixty-thousandth of an inch; and when these colors
are seen upon the bubble we are assured that the
interferences are produced by thicknesses due to fractional
parts of such wave lengths. As the ray must go
through the thickness twice in order to fall behind one-half
of a wave, it follows that the thickness of the film
where the last set of colors appear can be no more than
one-fourth of the wave length of the shortest wave we
can see, that is,
\[
\frac{1}{4} × \frac{1}{60,000} = \frac{1}{240,000} \text{ of an inch.}
\]
When a bubble has reached this degree of thinness, so
that no more colors are to be seen, a rather remarkable
physical effect may be noticed. The film becomes
almost jet black, with a jagged edge well defined
between it and the brighter colored rings where the
adjacent tint is purplish. The thickness of the film
has fallen suddenly off here to about one-fortieth of
the thickness it has where the tint is visible, and the
bubble breaks in a second or two after this black patch
appears; that is, when its thinness at any point becomes
as small as
\[
\frac{1}{240,000} × \frac{1}{40} = \frac{1}{9,600000} \text{ of an inch.}
\]
As the bubble, however, does persist for a short time,
and the thin film has cohesion enough to enable it to
support the weight of the bubble, it seems highly probable,
but is not absolutely certain, that it must be more
than one molecule of water thick at the thinnest
place, which is, as shown, only about the one ten-millionth
\DPPageSep{025.png}{13}%
\index{Molecules, size of}%
of an inch thick. If one thinks it probable that
it be, say five molecules thick in order to have the
degree of cohesion it shows, then the size of such\DPnote{** [sic]}
molecule of water out of which the bubble is made
can be but the one-fifth of the above small fraction,
which gives about the one fifty-millionth part of an
inch as the diameter of a molecule of water.

But a molecule is not the same thing as an atom: it
is made up of atoms, chemically combined, and is
defined generally as being the smallest fragment of a
compound body that can exist and possess the physical
characteristics that belong to such body. Thus, a drop
of water possesses all the characteristics of any larger
quantity of it, and a drop may be divided into smaller
and smaller globules, perhaps a million of them, each
one being visible with a good microscope; but if the
division be carried to a higher degree, as it can be by
various methods, chemical, electrical, and thermal, the
qualities of water disappear, and two different substances,
oxygen and hydrogen, are left, both gaseous
under all ordinary conditions, and neither of them exhibiting
any properties like water or from which any
of the properties of water might be inferred. It may
be well to remark here that this is only one illustration
out of multitudes that might be named throughout the
whole domain of physical science, that the properties
of things under common observation are not simply
the properties that belong to the elements out of
which the things are built up; such properties
being the result of collocation rather than inherent
qualities.
\DPPageSep{026.png}{14}%

The molecule of water is then a compound thing, and
is made up of three atoms,---two of hydrogen and one
of oxygen,---and therefore the actual size of an atom
of hydrogen must be less than that represented by the
above small fraction of an inch. Evidently a thing
made up of three individual parts and two dissimilar
substances cannot be spherical, and it will be well to
bear this in mind in thinking of molecular forms. One
may imagine the atoms themselves to be spheres, or
cubes, or tetrahedra, or rings, or disks, or any other
forms he likes, for the purpose of getting some sort of
a mental picture of what a molecule might look like if
it could be seen with a microscope; and it is probable
that very many persons have hoped or thought that
the microscope would sometime be so far perfected as
to enable one to actually look upon the molecules of
matter and perhaps upon their individual atoms. Let
us therefore consider the problem of how much more
powerful a microscope must need to be than any we
possess to-day, in order that one should see a molecule!
We will assume atoms to be about the one fifty-millionth
of an inch in diameter, and that when combined
into molecules they are geometrically arranged
so that the diameter of a molecule made up of a large
number of atoms is proportional to the cube root of
the number of atoms, as is the case with larger bodies,
say a box of bullets.

A molecule of water contains three atoms, a molecule
of alum about one hundred, while, according to
Mulder, a molecule of albumen contains nearly a
thousand atoms. Then, according to the assumption,
\DPPageSep{027.png}{15}%
the molecule of alum would have a diameter
equal to
\[
\frac{\sqrt[3]{100}}{50,000000} = \frac{1}{10,776000} \text{ of an inch},
\]
and that of albumen would be equal to
\index{Albumen, size of molecule}%
\[
\frac{\sqrt[3]{1,000}}{50,000000} = \frac{1}{5,000000} \text{ of an inch.}
\]

Now, the best microscopes made to-day will enable
\index{Microscope, magnifying powers}%
one to see as barely visible a point the one hundred-thousandth
of an inch, so that such a microscope would
need to be as much more powerful than it now is as
one hundred thousand is contained in five millions, that
is, fifty times, in order to see the albumen molecule, and
for the alum molecule as many times as one hundred
thousand is contained in ten million seven hundred
thousand, that is, one hundred and seven times. Now,
one who is familiar with the microscope would probably
admit that one might be made through improved
methods of making and working glass hereafter to be
discovered, two or three, or even ten times better than
the best we have now; but the idea of one being made
fifty or one hundred times more powerful than we have
to-day, I do not think would be allowed to have any
degree of probability. The case may be illustrated as
follows: Suppose in the days of the stage-coach
some one had imagined that by some improvement in
methods of travelling one might some day travel one
hundred times faster than the stage-coach could then
go. Twelve miles an hour was not an uncommon rate
then; but one hundred times that would be twelve
\DPPageSep{028.png}{16}%
hundred miles an hour, and that is sixteen times faster
than the best we can now do, and about twenty-five
times faster than express-trains now go. As a matter
of fact, we travel about three or four times faster than
the best stage-coaches did, and, on a spurt, may go six
or eight times faster. The powers of the microscope
have not been doubled within the last fifty years, and I
suppose more time and ingenuity have been given to
the problem of improving it than will ever be given
to it in the same interval again.

There is another and still more serious reason why
there is no probability that any one will ever see a
molecule, even though the microscope had the magnifying
power sufficient to reveal it; namely, the motions
that molecules are known to have would absolutely
prevent one from being seen. A free molecule of
hydrogen has a velocity of motion at ordinary temperatures
of upwards of a mile in a second, and its direction
of motion is changed millions of times in a
second. A microscope magnifies the movements of an
object as much as it does the object itself. An object
in the field of a microscope that should have a movement
no greater than the hundredth of an inch in a
second could only be glimpsed, so there is no possibility
of one's being able ever to see a free gaseous
molecule. Supposing one should be seized and held in
the field, even then it is to be remembered that it is in
a state of vibration, changing its form constantly on
account of its temperature, so that its wriggling would
prevent any inspection.

Lastly, there is every reason to believe that the
\DPPageSep{029.png}{17}%
molecules of all bodies are so perfectly transparent
that they can no more be seen than can the air, even
if there were no difficulty from their smallness and
their motions.

If the atoms of a single element like hydrogen are
so minute, so restless, and so transparent that no one
can hope to see them so as to make out their forms
and what gives them their characteristic properties,
what shall be said of the case of seventy or more elements
similarly minute and restless and transparent,
yet each one easily identified in several ways, physical
and chemical? Does it seem in any way probable that
such differences in properties as are exhibited by gold,
carbon, iron, and oxygen can be due simply to differences
in size or shape of the atom? Presumably not;
and the constitution of matter has therefore always
been a mystery to philosophers, for if one is to attempt
to philosophize upon the subject in accordance with
such other knowledge as we have, one would need to
conclude that if the different kinds of matter, the elements
as we know them, were formed out of some
prior kind of substance, as bullets and marbles are
formed out of lead and clay, then there must be as
many different kinds of substances out of which the
different elementary atoms are formed as there are
different elements, which proposition does not seem to
have such a degree of probability that any one could
adopt it. If one sought for the explanation of the
different properties by assuming that all the different
kinds of elements were formed out of one and the
same fundamental substance, then it is equally difficult
\DPPageSep{030.png}{18}%
to understand how mere differences in size and shape
could give such profound differences in quality as the
elements possess.

Then, again, it appears that the individual atoms of
\index{Atoms}%
each element are precisely alike. One atom of hydrogen
is precisely like every other atom, so far as we
have definite knowledge. Sir~John Herschel likened
them to manufactured articles on account of their
exact similarity. A machine may turn out buttons or
hooks or wheels or coins so exactly like one another
that no one can tell them apart. It is really appalling
to think of the immense numbers of atoms of every
one of these seventy elements. It is a simple matter
to calculate how many atoms there must be in say a
cubic inch. It requires no other process than the
application of the multiplication table. If the diameter
of one be the fifty-millionth of an inch, then fifty
\index{Molecules, size of}%
million in a row would reach an inch, and a cubic
inch would contain the number represented by the
cube of fifty millions, which is
\[
125000,000000,000000,000000,
\]
($125$~followed by twenty-one ciphers) a number which
is more conveniently represented by $125 × 10^{21}$. The
utter impossibility of conceiving such a number will
be apparent if one would try to represent to himself
what the magnitude of only one million really is. Go
out on a clear but moonless night and the heavens
appear to be filled with stars. Count all that can be
\index{Stars, their number}%
seen in a certain portion of the sky, say one-tenth, as
nearly as can be estimated, and then determine the
\DPPageSep{031.png}{19}%
number in the sky that are in sight by multiplication.
It will be discovered that only about two thousand can
be seen in the whole sky. If one million stars were to
be thus visible, it would require five hundred firmaments
as large and as well filled as the one looked at
to contain them. With the largest telescopes less than
a hundred millions of stars are visible; but what shall
one say when he learns that beyond a peradventure
the number of atoms in a single cubic inch of matter
\index{Atoms}%
of any sort is more than a million of millions times
all the stars in all the heavens visible in the largest
telescope.

If one fancies that kind of work he may compute
the number of atoms that make up the world. Of
course it will make the number much larger; but when
written out not so much longer as one might think, for
when it is multiplied a million times it will add but six
ciphers to it. Some mathematicians have been to the
pains to compute the number of atoms there are in the
visible universe, or, rather, the number that cannot be
exceeded; for if the number stated above fills a cubic
inch, if one knows the diameter of the visible universe,
the space it occupies can readily be known in cubic
miles and cubic inches, and if all this space was filled
with atoms one could know and write down their number.
Astronomers tell us that some stars are so distant
\index{Stars, their distance}%
that their light requires as long as five thousand
years to reach us, although the velocity of light is as
great as $186,000$ miles in a second, and this distance is
to be measured in every direction about us. If this be
our visible universe, then the maximum number of
\DPPageSep{032.png}{20}%
\index{Universe, atoms in}%
atoms in it are calculable, and are stated to be represented
by the figure 6 followed by ninety-one ciphers,
or, as it is usually written,
\[
6 × 10^{91}.
\]

If we return to microscopic dimensions, and compute
the number of atoms, there will be in the smallest
amount of matter that can be seen with the highest
powers of the microscope, the one hundred-thousandth
of an inch, it will be seen that five hundred atoms in
a row would just reach the distance; and the cube of
$500$ is $125,000,000$, that could be contained in a space
so small as to appear like a vanishing-point and the
structure or details be utterly invisible. We have read
of spirits that could dance upon the point of a needle,
but the point of a needle would be a huge platform
when compared with this last visible point with the
microscope; and the spirit that should dance upon it
might be a million times bigger than an atom of matter,
and not be in danger from vertigo. One may be
astonished at the amount of intelligence associated
with the minute brain structure of some of the smaller
forms of animal life---say the ants; but from the above
it will be seen that so far as such intelligence is associated
with atomic and molecular brain structure, the size
of the brain in the smallest ant, though measured in
thousandth of an inch, is sufficiently large to involve
billions of atoms, and the permutations possible are
almost unlimited. The same idea is applicable to the
brain of man, and seems to indicate that such differences
in quality of mind as we see are not so much due
\DPPageSep{033.png}{21}%
to the differences in amount of brain, measured in
cubic inches, as in atomic and molecular structure.

The work of physicists and chemists, carried on for
many years, has convinced them that none of the processes
to which matter has been subjected has affected
its quantity in the slightest degree. A definite quantity
\index{Atoms, unalterable}%
of hydrogen, or, what is precisely the same thing,
a definite number of hydrogen atoms, may be subject
to any conditions of temperature, may be made to combine
with other elements successively, forming with
them solids or liquids or gases, and no atom is
destroyed nor its individual properties changed in any
degree. Neither has any phenomenon been discovered
indicating that new atoms of any kind are ever produced
by any physical or chemical changes yet known.
Time does not alter them. Elements that have been
imbedded in rocks from primeval times, reckoned by
millions of years, when liberated to-day and tested,
exhibit precisely the same characteristics as those
obtained from other sources and that have been subject
to many artificial conditions. Sometimes a meteorite
\index{Meteors}%
reaches the earth, a sample specimen from distant
space, having moved in some orbit about the sun for
millions of years. Thousands of such bodies are in
our possession, and they have been carefully analyzed,
but no element unfamiliar to the chemist has been
found among them; and the iron, the nickel, the carbon,
the hydrogen, and all the rest of the elements that
compose them, behave in every particular like those
found on the earth.

So far as spectroscopic evidence goes, it testifies to
\DPPageSep{034.png}{22}%
the presence of the same elements in the sun and
planets and comets; and it is as certain as anything
physical can be, that the expert chemist here would be
an equally expert chemist in the planet Mars, if he
could find a way to cross the immense space that separates
that star from us.

These facts and conclusions are frequently stated in
such a form as this, namely, that matter cannot be created
\index{Atoms, unalterable}%
or annihilated. All that can fairly be meant by
such language is that under all the conditions at present
known, the quantity of matter remains constant;
and this proposition has a high degree of importance
in social affairs as well as in philosophy. If matter
were liable to change in its quantity or quality by being
subject to various physical conditions, all industries
involving commercial interests would be in an unstable
state. If the ton of iron ore should turn out, when
smelted, only fifty per cent of iron instead of sixty
per cent, as now,---the rest being either annihilated or
transformed into lead or gold, or something else,---the
smelting company would soon go bankrupt, even if
gold were the product instead of iron, for if gold
were liable to be produced in that kind of a way,
its value would be next to nothing as a standard of
value.

The old alchemists sought to transmute what they
called the baser elements into gold. It is safe to say,
if it were physically possible to do it and some one
should discover the art, and it were an economical process,
commercial disaster such as the world has never
known would follow its announcement. It would be as
\DPPageSep{035.png}{23}%
if the volcanoes of the world should suddenly begin to
eject gold in the place of lava.

Stability of physical properties is as essential for
the stability of society as the regular recurrence
of day and night; and philosophy would be impossible
if fundamental data were not in every way immutable.

These physical principles lead to some curious and
most interesting conclusions with regard to the great
difference there is between bodies of matter of any
and all kinds that are familiar to our senses and the
atoms out of which these larger bodies are composed.
In every case, where there is a difference in movement
between two of these larger bodies made up of atoms,
there is what we call friction, which invariably results
\index{Friction, its effects}%
in wearing away some of the material of both. It is
the result of mechanical friction, to tear away some of
the surface molecules of the two bodies. Bodies in use
much, and therefore most subject to friction, become
worn out. Our clothing is a familiar example; the journals
of machinery, the tires of wheels, the sharpening
of tools, the polishing of gems, the weathering of wood
and stone,---all show that attrition removes some of the
surface materials of such bodies, but there is nothing
to indicate that attrition among atoms or molecules ever
removes any of their material. It appears as if one
might affirm in the strongest way that the atoms of
matter never wear out, are not subject to such friction
and the consequent destruction as comes to all bodies
made up of them. The molecules of oxygen and nitrogen
that constitute the air about us have been bumping
\DPPageSep{036.png}{24}%
and brushing against each other millions of times a
second for millions of years probably, and would have
been worn out or reduced, as the rocks upon the seashore
have been beaten and ground into sand, if they had
been subject to friction. So one may be led to the
conclusion that whatever else may decay atoms do not,
but remain as types of permanency through all imaginable
changes---permanent bodies in form and in
all physical qualities, and permanent in time, capable,
apparently, of enduring through infinite time. Presenting
no evidences of growth or decay, they are in strong
contrast with such bodies of visible magnitude as our
senses directly perceive. Valleys are lifted up and
become mountain-tops; mountains wear away and are
washed into the ocean; the beds of the ocean sink and
rise; and the boundaries of continents may be worn and
washed away through the incessant beatings of waves
against their coasts. Wear and tear go on in all inanimate
nature unceasingly, so that it is only a question
of time when everything we see upon the earth will
have changed beyond identification. The sun is shrinking,
and must some time cease to shine. The stars,
too, are changing likewise, because they shine, and
their places in the firmament will be vacant. All living
things grow because of change, and decay because
of more rapid change, and there appears to be nothing
stable but atoms. If it could be shown that life itself
and the mind of man were in some way associated with
\index{Mind, a material habitat for}%
\index{Mind and matter}%
atoms of some sort, as inherent properties, the hopes
\index{Atoms, life associated with}%
and longings cherished by mankind for continuous existence
\index{Immortality}%
beyond the short term of three score years and
\DPPageSep{037.png}{25}%
ten would give way to convictions as strong as one
has in any physical phenomenon whatever; the evidence
would be demonstrative in the same sense as
it is for the existence of atoms and their physical
qualities.
%\DPPageSep{038.png}{26}%


\Chapter{II}{The Ether}{26}

\index{Ether}%

\First{An} incandescent electric lamp consists of a fine
thread of carbon fixed in a glass bulb from which the
air has been exhausted. When a proper current of
electricity is permitted to traverse the carbon filament,
it becomes white-hot and gives out light like any other
hot body. Other luminous bodies are in the air, and
one might infer that the light was transmitted from the
heated body to the eye by the material of the air itself.
The light in the vacuum shows that this is not necessarily
so, for the more perfect the vacuum is made the
more freely does the light from the filament reach the
glass bulb that encloses it. One is therefore led to
infer that matter is not the agent that transmits light.
The light of the sun reaches us after travelling through
ninety-three millions of miles of space in about eight
\index{Light, its velocity}%
minutes. There are the best of reasons for believing
that the atmosphere of the earth does not reach at
most more than two hundred miles upwards from the
\index{Atmosphere, height of}%
surface, and its density at the height of only one hundred
miles is such that there would be only about one
molecule to the cubic foot.

It is not unlikely that there are free-roving molecules
in space, as there are meteors in all directions about
\index{Meteors}%
\DPPageSep{039.png}{27}%
\index{Light, its nature}%
us, varying in size from fractions of a grain to masses
weighing some tons, but the distance apart of these
bodies is so great on the average that they cannot be
considered as either help or hindrance to the passage of
the light of either sun or stars. It is known with certainty
that what we call the light from shining bodies
is a kind of wave motion. The phenomena of interference,
which can be brought about in several different
ways, and which was referred to in the first chapter
when speaking of the colors of soap-bubbles, show
this. It is possible to annihilate two rays of light by
making one of them to follow the other in a certain
way; and one cannot conceive that two particles of matter
of any sort could annihilate each other by simply
changing their positions, but this is precisely what
happens in light.

Wave motions of all kinds can cancel similar wave
motions; for the wave consists of periodic movements,
a crest and a trough, and when the crest and
trough of one wave are superposed upon the trough
and crest of another similar one, the result is the
destruction of both waves. The lengths of these waves
have been measured by a great many persons in various
parts of the world, and they all concur that light
can only be explained by wave motions such as they
measure.

If there be wave motions, evidently there must be
something moved. One cannot conceive of a wave
movement when there is nothing that can be moved;
so men have been compelled to believe that there is
some medium between the sun and the earth that is
\DPPageSep{040.png}{28}%
\index{Light, its velocity}%
\index{Stars, their distance}%
\index{Sun, its distance}%
\index{Universe, its size}%
capable of wave motion, and this medium they have
agreed to call \emph{the ether}.

If one admits the existence of ether between the sun
and the earth as the agency for the transmission of
light, he will need to do much more than that. The
sun is but about ninety-three millions of miles distant,
but most of the planets are hundreds of millions and
some of them thousands of millions of miles from us,
and the light comes from them too; so the ether must
extend through the space occupied by the solar system,
the diameter of which is six thousand millions of miles,
and to cross this space light requires nine hours,
though going at the rate of one hundred and eighty-six
thousand miles per second.

Then there are the stars beyond our solar system,
the nearest one so distant as to require three and a
half years for the light to get to us at the same rate;
and some of these are so remote that thousands of years
are needed for their light to arrive. That light we see
from them to-day left them before America was discovered,
before Jesus was born, before the pyramids
were built, and for all we should be able to see they
might have ceased to exist long ago, though their light
continues to shine. So the ether must extend to those
most distant stars we can see, and that, too, in every
direction. There is no exaggeration in the statement
that our visible universe is so great that light requires
ten thousand years to cross its diameter. There is no
reason, either, for setting that as a boundary to its
magnitude; but wherever light comes from to us, there
must this medium, the ether, be.
\DPPageSep{041.png}{29}%
\index{Medium, necessity for}%

But there are other and just as good reasons for
thinking there must be some medium between bodies,
even when all atoms and molecules have been removed.
For instance, everybody knows that one magnet affects
another at a distance from it, and there is no kind of
substance known that will prevent such action when
interposed between them.

If one of these magnets be placed in the most perfect
vacuum that can be made, it still acts as it would
in the air, only with still greater freedom. One cannot
believe that one body can thus act upon another body
without some kind of a medium between them. Is it
not absurd to think otherwise? One may, if there
appears to him to be a good reason, suppose that there
is a magnetic medium or ether different from that one
employed in the transmission of light; but there is a
similar need for imagining one for the effects produced
by electrified bodies upon other bodies in their neighborhood.
An electrified glass rod will attract a pith
ball or anything else just as well in a vacuum as out of
it; and it is certain that electrical attraction and magnetic
attraction are not identical, for an electrified body
will attract one kind of thing as well as another, while
a magnet is selective in its effects, and affects iron
chiefly. Hence, if each different effect in a vacuum
is to be attributed to some different kind of medium,
there would need to be an electric ether in addition
to the other two.

Then there is gravitative attraction, which has before
been mentioned. If it is not rational to think that one
body can act upon another body not in contact with it
\DPPageSep{042.png}{30}%
\index{Newton, Sir Isaac}%
and without some medium between them, then one is
bound to admit that the gravitative effects observed,
say between the moon and the earth, the sun and the
earth, and in every other case, are due to the action of
some medium between them. Neither is it at all needful
to be able to explain \emph{how} the medium acts thus and
thus, or even to imagine how it might, in order to firmly
believe that there must be one.

Here are four cases of apparent action at a distance
of one body upon another, requiring some sort of an
intermediate agency; and, unless there be some good
reason for thinking there are several such media occupying
the same space apparently, it is much more
philosophical to believe it likely that one medium
exists capable of transmitting effects of the different
kinds; and especially will this appear to be truer if it is
known, as it is known, that the magnetic and electric
effects are transmitted with the same velocity as is the
light. So that physicists to-day quite concur in the
belief that what was called at first the luminiferous
ether, on account of its function in transmitting light,
is the same medium that is concerned in the other phenomena
of magnetism, electricity, and gravitation.

It is likewise true that there are some physicists who
hold rather lightly upon this belief, taking it as a convenient
working hypothesis, and who would seem to be
ready in a minute to surrender the idea, unless it had
been demonstrated in the same way as the existence of
matter and of motion has been. But this is not the
attitude of philosophic minds.

Sir Isaac Newton deduced from the observed motions
\DPPageSep{043.png}{31}%
of the heavenly bodies the fact that they attract
each other according to the law now known as the law
of gravitation, but he says nothing about \emph{how} bodies can
affect each other. That is, in his ``Principia'' he does
\index{Principia}%
not attempt to explain gravitation. He explicitly does
say, however, that he has not employed hypotheses in
his work, yet we know from other of his writings that
the idea of a medium was constantly in his mind. His
``Principia'' closes thus:---
\begin{Quote}
``And now we might add something concerning a
most subtle spirit which pervades and lies hid in all
\Pagelabel{31}%
gross bodies; by the force and action of which spirit
the particles of bodies mutually attract one another at
near distances and cohere if contiguous; and electric
bodies operate to greater distances as well repelling
as attracting the neighboring corpuscles, and light is
emitted, reflected, inflected, and heats bodies; and all
sensation is excited, and the members of animal bodies
move at the command of the will, namely, by the vibrations
of this spirit mutually propagated along the solid
filaments of the nerves from the outward organs of
sense to the brain, and from the brain to the muscles.
But these things cannot be explained in few words, nor
are we furnished with that sufficiency of experiments
which is required to an accurate determination and
demonstration of the laws by which this electric and
elastic spirit operates.''
\end{Quote}

This shows plainly enough that he believed that
some medium, different from matter, was essential for
a mechanical conception of the phenomena he alluded
to. In a letter to Bentley he states his philosophical
judgment upon the subject in still stronger terms, and
it shows, too, the sense in which he is to be understood
when he says: ``I frame no hypotheses''---%
\DPPageSep{044.png}{32}%
which has frequently been repeated to adventurous
hypothecators as the example of the model scientific
man. Hear him!
\begin{Quote}
``It is inconceivable that inanimate brute matter
should, without the mediation of something else which
is not material, operate upon and affect other matter
without mutual contact, as it must do if gravitation in
the sense of Epicurus be essential and inherent in it.~\ldots
That gravity should be innate, inherent, and essential
to matter so that one body can act upon another at
a distance through a vacuum, without the mediation of
anything else, by and through which their action and
force may be conveyed from one to another, is to me
so great an absurdity that I believe no man who has in
philosophical matters a competent faculty of thinking
can ever fall into it.''
\end{Quote}

Newton uses the word \emph{Spirit} in the sense of a substance
entirely different from matter (see \Pageref{page}{31}).
Evidently Newton was so strong a believer in the
medium that we call the ether, though he could not
\index{Ether}%
work out its mode of action, that he was ready to discount
the intelligence of any man who doubted it.\footnote
  {In 1708 Newton wrote thus: ``Perhaps the whole frame of nature may be
  nothing but various contextures of some certain etherial spirits or vapors, condensed,
  as it were, by precipitation; and after condensation wrought into various
  forms, at first by the immediate hand of the Creator, and ever after by the power
  of nature.''

  These with his other acute remarks concerning what we now call the ether
  lead us to infer that his mechanical instincts were more to be trusted in this field
  than his more labored efforts.}

If our knowledge of the existence of the ether is
not so positive as it is for matter, but is inferential, it
will be readily understood that the knowledge we have
of its properties cannot be very exhaustive. Some
have imagined that it was only a finer grained kind of
\DPPageSep{045.png}{33}%
matter than that we know as the elements, and that it
must be made up of atoms, though almost infinitesimal
in size. Others think it cannot be granular at all, but
forms a continuous substance throughout space. By
``continuous'' is meant that there are no interstices in
it: that it is constituted like a jelly, only not made up
of distinct parts or atoms, so there can be no such thing
as separating one part from another, leaving a vacuous
cavity or rent between them. One of the reasons for
thinking this to be the case is, that if it were made up
of finer atoms or of atoms at all, such waves as those
of light could not be transmitted by it. Longitudinal
waves, like those of sound in air, can be transmitted
by atomic or molecular structures but not transverse
waves, that is, such as are at right angles to the direction
of propagation. Some of these light waves are as
short as the hundred-thousandth of an inch, and some
are as long as the one two-thousandth of an inch, and
perhaps longer. Yet all of them are transmitted with
the same velocity in any and every direction. From
the fact that light travels with the same velocity in
every direction, it is inferred that the ether is not only
homogeneous, but its properties are alike in every
direction. As light is transmitted in straight lines, it
seems to follow that there is no difference in its quality
in different parts of space.

That wave motions travel with such high velocity in
it has been interpreted as proving it to have a high
degree of elasticity, while the fact that it offers no
appreciable resistance to the movements of bodies of
matter in it is supposed to indicate that its density is
very small.
\DPPageSep{046.png}{34}%
\index{Earth, velocity of, in space}%
\index{Friction, its effects}%

There are some, however, who think that such terms
as elasticity and density are not appropriately applied
to the ether. These terms signify properties of atoms
\index{Ether}%
and molecules. If density signifies compactness of
atoms, then the word could not apply to something not
composed of atoms. In like manner, if elasticity
means ability to recover form after deformation, then it
is not applicable to substances that cannot be deformed,
and it is customary to speak of the ether as
being incompressible. Still, it is certain that stresses
may be set up in it in various ways, and that these
conditions may be propagated, in certain cases in
straight lines, in other cases in curved lines, so whether
the explanation be forthcoming or not, there is no
doubt about the facts.

There is no evidence at all that the ether is subject
to gravitative action, or that it offers any resistance to
a body moving in it. That is to say, it gives no evidence
of friction. Here is the earth rotating upon its
axis, and the velocity of rotation at the equator is a
thousand miles an hour, and if there were an appreciable
amount of friction the earth must slowly be coming
to rest like a top spun in the air. Yet the astronomers
tell us that the length of the day has not changed so
much as the hundredth of a second within the last two
thousand years. Again the earth revolves in its orbit
about the sun at the average rate of nineteen miles a
second, and if the ether through which it moves offered
any resistance to the motion, the length of the year
would be changed, but no such change has happened
in historic times. Again, such bodies as comets move
\DPPageSep{047.png}{35}%
\index{Thomson, Sir Wm.}%
\index{Vortex rings in air}%
very much faster than the earth; some have been
known to have a velocity of three hundred miles per
second when near the sun, but the comets complete
their circuits and give no evidence of slackened speed
due to friction in space.

If, then, the ether \emph{fills} all space, is not atomic in
structure, presents no friction to bodies moving through
it, and is not subject to the law of gravitation, it does
not seem proper to call it matter. One might speak of
it as a substance if he wants another word than its
specific name for it. As for myself, I make a sharp
distinction between the ether and matter, and feel
somewhat confused to hear one speak of the ether as
matter.

Nearly thirty years ago Helmholtz investigated, in a
\index{Helmholtz}%
mathematical way, the properties of vortical motions,
and, among others, pointed out that if a vortical motion
was set up in a frictionless medium, the motion would
be permanent, and it could not be transformed. Sir
William Thomson at once imagined that if such
motions were set up in the ether, the persistence of
their form and the possibility of a variety of motions
would correspond very closely with the properties that
the atoms of matter are known to possess. Such vortical
motions as are here alluded to, all have seen, as
they are often formed by locomotives when about starting,
if the air be quiescent. Horizontal rings, three
or four feet in diameter, may be seen to rise wriggling
into the air sometimes to the height of several
hundred feet. They may be formed also by smokers
by a vigorous throat movement forcibly puffing the
\DPPageSep{048.png}{36}%
smoke from their mouths, and they can be made
% [Illustration: ]
\begin{figure}[hbtp]
  \begin{center}
    \fbox{\Graphic{0.9\linewidth}{048a}}
  \end{center}
  \Caption{1}{Diag.\ 1.}
\end{figure}
artificially by providing a box having a hole on one
side an inch or two in diameter and the side opposite
covered with a piece of cloth. A saucer containing
strong ammonia water and another with strong hydrochloric
acid may be set inside, and dense fumes will
fill the box. If the cloth be struck by the hand, a ring
will issue from the hole, and may go forward several
feet, and its behavior may be studied. Such as are
formed in the air under such conditions present so
many interesting phenomena that it is worth the while
here to allude to them for the sake of helping the
mind to a clearer idea of how some of the properties
exhibited by matter may be accounted for.\footnote
  {The method of producing these vortex rings and their phenomena are fully
  explained in ``The Art of Projecting.'' By Prof.\ A.~E. Dolbear. Illustrated\DPtypo{}{.}
  \$2.00. Published by Lee and Shepard, Boston.}

\DPPageSep{049.png}{37}%
\index{Vortex rings, properties of}%

1.  The ring once formed consists of a definite
amount of the gaseous material of the air in a state of
rotation, %[** PP: Width-dependent line break]
% [Illustration]
\begin{wrapfigure}[11]{r}{1.5in}
  \Graphic{1.375in}{049a}
  \Caption{2}{Diag.\ 2.}
\end{wrapfigure}
and in its movements afterwards retains the
same material. It is to be noted
that the ring is formed in the air,
the white fumes serving merely to
make the ring visible. The ring
moves forward in a straight line
in the direction it is started, just
as if it were a solid body. It may
move very fast too,---ten feet a
second or more, and reach the
distant side of the room, but it
always moves of its own motion in a direction perpendicular
to the plane of the ring.

2. It possesses momentum, and will push against
the object it hits.

3. If made to move rapidly adjacent to a surface
like a wall or table, it will move towards it as if it were
attracted by it, and generally will be broken up by
impact against it.

4. A light body, like a feather or thread, will be
apparently pushed out of the way in front of it, and
drawn towards it if behind it---phenomena like attraction
and repulsion.

5. If two such rings bump together at their edges,
each one will vibrate with well-marked nodes and loops,
showing that, as rings, they are elastic bodies, and that
their period of vibration depends upon the rate of the
rotation.

6. If two such rings be moving in the same line, but
\DPPageSep{050.png}{38}%
the hindmost one swifter so as to overtake the other,
the foremost one enlarges its diameter while the hinder
one contracts until it can go through the former, when
each recovers its original dimensions.

7. If two meet in the same line, going in opposite
directions, the smaller one goes through the larger and
may be brought to a standstill in the air for a short
time until the other has got some inches away, when it
starts on in the same direction as before.

8. If two similar ones are formed at the same time,
side by side, at a distance of an inch or two, they always
collide at once as if they had a mutual attraction. The
result of the collision may be the destruction of one or
both, or---

9. Each one may break at the point of impact, and
the opposite ends may weld together, forming a single
ring which will move on as if it had been singly formed,
or---

10. Instead of breaking they may rebound from each
other, but always at right angles to the plane in which
they were moving at first; that is to say, if they were
moving in a horizontal plane before impact, they will
rebound from each other in a vertical plane.

11. Three rings may in like manner be made to join
into one.

12. The material of the ring may often be seen to
be in rotation about the ring, while the ring, as a whole,
does not rotate at all, a rotary wave.

13. The parts of a ring may be in a state of vibration
in the ring without changing its circular form,
somewhat as if the ring were tubular and two bodies
\DPPageSep{051.png}{39}%
\index{Elasticity due to motion}%
should move up on opposite sides till they met and
rebounded to meet below, and so on.
\Pagelabel{39}%

All these, and some other just as curious phenomena,
may be observed in vortex rings, and may fairly be said
to be due to the properties of the rings themselves.
For instance, the vibratory motions alluded to in the
fifth show that elasticity is a property of the ring,
and that the degree of elasticity does not depend upon
what the ring is made of, but upon the kind and
degree of motion that constitutes the ring. If such a
ring could be produced in material not subject to friction,
none of the motion could be dissipated, and we
should have a permanent structure, possessing several
properties such as definite dimensions, volume, elasticity,
attraction, and so on, all due to the shape and
motions involved.

Imagine, then, that vortex rings were in some way
formed in the ether, constituted of ether. If the ether
be, as it is generally believed to be, frictionless, then
such a thing would persist indefinitely: it would have
just that quality of durability that atoms seem to possess.
It would possess physical attributes, form, magnitude,
density, energy, that is, it would not be inert.
It would be elastic, executing a definite number of
vibrations per second. This property of elasticity has
generally heretofore been assumed to be a peculiar
endowment of ordinary matter, and one was at liberty
to imagine some matter without it because not so made.
This view implies that elasticity is a necessary property
of vortex rings; for as the velocity of rotation is
reduced, so is the degree of elasticity, and if there was
\DPPageSep{052.png}{40}%
\index{Bonnenburger's apparatus}%
simply a ring without being in rotation, it would have
no elasticity at all, neither would it have any qualities
different from the medium it was imbedded in.

That such a quality as elasticity may be due solely to
\Pagelabel{40}%
motion, and varying with it, one may assure himself
with that piece of apparatus to be found in most collections
in schools known as Bonnenburger's. It consists
of a disk of metal, mounted in gimbals so it can
be set spinning %[** PP: Width-dependent line break]
% [Illustration]
\begin{wrapfigure}{l}{1.5in}
  \Graphic{1.375in}{052a}
  \Caption{3}{Diag.\ 3.---\textsc{Bonnenburger's Apparatus.}}
\end{wrapfigure}
in any plane. If
this be set spinning in a vertical
plane it becomes tolerably rigid
in that plane, and cannot be moved
out of it but by the employment
of quite a degree of pressure. If
the framework be quickly struck
by the finger while thus spinning,
the wheel will begin to rock back
and forth like the prong of a
tuning-fork, and the more rapid
the rotation the higher the rate
of vibration. When the velocity
of rotation becomes slow the
vibratory motion may be as slow
as once a second, and, of course, when the ring is not
revolving it will not vibrate at all. Thus there is fairly
good physical reason for thinking that what we call
elasticity in the atoms of matter may be due simply
to the motion they possess, and \emph{how} that may be one
can understand if atoms be vortex rings.

One may properly ask how one vortex ring can differ
from another so there could be so many as seventy or
\DPPageSep{053.png}{41}%
more different kinds of atoms. To this it may be said
that such rings may differ from each other not only in
size but in their rate of rotation: the ring may be a
thick one or a thin one, may rotate relatively fast or
slow, may contain a greater or less amount of the ether.
The word ``mass'' in physics is used to denote a quantity
of matter as measured by its resistance to pressure
tending to move it as a whole. Thus if a pressure of
one pound be applied to two different bodies for say
one second, and one of them was moved an inch and
the other but half an inch when otherwise they were
alike free to move, we would say that one had twice the
mass of the other---its resistance to being moved was
twice as great as the other.

In the case of the Bonnenburger's rotating disk, the
resistance to the pressure tending to move it depends
upon the rate of rotation, and a thin and swift moving
disk would offer much greater resistance than a much
larger one with a slower speed. So one might infer
that the difference in what is called mass among the
atoms of matter might be due simply to the different
speeds with which the rings rotate, rather than in the
absolute volume of ether in the state of rotation.
There are other reasons than these for thinking that
motion is the chief characteristic of matter. Chemists
have discovered that both the chemical and physical
properties of all kinds of matter are functions of their
mass or relative atomic weights, and that they may be
arranged in a harmonic series. Harmonic relations
may imply either relations of position or of motion.
But the fundamental properties of matter do not change
\DPPageSep{054.png}{42}%
by changing its position, and one is therefore led to the
conclusion that one must look to the various kinds of
motion involved among atoms for the explanation of all
their properties and all their phenomena.

There is another very important and peculiar property
possessed by vortex rings; viz., there cannot be
such a thing as half a ring or any fragment of one.
Break such a ring in two and there is not left the two
halves; not only is the ring broken, but each part at once
vanishes into the indistinguishable substance that composed
it, and all the properties that characterized it as a
ring have vanished with it.

This greatly aids one to understand that matter may
not be infinitely divisible. Over and over again have
philosophers asserted that it was impossible to imagine
an atom of matter so small that it could not in imagination
be again broken into two or more parts. A vortex
ring, however, shows how the thing can be done.
If an atom be a ring, when it is disrupted it is at once
dissolved into ether, and that is the end of it. There
are no fragments of the ring.

One, however, must not infer from the above treatment
that it represents knowledge of a demonstrated
kind, for it does not. It was remarked in the first
chapter that atoms are too minute to be seen and
studied as one would study an animalcule or a blood
corpuscle, and one's knowledge must be altogether
inferential concerning them; but what knowledge we do
have, and the inferences that may properly be drawn
from it, all tend to convince one that matter and the
ether are most intimately related to each other, and
\DPPageSep{055.png}{43}%
that some such theory as the vortex ring theory of
matter must be true.

Now, it is either that theory or nothing. There is
no other one that has any degree of probability at all.
If what is presented herewith is not the precise truth
concerning a most difficult subject, it may have the
merit of helping one to conceive the possibilities there
may be of deducing qualities from motions, and rid him
of the idea that matter consists necessarily of some
created things that have no necessary relations to the
rest of the universe beyond the properties impressed
by fiat. In the latter case one could never hope to
understand them, because there could be no \emph{necessary}
reason for their being as they are, rather than some
other way, whereas, in the former case, the mechanical
relations can be understood, and there is left the possibility
that by and by, with more light and knowledge,
one may know the physical conditions under which
matter itself came into existence.
%\DPPageSep{056.png}{44}%


\Chapter{III}{Motion}{44}

\First{Everybody} has so clear a conception of motion that
there would not seem to be any difficulty in defining it
absolutely, but philosophers and others from remote
times till now have been perplexed by its problems.
How can Achilles ever overtake the tortoise, though
he runs ten times faster? How can the top of a
cart-wheel move faster than the bottom? If the sun
cannot set above the horizon and cannot set below
it, how can he set at all? In the last chapter some
phenomena were alluded to which were attributed to
motions of different kinds, and one must needs have a
definite notion of what he is talking about in order that
his words shall convey to himself, as well as others,
the information he would impart. Rest and motion are
contrasted conditions of bodies, so if a body is at rest
we say it is without motion, and \textit{vice versa}. If two persons
sit side by side in a house they may be said to be
at rest, but if they sit side by side in a railroad car they
will be at rest relative to each other as they were
before, but may be in motion with reference to things
outside the car. If, as a vessel sails past the end of a
wharf, a person on board would talk with a person
standing upon the wharf, he will walk so as to keep
\DPPageSep{057.png}{45}%
opposite the man standing still, and the two will be
at rest in relation to each other, while one will be in
motion with reference to everything on board the vessel.
Thus it appears that rest and motion are relative
terms, and can only be understood to apply to the
relative continuous position of two bodies or objects.
Hence, if there were but one object in the universe there
could be no such thing as change of position, for that
implies another body with which position may be compared
at intervals. But such a single body might have
some internal motions by which there was a relative
change of position of its parts with reference to themselves.
For instance, a tuning-fork might be at rest as
a whole with reference to all other bodies, yet its prongs
might vibrate towards and away from each other, the
centre of mass or the centre of gravity of the fork itself
not moving in the slightest degree either with reference
to itself or anything outside itself. Again, a body might
spin like a top, and there would be no change of position
of the body as a whole with reference to any other
body, nor change of position of the parts with reference
to each other, yet there would be a change of position
of the parts with reference to all bodies outside itself.
Hence, a brief definition of motion is not so easy to
give.

One might say that motion was the change of position
of a body with reference to other bodies, or the change
of position of the parts of a body with reference to each
other, or the change of position of the parts of a body
with reference to other bodies. But these would not cover
all possible cases. There need be no trouble, however,
\DPPageSep{058.png}{46}%
\index{Molecules, size of}%
\index{Motion, kinds of}%
in particular cases, because there will always be data at
hand to determine the character and direction of the
motion.

One may study the geometry of positions and changing
positions of mathematical points, and attend only to
rates and direction of motion of all sorts, without considering
the motions of bodies of real magnitude possessing
physical properties like matter. The science
that has to do with such ideal conditions is called \emph{kinematics}.
\index{Kinematics}%
Whenever the motions of matter are considered,
the science is called \emph{kinetics}. Of course all
\index{Kinetics}%
phenomena involve the motions of matter. Although
one sees a great variety of motions, a few examples of
particular sorts may be helpful in analyzing them.

1. The drifting of clouds, the flight of birds, of
arrows, of bullets, of meteors, the sailing of vessels, the
running of locomotives, are examples of one kind of
motion; namely, where the change of position is that
of the body as a whole with reference to other bodies
external to it. The cloud may drift with the air, but
with reference to the surface of the earth it moves.
Where a body thus moves straight on continuously with
reference to other bodies, whether the distance moved
be long or short, the motion is called \emph{translatory} or
\emph{free-path motion}. The latter term is most frequently
applied to the movements of the molecules of a gas.
In ordinary air the distance apart of the molecules is on
the average about the one two-hundred-and-fifty-thousandth
of an inch, but the molecules themselves being
only one fifty-millionth of an inch in diameter, it will
be seen that they have a space to move in about two
\DPPageSep{059.png}{47}%
\index{Vacuum}%
hundred times their own diameter before coming in
collision with another one; and after collision their
direction is only changed when they go on to another
collision, and we say that their free path is on an average
about the two-hundred-and-fifty-thousandth of an
inch. With some modern air-pumps it is possible to
reduce the amount of air in a space so that the average
free path of a remaining molecule will be a foot or more;
but neither the size of the moving body, nor the distance
hundred times their own diameter before coming in
collision with another one; and after collision their
direction is only changed when they go on to another
collision, and we say that their free path is on an average
about the two-hundred-and-fifty-thousandth of an
inch. With some modern air-pumps it is possible to
reduce the amount of air in a space so that the average
free path of a remaining molecule will be a foot or more;
but neither the size of the moving body, nor the distance
it moves, nor the velocity with which it moves,
makes any essential difference in the specific kind of
motion: so the movements of air particles among themselves,
of billiard-balls between impacts, of a bullet on
its way to the target, and of a planet or comet in its
orbit, are all examples of the same kind of motion,
namely, translational.

2. The swaying of the branches of trees when
moved by the wind, the swinging of the pendulums
of clocks, the movement of the piston in a steam-engine,
of the prongs of tuning-forks, the reeds and
strings in musical instruments, are examples of a different
kind of motion, inasmuch as the changes of position
relate to the body itself rather than to external bodies.
The tuning-fork is the type of them all, and together
they are called \emph{vibratory} motions. Sometimes, when
the bodies that move thus are large and the motion conspicuous,
as, for example, in the pendulum of the clock,
and the steam-engine piston, the motion is spoken of
as \emph{oscillatory}. In such cases, as in the former one, it
should be borne in mind that mere differences in the
size of bodies, or of the rate of motion, does not in any
\DPPageSep{060.png}{48}%
\index{Motion, kinds of}%
manner change the character of the motion, so the
name that is applicable to one will be equally applicable
to all. If one calls the movement of a vibrating tuning-fork
\emph{vibratory}, the same term may be applied to an
atom if it goes through a like periodic change of form,
for that is the chief characteristic of vibratory motion;
and hereafter it will appear how needful it is to bear
this in mind, for what a given amount of motion will
do will be seen to depend altogether upon the kind of
motion.

3. The spinning-top, the balance-wheels of engines,
the wheels of machines of all kinds, the turning of the
earth, and each member of the solar system upon its
axis, are examples of another sort, where the displacement
is not, as in the last, between parts of the same
body, but a change in the relative position of each part
of a body to what is outside itself. The pendulum of a
clock swings to and fro, but its point of suspension does
not move; whereas every part of a turning-wheel is
presented to opposite parts of space in the plane of its
revolution. This motion is called \emph{rotary}, and just as in
the other two cases, I wish to emphasize the fact that
the term is properly applicable to masses of matter of
all degrees of magnitude; so an atom may spin on its
axis as well as the earth or sun, and the phenomena it
will be competent to produce by such spinning will be
very different from that produced by its vibrations or
free-path motions.

These three kinds are all of the primary ones: all
the others we see are made up of these or their compounds.
For instance, a compound of a free-path
\DPPageSep{061.png}{49}%
\index{Motion, kinds of}%
\index{Motion, molecular and atomic}%
motion with a vibratory motion will give a wave or
sinuous motion if the direction of the vibration be at
right angles to the free path. A combination of a free-path
with a rotary may give a spiral motion, as illustrated
by the movement of a screw when pushed and
turned into a piece of wood.

In a sewing-machine may be seen all of these kinds
of motion and some other compounds more complex
than the ones spoken of, but one may readily analyze
them into the three primary ones.

These forms of motion have been spoken of as if
they were peculiar to matter; but it ought not to be
inferred that motion is not attributable to the ether.
Indeed, we know that some sorts of motions are propagated
in the ether. For instance, what we call light
is an example. Its form is \emph{undulatory}; and, as we have
seen above, an undulatory motion is a compound of a
rectilinear and a vibratory. A spiral movement in the
ether is also known, and it is sometimes called rotary-polarized
light: its motion is like that of a screw, and
we know that such a motion is a compound of a rectilinear
and a rotary. Rotary motions in the ether are
also known as taking place in front of magnetic poles,
and are the results of the magnetism imparted to the
iron or other substance. I am not aware that any
simple rectilinear motion is known to occur in the
ether: there may be, and likely enough is, such.

For convenience, motions that are large enough to
be visible are called \emph{mechanical motions}, while those
too minute to be seen are often called \emph{molecular} or
\emph{atomic}. Sometimes these molecular and atomic motions
\DPPageSep{062.png}{50}%
\index{Motion, velocity of}%
are spoken of as if they were mysterious, and not to be
understood in the same sense as the larger ones that
are visible to us; but it is difficult to justify any such
distinction, and difficult to imagine that any kind of a
motion a large piece of matter may have, a small particle
or atom cannot have, and \textit{vice versa}. It would
seem probable that whoever finds a difficulty in this
cannot have strong mechanical aptitudes, and is not
gifted with an adequate scientific imagination.

A free body of any kind and of any magnitude may
have any kind of a motion whatever, and may move in
any direction and with different velocities, but the term
\index{Velocities}%
velocity is used in different senses when applied to different
kinds of motion. Thus the velocity of an atom
in its free path, of a musket-bullet, of sound-waves, is
measured in feet per second. The velocity of vibrating
bodies is indicated by the number of vibrations they
make per second. A tuning-fork making two hundred
and fifty-six vibrations in a second is said to have that
rate of vibration, whether the actual distance moved be
one distance or another, which, of course, will depend
upon the amplitude of each individual swing; while
rotational velocity is generally specified by giving the
number of rotations per second, or per minute, or some
other unit interval of time. A top may spin a hundred
times a second, a balance-wheel of a steam-engine turn
four times, while the earth makes one revolution in a
day of twenty-four hours. The range in velocities of
these different kinds that have been measured is very
great indeed. In free-path or translational motion,
there may be the snail's pace, perhaps less than an
\DPPageSep{063.png}{51}%
inch a minute, the pace of a man walking say three
miles an hour, which is at the rate of eighty-eight feet
per minute. A race-horse may trot a mile in two
minutes and ten seconds, which is forty feet per
second. A steam-locomotive may run seventy miles
an hour, which is nearly one hundred feet per second.
A rifle-bullet may go a thousand feet, and a cannon-ball
two thousand feet in a second. The earth in its orbital
motion goes seventeen miles per second; meteors come
to the earth, from space, sometimes having a velocity
of fifty or more miles per second, while comets may
reach the velocity of nearly four hundred miles in the
same time when near the sun. These are the velocities
of bodies of visible magnitude, but some of the motions
of molecules are fairly comparable with some of these.
Thus a molecule of common air is moving in its free
path about sixteen hundred feet per second, while a
molecule of hydrogen, which is much lighter, goes
more than six-thousand feet---upwards of a mile---in the
same time. As remarked before, the free path for air
molecules having but about the two-hundred-thousandth
part of an inch, it must change its direction an enormous
number of times in a second,---as many times as
one two-hundred-and-fifty-thousandth of an inch is contained
in sixteen hundred feet;
\[
250,000 × 12 × 1,600 = 4800,000000.
\]
Four thousand eight hundred millions of times. How
one may assure himself that such a statement is not
fabulous will be pointed out farther on; so far one
needs only to trust the multiplication table.
\DPPageSep{064.png}{52}%

For vibratory rates there are also enormous ranges:
there are the slow oscillatory movements of swinging
pendulums of various lengths, sometimes occupying
several seconds for the execution of one vibration;
piano-strings having a range from about forty per
second to four thousand; the chirrup of crickets about
three thousand. Short whistles and steel rods have
been made that will make as many as twenty thousand
vibrations per second,---a rate much higher than can be
\index{Vibrations per second}%
perceived by most persons, though occasionally abnormal
hearing in an individual enables him to hear sounds
to which ordinary ears are entirely deaf. When the
number of vibrations per second becomes so great that
they cannot be individually seen nor heard, one must
trust his judgment and the properties of matter in
determining whether there really are any still more
rapid. It has been found by experiment that the number
of vibrations a given body can make when it is
struck so as to produce a sound depends upon its shape,
its size, its density, and its degree of elasticity. If a
steel rod, having a given diameter and length, makes,
when struck, five hundred vibrations per second, another
similar one with but half the length will make twice as
many in the same time. If one were made of something
still more elastic than steel, and of the same size,
the vibratory rate would be higher still.

A steel tuning-fork three inches long may make five
hundred vibrations per second; if it were only the one
fifty-millionth of an inch long it would make not less
than $30000,000000$ vibrations per second; and if it
were made of a substance like ether it would make as
\DPPageSep{065.png}{53}%
many as $1000,000000,000000$---a thousand million
of millions per second. As large as this number is,
and as improbable as it would seem to be, there is indubitable
evidence that the atoms of matter do actually
make such a number of vibrations per second.
\index{Vibrations per second}%
\Pagelabel{53}%

If one knows the rate at which vibrations are propagated
in a medium and the wave length, one can readily
determine the number of vibrations the body is making
that sets up the waves. Thus, if the velocity of sound
in the air be $1100$~feet per second, and the length of
one wave be $1$~foot, then the body must be making
$\dfrac{1100}{1}=1100$ vibrations per second: that is, the velocity
divided by the wave length will give the number of
vibrations.

The velocity of light is known to be $186000$ miles
per second; the wave lengths of light are also known with
great precision, and are all only small fractions of an
inch. If they were only one inch long, their number
would be the number of inches there are in $186000$
miles, or $12 × 5,280 × 186000 = 11784,960000$ per
second. In reality they are only one forty-thousandth
or the one fifty-thousandth of that.
\[
11784,960000 × 50000 = 589,248000,000000,
\]
nearly six hundred millions of millions per second. No
one can pretend to comprehend such a number; but in
proportion as he understands the process and the data
by which such a result is reached, will he have an abiding
confidence that it is legitimate and that it expresses
the actual truth.
\DPPageSep{066.png}{54}%

Sometimes it is convenient to know the actual space
that is moved over by a vibrating body in terms
of free-path or translatory motion, that is, how far
would the body move in the same time if, instead of
vibrating, it went on in a straight line. If the prong
of a tuning-fork moves through the one-hundredth of
an inch each swing, and vibrates one hundred times in
a second, obviously its rate of motion measured that
way would be only one inch, which would be a relatively
slow motion when compared with many others.
If the same computation be applied to atoms, however,
whose rate of vibration is so enormously high, it leads
to some very respectable translational velocities. Thus,
\index{Velocities}%
suppose the amplitude of vibration of an atom of hydrogen
be as great as one-half its diameter, that is, one
hundred-millionth of an inch, if it vibrates five hundred
millions of millions of times per second, the actual
space moved through will be
\[
\frac{500,000000,000000}{100,000000}
  = 5,000000 \text{ inches} = 80 \text{ miles,}
\]
which is more than four times that of the earth in
its orbit. It does not appear probable, however, that
the amplitude of motion is anywhere near as much
as that assumed, at any rate for ordinary temperatures;
but if it be only the one-hundredth of that amplitude
the velocity exceeds that which can artificially be given
to any visible object, as it will then be nearly a mile a
second.

Rotary speeds have wide ranges. The earth takes
twenty-four hours to make one revolution; the moon
about twenty-eight days, and the sun twenty-six, and
\DPPageSep{067.png}{55}%
\index{Earth, diameter of}%
some others of the planets perhaps much longer than
that. Some astronomers have concluded from their
observations of the planets Venus and Mercury, that
\index{Mercury}%
\index{Venus}%
their axial rotation corresponds with their time of revolution
about the sun, being $224$~days for Venus, and $88$
for Mercury. Tops have been made to spin eight hundred
or a thousand times per second; and if molecules
ever rotate their rate has not been measured. The
velocity of rotation, when measured as a translation,
must evidently depend upon the diameter of the body
rotating. The diameter of the earth being nearly eight
thousand miles, a point on the equator moves twenty-five
thousand miles in twenty-four hours---something
over a thousand miles an hour, or about seventeen miles
a minute. A driving-wheel of a locomotive that is six
feet in diameter will advance nearly nineteen feet every
revolution. To have a speed of a mile a minute, which
is $88$~feet per second, it must turn round $\dfrac{88}{19}=4.6$~times
per second\DPtypo{}{.} A disk $4$~inches in diameter, spinning $800$
revolutions per second, which was the speed given by
Foucault to one of his gyroscopes, would advance, if
allowed to roll, with the speed of $837$~feet per second---nearly
ten miles a minute.

There are some facts, and inferences we draw from
them, with regard to motion and the geometry of space
that it may be well to mention here. When we speak
of the velocity of a body at a given time we mean by it
that its rate is such that if continued for the whole
interval of the unit of time, whether it be a second, or
a minute, an hour, or any other, the body will move
\DPPageSep{068.png}{56}%
\index{Sun, its distance}%
through the whole specified distance. A body will not
need to go a mile in a minute in order to have a velocity
of a mile a minute. It may not move ten feet, yet
may have that or any higher velocity. This is obvious
enough of course. Every one trusts arithmetical processes
to lead him to correct results in velocities and
\index{Velocities}%
time and all such familiar matters. One will say
frequently, ``It is six hours to New York'' instead of,
``It is two hundred miles to New York,'' and will not
be misunderstood. Some persons have computed how
long a time it would take to reach the sun if they were
to take an express-train running at the rate of fifty
miles an hour, without stopping for food or fuel; and
they find it comes out nearly two hundred years,---a
time of transit equivalent to five generations of men.
In like manner, presuming one knows the distance to
any remote point in space, the time required to get
there at a given velocity one would call a simple problem
in arithmetic, and it is. But there is an assumption
one has to make which is rarely considered: that is,
the properties of space and of time are the same everywhere,
and that the geometry of the space in which we
\index{Geometry}%
live is a geometry that holds everywhere and always:
that its propositions are absolutely and irrefragably true
always and everywhere. We assume, because we find
them practically true on a small scale, that they are
equally true on the largest scale.

Within the past fifty years the great geometers have
made some very wonderful discoveries---one might say,
astounding discoveries; for they tell us that we do not
know that the sum of the interior angles of a plain
\DPPageSep{069.png}{57}%
triangle is equal to a hundred and eighty degrees,
that we do not know it within ten degrees if the
triangle be a very large one, such as is formed by
the spaces between remote stars and the sun; furthermore,
we are assured that, for all we know, and therefore
for all we can reason from, space itself may be
\Pagelabel{57}%
curved so that if one were to start in what we call a
straight line, in any direction, and travel in it on and on
he would find himself after a long time coming to his
starting-point from the opposite direction; that what
one would see if his sight were prolonged in any direction
would be the back of his own head much magnified.
Methods have been proposed for discovering if it be
true or not. Some folks have called this nonsense, and
have used descriptive adjectives to express their contempt
for it; but none of those who have spoken thus
of the new geometry are themselves mathematicians,
\index{Geometry}%
and one is therefore left with the fair inference that
they did not so well know of what they condemned as
did the mathematicians who reached the conclusion.\footnote
  {See \hyperref[page:400]{Appendix}.}

Now, we all of us trust such mathematical processes
as we can ourselves handle, even when they lead us to
magnitudes and distances too great for comprehension.
All that one needs to know is, that the process is a
legitimate one and is correctly worked out. This new
geometry I have alluded to has been worked at by the
best mathematicians of all the civilized nations, and
they agree in the conclusions. They certainly would
not do so if there were the slightest apparent reason
for rejecting them; for national jealousies are too
\DPPageSep{070.png}{58}%
strong, and a sense of the value of truth too great, to
allow any such notions to gain currency anywhere if
there were any possibilities of breaking them down.

If the space we live in and the geometric relations
\index{Space}%
are only practically true upon a small scale; if we may
have a kind of space of four or more dimensions, whether
we now can conceive of it or not, then should one understand
that spaces and distances and velocities and all
computations formed upon them, though practically
true, for all of our experience must not be pushed up
into statements that shall embrace all things in the
heavens as well as on the earth. Perhaps even the
visible universe is not to be measured by our span,
much less things invisible in it and beyond it.
%\DPPageSep{071.png}{59}%


\Chapter{IV}{Energy}{59}

\First{Whenever} a body of matter having any motion
strikes another body, it always imparts some of its
motion to it, and the second body moves. The ability
one body has to move another one is sometimes called
its energy, and the amount of energy received is proportional
to the amount of similar energy the first body
possesses. A body at rest can impart no motion to
another one, so it appears that the energy a body has
depends upon its own amount of motion. Neither can
a body impart to another one more motion than it possesses
itself, and rarely or never can it do so much as
that. Inasmuch as every kind of a phenomenon is the
\index{Phenomena, nature of}%
result of the transfer of some kind of motion from one
body to another, one may rightly infer that to understand
phenomena and their relations, one must need to
know, not only the kinds of motion that are transferred,
but must also know their quantitative relations, and he
must therefore have some units and standards for comparison.
This requires some measure for the amount
of matter involved, also some measure for the motion
it has. For the former it is customary to employ a
weight. A certain mass of matter called a pound is
adopted in England and America. Exact duplicates of
\DPPageSep{072.png}{60}%
\index{Falling bodies}%
\index{Falling bodies, energy of}%
\index{Weights, standards of}%
\index{Work, standard of}%
its standard weights are made and preserved by each
nation; so as weights become worn by usage, they
may be exactly replaced. Any unit space may be
adopted, as the foot, which is common. If a pound
has been raised a foot, a certain amount of work has
been done, which is called a \emph{foot-pound}, and it is important
\index{Foot-pound}%
to keep in mind just what it signifies. If ten
pounds be raised one foot, or if one pound be raised
ten feet, the same amount of work---ten foot-pounds---has
been done; and with this as a starting-point, it
will be easy to see how energy may be measured, for
the measure of it will be the amount of work, measured
in foot-pounds, it can do. It is found by experiment
that if a body be left free to fall in the air, it will fall
sixteen feet in a second, and its velocity at the end of
the second will be thirty-two feet. If a very elastic
ball weighing a pound should fall thus in the air upon
an elastic pavement, it would rebound nearly to the
height of sixteen feet. If it does not quite reach that
height, it is because the air retards it somewhat, and
some of its motion has been imparted to the pavement
upon which it falls. Adding those losses to the height
it did rise, and it would make the sixteen feet. Now, to
raise a pound sixteen feet required sixteen foot-pounds
of work; there must therefore have been sixteen foot-pounds
of energy at the instant of impact. Its velocity
was thirty-two feet per second. Hence a body weighing
one pound, having a velocity of thirty-two feet in a
second, is capable of doing sixteen foot-pounds of work.
It is found also that if the same body falls for two
seconds, it will fall sixty-four feet, and its velocity at
\DPPageSep{073.png}{61}%
the end of the second second will be sixty-four feet,---twice
as great as it was for the fall of one second; but
the pound weight in this case will rise under similar
\index{Weight}%
conditions to the height of sixty-four feet, which is four
times higher than for thirty-two feet per second; so it
is seen that in this case, when the velocity is doubled,
the power of doing work, measured in foot-pounds, has
been increased four times, and this is generally expressed
by saying that the energy of a body is proportional
to the square of its velocity. The particular
direction in which a body moves has not been found to
make any difference in this regard, so the statement is
a general one. If a mass weighing two pounds were
dropped, as in the first instance, it would rise no higher
than if it weighed but one; but two pounds raised sixteen
feet would give thirty-two foot-pounds, so the
work would be proportional to the weight as well as to
the square of the velocity.

The amount of matter there is in, say, a pound weight
would be just the same in one place as in another; but
the attraction of the earth upon it depends upon where
it is. At the surface, where we measure it, it has a
certain value; but at the centre of the earth it would
weigh nothing. The farther it were removed from
the surface of the earth upwards, the less would its
weight be. At the height of a thousand miles it would
be but four-fifths of a pound; at a million miles it
would be but sixteen-millionths of a pound, or only
about the tenth of a grain.

For that reason it has become necessary to find
some measure for matter that shall be independent of
\DPPageSep{074.png}{62}%
\index{Foot-pound}%
\index{Work, measure of}%
position, and this has been found by dividing the weight
of the body at a given place by the value of gravity at
that place, and calling the quotient the \emph{mass}; so if $w$~represents
the weight of a body at a given place, and
$g$~the value of gravity at the same place, that is, the
velocity that gravity will give to a body in one second
if left free to fall, then $\dfrac{w}{g} = m$, the mass. The distance
in feet that a body will fall in a second is equal
to the square of the velocity divided by twice the value
of gravity, or~$d$, the distance,~$= \dfrac{v^2}{2g}$; and as the weight
equals~$mg$, the product of the two is $mg × \dfrac{v^2}{2g} = \dfrac{mv^2}{2}$,
one-half the product of the mass into the square of the
velocity will give the energy of a body. But it is
generally more convenient to use the weight of the
body instead of its mass. As $m = \dfrac{w}{g}$, let it be substituted
for~$m$ in the expression of energy, and we shall
have $\dfrac{wv^2}{2g} = pd$ (pressure in pounds into distance in
feet), or foot-pounds, a very convenient expression to
keep in mind if one has any problems in motion and
energy for solution.

An example will make plain the utility of this. A
body weighing ten pounds is moving with the velocity
of one hundred feet in a second; how much energy has it?
$\dfrac{wv^2}{2g} = \dfrac{10 × 100^2}{64} = 1562~\text{foot-pounds}$; that is, it has
energy enough to raise $1562$~pounds a foot high, or ten
pounds $156.2$~feet high.
\DPPageSep{075.png}{63}%

This is applicable to all bodies, big and little, whose
weight and velocity of translation are given.

When a person who weighs one hundred and fifty
pounds climbs a flight of stairs---say, to the height of
ten feet---he has done $150 × 10 = 1500$ foot-pounds of
work. Whether he has gone up fast or slow makes no
difference in the amount of work done; it will only
make a difference in the \emph{rate} of doing work. Now, a
horse-power is a rate of work, and is equal to $550$~foot-pounds
a second; and hence if the above individual
climbs the stairs at the rate of four feet a second, he
will be doing $4 × 150 = 600$ foot-pounds per second,
which is over a horse-power, and indicates the
probability that he would not climb so fast. If any
one thinks he can do it, it will be worth his while to
try it.

Work can be measured on a horizontal as well as a
vertical plane. Suppose the horses on a horse-car pull
two hundred pounds, as indicated by a dynamometer,
and the car is moved five feet in a second: the pull
into the distance measures the work done; that is,
$pd = 200 × 5 = 1000$ foot-pounds, a little less than
two-horse power. These illustrations are given because
not every one has clear enough ideas concerning the
meaning of energy and work, much less the ability to
apply them to examples that may often come up.
When one sees the long trail of a meteor in the sky,
and remembers that its velocity may be as much as
twenty or more miles per second, he will now see that
it may have a good deal of energy, though its weight be
but a few grains.
\DPPageSep{076.png}{64}%
\index{Energy of translation}%
\index{Meteors}%
\index{Work, measure of}%

The energy of a pound moving twenty miles a second
would equal
\[
\frac{1 × (20 × 5280)^2}{64} = 174,240000 \text{ foot-pounds.}
\]
A grain is one seven-thousandth of a pound, and its
energy would therefore be but the one seven-thousandth
of that quantity. $\dfrac{174,240000}{7000} = 24891$, which is the
number of foot-pounds of work a meteor weighing one
grain, at that velocity, may have: enough to raise a
ton twelve feet high.

As a matter of fact, the great friction it is subject to
in its path through the air heats it shortly to incandescence,
and it is presently dissipated. If it were not for
the air, therefore, even if we could subsist without it,
mankind would be in constant danger from the flying
missiles; for though they would weigh but a little,
their velocity would enable them to do destructive
work upon everything they struck. As there are some
millions that come into the atmosphere every day, no
one could be safe from them in any place.

The energy of a workingman is measured in the
same way; namely, by the amount of work in foot-pounds
he can do.

One of the most direct ways of knowing this for an
individual is to ascertain the amount of earth or stones
he can load into a cart, or the bricks he can carry up a
ladder to the mason. Suppose he throws fifteen shovelfuls
per minute, each one holding ten pounds, and each
one is raised four feet high: then in a minute he has done
\DPPageSep{077.png}{65}%
\index{Goose, work in flying}%
$15 × 10 × 4 = 600$ foot-pounds of work, or $10$~per second.
This is rather a small quantity, only the one fifty-fifth of
what a horse-power would do, and most men have been
found able to do forty or fifty foot-pounds per second;
still, there is a great difference in individuals in their
working ability. Climbing, in general, is hard work
because it is continuous lifting of one's self. One who
weighs one hundred and fifty pounds, and climbs one
hundred feet, has done $15000$ foot-pounds of work; and
if he has done it in a minute, he has spent nearly half a
horse-power, which is $33000$ foot-pounds a minute.

Once more: a bird in flying has to do work; and one
may see how much is demanded of such birds as geese,
that make long voyages through the air in the fall and
spring,---sometimes for twelve hours or more continuously.
As work is measured by pressure into distance,
one may apply it thus. Geese are known to fly at the
rate of thirty miles per hour, which is forty-four feet per
second. In flying, of course, there has to be a push
forward by means of their wings, not only to advance,
but to maintain their elevation. Supposing that a large
bird flying at this rate should have to exert a push of
one pound continually: it would be expending then forty-four
foot-pounds per second, nearly one-twelfth of a horsepower;
and to maintain such a rate for twelve hours
would imply that it had a supply of energy to start with
of $44 × 60 × 60 × 12 = 1,900800$ foot-pounds for one
day's expenditure. This does not seem at all probable,
and one may therefore infer that the pressure exerted
when going at that rate is much less. If the pressure
were but one ounce instead of a pound, the rate of work
\DPPageSep{078.png}{66}%
\index{Energy of vibration}%
would be $\dfrac{44}{16} = 2.75$ foot-pounds per second, which is
much more likely; but this supposes the bird to have a
supply of energy of $\dfrac{1,900800}{2.75} = 700000$ foot-pounds.

In the chapter on ``\hyperref[chap:chemism]{Chemism},'' the source of the
energy of animals will be more particularly treated.

So far the energy involved in translatory or free-path---or,
as it is more often called, mechanical---energy
has been considered; but vibratory motions of matter involve
energy also, and the same expression is applicable
as in the first case,~$\dfrac{wv^2}{2g}$. Here the value of the~$v$,
or the velocity, has to be determined by analyzing the
motion itself. This is not simply the number of times
the body vibrates, but also the extent of each individual
vibration,---that is to say, the amplitude of vibration,---and
the product of these two factors will give the
value of~$v$ needed. So if $n$~be the number of times the
body vibrates a second, and $a$~be the amplitude of the individual
vibrations, the true velocity will be represented
by~$an$, and then the expression for the energy will be
\[
\dfrac{wa^2 n^2}{2g}.
\]
For most bodies of visible magnitude the amplitude of
vibration is so small a quantity that for frequencies of
only a few hundred per second, the velocity, measured
as a translation, is small, and therefore the energy is
small, and there are few cases where it is very important
to take it into account.

Suppose a vibrating body has an amplitude of the
\DPPageSep{079.png}{67}%
one-hundredth of an inch, and vibrates a hundred times
in a second: the total distance moved through in a
second would be but an inch, which would be the value
of~$v$, so the amount of energy it had would depend
more largely upon the weight of the body. On the
other hand, if a body is so small that its rate of vibration
is exceedingly high, as was shown in the case of
atoms on \Pageref{page}{53}, there might be a relatively large
amount of energy involved. In the case refered\DPnote{** [sic]} to, a
velocity of eighty miles a second was computed, on
\Pagelabel{67}%
the supposition that the amplitude of vibration was
equal to one-half the diameter of the atom; and what
amount of energy is possessed by a body weighing one
grain was computed. The amount in an atom with
that vibratory rate and amplitude would be calculated
by dividing the amount in the grain by the number of
atoms in a grain. Numerically it is a very, very small
quantity, and only becomes appreciable to any of our
senses when vast numbers of atoms act conjointly.

There are some cases where energy is apparently
expended when there is no apparent motion, as is the
case when a man holds up a weight. If the weight be
\index{Muscular work}%
\index{Work, muscular}%
a heavy one, exhaustion will be the result as much as if
energy was spent in any other way. This muscular
work is called physiological work, and for a long time
it was not understood. It is now known, however, that
when a muscle is put in a state of tension, it is in longitudinal
vibration a great many times a second. This
may be perceived by putting the end of a finger into
the ear, pressing but gently, at the same time squeezing
with the rest of the hand as if grasping something
\DPPageSep{080.png}{68}%
\index{Energy of rotation}%
tightly; a low sound will be heard, made by perhaps
no more than thirty or forty vibrations per second.
The muscles in a state of tension produce this. When
one holds up a weight---say, a pail of water---the muscles
involved yield and contract rapidly, so the weight
is really raised in a vibratory way a short distance, but
a great many times in a second; and the heavier the
weight, the more the work done, and this too is measured
in the same way as other more visible kinds.
There is good reason for believing that a book resting
upon a table is supported by the vibratory motions
going on among the particles of the table, and therefore
energy is expended to do it, and that this is supplied
by the heat present in the body; that is, the
temperature of the table is a little different from what
it would be if it did not have any weight to support.

Walking involves the expenditure of energy in the
same way. Each step requires the whole body to be
raised somewhat. Suppose it be only an inch. A
person weighing $150$~pounds would, for each step, do
$\dfrac{150}{12}$ foot-pounds~$= 12\frac{1}{2}$. If he takes two steps per
second, then each minute he does $2 × 12\frac{1}{2} × 60 = 1500$
foot-pounds of work. Thus one can see how physiological
processes are measurable in terms of mechanical
units.

The energy of a rotating body is more complicated
than translational energy, because a part of the body is
at rest,---the axis; and the velocity of movement at
any point away from that is proportional to its distance
from it. In the case of the balance-wheels of steam
\DPPageSep{081.png}{69}%
engines, where the most of the weight of the wheel is
in the rim, the velocity of the latter would be equal to
its circumference multiplied by the number of turns
per second or per minute. Thus if a fly-wheel, having
nearly the whole of its weight in the rim, weighs, say, a
ton ($2000$~lbs.), is six feet in diameter, and rotates four
times a second, its velocity will be $75.4$~feet per second,
and its energy will be $\dfrac{wv^2}{2g} = \dfrac{2000 × 75.4^2}{64} = 177661$
foot-pounds, an amount of energy which is stored up,
\Pagelabel{69}%
and may be drawn upon to prevent fluctuations in
speed to which engines in workshops are liable.

If a body having rectilinear motion be left to itself
in the air, it will speedily be brought to rest, for gravity
will bring it to the earth whether it be moving this way
or that. The air, too, will retard its motion, and would
ultimately bring it to rest if nothing else did, as it
would either of the other kinds of motion. If, however,
one could contrive to give to a body above the atmosphere
a sufficient velocity in a tangential direction, the
body would become a satellite, and revolve round the
\index{Satellite}%
earth. The curvature of the earth is about eight
\index{Earth, curvature}%
inches to the mile, and such a body would then need to
move a mile in a horizontal direction in the same time
it falls eight inches in order that it should continue to
go about the earth. As it takes about two-tenths of a
second to fall this distance, its velocity would need to be
five miles a second to prevent it from falling to the
earth; this velocity would carry it quite round the earth
in a little less than an hour and a half.

Thus it is seen that, in order that matter should
\DPPageSep{082.png}{70}%
\index{Energy, factors of}%
\index{Motion, laws of}%
possess energy, it must have motion of some kind;
indeed, that energy has two factors, mass and motion.
When either of these is zero, there is no energy. This
is a consideration of great importance both in a scientific
sense and a philosophical one. One may often
hear it said and read it in carefully written books that
matter and energy are the two realities or physical
things in the universe, and energy is spoken of as if it
were an entity, or something that might exist though
there were no substance to move. If energy be a
product, and motion be one of the factors, then in the
absence of this there is no energy. This perhaps will
be seen still clearer after considering what are called
the laws of motion, which were first formulated by
Newton, and which, in conjunction with the law of
gravitation, were the fundamental principles that
enabled him to produce the ``Principia,'' which is what
\index{Principia}%
to-day we would call a treatise on mechanics.

Of course, the science of mechanics is applicable to
motions of matter of any magnitude and in any place;
and Newton chose to follow out his newly discovered
principles into astronomy to the largest extent, and it
remained for later generations to employ the same principles
in other directions, largely molecular and atomic.

The first law of motion is, that whether a body be in
a state of rest or of motion, it will remain in that state
of rest or motion until compelled by the action of some
other body upon it to change its state. This is sometimes
expressed by saying that all matter has \emph{inertia},
\index{Inertia}%
\Pagelabel{70}%
or an inability to move or change its direction or velocity
if it has motion. This appears to be experimentally
\DPPageSep{083.png}{71}%
\index{Explosion products}%
true of all bodies whose magnitude and state
we can see. But it may very well be doubted if the
ordinary conception of the inertness of matter be true.
Many of the facts of chemistry indicate that matter in
its atomic form is not altogether so helpless as it has
been supposed to be. A stone may lie in the road for
an indefinite time and no one would suspect it possessed
any energy to do anything, and so of any other kind of
matter. Here is a piece of charcoal. Has it inertness in
any extreme sense of that word? Here is some sulphur
and some nitrate of potash; they, too, will lie as
quiescent as the coal and as long. Pulverize them and
mix them together, and we have powder the energy of
which would wreck a building. The products of the
explosion are gaseous mostly, and the carbon, the sulphur,
and the nitrate of potash have vanished as such,
and have entered suddenly into new combinations;
they have developed also a large amount of heat, while
at the beginning their temperature was that of other
bodies around them. This source of energy must have
been resident in the atoms; and if it is perceived that
for a body to have energy it is necessary for it to have
motion of some sort, it will be apparent that the
material itself must have possessed a large amount of
motion, even when it appeared to be at rest. If one
thinks that the law of inertia might still apply to atoms,
and that they cannot individually move except as they
are acted upon by other atoms, and even then only as
much as by the measure of the motion thus imparted,
he had better figure out to himself the energy of such
explosions per molecule, and see if anything initially
done will account for it.
\DPPageSep{084.png}{72}%
\index{Motion, antecedent of}%
\index{Top, sleep of}%
\index{Vortex rings, properties of}%

When the mechanism of a clock is running, the
motion may be traced to a falling weight, and the work
done is measured by the product of the weights into
the distance it falls as the clock runs down; but in
the case of the powder, though the amount of energy
developed by the explosion is definite, it is not measured
by the work done in pulverizing and mixing and igniting
it. The case is much more nearly analogous to
that of a sleeping man. While asleep he would neither
move nor stop moving unless some other agency acted
upon him, any more than would a stone or other mass
of matter; and in that sense he would be inert, yet no
one would think of calling a sleeping man inert, except
in a very loose sense.

Furthermore, there is an experimental analogy that
may help one to see a little deeper into this. Every
one knows what is meant by the ``sleep'' of a spinning
top. It appears to be absolutely at rest, and may not
even hum; but touch it, and the effect upon it will be
out of all proportion to the slightness of the touch.

It has been observed as a property of vortex rings that
they have a tendency to move forward in the direction
of their axes, and when prevented from going forward
they press upon the body that arrests them. If they
be brought to rest, and then the barrier be removed,
\emph{they, of their own accord}, start on in the same direction
as if pushed from behind. Such a body cannot be
said to be inert without modifying the common meaning
of the word.

This is not alluded to here as proving anything; but
inasmuch as the vortex-ring theory of matter has a good
\DPPageSep{085.png}{73}%
\index{Motion, laws of}%
probability in its favor, this property I have mentioned
helps one to understand how the atoms might be other
than inert, and yet large bodies of them together exhibit
that property with the rigorousness our observations
upon such bodies demonstrate. Suppose each
atom had the ability to move forward of its own impulse
when not acted on by any other atom. If there
were a million atoms joined together, no matter how,
provided they were promiscuously faced, they would
mutually neutralize each other's ability to move in any
direction, and the resultant of the whole would be that
passivity which we call inertness.

We may by and by see that there may be still other
good reasons for thinking matter not to be so passive
as it has been often assumed to be.

The second law of motion is, when two or more
bodies act upon a third body, the effect of each is the
same as if it alone acted, and the combined effect is
called the resultant; and the third law is, that action
and reaction are always equal and opposite in direction.
This third condition of action, or the relation of
motions in two bodies, is of a high degree of philosophical
importance, perhaps not more so than the others,
but of so much that it is worth while to attend to it
more particularly than to the second law. If a rope be
tied to the wall and one pulls upon it so as to make it
taut, the wall pulls back in the opposite direction as
much as the arm pulls forward. A spring-balance
attached to the wall would indicate the strength of the
pull, the pull of the arm representing the action, and
measured by the muscular vibration, as already described,
\DPPageSep{086.png}{74}%
and the pull of the wall representing the
reaction, and equal to the action in quantity and maintained
by molecular vibration. Imagine the action of
the arm to be steadily increasing in quantity: the
reaction of the wall would correspondingly increase
until the molecular tension could no longer be increased,
and either the rope would break, the hook be pulled out
from the wall, or the wall itself be broken away; but in
no case could the action exceed the reaction or \textit{vice
versa}. Now, if the amount of matter in the arm were a
constant quantity, as well as that of the rope, the hook,
and the wall, then it would follow that all the physical
changes noted in either the one or the other, so far as
energy is concerned, must be due to the motions involved
on either side. And if action and reaction be
equal, and the quantity of matter be uniform, then the
amount of motion involved must be equal on the two
sides. If a body in motion strikes another body, and
the second one is set in motion, the amount of motion in
the two will be just equal to the amount of motion
in the first. The amount of motion gained by one
body is just equal to that lost by the other, and there
has been simply an exchange of motions, one having
gained, the other lost; the one that gained being the
one that had less, and the one that lost having had
more, than the other one. In books of physics it is
customary to speak of the amount of motion a body has
as its \textit{momentum}; and it may be measured by multiplying
\index{Momentum}%
the mass of the body by its velocity, and oftentimes
one may read that in the physical exchanges that are
all the time happening in matter the momentum is
\DPPageSep{087.png}{75}%
conserved; that is to say, is neither increased nor
diminished. Seeing, therefore, that the amount of
matter is a constant quantity, and the momentum a
constant quantity, it follows that the amount of motion
is constant. Motion is conserved as well as matter. If
the amount of matter in the universe be constant, then,
according to this statement, the amount of motion must
be constant, and the amount of energy constant also.

It is generally agreed that this statement concerning
energy is true, and one hears often about the law of
the conservation of energy. It seems to be less clearly
recognized that the third law of motion implies the conservation
of motion, provided matter is itself a constant
quantity. But there is another condition of things that
is as uniform as any other condition of things in
nature that has not been recognized as a law, and yet it
deserves to be perhaps as much or more than most
others, since, in our experience, it is never known to
vary; it is this: Wherever there is an interchange of
motions between two bodies, the transfer is always
from the one having more to the one having less. As
exchange of motions implies transfer of energy, it follows
that all transfers of energy of any given kind are
from bodies having more to those having less.

Cause and effect are always determined by such a
\index{Cause and effect}%
disposition of things, though not every one has apparently
seen that questions involving what they please
to call causes and effects presume a kind of antecedent
and consequent that always work both ways at
the same time, for there is no such thing as an isolated
phenomenon. If everything takes place so and so
\DPPageSep{088.png}{76}%
because there is an exchange of motion going on,
then this thing that now moves faster than it did has
been acted upon by a body that had more motion in
this direction than the former one had, and it has
imparted some of its motion at the expense of its own
energy. If one inquires what caused the increased
velocity to this body, it may be said it was caused by
the impact with another body. In like manner one
may inquire what caused the slowing-up motions of the
second body, and the answer still must be, the same
impact with the first body. So, for every phenomenon
there is a corresponding and complementary phenomenon,
which it is just as appropriate to consider as a
cause as it is the first, and either element is just as
much a cause as the other, and in each and every case
all there is involved are exchanges in the amount and
kinds of motion in matter.

There remains now the consideration of a topic
which those who have studied physical subjects only a
little must be more or less familiar with. The term
``potential energy'' has been much employed within the
last twenty years to express a certain condition of matter
that renders it a source of energy when no motion
is supposed to be involved: thus, where a weight is
raised, like that of a clock, or of a stone raised to the
roof of a house. By falling, either of them can be
made to do work; but so long as they remain raised
and are apparently quiescent, their stock of energy is
measured by their weight into their height, i.e., foot-pounds;
and this is said to be \textit{potential energy}. Examples
of this sort are numerous. The wound-up spring
\DPPageSep{089.png}{77}%
\index{Energy, factors of}%
of a clock or watch, a bent bow, compressed air or
steam, powder, nitro-glycerine, and the like explosives,
coal, wood, and other kinds of fuel, are all varieties of
so-called potential energy. Let it be remembered that
we have in natural phenomena matter and ether and
space and time and motion. If matter and ether be
substances, then the product of one into the other
would signify nothing; it would be physical nonsense.
So likewise would be the product of matter into space
or time; and yet if matter is to be possessed of energy,
and motion is \emph{not} one of the factors, then either space
or time must be, and no one can imagine how energy
can in any way depend upon time as a factor, and there
is no degree of probability that it is or can be so; and
hence, though we had no hint of how it might be, one
would need to avow his belief that in some way motion
was involved in every case where physical energy was
involved, for in any case where it had been hitherto
possible to trace it, it had been found to be present as
a factor in precisely the same relations as in all other
known cases, and hence he would avow a disbelief in
the existence of potential energy in any other than a
loose sense for a condition where the character of the
motion involved was obscure. This would imply that
all energy is kinetic, whether the character of the
motion was determined or not. This view is now held
by those who have taken the pains to think out the
necessary relations that are involved in this subject.

In the last edition of the ``Encyclopædia Britannica,''
Professor Tait, who contributed the article on ``Mechanics,''
says, ``Now, it is impossible to conceive of a truly
\DPPageSep{090.png}{78}%
\index{Molecular fatigue}%
dormant form of energy whose magnitude should depend
in any way on the unit of time; and we are therefore
forced to the conclusion that potential energy, like
kinetic energy, depends in some unimagined way upon
motion;'' also, ``The conclusion which appears inevitable
is that whatever matter may be, the other reality
in the physical universe which is never found unassociated
with matter depends in all its widely varied forms
upon motion of matter;'' and in another place, ``Potential
energy must in some way depend upon motion.''

It was pointed out (on p.~67) that what was called
physiological work is now known to depend upon
the vibratory state of muscles in a state of tension.
Before that explanation was known, one might have
called such, potential energy, if it had not been for the
sense of fatigue felt by one who was doing such physiological
work that forbade him to assume that actual
energy was not employed to maintain such a stress;
and when it becomes evident, as it has, that one cannot
press upon a table, or pull upon a rope, or bring about
in any way a push or a strain upon matter, without
varying the temperature of the body, it is no longer
difficult to understand that all changes of that sort
upon matter result in atomic and molecular stresses,
for they are placed in abnormal positions as well as
stretched muscles, and their energy is spent in a similar
manner. There is a curious phenomenon exhibited
by all bodies that are made to do atomic and molecular
work for a considerable time. They become exhausted,
like living things, and require rest to recover their
properties. Thus, a tuning-fork, if kept artificially
\DPPageSep{091.png}{79}%
\index{Energy in the ether}%
vibrating for some time, will stop almost instantly
when the driving force is stopped, though at the outset
it would continue to vibrate for a minute or more when
left to itself. This is caused by what is called the
fatigue of elasticity: the body loses some degree of its
elasticity, and requires time to recover it. I have called
the phenomenon curious. Perhaps it is no more so
than any other phenomenon manifested by matter; but
it is so similar to what is so characteristic of living
things, that it almost excites one's sympathy. One
can have compassion for an overworked and exhausted
horse, but an overworked tuning-fork! The expression
would seem to be wholly inapplicable, but the fact is as
stated. The only difference between the cases is, one
has nerves, and becomes conscious of the exhaustion,
the other not.

So far, both motion and energy have been considered
as related to matter, and matter as defined in the first
chapter, as distinguished from the ether, though immersed
in it, and can by no means be isolated from it;
but energy exists in the ether as well, as we are assured
by many phenomena. That light requires about eight
minutes to come to us from the sun has been proved in
numerous ways. When it gets to the earth it is found
to be able to impart energy to the matter it falls upon:
it may heat it and affect it in other ways that are
measurable, so energy gets to us from the sun, and is
eight minutes in transit in the ether. If we do not
call ether matter, and it has been shown that there are
good reasons for not doing so, then it follows that
energy exists outside of matter, and it is a proper line
\DPPageSep{092.png}{80}%
\index{Light, energy of}%
\index{Light, its nature}%
of inquiry to learn what shape the energy exists in,
and what mechanical conceptions are appropriate when
thinking about it. In matter one may isolate motions
of various sorts. A mass of matter, say, like a baseball,
may have translatory motion: it may vibrate or it
may spin. In each case one may contemplate the kind
of motion, and compute the energy involved in the
movement, and this is true for atoms as well as larger
masses; but when the substance is not made up of
discrete parts, but is absolutely homogeneous with no
interstices, and apparently incapable of changing either
its position or its form, as there is good reason for
thinking to be the case with the ether, it becomes
\index{Ether}%
much more difficult to picture to one's self just what is
happening when motion of any sort is involved. As
has already been said, we know that light consists of
waves, measurable quantities, and we know how much
energy reaches the earth from the sun and falls upon a
square mile or square foot. There have been several
estimates of this quantity, and it is found to be equal to
about one hundred and thirty foot-pounds per second for
each square foot section of sunshine. This signifies, of
course, that that is the amount of energy in a column
of ether one foot square and a hundred and eighty-six
thousand miles long, for that is the amount that arrives
per second. So one may calculate the amount of energy
there is in a cubic mile of sunlight to be about twelve
thousand foot-pounds, and also that the amount given
out by the sun in a second is about four millions of
foot-pounds, or nearly seven thousand horse-power for
each square foot of the sun's surface. All of this energy
\DPPageSep{093.png}{81}%
\index{Electro-magnets}%
\index{Magnetic waves}%
\index{Magnet, electro}%
is handed over to the ether, which distributes it in all
directions as undulatory movements which we call light.
Such wave motions do not exhibit anything like what
we call momentum as waves in water or air always do,
and they are therefore in striking contrast with waves
in matter. Moreover, being waves, having the amplitude
at right angles to the direction of propagation,
they must be compounded of two motions,---a rectilinear
and a vibratory one,---and not a simple one such
as a particle of matter may have.

The ether is capable of being affected by other
motions of matter than simply the vibratory one of
atoms and molecules.

Whenever an electro-magnet is made, it reacts upon
the ether in such a way as to affect other matter that
chances to be in the range of ether so affected. It
appears as if the ether were thrown into a state of
stress which it retains so long as the magnet retains its
property; and this condition extends to an indefinite
distance in all directions. If such an electro-magnet is
made and unmade by opening and closing an electric
current in its coils, there will be formed a set of electro-magnetic
waves in the ether which will travel outwards
from the magnet in a manner similar to light-waves,
only they will have an enormous wave length. If the
circuit be closed but once a second, the waves will be a
hundred and eighty-six thousand miles long; for a wave
in the ether travels in it with a velocity that depends
solely upon the property of the ether to transmit disturbances,
and not at all upon the source of the disturbance.
That such an electro-magnetic wave possesses
\DPPageSep{094.png}{82}%
\index{Gravitation}%
\index{Newton, Sir Isaac}%
energy, and can do work, one may satisfy himself by
observing the motions produced by them upon magnetic
needles within the affected space.

In like manner an electrified body puts the ether into
a different kind of a stress from the magnet; and when
this is done periodically, as it may be by an induction
coil, and in other ways, electrostatic waves are set up,
and these too travel with the speed of light, and are
capable of affecting matter to a great distance, thus
showing that the ether may possess energy in an electro-static
form, as distinguished from the electro-magnetic
and light. There are some physicists who think these
last two to be identical, and the reasons for their
opinion will be given in a subsequent place.

It only remains to point out that whatever the nature
of gravity may be, there can be very little doubt that
the ether is intimately concerned in it, as Sir Isaac
Newton supposed was the case. But if it is, and ether
is the agency by which one mass of matter is able to
affect another mass, then ether is in a state of stress
produced by the atoms of matter all the time, and
therefore in some way gravitative energy is lodged in it.
As the ether is so universal in its extension, one cannot
but see that it is a storehouse of an almost unlimited
amount of energy of many kinds; so that if every
particle of matter were instantly annihilated, there
would still be a universe filled with energy, though it
might not be serviceable, because lacking the conditions
for transformation into useful forms. This may
be said to be one of the functions of matter---the transformation
of the energy it gets from the ether.
%\DPPageSep{095.png}{83}%


\Chapter{V}{Gravitation}{83}

\index{Attraction, gravitative}%
\index{Newton, Sir Isaac}%

\First{That} all bodies will fall towards the earth if raised
above its surface and left unsupported everybody
knows and must always have known, for it is a fact
thrust into everybody's notice constantly and as long
as he lives. Also that bodies resting upon the earth
require energy to be spent in order to raise them
from it is equally well known. Thus all bodies act as
if they were attracted by the earth, and the weight of
a body is the measure of the attraction of the earth
upon it.

One not unfrequently comes across statements by
authors implying that Newton was the discoverer of
this attraction which is called gravitation. This is a
mistake: not only was this idea common in Newton's
day, but the word itself was in extensive use. Kepler
had affirmed that the sun attracted the earth and the
planets, and Galileo had busied himself very much
with the study of attraction of the earth upon bodies.
The problem that Newton had before him was not
as to the existence of gravitative action, but what
was its law of operation and the limits of it, if it had
any limits. The familiar story of the fall of the apple
leading to the great discovery is generally believed to
\DPPageSep{096.png}{84}%
\index{Gravitation, law of}%
be mythical; at any rate, other facts well authenticated
do not accord with that story. When he was twenty-three
years old he undertook to apply the law as we
now have it, to the moon, using the size of the earth
and the moon's distance from it, as they were then
best known. The result satisfied him that his surmise
could not be the law, if the measure of the earth then
had was accurate. This was in 1666. In 1683 he
learned of some new measures recently made of the
magnitude of the earth, indicating it to be larger than
had been supposed. Then, with the new measures for
data, he made a new computation. It was then, when
he saw that the results were to prove his conjecture,
and he perceived the immense importance of the discovery,
that he handed over the unfinished work to an
amanuensis, because he was too much agitated to complete
it. If the discovery was made when he first
thought of putting the idea to the test, it is strange
that his emotional excitement should have been postponed
for seventeen years. Evidently it was at the
latter date when he thought he had made the discovery.
It was the \emph{law} of gravitation that Newton discovered,
and that it was universal. Every particle of matter
attracts every other particle; and the strength of this
attraction varies as the mass of each, and inversely as
the square of the distance between them. Thus, if at
the surface of the earth gravitation gives a weight of
one pound to a body, at the distance of ten radii of the
earth $= 40000$~miles, the weight would be $\dfrac{1}{10^2}$, one-hundredth
of a pound, and at the distance of the moon,
\DPPageSep{097.png}{85}%
\index{Attraction depends upon distance}%
or sixty radii of the earth, the body would weigh but
$\dfrac{1}{60^2}$=one thirty-six hundredth of a pound, and would
fall towards the earth in a second but $\dfrac{1}{3600}$ of the distance
it would fall at the surface of the earth, where it
is about sixteen feet. One thirty-six hundredth of sixteen
feet is about the one $\dfrac{1}{224}$ of a foot, which is
therefore the departure from a straight line the
body at the distance of the moon must make per
second to move round the earth. The mutual attraction
of these bodies at that distance is sufficient to produce
this amount of deflection, and hence accounts for
the rotation at that distance. When the same mathematical
relation is applied to the planets, comets, and
meteors that revolve about the sun, it is found to be
applicable to every one of them; and in the depths of
space in every direction are to be seen multitudes of
stars revolving about each other in similar manner, and
hence it is concluded that gravitation is a universal property,
and the law is applicable throughout the universe.

There are other kinds of attraction that matter
exhibits, such as electric and magnetic, that follow a
part of the above law, but do not the other part. The
law regarding the distance is true for electrified bodies,
but the mass of the bodies does not enter as a controlling
condition. So it appears that the variability of
attraction with the distance is a geometrical condition,
and depends upon the property of space, and is not
peculiar to any physical phenomenon. Sound, light,
\DPPageSep{098.png}{86}%
heat, electricity, magnetism, as well as gravitation,
exhibit the property, as do circles and spheres. The
peculiar thing about gravitative attraction is that it
depends upon the masses of the attracting bodies, and
is not modified in the slightest degree by the interposition
of any substance of any magnitude between the
attracting particles or masses. In this particular it is
strikingly unlike magnetic attraction. If, for instance,
a piece of iron is brought between two magnets that at
a distance are attracting each other, the strength of
their action upon each other is decidedly less. The
strength of the attraction of the sun is just as great
upon a particle in the centre of the earth as for any
similar particle at an equal distance that is not
shielded.

There have been numerous attempts in the past to
account for gravitation. It has been imagined that
space was full of particles swiftly moving in every direction
that produced a pressure upon all bodies by their
impact; that each body shielded other bodies in a measure,
and hence the pressure produced upon the adjacent
sides would be less than elsewhere, and, as a consequence,
each body would be pushed in the direction of
an adjacent body. But a push represents expended
energy, and this would imply that the moving particles
must be losing energy at the expense of their velocity;
and as no such particles are known, and if there were,
their velocity would have to be so much greater than
that of light, there is no degree of probability to be
allowed for the idea. The effect of vibrations upon
the ether has been a very common manner of attempting
\DPPageSep{099.png}{87}%
\index{Attraction of vibrating fork}%
to explain gravitation. It has been observed that if
light bodies are brought near to a vibrating body like a
tuning-fork, they are apparently attracted by it so long
as the vibratory motion continues; and the action is
explained by the rarefaction produced by the vibratory
motion, which reduces the pressure in the space about
the body, so when another body is brought near the
pressure is greater on the remote side than it is on
the side adjacent, and thus the body is pushed towards
the one vibrating. It is known that all the atoms of all
bodies are in a state of vibration at all temperatures;
and hence it was inferred that the pressure of the ether
must be reduced next to their surface, so that between
two atoms or molecules the pressure must be less than
external to them, and hence the pressure of the ether
will crowd them together. This idea has been worked
out by a large number of persons in different countries.
There are two fatal objections to this hypothesis:
First, it would make the attraction of gravitation
dependent upon their temperature, and there is no evidence
to show that temperature makes any difference;
and second, that the velocity of gravitative action is the
same as that of light. There is an abundance of astronomical
evidence, that if it has any velocity at all it
must vastly exceed that of light. If it were as much
as a million times greater, astronomical phenomena
would exhibit it plainly.

Seeing that every particle of matter in the universe,
affects every other particle in a certain and definite
way, no matter what the distance between them, there
must be either the possibility that a body can act upon
\DPPageSep{100.png}{88}%
\index{Newton, Sir Isaac}%
another one at a distance without any medium between
them,---which is called action at a distance,---or there
\index{Action at a distance}%
must be a medium which is first affected by the bodies,
and which in turn reacts upon other bodies in it.
What Sir Isaac Newton thought of these contingencies
was cited in a former chapter (see \Pageref{p.}{31}). It
is now generally felt to be not only essential for consistent
mechanical thinking, but that in some way the
ether which is known to exist must have some essential
part in the phenomenon. It has been the subject
of curious speculation why Newton should so strongly
state his belief in the existence of a medium for the
propagation of physical conditions, and yet in his work
on light he should adopt the corpuscular theory---that
light consisted of emanations, which was a practical
denial of the hypothesis of the ether. The explanation
of the anomaly is probably in the fact, that he
could treat in his mathematical way the ideal corpuscles,
while he could not so treat the ether hypothesis of
waves. His work was developed with ideas he could
handle; and the outcome of it was that the science of
light was retarded by his misconceptions for a hundred
years, for every one now who knows anything about it
knows that Newton's hypothesis was a wrong one.
There are some persons who would curb the imaginations
of others in physical things by quoting Newton's
dictum, ``Hypotheses I do not touch,'' but they omit to
mention that Newton's work on optics was altogether
based upon a hypothesis that has wholly broken
down. Every one of the explanations he gave of
such phenomena is worthless, and no one gives attention
\DPPageSep{101.png}{89}%
\index{Neptune, discovery of}%
to them except for their historic relations to the
science.

It has been thus in other lines. A symbolic representation
of things such as offers the possibility of
mathematical treatment has been seized and worked out
to great length, when the actual phenomena pretended
to be treated gave no countenance to the conceptions.
Such has been the case in electricity and magnetism and
heat. The mathematicians fought Ohm's, Faraday's,
and Joule's mechanical conceptions until death stopped
them.

It is certainly true that all physical phenomena are
subject to strictly mathematical conditions, and mathematical
processes are unassailable in themselves. The
trouble arises from the data employed. Most phenomena
are so highly complex that one can never be
quite sure he is dealing with all the factors until
experiment proves it. So that experiment is rather a
criterion of mathematical conclusions and must lead
the way. Mathematics is a deductive science, yet the
\index{Mathematics}%
number of physical facts or phenomena that have been
discovered by its aid is so small that they may almost
be left out of the count. There is the discovery of the
planet Neptune, that has been spoken of as a triumph
of mathematical science, yet one of the most competent
mathematicians that ever lived---Professor Peirce of
Harvard---declared that it was only a lucky find, for the
computations would apply just as well to a planet $180°$~from
it. The conical refraction of light is another
one. Altogether they make but a small figure and
are unimportant. The law of gravitation was discovered
\DPPageSep{102.png}{90}%
\index{Gravitation}%
\index{Hypothesis, gravitation}%
\index{Kepler, the guesser}%
by trial, and although its importance is second
to none other yet discovered, it happens that it is one
of the very simplest and least complicated with other
laws we know of; but an explanation of how it can act
thus, or why it exists at all, or what its antecedents are
if it has any, these are questions that are matters for
the guessers, like Kepler, who kept guessing until he
guessed right, and so discovered what are known as his
laws. Meanwhile definite mechanical conceptions of
what the phenomena to be explained are like may be
helpful to those interested in them.

Suppose two bodies, \textit{A} and \textit{B}, a certain distance apart,
and they so react upon each other that they tend to
mutually approach each other. Given a medium, ether,
can one imagine stresses set up by either body in the
ether that will be capable of affecting the other?

Imagine a large space like a room occupied by glass
of uniform texture and properties throughout. If relieved
of gravitational property, the cohesion of all
its parts shows that every particle is in some sort of
stress, no matter what the origin of that may be. Now,
suppose there could suddenly be created somewhere
near the middle of the glass a bullet or a marble. It
would displace so much glass as would be equal to its
own volume, and the result of that would be that the
glass about it would be subject to a new stress, which
would be greatest, at the surface of contact of the
marble, and would be less as that surface is receded
from inversely proportional to the square of the distance
of the point of observation. If the glass be imagined to
be indefinitely great in magnitude, then the stress would
\DPPageSep{103.png}{91}%
extend in every direction through the whole extent of
it, and at any assignable point would still be in accordance
with the inverse law, diminishing outward.
Imagine now another similar marble to be created at
the distance of a foot from the first. Inasmuch as it
displaces so much glass it will set up a new stress in
the latter, and this stress must also be transmitted
throughout the whole mass as in the first instance.
Now, here will be two independent stresses overlapping;
and on account of the nature of the stress, it will be
greater between the marbles than it will be anywhere
else, because there the sum of the stresses will be at a
maximum. If one can now for the moment imagine
that the glass was of such constitution as to permit a
motion to the marbles, in any direction, when there was
a stress tending to move them, it would be obvious
that the marbles would separate from each other as the
medium, the glass, was under greater tension between
them than in any other direction.\footnote
  {Such bodies might be said to have \emph{negative weight}.}
And if the glass
thus mobile was indefinite in extent and without friction,
the two marbles would continue to separate indefinitely.
The energy making them thus to move comes directly
from the medium, which in turn got it from the bodies
themselves when they were thrust into it, no matter
how. Such a phenomenon as separation in a manner
like the above is exactly opposite in character to that
of gravitation, but it points at once to a consideration
of the condition necessary to be similar. It was the
forcing of new material into space already occupied
with other material that developed the stress and led
to the above results. It will be necessary to find a way
\DPPageSep{104.png}{92}%
\index{Stress in glass}%
to develop a stress \emph{towards} a point instead of away
from it.

Suppose, then, that instead of having a created something
imbedded in it, a cavity of equal volume to the
marble should be produced in its place. As part of the
material of the medium has been annihilated, there will
now be a less stress at its bounding surface than there
was when it was occupied with material, and the
direction of the stress will now be towards the cavity.
That is, the stress will be less there than anywhere
else in the glass; and this, too, if measured, will be found
distributed like the other, inversely as the square of the
distance from the origin. Let another similar cavity
be produced in the neighborhood of the first, and the
two stresses will overlap, and there will be less between
them than in any other direction. Let us imagine now
that the glass was mobile enough to permit the movement
of either of these cavities in any direction towards
which there was any pressure, and they would approach
each other because pushed by the stress in the glass
more towards each other than in any other direction.
If one of these cavities were larger than the other, one
would expect that the corresponding stress would be
greater, and so there would be a stress that for direction
and the resultant movement would correspond with
what is observed in the phenomena of gravitation.

But such a conception as that of a vacuum as constituting
what we call the atoms of matter has no mechanical
validity at all. Atoms have not only volume, they
have mass, and that requires energy to displace. One
cannot imagine that the displacement of an absolute
\DPPageSep{105.png}{93}%
\index{Stress in ether}%
vacuum, if such a thing could be done, would require
any energy, for there would be no mass to move.

Suppose, however,---instead of imagining, as was
done, the entire volume of the marble to be destroyed,---that
in some way the volume of the glass marble had
suddenly been reduced, no matter how, and that the
diminished volume was retained,---the material had been
condensed. This would bring about the same relative
condition of stress to the condensed portion, so that
there would be less adjacent to it than elsewhere, the
measure of it being the actual amount of condensation
represented in the body. What would be true of one
would be true of others,---an indefinite number,---and
no number of such stresses would in any manner interfere
with or neutralize that of others. At any point of
the space filled with such glass each such condensation
would have produced its effect at the outset, and if the
glass were practically limitless in extent this relationship
would be maintained so long as the reduced
volumes remained constant.

So far has been considered a condition of things
somewhat analogous to gravitation; and to apply it one
needs to imagine the ether to be substituted for the
glass and the atoms of matter for the imagined condensation,
and also that the two, the ether and atom,
are capable of mutual reaction.

There have been some physicists who have imagined
that the atoms of matter were condensations in the
ether, but I am not aware that any very satisfactory
reasons have been given for thinking so. That in itself
would be no reason for rejecting the idea in the
\DPPageSep{106.png}{94}%
\index{Attraction of disks}%
\index{Hypothesis, needful}%
absence of a better and more consistent one. For
scientific purposes a poor hypothesis is better than
none at all.

A very large amount of scientific work has been
done by employing hypotheses that are now known to
be wrong. A working hypothesis is needful. If it be
wrong, one will by and by find it out and be able to
amend it, or replace it by a better. If it be right, it
will be vindicated, and will justify itself, and be generally
adopted.

Until we know more definitely than is now known
what the constitution of matter really is, one can only
guess and try; and among the multitude of interested
workers in all civilized countries there will be some
who will guess right to the advantage of all.

If, then, one adopts the vortex ring theory of matter,
\index{Vortex ring theory of matter}%
and endeavors to trace the mechanical conditions that
might obtain with such kind of atoms, he would be
led to inquire whether a vortex ring does or does not
exhibit any evidence of condensation in the material
that is in rotation; that is, does the material of the ring
occupy the same space while it is in rotation as it does
when not?

There are several phenomena that seem to show that
it occupies less space. The reduction of pressure
in its neighborhood shows a rarefaction there, and the
mutual approach of such rings and of other light bodies
in their neighborhood indicates the same thing. If
one rotates a disk rapidly, any light bodies in front of
it will tend to approach it even from a distance of
several inches. If a dozen disks five or six inches in
\DPPageSep{107.png}{95}%
\index{Attraction of vortex rings}%
diameter are set loosely an inch apart upon a spindle a
foot long, so that they may be rotated fast, yet left free
to move longitudinally upon the spindle, they will all
crowd up close together as the pressure is less between
them than outside. If one can imagine the spindle to
be flexible and the ends brought opposite each other
while rotating, it will be seen that the ends would
exhibit an apparent attraction for each other, and,
if free to approach, would close up, thus making a
vortex ring with the sections of disks. If the axis
of the disks were shrinkable, the whole thing would
contract to a minimum size that would be determined
by the rapidity of the rotary movement, in
which case not only would it be plain why the ring form
was maintained, but why the diameter of the ring
as a whole should shrink. So long as it rotated it
would keep up a stress in the air about it. So far as
the experimental evidence goes, it appears that a vortex
ring in the air exhibits the phenomenon in question.
There is no doubt at all that two vortex rings in the
air attract each other, for they will mutually approach
if free to do so, and the explanation is plain that there is
reduced pressure between them; in other words, the
characteristic motion of the ring reduces the air
pressure about it, so that another body within that field
is pushed towards the place where the pressure is
least. The reduction of the pressure about any ring
must evidently depend upon the amount of material
embodied in it, and more especially the degree of
rotation which it has. A small, thin but rapidly
rotating ring might produce as great a rarefaction about
\DPPageSep{108.png}{96}%
it as a much larger one with less velocity, hence there
is something about it that corresponds to what is called
mass. It is not \emph{simply} an amount of material, but the
\emph{energy} the material has, which gives it its characteristic
properties.

Analogy must not be mistaken for identity. There
is so great a difference between the properties of the
air and other gases and those of the ether that one
cannot affirm that what holds true of one must hold
true of the other; yet that is what is generally done by
such persons as those who try to show the properties
of the ether to be identical with those of matter.

We know what conditions are necessary in order that
a ring should be formed in the air, and one of them is
that there must be gaseous friction. If that were not
the case a ring could not be formed. If the ether be
the frictionless medium it is generally supposed to be,
one would not know how to make a vortex ring in it.
On the other hand, the reason a ring in the air is so
soon destroyed is because of friction; and hence if one
were made in some unimagined way in the ether it
would continue to exist indefinitely, but how it could
act at all upon the ether surrounding it would be a
mechanical puzzle, and that is the present state of the
case. The puzzle is no greater with the conception of
a vortex ring than if the atom were made up in some
other way, and therefore that objection is not peculiar
to this hypothesis. It has been confessedly a puzzle
to see how the vibratory motions of atoms and molecules
could set up transverse waves in the ether if the
ether be without friction; nevertheless, they do set up
\DPPageSep{109.png}{97}%
such waves. A common objection to all attempts that
have been made to account for gravitation by means of
the motions of the atoms themselves is that it not
only requires a constant expenditure of energy, but that
the velocity of transmission must be so much greater
than that of light. Light is transverse vibratory movement.
A direct longitudinal wave may be much swifter
than the other. A pull upon a taut rope will travel
much faster in it than will a wave produced by a transverse
movement of the hand.

It is not to be understood that what is presented here
is given as a proof that gravitation is but a simple
mechanical condition of things. It is probable that
every one who thinks about it believes that its explanation
is purely mechanical. Some perhaps are pessimistic,
and doubt that man will ever be able to understand
its mysteries, but pessimists are not discoverers. They
frequently so chill the air about them that more hopeful
ones, who are not persuaded that the end has yet
been reached, are sometimes deterred from venturing
into fields where they have to pass such self-constituted
gate-keepers.

There are few physical problems of any generality
and complexity that are abruptly and completely solved
by one person. Tentative steps must be taken, and
much labor is oftentimes spent upon ideas that by and
by are proved to be worthless. A good deal of the
work done by Laplace upon the Nebula theory was
\index{Nebula theory}%
of that sort; yet all astronomers hold the Nebula theory
in some form: what the exact process was, if solely
mechanical, may be interesting, but not very important
from a philosophical standpoint.
\DPPageSep{110.png}{98}%

So one may hold that gravitation is a mechanical
action, and in some way explainable on mechanical
principles, even if he does not see how at all.

This chapter may help some to see not only what
the character of the problem is, but what factors are
present, and how somewhat similar phenomena may be
reproduced at will; but the radical distinction that
exists between the ether and matter must always be
kept in mind.
%\DPPageSep{111.png}{99}%


\Chapter{VI}{Heat}{99}

\index{Heat, mechanical origin of}%

\First{Heat} and cold are two words we apply to contrasted
sensations, either of which may imply comfort or discomfort;
and what is meant by either word in a given
case depends altogether upon what the sensation is
compared with. Thus, one would speak of a day when
the thermometer indicated one hundred degrees in the
shade as being a hot day, while if his cup of coffee had
the same temperature it would be called cold; so the
terms imply only roughly some departure from a
standard of comfort. To obtain more definite knowledge
of that physical condition which gives us the
sensation we call heat, it is necessary to attend to its
origin and its effects upon other bodies.

\Section{I. MECHANICAL ORIGIN.}

When a blacksmith hammers a small piece of iron,
like a nail, upon his anvil, it becomes too hot to hold,
and it even may be made to glow, red-hot, by the
repeated blows of the hammer. If a bullet be shot
against a target and be quickly picked up, it is found to
be hot; and in general the impact of any two bodies
always results in heating both of them. In the above
cases both the hammer and the target are heated, but
\DPPageSep{112.png}{100}%
on account of their size the degree of heat is not so
noticeable as it is with the smaller bodies.

In like manner if the knuckles be rubbed briskly
upon one's sleeve, the sensation of heat becomes
unbearable in a very brief time. The friction of the
surfaces develops the heat, as may be learned by
taking a button or some similar object, and in the same
brisk manner rub it on the sleeve or other convenient
surface, and it will get too hot to be safely touched
against the skin. On a larger scale the brakes upon
railroad-cars exhibit the same quality when they have
been applied for a few seconds. The sparks that may
be seen flying from them in the dark is testimony to
the same thing; while the car-wheel boxes are often so
heated by the constant friction when the lubricating
oil is wanting, that the cotton waste takes fire, and
even locomotives may be delayed by their hot journals.
This source of heat is so common that instances may
be cited indefinitely. It is universally true that the
friction of one body moving in contact with another
heats them both, and the heat developed depends upon
the pressure and the velocity of the moving surfaces.
It is true not only for solids, but for liquids and gases
as well, and the friction of solids moving in either
liquids or gases. An extreme case of the latter kind is
illustrated by the shining trail of a meteor when it
enters the atmosphere. Its velocity is very great---twenty
or thirty miles a second---and the friction of the
air is so great on account of the high speed that it
renders the surface of the meteorite red-hot, and some
of its molecules are ground off as they would be if it
\DPPageSep{113.png}{101}%
were held against a swift turning emery-wheel that
scatters the sparks in the air. The luminous trail consists
of these heated particles. If the body is not large,
and most meteors are quite small, they may be entirely
ground to powder and dissipated before they can reach
the earth. Most meteors in this way rarely pass
through more than fifty or sixty miles of our atmosphere
before this happens.

Another mechanical source of heat is compression.
Let a bullet be hard squeezed in a vise, or in any other
% [Illustration: ]
\begin{figure}[htb]
  \begin{center}
    \Graphic{4in}{113a}
  \end{center}
  \Caption{4}{Diag.\ 4.}
\end{figure}
way, and it is found that its heat is perceptibly increased.
Small differences of this sort may be easily detected
by the use of the thermopile and galvanometer.

The rubbed button or pounded or squeezed bullet
placed upon the face of the thermopile shows the presence
of an amount of heat which the sense of heat
would %[** PP: Width-dependent line break]
% [Illustration]
\begin{wrapfigure}[11]{l}{.5in}
\null\hfill\Graphic{.25in}{114a}\hfill
  \Caption{5}{Diag.\ 5.}
\end{wrapfigure}
never detect. Gases exhibit the heating effect
through pressure in a high degree. Before the invention
of friction matches, which are themselves good
\DPPageSep{114.png}{102}%
\index{Heat, chemical origin of}%
examples of the production of heat by friction, metallic
tubes, closed at one end with a tight-fitting plunger to
be worked by hand, were in common use for lighting
fires. A bit of punky wood was fixed to the
end of the plunger, and the latter was then
quickly driven to the bottom of the tube. The
air was compressed to so great an extent that
the heat developed became sufficient to ignite
the punk. The same heating effect of compression
may be shown by the thermopile and galvanometer
by compressing the air with an air-condenser,
and permitting the air thus condensed to
strike on its exit upon the face of the pile.

Thus impact, or \emph{sudden} stopping of mechanical
motion, friction, or the \emph{gradual} stopping of mechanical
motion and condensation, or compelling molecules
to occupy less space, all of them of a purely
mechanical nature, result invariably in heating the
matter that is subject to the action.

\Section{II. CHEMICAL ORIGIN.}

The heat that results from the combustion of fuels
of all sorts is due to the chemical changes that take
place. When coal burns, its substance, carbon, is
entering into combination with the oxygen of the air,
and a new chemical product is formed called carbon
dioxide, which is a gas; and the change is accompanied
by the production of a large amount of heat, which we
utilize for our comfort or for the various arts that
depend upon heat as an agent. Wood, alcohol, the
various oils,---everything capable of burning, and which
\DPPageSep{115.png}{103}%
may be called fuels---are, in the process of burning,
\index{Fuels}%
undergoing what is called oxidation, in which new
chemical compounds are formed and which are nearly
all gaseous. Thus the products of the combustion of
\index{Combustion}%
wood, alcohol, coal-oil, etc., are always carbon dioxide
gas, and the vapor of water; and the heat developed is
proportionate to the amount of these produced.

But combustion is not the only chemical source. If
sulphuric acid be mixed with water, the compound
becomes very hot although it is liquid. The two
substances enter into an intimate chemical combination.
A pint of each mixed together will not make a quart,
but will fall short of that volume a good deal when
they have cooled. This shows that condensation has
taken place; and, knowing that condensation produces
heat when brought about in other ways, one might have
suspected that chemical condensation would result in
a similar development of heat.

Some substances when in a finely divided state,
though what we generally call solids, are capable of
entering into combination with each other at a very
rapid rate and then develop a great deal of heat.
Such a substance as gunpowder, a combination of carbon,
\index{Gunpowder}%
sulphur, and the nitrate of potash, when intimately
mixed, will combine with explosive violence, and great
heat results from it, as shown by the attending flash
and the scorching effects it produces upon some bodies
that do not happen to be destroyed by the explosion.
All chemical reactions whatever involve in some degree
temperature changes; and by so much one might be
led to suspect that there might not be so great a
\DPPageSep{116.png}{104}%
\index{Heat, electrical origin of}%
difference between the mechanical \DPtypo{souces}{sources} of heat at
first considered and the more obscure chemical ones as
one might think who attends only to the more prominent
features of the two. If one should adopt for
a basis of his philosophy that like causes produce like
effects, what shall he say when he sees the same effect
produced by pounding with a hammer, condensing a
gas, and burning a piece of wood? Either unlike causes
can produce similar effects, or fundamentally these
three processes are the same. We will attend to that
question more at length farther on.


\Section{III\@. ELECTRICAL ORIGIN.}

As a chapter is to be given to electricity and its
phenomena, it will be sufficient here to point out that
wherever a current of electricity is flowing in a conductor,
there heat is invariably produced. The heat in
an electric arc is so great that all known substances are
either fused or volatilized in it. Gold, platinum, the
ruby, are easily reduced to the liquid form, and the
diamond slowly wastes away, being oxidized like a piece
of coal. Electric furnaces are now in use where the
most refractory substances, like clay, are reduced, and
the metal aluminum extracted from it. So long as it
cost so much to produce electricity as it did before the
dynamo was perfected, no one could afford to use it for
heating purposes. Now there will shortly be electric
heaters in houses, replacing stoves for cooking and
furnaces for warmth. The electrical current can be
brought on the wire where it is wanted, and the heat
developed from it to any degree desired. Electricity,
then, is another source of heat.
\DPPageSep{117.png}{105}%
\index{Energy in the ether}%
\index{Heat, radiational origin of}%


\Section{IV\@. RADIATIVE ORIGIN.}

When one stands near a blazing fire the warmth felt
does not come from the heated air between the fire
and the person; for when one shields his face or hands
the warmth ceases to be felt, though the temperature
of the air might be the same in both cases.

In like manner sunshine warms the earth, although
between the sun and the earth there is an enormous
space without air or other matter, through which the
sun's rays come producing warmth \emph{when they get here}.
This process of giving out rays to the ether independent
of matter, which is possessed by hot bodies, is called
radiation. It has been shown that all bodies are at all
times giving out such radiations; and oftentimes the
radiation itself is called radiant energy, sometimes it
is called light, and sometimes simply ether waves.
Here we do not attend to the origin of the waves, but
to the fact that when such waves fall upon matter they
result in heating it, and therefore radiation must be
looked upon as a fourth source of heat.

I would again suggest the thought presented a page
or two back, as to the similarity or dissimilarity of each
of these four kinds of origins of heat,---mechanical,
chemical, electrical, radiant. They appear to be utterly
unlike each other, yet their effects upon matter are identical,
always thus and never different, so far as our experience
goes. Evidently there must be some factor
common to them all; and if this could be known for any
one of them, it would throw light upon all the rest. If
we take, for instance, the mechanical origin of heat,
\DPPageSep{118.png}{106}%
say, impact, which is one of the most obvious, and note
the factors present, it is plain there are but two;
namely, a mass of matter with a certain measurable
amount of motion of the translational variety. These
two embody the energy represented by the impact, and
of these the translational motion is destroyed when the
heat appears. The other factor, the mass of matter,
remains constant. The motion that was seen needs to
be accounted for; and as the heat that appears is the
result of that motion, it appears probable that in some
way the translational motion has been transformed into
some other kind of motion, not that it has been annihilated.


\Section{TEMPERATURE.}
\index{Temperature}%

If a pint of boiling-hot water be mixed with a pint
of ice-cold water, the mixture will have all the heat
there was in the pint of hot water, but it would not
injure the hand thrust into it. The heat that was in
one pint has been distributed through two pints, and
hence each pint has one-half the heat that was in the
hot pint. A red-hot bar of iron will be cooled by being
thrust into a pail of water. The water will be heated,
and will have all the heat the bar lost; but as it is distributed
through so great a volume of water, the
amount of heat in a cubic inch of it will be but a small
proportion of the whole.

The word ``temperature'' is used to denote the degree
of heat there may be in a unit volume of a substance, and
this is measured by means of thermometers in which
the property that heat possesses of expanding the volume
of bodies is made to indicate their degree of heat. The
\DPPageSep{119.png}{107}%
standard for this is an arbitrary one altogether. In the
common Fahrenheit thermometer there is a tube of glass
\index{Thermometer}%
with a bulb upon it filled with mercury. This, when put
into ice-water, acquires the same temperature, and the
mercury stands at a certain height in the tube, which is
marked. Then it is put into boiling-hot water, where
the mercury expands and reaches another height in the
tube, which is also marked. The space between the
two marks is divided into one hundred and eighty equal
parts, and the same scale of division is carried beyond
in both directions. A point thirty-two of these divisions
below the mark of the melting ice is called zero;
so between it and the boiling-point are two hundred
and twelve divisions, called degrees. The centigrade
thermometer is more generally used in scientific work.
In this the space between the freezing and boiling
points is divided into one hundred equal parts, called
also degrees. A centigrade degree is $\dfrac{9}{5}$~larger than a
Fahrenheit degree. The scales of either may be extended
indefinitely for the measurement of temperatures
departing from the more usual ones. For a lower
limit one cannot use the mercury below about forty
degrees below zero; for it freezes at that temperature,
and no longer follows the same law of contraction. As
alcohol does not freeze, thermometer tubes filled with
it are used to indicate such low temperature. In the
Arctic regions, and even in Siberia, the temperature
falls to fifty or sixty degrees below zero not infrequently
in winter, but temperatures have artificially been produced
as low as $400°$~below zero.
\DPPageSep{120.png}{108}%

For the higher limits mercury thermometers can be
used for higher temperatures than alcohol, for the latter
boils and becomes vapor at~$174°$. The following table
of temperatures may be interesting:---
\begin{center}
\TableFont%
\begin{tabular}{p{3in}@{\ }r}%[** PP: Hard-coded width]
Absolute zero                       \dotfill & $-460°$ \\
Lowest degree artificially produced \dotfill & $-400°$ \\
Lowest degree measured in Siberia   \dotfill & $-72°$ \\
Mercury freezes                     \dotfill & $-39°$ \\
Water freezes                       \dotfill & $32°$ \\
Blood in man                        \dotfill & $98.6°$ \\
Temperature observed in India       \dotfill & $140°$ \\
Alcohol boils                       \dotfill & $174°$ \\
Water boils                         \dotfill & $212°$ \\
Lead melts                          \dotfill & $612°$ \\
Mercury boils                       \dotfill & $650°$ \\
Red heat visible in dark            \dotfill & $1000°$ \\
Silver melts                        \dotfill & $1873°$ \\
Gold melts                          \dotfill & $2200°$ \\
Iron melts                          \dotfill & $2700°$ \\
Platinum melts                      \dotfill & $3600°$ \\
\end{tabular}
\end{center}
\index{Temperature, table}%

Gases, like liquids and solids, are increased in volume
by heat when permitted to expand. If not permitted,
the pressure upon the walls of the containing vessel is
increased; and it is found that this pressure is proportionate
to the temperature, and also that the pressure
diminishes about~$\dfrac{1}{273}$ for each centigrade degree of cooling,
starting at the freezing-point of water. If, therefore,
a gas could be cooled from that point $273°$~centigrade,
it would have no pressure, as it would have no
temperature. Such a degree has never yet been reached;
but all phenomena having any bearing upon the subject
\DPPageSep{121.png}{109}%
indicate that at~$-273°$ there is no heat: it is an
absolute zero. The molecules %[** PP: Width-dependent line break]
% [Illustration]
\begin{wrapfigure}{r}{0.5in}
\null\hfill\Graphic{0.25in}{121a}
\Caption{6}{Diag.\ 6.}%
\end{wrapfigure}
would have no translational
motion, otherwise they would produce
some pressure upon the walls of the vessel that
contained them. Air thermometers may be
\index{Thermometer, air}%
made with bulbs blown upon the end of a glass
tube. A small drop of water in the tube will
be pushed in or out as the temperature varies,
and is much more sensitive than ordinary thermometers;
but barometric pressure affects it
and renders it unfit for common use, but its indications
are proportionate to the absolute scale;
that is, the volume of the air at the melting-point
of water will be increased or diminished~$\dfrac{1}{273}$
by every change of one degree in cooling or heating,
or~$\smash[t]{dfrac{1}{490}}$ if the degree be Fahrenheit.


\Section{MECHANICAL EQUIVALENT.}
\index{Heat, mechanical equivalent}%

For a long time it was supposed that heat was a kind
of substance that ordinary matter could absorb and
emit. It was sometimes called caloric; and that word is
in common use to-day, but not in the sense it originally
had. Sometimes it was spoken of as one of the imponderables---a
substance without weight. Now there is
only one imponderable recognized, that is the ether. Sir
Humphry Davy and Count Rumford found they could
produce an indefinite amount of heat by the friction of
one body upon another; and that implied if heat was a
substance of any sort, that any piece of matter contained
an infinite amount of heat, else one could get
\DPPageSep{122.png}{110}%
out of a body what was not in it. These two men concluded
that heat was a kind of molecular motion, and
that what their experiments showed was that friction
only transformed the mechanical motion into molecular
motion, which was called heat.

The old conceptions had got so thoroughly incorporated
into both the thoughts and the writings of others,
that they could not easily be dislodged, and men went
on as they had done. It was easier to do that than to
change notions and terms that were familiar for others
that were strange, even if true. A whole generation of
men had to be buried before any attention was paid to
what had been proved in the early part of the century.
Soon after 1840 it occurred to a number of persons in
different countries that if heat were but transformed
mechanical motion there should be some quantitative
relationship between them that might be discovered;
that is, a given amount of mechanical motion ought to
produce a definite amount of heat, and \textit{vice versa}.
This was worked out in the most complete and satisfactory
way by Joule of England. His method consisted
\index{Joule}%
in churning a definite amount of water and observing
the rise in temperature in it. The churn paddle was
driven by a known weight falling a known distance, and
therefore the work done in driving the paddles was
known in foot-pounds. In this way he found that $772$~pounds
falling one foot would heat a pound of water
one degree, and he called this number the mechanical
equivalent of heat. In like manner it is said that when
a pound of water loses one degree in temperature, it has
lost energy enough to raise $772$~pounds one foot high.
\DPPageSep{123.png}{111}%
This relationship renders it easy to determine the
amount of work a given amount of heat can do, and
also the temperature that will be acquired by a given
amount of water when a definite amount of work is
done upon it. But the scientific importance of this
new step is much greater than its practical utility.
Before that time men had thought there were such
things as \emph{forces}, independent of each other; and such an
idea as mutual convertibility had not dawned upon any
philosophic mind. Physical philosophers were so much
misled by their terminology and the accompanying
notions, that Joule's work, though demonstrative, made
no impression upon them for several years, and it was
refused a place in the transactions of their society for
seven years. The reason for this common hostility to
new knowledge is probably not far to seek. When one
has achieved distinction in his line of work, especially
in physical science, he is likely to possess his own philosophy
of things, in which not a small part of the data
is symbolic and is represented in mind only by a name;
and if this chances to suggest something mysterious, as,
for instance, an imponderable, the less is one likely to
attempt, or suffer others to attempt, to displace it by
definite mechanical conceptions. To change one's
fundamental conceptions necessitates a change in his
philosophy throughout,---a change that is not only difficult,
but highly \DPtypo{distaseful}{distasteful}; and one ought not to expect
a welcome to a man whose work necessitates such a
change.

Within the present century the advance in all directions
has been such as to give definite mechanical
\DPPageSep{124.png}{112}%
\index{Thermodynamics}%
conceptions and relations where before only ghosts and
genii were supposed to do duty; and what can a man do
when his genii have been slain and he must now depend
upon~$mv^2$? To become acquainted with his new associate
is generally the last thing he sets himself about.
It was with Joule as it was with all the prophets and
discoverers. Joule, however, was young, and he lived
to attend the funeral of all his detractors.

That heat and work are mutually convertible is now
called the first law of thermo-dynamics; and it has led
directly to a knowledge of the working-power there is
in fuels, and made the duty of steam-engines and other
sources of power beautifully simple.

The amount of heat needed to raise the temperature
of a pound of water one degree Fahrenheit is called a
\emph{heat unit}. The amount of heat needed to raise the
\index{Heat unit}%
temperature of a kilogram of water one centigrade
degree is sometimes called a calorie, and this is a
unit in common use. It is found by careful experiment
that a pound of coal when burnt gives up $14500$
\emph{heat units}, or would raise the temperature of $100$~pounds
of water~$145°$, or to any other equivalent. A
pound of hydrogen, in like manner, burning with oxygen,
will give $61000$ units, a pound of wood about
$7000$, and so on. Each different substance has its own
equivalent of such heat units. As each unit will do
$772$ foot-pounds of work, a pound of coal, when burnt,
will give $14500 × 772 = 11,194000$ foot-pounds of
work, and so on for any other. This equivalency is
independent of time or place. Whether the coal burns
fast or slow makes no difference. When wood is
\DPPageSep{125.png}{113}%
burned in the fire it develops its work-power fast; but
when it slowly rots it is undergoing the same process,
oxidation, and the same amount of heat is developed,
though at no time does the temperature appear to be
above that of surrounding things. The food we eat possesses
its mechanical equivalent, which is the maximum
amount of work it would enable one to do. If bread
and butter were used for the fuel of an engine, it would
develop about $21000$ heat units (or calories) per pound,
and this is equal to $772 × 21000 = 16,212000$ foot-pounds,
and it has the same value when used for food;
and thus one may know approximately the amount of
energy he is supplied with from day to day; also, he
may compare the amount of work he does, in lifting,
walking, or otherwise, in a day with the food equivalent
absorbed. Some of this is, of course, used to
maintain the temperature of the body, the circulation
of the blood, and so on---conditions that are tolerably
constant.


\Section{THE STEAM-ENGINE.}
\index{Steam-engine}%

The steam-engine is a machine for utilizing the
heating-power of fuels, and, when complete, consists of
furnace, boiler, and engine. The furnace transforms
the energy of the fuel and air into heat units in the
boiler, and the engine transforms this into the work of
whatever sort it may be applied to.

Evidently the efficiency of such an engine must depend
upon how large a proportion of the heat units it
utilizes compared with the heat units supplied to it.
Steam-engines permit the steam to escape into the air
\DPPageSep{126.png}{114}%
\index{Steam-engine, efficiency of}%
generally with a temperature higher than boiling water,
and that means a great waste of unused heat; for the
steam in the engine loses temperature proportionate to
the work done by it, and, as stated before, the steam
pressure is proportionate to its absolute temperature,
not its temperature as indicated by common thermometers.
And the absolute temperature on Fahrenheit scale
will \DPtypo{he}{be} found by adding~$460$ to the indicated temperature.
Suppose, then, an engine-boiler delivered steam
to the engine at $248° \text{ Fah.} = 708 \text{ absolute}$, and on exit
from the cylinder it was $212° \text{ Fah.} = 672 \text{ absolute}$, then
the proportionate amount of work done compared with
the whole supplied would be $\dfrac{708 - 672}{708} = \dfrac{36}{708}$, or only
about five per cent of the heating-power of the fuel.
Higher efficiency must be looked for chiefly by using
steam at higher temperature and, therefore, higher pressure,
which would increase the value of the numerator.

The efficiency of engines is generally given in the
amount of coal required to maintain one horse-power
per hour. A horse-power for an hour is equal to
$33000 × 60 = 1,980000$ foot-pounds; and the coal required
varies from about two pounds in the best engines
to six or eight pounds, locomotive engines generally
being less efficient. As one pound of coal when burnt
has an equivalent of $11,194000$ foot-pounds of work,
two pounds will give $22,398000$ foot-pounds. When
that maintains a horse-power for an hour, or $1,980000$
foot-pounds, the efficiency is $\dfrac{1,980000}{22,398000} = 8 \text{ per cent}$.
This appears very low; but it is to be remembered that
\DPPageSep{127.png}{115}%
\index{Heat, nature of}%
the coal is seldom anywhere near pure; that much heat
escapes by the flues without heating the water; that
much is lost by heating the engine, boiler, and the
pipes, etc., that does no good, and most of that that does
go through the engine escapes to the air without having
done any work; and it cannot be helped, for steam condenses
to water at~\DPtypo{$212$,°}{$212°$,} and is no longer able to do
steam service. In reality, such an efficiency is relatively
high.


\Section{AS TO THE NATURE OF HEAT.}

It has been pointed out that it was concluded early
in the century that heat must be some kind of motion,
because its production depended solely upon antecedent
motion, and that later the quantitative relationship
between the two was accurately defined. The
\emph{nature} of heat was ascertained, but the particular kind
of motion that gave it its characteristics was not made
out; that is, whether the motion was one of free path
of the molecules,---a swinging to and fro in space,---or
a true vibratory motion, such as a change of form of
the molecules and atoms that made up the heated body,
or a rotation of them, or a combination of any or all of
these, was unknown. At first the conjecture prevailed
that it was an oscillatory motion of the molecules
among themselves even in a solid body; but after the
discovery of spectrum analysis it became apparent that
the atoms and molecules were in a state of true vibration,
and their temperature depended upon the amplitude
of that vibration. If one will remember that the
atoms of matter are certainly elastic, and are not solid,
\DPPageSep{128.png}{116}%
\index{Hydrogen vibrations}%
\index{Vibrations, gaseous}%
and will also picture to himself what mechanically
must happen when such a body is struck in any manner,
that it \emph{must} vibrate, for the same reason that any
visible elastic body must vibrate if struck, he will see
quite clearly the condition of things among elastic
atoms that collide with each other so many times per
second.

That they do thus vibrate is proved by the spectrum
of substances in the gaseous state where between impacts
they have time to vibrate a great number of
times per second. At ordinary temperatures and density
a gaseous molecule of hydrogen, having a mean free
path of about the two-hundred-and-fifty-thousandth of
an inch, and moving at the rate of $6000$~feet per
second, will collide with its neighbors $17750$ millions
of times per second, but its spectrum shows that it
makes $450$~millions of millions of vibrations in the same
interval, so that in each interval between impacts it
would be able to make $\dfrac{450,000000,000000}{17750,000000} = 25352$,
more than twenty-five thousand vibrations.

Now, imagine a number of bells suspended by cords
of equal length from the ceiling, but not so near as to
touch each other. Suppose each bell to have the same
musical pitch as every other one, and now let one of
the outer ones be pulled away from the rest and forcibly
swung back among them; presently every bell
among them would be set swinging by the impact of
others upon it, and each impact would cause each bell
to sound its own particular pitch, and the elasticity of
each individual one would maintain that vibration in
\DPPageSep{129.png}{117}%
some degree until the next impact, when it would be
strengthened, and one would hear along with the
bumping of the bells the sound due to the pitch of
the individual bells. Something very like this goes on
among the molecules of the gas. Their vibratory
movements we cannot hear, but with the spectroscope
they are detected and measured. Now, hot bodies cool
by radiation---the giving-off of just such waves in the
ether as we are describing,---and the fact that such cooling
molecules of a gas give out constant wave-lengths,
as is shown by their spectrum lines, is proof that the
vibrations that originate the waves
are not %[** PP: Width-dependent break]
% [Illustration]
\begin{wrapfigure}{r}{1.25in}
\Graphic{1.25in}{129a}
\Caption{7}{Diag.\ 7.}
\end{wrapfigure}
free-path or oscillatory motions,
but true atomic ones, due to a
\emph{change in form}. How this can be is
easily seen by considering the change
in form made by any vibrating body,
say, a ring. Let the heavy lined ring
represent an elastic atom: if it be subjected to impact it
will assume an elliptical outline, and go through a series
of phases represented by the dotted lines. This change
of form, and uniform vibration, is a mechanical necessity,
and is independent of the size or particular form a
body may have. It is this kind of motion that embodies
the energy represented by the temperature of
an atom or a molecule, and the temperature varies with
the square of the amplitude of this motion; and two
bodies have the same temperature when their molecules
have the same vibratory energy. A single molecule in
free space would radiate all its heat away, and thus be
reduced to absolute zero, if it were not continually
\DPPageSep{130.png}{118}%
\index{Heat, nature of}%
receiving from other bodies an amount that depended
upon its nearness to them and their own amplitude of
similar motion. Hence the temperature of a body
depends upon the amplitude of vibration of its molecules,
and not upon any translatory or oscillatory or
rotatory motions. This is not saying that molecules
that are heated do not have other motions than the
vibratory ones constituting their temperature, but
when they do have others it is at the expense of the
vibratory, and therefore has reduced the temperature;
and such free-path motion as all gases have, and which
produces pressure upon the walls of vessels, is maintained
by the vibratory. It is not heat, but the result
of heat, in the same way as the translatory motion of
a bullet is not heat, but the result of heat. Most books
on heat do not make the distinction here made, but
combine the heat-motion of the molecules themselves
with the translatory motion they have, calling the sum
of them the heat of the gas. So long as one is concerned
only with the energy involved in the actions it
will make no difference; but if one analyzes the process
for the factors it is plain that there are two distinct
kinds of motion---one of them capable of setting
up waves in the ether, the other not, for it is not known
that any free-path or translatory movement of a body
ever disturbs the ether; and if distinctions of such
marked characters as these exist, and one of them involves
temperature and ether waves, and the other
does not, they ought not both to be called by the same
name. The peculiar character of the energy involved
in heat as distinguished from so-called mechanical
\DPPageSep{131.png}{119}%
\index{Heat of the sun, origin of}%
energy, is that the factor of motion is of the vibratory
sort, whereas the other is more or less translatory,---one
capable of easy transformation into ether waves,
the other incapable of such transformation, but each
of them easily transformed into the other by impact.
Equivalent velocities give the same amount of working
ability, or $\dfrac{W v^2}{2g} = \dfrac{W a^2 n^2}{2g} = P d$ (see \Pageref{p.}{69}). So it
can be understood how ordinary visible motion can be
transformed into heat, and \textit{vice versa}, as easily as one
can understand how the motion of the clapper of a bell
is transformed into sound.


\Section{ORIGIN OF THE SUN'S HEAT.}

There has been much speculation as to the source of
the heat of the sun. Unless one assumes that it has
some miraculous or non-physical origin he is bound to
account for it, if at all, upon the assumption that physical
conditions and relations, such as we find at the
earth, hold good at the sun as elsewhere.

At the beginning of this chapter the various sources
of heat were considered,---the mechanical, the chemical,
the electric, and the radiative. If these be tested as
to their sufficiency to account for the temperature of the
sun, one may reach a conclusion as to the probability
of any or all of them being concerned in it and their
relative importance.

It will be convenient to consider them in the reverse
order, and first as to radiations. In order that a body
should become heated by radiations, there must first be
some body or bodies having as high or higher temperature
\DPPageSep{132.png}{120}%
to give rise to the radiations; and in this case, if
the sun's heat came from such a source, one would need
to look for the other bodies in the universe having such
high temperature. The millions of stars shining by
their own light would at first seem to furnish the proper
source; for the testimony of the spectroscope is that
they all are highly heated, and some astronomers think
some of them to be much hotter than the sun is. One
of the conditions under which radiant energy is distributed
in space is that its amount upon a given surface is
inversely as the square of the distance from the source;
and as every one of these bodies is at such an amazing
distance away, it is only with the most delicate instruments
that their radiant energy can be measured, and a
given surface upon the earth would receive as much as
the same surface upon the sun, and the earth would be
heated from the same source as much as the sun would
be. Practically it is found to be but a very small quantity,
and hence radiation from other bodies cannot
possibly account for the sun's heat.

Second, as to electrical currents: it may be said at the
outset we have no direct knowledge that there are such
at the sun, and from other knowledge we have of its
constitution it would appear to be highly improbable
that there were or could be electric currents there.
Electric currents imply some generator and some conductor
for their transference; and from what is known
or may fairly be inferred that every substance we are
acquainted with as a conductor of electricity which is
present in the sun---and there are a good many of
them---iron being particularly abundant, yet they are
\DPPageSep{133.png}{121}%
all at such a high temperature as to be a far reach from
the conductibility we know anything about. There
may be, but it is by no means certain, something solid
in the sun, but the most of it is as gaseous as a bubble,
and gases do not conduct currents of electricity.

Third, chemical action is known to be the antecedent
of vast quantities of heat. It may be recalled that a
pound of hydrogen, for instance, when allowed to combine
chemically with oxygen will give out $61000$ heat
units. The atmosphere of the sun appears to be made
up of elements mostly in an uncombined form, except
in the cooler, outlying parts; that is, the temperature is
so high that chemical combination is impossible except
in exposed places where radiation can allow cooling to
take place. It is tolerably certain that chemical combinations
are taking place there whenever it is possible,
and with such combination heat must be produced, if
physical laws are in operation there as they are at the
earth, but the amount of it going on, or possible, if the
whole body of the sun were to combine its elements in
this way, does not appear to begin to be equal to the
expenditure of heat actually taking place.

There remains only the mechanical sources of impact,
friction, and condensation. There is good evidence
that there is a large body of meteors in the neighborhood
of the sun that must be falling upon its surface.
The sun's attraction can give a velocity of nearly four
hundred miles a second to any body reaching him from
distant space, and such a velocity would, on impact,
produce heat enough to reduce the whole body to a
gaseous state almost instantly.
\DPPageSep{134.png}{122}%
\index{Sun, its magnitude}%
\index{Sun, its heat}%
\index{Sun, its age}%

Given the mass and velocity of a body, and one may
calculate how much energy it has, and how much heat
is the equivalent of the mechanical energy. Such a
computation shows that even if the earth were to fall
into the sun, it would be volatilized in a very brief time.
If the sun's surface were solid the impact would be
sufficient to effect it almost instantly. If the shell of the
sun were liquid it would be changed more slowly through
friction, but, in the end, the result would be the same.
It does not appear, however, that there is sufficient
material that finds its way to the sun to furnish but a
small proportion of the sun's heat, so neither impact
nor friction can be admitted as sufficient agencies.
There remains but one more, namely, compression. Is
there any evidence that condensation is taking place?
The body of the sun is $866000$ miles in diameter, and
is so far away that this immense magnitude occupies
but about half a degree of arc. If it were to shrink at
the rate of a mile in twenty years, it would account for
the present rate of expenditure, but such a shrinkage
could not be observed from the earth for several thousand
years, for nothing much less than a second of arc
can be observed with certainty, and a second of arc at
the sun's distance is equal to about $465$~miles, so it would
require $465 × 20 = 9300$ years to produce an observable
effect.

Now, if the nebula theory be true, the sun once occupied
all the space between itself and the outer boundary
of the solar system and has shrunk to its present dimensions,
a process which, if heat alone were concerned,
would require about eighteen millions of years. It is
\DPPageSep{135.png}{123}%
\index{Heat, effects}%
not probable that heat alone has been concerned, so
it is probable that the sun is older than that, but the
shrinkage will account for the heat, and it appears as
the only probable conjecture. It will be understood
that the gravitative action is the occasion of the compression,
and that the approach is constant and as fast
as the generated heat can be radiated away. It has
been calculated that at the above rate of condensation
it may be reduced to one-half its present diameter with
its present radiation rate, in about five million years,
when its density will be about twice that of water.

From such considerations it appears in a high degree
probable that the heat of the sun is due to condensation,
the condensation is due to gravitation, and thus
one is led back to a time when the substance of the
sun and all the planets was scattered through that
immense space, the diameter of which is not less than
six thousand millions of miles. How matter came to
be thus scattered is at present an enigma. It is important
to remark here, though, that until there was impact
among atoms, and molecules were formed, there evidently
could be no such condition as what we call heat, and
until these atoms and molecules vibrated there could
be no light, that is, ether waves.


\Section{EFFECTS OF HEAT.}

Once in possession of a good, mechanical conception
of the action going on in a heated body, one can proceed
to trace out the various effects of heat in all
directions. Thus to take the familiar one of pressure
in a gas. A gas is simply a large number of individual
\DPPageSep{136.png}{124}%
\index{Molecules, number of, in universe}%
molecules moving about with great velocity and bumping
against each other and the sides of the containing
vessel. Each molecule, though small, has some momentum;
but the enormous number of them in, say, a cubic
inch, five hundred millions of millions of millions, and
their relatively high translatory velocities,---say fifteen
hundred feet per second, gives them momentum which,
when spent upon the side of the vessel, gives a pressure
equal to about fifteen pounds per square inch. If one
were to hold up a shield against which many balls were
thrown per second, he would need to brace himself to
withstand the pressure that would appear to be constant.

If the gas be heated the molecules have increased
amplitude of vibration, and they rebound from each
other with greater velocity, and strike the side with
more momentum, and hence the pressure is greater.
As the pressure is proportional to the absolute temperature,
it is plain there could be no pressure if there
was no vibratory motion. If the density of the gas
be increased by adding more molecules per cubic inch,
there must a greater number of them strike upon the
sides of the vessel in a second, which will increase the
pressure, that is, the pressure varies as the density.

When it is said that gases have a tendency to expand,
or that they exhibit a repulsive action, all that is signified
is this; as elastic bodies, the molecules rebound
after impact, and continue on in their direction, according
to the first law of motion, until otherwise obstructed.
When a ball rebounds from the side of the house it
has been thrown against, it is not because there is any
repulsion between the ball and the house.
\DPPageSep{137.png}{125}%
\index{Boiling-point pressure}%


\Section{EFFECT OF PRESSURE UPON BOILING AND FUSION.}

When it is said that the boiling-point of water is~$212°$,
it is to be understood that the pressure of the air
upon the surface of the water is fifteen pounds per
square inch. At elevated places water boils at a much
lower temperature; and when in a tight vessel, like the
boilers of steam-engines, the pressure of the steam
affects its boiling-point in the opposite way, raising it.
Thus at twenty pounds steam pressure, the temperature
required to boil water is~$228°$, at sixty pounds it is~$291°$,
at ninety pounds~$319°$, and at the high pressures
employed in locomotives of one hundred and fifty pounds
or more to the square inch, the temperature of the
steam and water is $360°$~or more. As one goes down
into a mine the pressure of the air becomes greater,
and higher temperature is needed to boil water. The
explanation of this phenomenon is that the heated molecules
of the liquid are bumping against each other in
all directions, but the surface molecules can receive
such bumps only from below and on their sides. If
there were no molecules above to beat downwards, the
surface molecules would fly rapidly up into the free
space, which would be what we call a vacuum. This
escape of the surface molecules of a liquid into the
space above is called evaporation, and the higher the
temperature of the liquid the harder the bumps, and
the more will be flipped away from the liquid and
become free rovers, having a long, free path. When,
however, the gaseous particles are numerous and strike
back upon the surface, that is, when there is a gaseous
\DPPageSep{138.png}{126}%
\index{Earth, solidity of}%
pressure upon the surface, the surface molecules are
prevented from rising, that is to say, evaporation cannot
go on so fast, boiling is prevented until more energy is
given to the water, and that means a higher temperature.

The melting-point of substances is likewise affected
by the pressure to which they are subject, and increasing
the pressure increases the temperature needed to
fuse them. Such small variations of pressure as only
a few pounds per square inch do not make much difference,
but pressure measured by tons per square inch
makes a great deal. The condition of the interior of
the earth appears to depend upon this as a most important
factor. As one goes beneath the surface of the
earth in mines and tunnels, it is observed that the temperature
rises about one degree for every fifty or sixty feet
of descent; and it was formerly inferred from this that at
the depth of a few miles a temperature would be reached
high enough to melt the most refractory bodies, and hence
the interior of the earth was probably in a fused state
while the crust was relatively thin. Such a view took
no account of the effect of pressure upon the state of
bodies. At the depth of a mile of water the pressure
must be equal to $62.5×5280=330000$ pounds per
square foot, and as rock is $2\frac{1}{2}$~times\DPnote{** PP: Slant fraction in original} the weight of
water, the pressure must be $825000$ pounds, or over
four hundred tons; and at five, ten, or a hundred miles,
it is obvious the pressure is correspondingly greater.
A body that at the surface of the earth would melt at any
assignable temperature would require a much higher
temperature to fuse when subjected to such enormous
\DPPageSep{139.png}{127}%
\index{Temperature, maximum}%
pressure. It appears that the pressure increases faster
than the observed temperature; and hence the earth
must be solid to the centre, instead of being liquid as
formerly supposed. This makes it appear that the
phenomena of volcanoes are only local, and do not indicate
\index{Volcanoes}%
any general melted condition of the earth. If a
body that would melt at a thousand degrees on the surface
of the earth be subject to such pressure that it is
not melted when its temperature is two thousand
degrees, then, if the pressure be suddenly removed
from it, the heat it has will instantly liquefy it. This
may be the condition at the base of volcanoes, where
shrinkage of the earth's crust in some direction may
relieve the pressure in some other direction; and a
large mass of heated material may become liquid, expanding
in volume, and overflow in any direction where
there is a vent, and this would be called a volcanic
eruption.

\Section{MAXIMUM TEMPERATURE.}

We have considered the condition called absolute
zero, wherein the molecules have no vibratory motion
whatever; and it has also been pointed out, and it is
generally agreed, that the temperature of a body varies
as the square of its amplitude of molecular vibration.

It has often been assumed in treating of high temperatures,
such as that of the sun for instance, that
there is no limit to the temperature to which matter
can be raised. So some have estimated the temperature
of the sun to be several millions of degrees; but
a consideration of the factors involved will show such a
\DPPageSep{140.png}{128}%
conclusion to be impossible, for the dimensions and
form of a body set a limit to the amplitude it can have.
A tuning-fork cannot have its prongs vibrate beyond
the limit where its prongs touch each other, and a
vibrating ring cannot have an amplitude greater than
one-fourth its circumference; and this degree is only
possible to a mathematical circle having no thickness.
Make a ring of a piece of twine, and elongate any
diameter until the opposite sides touch, then move the
middle points through a similar distance, and it will be
seen that the limit will be equal to a quadrant of the
circle; but if the ring be a thick one, say made of rope,
it would be less than that, and how much less will
depend upon the relative thickness of the rope to the
diameter of the ring. If the thickness of the rope
were one-fourth the diameter of the ring, then the
amplitude could be but one-half the quadrant, and so
on. Now, the atoms of matter have a definite size, and
no one has ventured to suggest that they were variable
in size in any degree; and one may, therefore, compute
the greatest amplitude such a body could have, whether
it were a circle or a hollow sphere without thickness.
If the diameter be as before stated, one fifty-millionth
of an inch, calculation shows that the greatest amplitude
it could have would be about one sixty-four-millionth
of an inch. This, multiplied by the number of
vibrations it makes per second, will give the equivalent
velocity from which its energy can be calculated. On
\Pageref{page}{67}, it is shown that the velocity of a vibrating
atom, if the amplitude be one-half of the diameter,
will be about eighty miles a second. If the amplitude
\DPPageSep{141.png}{129}%
be equal in measure to the quadrant, as is here supposed,
this velocity would be not far from a hundred
miles per second, and the energy represented by that
velocity would be the utmost energy of heat, or highest
temperature that the body could have. The pressure
of gases enables one to determine the velocity of
the particles; and when this is known at a given temperature,
the temperature at any other velocity may be
computed.

The statement that atoms and molecules can have a
maximum temperature must not be understood to imply
that the energy they can have is fixed at that limit,
because aside from their temperature energy, represented
by their vibratory motion, they can have any
assignable translatory velocity in addition. But it does
imply that ether waves, arising from temperature,
have a fixed limit for each element; and such radiant
energy from a given source cannot be transmitted beyond
a certain rate, because its amplitude has a limit,
so that whatever actual energy the sun as a whole may
have, it cannot lose that energy by radiation faster than
an assignable rate.

This has an important bearing upon the question of
the age of the sun. Computations have been made of
the length of time the sun can have been giving out
its energy, on the assumption that the sun is a cooling
body, and that it was formerly much hotter than it is
now. If the above statements are correct, the probability
is that the sun is as hot now as it ever was, and
that its rate of loss of heat by radiation has not been
greatly different from what it is to-day; so, instead of
\DPPageSep{142.png}{130}%
being only fifteen or twenty millions of years old, it
may be very much more.

As the temperature of a body represents its molecular
energy, and is measured by $\dfrac{mv^2}{2}$, it follows that if two
different kinds of molecules, such as hydrogen and
oxygen, have the same temperature, they will have the
same amount of energy; but the mass of an oxygen
molecule is sixteen times greater than the mass of a
hydrogen molecule. In an equal weight of the two
there will be sixteen times more molecules of hydrogen
than of oxygen, and therefore the hydrogen will have
sixteen times the energy of the oxygen at the same
temperature. To produce a rise of temperature of one
degree in a pound, or any given weight of hydrogen,
would require sixteen times as much heat as the same
weight of oxygen would need. This difference in
thermal capacity of different substances is called their
specific heat. In general, the lighter the molecules
\index{Specific heat}%
that make up a substance, the more numerous must
they be to make up a given mass, and the higher will
be its specific heat; i.e., the more heat must be expended
upon it to produce a given rise in its temperature.
The specific heat of water is chosen as a standard
and is unity, as it is found to require more heat to
raise a given weight of it one degree than any other
substance. One heat unit will raise the temperature
of a pound of it one degree; all other substances
require but a fraction of this. From what is said, it
appears that the specific heat of an element varies
inversely as its atomic weight. The specific heat of
\DPPageSep{143.png}{131}%
\index{Dissociations}%
a substance determines the temperature it will attain
when a definite quantity of heat is supplied to it. If
a pound of hydrogen and eight pounds of oxygen are
exploded together, and not allowed to expand in volume,
$51444$ heat units calories are produced. The $51444$
heat units would be divided among nine pounds of
water vapor, that has a specific heat under such conditions
of~$.37$. The temperature attained would be
$\dfrac{51444}{9×.37}=15450°$. This temperature is much higher
than the limit of possible combination of the two
gases, which, at about~$3000°$, are unable to combine, so
such an action could not take place any faster than the
parts could cool down to the latter temperature. If
the mixture be allowed to expand, the temperature of~$3000°$
may not be reached, and the action of the whole
is so rapid it is called an explosion.

\Section{DISSOCIATION.}

When compound molecules are broken up into their
elementary constituents in any manner, the process is
called dissociation. It may be effected by electrical
action, as when water is decomposed by it, or by chemical
action, as when wood is decomposed under water,
setting the carbon free; but heat is competent to effect
the same end. At the temperature of about~$3000°$ the
existence of water is impossible, as the elements cannot
stay united, and the reason is obvious. Whatever the
nature of the attraction that holds atoms together in
chemical compounds, if the elementary atoms are themselves
in brisk vibratory motion, as we know they are,
\DPPageSep{144.png}{132}%
\index{Matter, effect of temperature upon}%
they must be straining their bonds continually to separate;
and when the amplitude of such motion reaches a
certain maximum, the impacts are so violent as to make
the atoms rebound out of each other's neighborhood,
and thus prevent cohesion. The atoms then either
enter into new combinations with others, if possible,
and if not they remain as gaseous particles, and subject
to the laws of gases.

If one starts with a piece of ice and applies heat it
melts, and we call the liquid water. Apply more heat
and the water becomes steam, in which the individual
molecules are no longer able to cohere, because of their
energetic motions; but each molecule remains intact,
having a long free path, for a cubic inch of water
becomes nearly a cubic foot of steam under ordinary
air pressure. If still more heat be applied, the molecules
become more and more unstable until they too
are broken up in the same way and for the same reason
that the solid and the liquid forms were. When it is
no longer possible for hydrogen and oxygen to combine,
it is still possible for the atoms of each to combine
with each other, hydrogen with hydrogen and oxygen
with oxygen, forming elementary molecules \textit{H H}, and
\textit{O O}; but if a still higher temperature be applied, even
this combination becomes impossible, and the atoms
themselves become free rovers and individually independent.
Thus it is seen that the different states
of matter depend altogether upon temperature. At
absolute zero there can be no such thing as a gas, for
the molecules would have no individual vibrations and
therefore no free paths. They would probably fall to
\DPPageSep{145.png}{133}%
the bottom of the vessel and remain quiescent. It is
also probable that both liquids and solids too would
cease to exist, not that matter would be annihilated, but
a solid, a liquid, and a gas are simply each a bundle of
physical properties that depend mostly upon temperature,
and those properties would probably disappear
with the disappearance of the conditions upon which
they depended.
%\DPPageSep{146.png}{134}%


\Chapter{VII}{Ether Waves}{134}

\index{Ether waves}%
\index{Ether wave qualities}%
\index{Light, its nature}%

It has already been stated in what has preceded this
that translational motions of matter are not competent
to originate ether waves, and that vibratory motions
of both atoms and molecules can originate them. A
consideration of the origin, transmission, and effects of
such ether waves constitutes the subject-matter of what
is called the science of light. The word ``light'' is
commonly used to signify that agency in nature which
is capable of affecting the eye and causes vision, or the
sensation of sight, and until within a very few years
has been supposed to be a peculiar kind of a wave
motion in the ether quite distinct from other waves
known to exist which were competent to produce heating
and chemical effects, so such waves as were known
from their effects were called heat waves, light waves,
and actinic or chemical waves, according as they heated
bodies, produced light, or brought about chemical reactions.
These three sorts of waves were supposed to
coexist generally, but were capable of being separated
from each other so there could be a beam of either
without the others. This is now known to be a mistaken
view, for what a given ether wave will do depends
upon what it falls on rather than on its own peculiarity.
The same waves that fall upon the eye and produce the
sensation of sight will heat other kinds of matter, and
\DPPageSep{147.png}{135}%
\index{Ether waves, their source}%
\index{Light, a sensation}%
if they fall upon a surface of molecules that are unstable,
that is, in which the atoms that make up the molecules
are not strongly cohesive, the molecules are
disrupted by the waves, and the atoms enter into new
combinations, and this process is called a chemical process;
and while it is true that some waves will not produce
vision, there are none that will not produce both
heating and chemical effects, so there is no such distinction
among ether waves as was supposed, and this
leads to another conclusion also; viz., if there is no
such distinction between waves, then there is no such
thing as light at all, unless we classify all rays as light,
whether they can produce sight or not, which is sometimes
done to save explanations, but it leads to the
anomaly that there is such a thing as dark light, which
is absurd. There will be no difficulty whatever if light
be defined as a sensation merely, and the waves competent
to produce the sensation be called visual waves.
Up to the present time, however, the old terminology
is quite generally adhered to in spite of the difficulty of
reconciling the old signification with the new knowledge.
There is no single word that signifies ether
waves in general, and independent of the effects that
may be produced in specific cases, and for that reason
this term has been adopted. The word ``light'' is
entirely inadequate, and likely to mislead one not well
versed in the phenomena.

\Section{ORIGIN OF ETHER WAVES.}

The source of ether waves of all degrees whatever
is the vibratory motions of atoms and molecules as distinguished
\DPPageSep{148.png}{136}%
\index{Elements}%
from their translatory, or free-path motions,
but their rates of vibration are determined by their
atomic weights. An atom of hydrogen, for instance,
has a different rate from oxygen, for the same reason
that two tuning-forks, though made precisely alike,
would have different rates if one were made of steel
and the other of aluminium. If they have different
rates, then the number of waves produced by them per
second will be different, and as all waves travel in the
ether with the same speed, namely, $186000$ miles per
second, the length of the waves produced by them
must be different.

There are about seventy different elementary atoms,
each setting up its characteristic waves in the ether all
the time. It is to be remembered that all atoms and
molecules are always to be considered as hot bodies;
that is, bodies having some temperature, and mostly
a long way above absolute zero; and also that their
energy of this kind may be spent upon the ether. If
the waves from one molecule have more energy than
those given off by a second molecule upon which they
fall, the second one absorbs some of it so as to have its
own temperature raised until it is the same as the other;
that is, until the energy given off by them both is
equal. And this is universally true. Matter is continually
exchanging energy in this way, always tending to
bring about equality of temperature. But the number
of vibrations a body makes does not need to be the
same as that of another body in order to possess the
same amount of energy, for the energy depends upon
both mass and velocity. If the mass be small, the
\DPPageSep{149.png}{137}%
velocity must be greater, and \emph{vice versa}. And thus it
is that the seventy elements that make up the kinds of
matter we know are everywhere and at all times setting
up ether waves, each kind its particular rates, when not
otherwise interfered with.

There is, however, a qualification that must be added
that has a high degree of scientific importance. Every
elementary substance is vibrating at several rates at the
same time, as do piano-strings, bells, and musical instruments
in general. Every particular rate of vibration
produces its own waves, and thus each atom and
molecule is continually producing, when not interfered
with, its own characteristic set of waves. This must
make the ether waves from the different kinds of matter
exceedingly complex, and disentangling them correspondingly
difficult; yet it has been done.

When we look at luminous bodies, like the sun or
stars, or flames, or gas, they seem to differ from each
\index{Flames}%
other in brightness and sometimes in color, as is seen
in fireworks. A flame of alcohol has a bluish tint, a
little salt in it makes it yellow, some lithium makes it
red, and copper, green or bluish, while sunlight is white,
as is the electric light. If one looks through a common
prism at the landscape the edges of objects appear in
rainbow tints, and with the colors arranged in the same
order, while at the same time the shape of things is
more or less distorted. If a beam of sunlight be sent
directly through such a prism, a patch of colors may be
seen on the floor or wall, and this is called a solar
spectrum; and if this light of different tints has its
wave length measured, it appears that the red light has
\DPPageSep{150.png}{138}%
a wave length of about the one forty-thousandth of an
inch, and the violet light at the other extreme a wave
length of about the one sixty-thousandth of an inch,
while the intermediate tints range regularly from the
one to the other. There is in this spectrum that can
be seen an almost infinite number of wave lengths;
% [Illustration: ]
\begin{figure}[hbt]
  \begin{center}
    \Graphic{\linewidth}{150a}
  \end{center}
  \Caption{8}{Diag.\ 8.---Visible Solar Spectrum.}
  \index{Spectrum, solar}%
\end{figure}
there is no break among them apparently. The same
thing holds true of a spectrum produced by letting the
light from a lamp or candle go through the same prism:
\index{Prism}%
the tints, their order, and their wave lengths are found
to be the same. The prism then receives ether waves
of any or all wave lengths, and separates or disperses
them in the order of their wave lengths. In doing this
it deflects the longer waves less than it does the shorter
ones. The deflection of the waves from their original
course is called \emph{refraction}, and the separation from each
\index{Refraction}%
other so as to produce the spectrum is called \emph{dispersion}.
\index{Dispersion}%
A prism effects both at the same time, and thus enables
one to isolate at will any particular tint or part of the
spectrum; and if one takes a single narrow portion in
any such spectrum, he has a bundle of light rays of
uniform wave lengths, and he may then determine their
value. In this way the wave lengths of the different
colored parts of the spectrum of sunlight have been
found to be as follows:---
\DPPageSep{151.png}{139}%
\begin{center}
\TableFont%
\begin{tabular}{ll<{\qquad\qquad}l}
Red,     & about & $39000$ to the inch
\\
Orange,  & \PadTo{\text{about}}{\Ditto}  & $41000$ \PadTo{\text{to }}{\Ditto}\PadTo{\text{the }}{\Ditto}\PadTo{\text{inch}}{\Ditto}
\\
Yellow,  & \PadTo{\text{about}}{\Ditto}  & $44000$ \PadTo{\text{to }}{\Ditto}\PadTo{\text{the }}{\Ditto}\PadTo{\text{inch}}{\Ditto}
\\
Green,   & \PadTo{\text{about}}{\Ditto}  & $47000$ \PadTo{\text{to }}{\Ditto}\PadTo{\text{the }}{\Ditto}\PadTo{\text{inch}}{\Ditto}
\\
Blue,    & \PadTo{\text{about}}{\Ditto}  & $51000$ \PadTo{\text{to }}{\Ditto}\PadTo{\text{the }}{\Ditto}\PadTo{\text{inch}}{\Ditto}
\\
Indigo,  & \PadTo{\text{about}}{\Ditto}  & $54000$ \PadTo{\text{to }}{\Ditto}\PadTo{\text{the }}{\Ditto}\PadTo{\text{inch}}{\Ditto}
\\
Violet,  & \PadTo{\text{about}}{\Ditto}  & $57000$ \PadTo{\text{to }}{\Ditto}\PadTo{\text{the }}{\Ditto}\PadTo{\text{inch}}{\Ditto}
\\
\multicolumn{2}{l}{Extreme visible, about} & $60000$ \PadTo{\text{to }}{\Ditto}\PadTo{\text{the }}{\Ditto}\PadTo{\text{inch}}{\Ditto}
\\
\end{tabular}
\end{center}

A spectroscope is an instrument composed of a prism
\index{Spectroscope}%
mounted between two tubes, one of them having an
adjustable slot for the light to be examined to pass
through on its way to the prism, the other being a short
telescope to magnify somewhat the image of the
spectrum that %[** PP: Width-dependent break]
%[Illustration]
\begin{figure}[hbt]
  \begin{center}
    \Graphic{\linewidth}{151a}
  \end{center}
  \Caption{9}{Diag.\ 9.---Spectroscope.}
\end{figure}
it may the better be seen. With this,
light from any source may be examined. Light made
up of all wave lengths that can be seen shows as
a complete spectrum, while any light made up of but
a part of these gives a corresponding incomplete
spectrum. The flame of an alcohol lamp, or a Bunsen
\DPPageSep{152.png}{140}%
\index{Spectrum analysis}%
gas-flame, gives but little brightness and not much to
produce a spectrum; but a little salt in the flame gives
to it a bright yellow tint, and shows in the spectroscope
a single narrow band of yellow light in the same place
as the yellow seen in sunlight, and therefore having the
same wave length. Such a beam made up of waves of
one wave length is called homogeneous light. This
sodium light has a wave length of about the one forty-four-thousandth
of an inch. With other more refined
methods, which cannot be described here, sodium is
found to have other wave lengths beyond both the red
and blue ends, and which cannot be detected by the
eye alone. Hydrogen, another element, gives a bright
red line and a blue line that are easily seen; and several
others may be detected with more delicate apparatus.
In this manner all the elements have been attentively
studied during the past thirty years, and many treatises
may be found that give full particulars of the processes
and results. The substance of knowledge obtained by
the study of the spectra of the elements may be briefly
stated to be,---

1st, Each element has its own vibratory rates at
a given temperature, and sets up corresponding ether
waves; some of these can be seen, and others require
more complicated apparatus to discover.

2d, In order that the characteristic vibrations of any
atoms or molecules may take place, it is necessary that
they be allowed a free path to vibrate in; in other words,
they need be in the gaseous state. If they be crowded
together, as they are in solids and liquids, they have no
chance to vibrate without interference. A pailful of
\DPPageSep{153.png}{141}%
school-bells might make a jangling noise, but would give
no particular pitch or characteristic sound of any of the
bells, and only when not interfered with for a part of the
time at least could one give out its true sound. This
gaseous state is generally obtained by igniting in flames
or by the electric spark the substance to be examined.
In an electric arc all substances are volatilized, and may
be then studied with the spectroscope to great advantage.
Sometimes substances that remain in the gaseous
state at ordinary temperatures, such as hydrogen, oxygen,
chlorine, etc., are hermetically sealed in glass tubes,
after rarefication, in order to obtain long free paths, and
are lighted up by means of electric discharges through
them.

3d, On account of the lack of vibratory freedom, the
molecules of solids and liquids give out vibrations of all
wave lengths, for every partial and incompleted movement
disturbs the ether; and there are all degrees of
these, but the energy of the shorter ones is rarely great
enough to affect the eye, and hence are not visible at
ordinary temperatures. If a body like a cannon-ball be
gradually heated in the dark, it will presently begin to
glow with a dim red tint. If looked at through the
spectroscope, only red light on the extreme red border
can be seen. As the temperature rises, additional
shorter waves appear, and the spectrum broadens to the
orange, then the yellow, and so on; the ones already
showing growing brighter meanwhile, until the ball is
in a bright glow, and a full continuous spectrum is produced.
As the ball cools, the reverse holds true; and
the violet waves are the first to disappear, then the blue,
\DPPageSep{154.png}{142}%
and lastly the red vanishes from sight. Still the ball is
much too hot to safely touch, and continues to cool by
giving off ether waves differing from the rest only in
being too long to affect the eye. They still are refracted
by the prism, and an invisible spectrum is produced,
and this spectrum has been traced out to ten
times the length of the visible spectrum.
%[Illustration: ]
\begin{figure}[hbt]
  \begin{center}
    \Graphic{\linewidth}{154a}
  \end{center}
  \Caption{10}{Diag.\ 10.---Complete Solar Spectrum.}
\end{figure}

The sun, an electric arc, and other solid hot bodies,
\index{Spectrum, solar}%
give out similar long, invisible spectra.

In like manner, where the body is white-hot, and giving
out the shortest waves the eye can see, there can still
be found, a long way beyond that limit, waves that can
do photographic work, which is but a kind of molecular
dissociation.

4th, Where waves of a given length are made to pass
through a gas having similar vibratory rates, or capable
of producing waves of the same length, the molecules
of the latter will absorb such waves, and therefore stop
their progress, especially if they have more energy than
the waves the absorbing gas can give out. So if sunlight
containing the same yellow light as that of sodium
gas be made to pass through the latter, it will be stopped;
and if this be done where there is a spectrum of sunlight,
the yellow will be cut out from it, and there will be
but a black line instead. This is called gaseous absorption,
\index{Gaseous absorption}%
and is an illustration of what was said a little way
\DPPageSep{155.png}{143}%
\index{Sun, its structure}%
back about the exchange of energy always going on.
The absorbing power of a gas has a significance like its
radiations, and indicates its presence as well.

The yellow light of sodium gas has a definite place
in the spectrum; and hence if one perceives those wave
lengths in a gaseous spectrum, he knows that sodium
must be present in a state of incandescence, giving rise
to the waves. But if the light from a white-hot cannon-ball
were to be sent through that same vapor, and afterwards
examined with a prism, the yellow light would be
absent, and the absence would still proclaim the existence
of sodium vapor.

Hence, if an incandescent body gives a continuous
spectrum, it must be a solid or a liquid; the molecules
must be so compact that the individual vibrations are
prevented, and only irregular ones can be made. If a
discontinuous but bright line spectrum is shown, the
matter must be in a gaseous state, and the molecules
have free path.

If a bright spectrum have black spaces or bands
across it, there is indicated a solid or liquid incandescent
body shining through gas that acts by absorption
upon it, and thus both the solid and gaseous conditions
are detected, as well as the nature of the substance in
the gaseous state.

This knowledge has been applied to the discovery of
the substance and condition of the sun and other celestial
bodies, and it is concluded that the sun has a solid
or liquid surface as a shell to a gaseous interior, and
that the atmosphere of it consists of the various
elements that make up the body of the sun in so highly
\DPPageSep{156.png}{144}%
\index{Jupiter, temperature of}%
\index{Mars, atmosphere of}%
\index{Saturn, temperature of}%
heated a condition as to keep them in a vaporous or
gaseous state. The characteristic spectroscopic lines of
about forty elements have been found there. Some of
the elements have a very large number of spectroscopic
lines. Iron, for instance, has several hundred lines.
Hydrogen is particularly abundant. Perhaps the most
important discovery due to the spectroscope has been
this: that there are a very large number of gaseous
bodies, called nebulæ, in the heavens; some of these fill
immense spaces; they are in a condensing state, and
all of them are mostly made up of hydrogen. This
discovery gave an additional probability to the nebula
theory of the origin of the solar system, for it showed
that process in its various stages in more distant
parts of space: and in addition to that, it has led to
the surmise that in some way some of those we now
call elements are really compounds of more elementary
substances, probably hydrogen; but that is a speculation
merely, for there is no other than such spectroscopic
evidence that anything like transmutation of what we
call elements into others can take place.

The spectroscopic examination of the other members
of the solar system has shown that Mars has an
atmosphere like ours, holding watery vapor in it;
that Jupiter is red-hot; that the temperature of Saturn
is probably much too high for any such living things
as exist on this earth---and in this way has answered
the question so interesting to most thoughtful persons
as to whether the planets are inhabited or not. Jupiter
certainly cannot be inhabited by any such beings as we
are, for the temperature would destroy all organic things.
\DPPageSep{157.png}{145}%
\index{Motion, kinds of}%
\index{Stars, their motions}%

Velocities of translation can also be measured when
as high as two miles a second or more, by the displacement
of spectroscopic lines towards one or the other
end of the spectrum. If a star is approaching us, the
wave lengths are shortened a small quantity, and that
changes the position of a line towards the blue end,
while recession makes it longer and moves it towards
the red end, so it has been found that Sirius is receding
\index{Sirius}%
at the rate of nineteen miles per second; that Arcturus
\index{Arcturus}%
is coming towards us at the rate of sixty miles
per second. In like manner is shown that the sun, and
with him the whole solar system, is travelling in the
direction of the constellation Hercules at the probable
rate of about sixteen miles per second.

Now, all this presupposes that the principles established
in the laboratory for substances there investigated
are applicable wherever such matter exists;
for instance, that the spectrum of sodium and of hydrogen
and iron, which depends upon temperature and
pressure, is as reliable if the light comes from a body
a million miles or a thousand million miles away as if it
came from only one mile or a foot distant. If it be
thus widely applicable, then do we have the best of
testimony that matter, its conditions, and its laws are
the same everywhere, and that the earth is a fair specimen
of the rest of the universe.


\Section{OTHER PHENOMENA OF ETHER WAVES.}

Whenever a line of ether waves---which is generally
called a ray, whatever the wave length may be---falls
\DPPageSep{158.png}{146}%
upon matter, the ray may be either absorbed, transmitted,
or reflected. Neither of these results takes
place singly in any case. There is no known body, for
instance, that can wholly absorb all the rays that fall
upon it, nor wholly transmit or reflect them. If a body
should be able to absorb all the rays that fall upon it,
we should not be able to see it unless itself were a self-luminous
body, for we only see other than self-luminous
objects by means of the light reflected from them,
and such a body would reflect no light, and hence could
not be visible.

Bodies which absorb most of the rays that fall upon
them we call black and opaque; that is, a body that
reflects but a small portion of the waves that are incident
upon it is a dark or black body, because we see
but little of it. If it reflected none at all, it would be
quite invisible. In like manner, a perfectly transparent
body would be one that would neither absorb nor
reflect any rays, and for that reason would be quite as
invisible as space itself. The air is perhaps as near an
approach to perfect transparency as anything that can be
\index{Transparency}%
named; yet if it reflected no rays at all, there would be
nothing of the diffused light that is now so plentiful on
the clearest day, but there would be only what would
come direct to us from the sun or other luminous body.
We call clear glass and water transparent because objects
can be plainly seen through them; and a sheet of hard
black rubber we call opaque, for nothing whatever can
be seen through it, nevertheless it has been shown
that waves longer than those that affect the eye, go
through such hard rubber as easily as the shorter ones
\DPPageSep{159.png}{147}%
we call light go through glass, hence transparency and
opacity are terms only relative to particular kinds of
waves. All kinds of matter reflect more or less of the
waves that fall upon it. This reflection is merely the
\index{Reflection}%
change in direction of the ray; but it always follows a
definite law, keeping to its original plane, and making
the angle of reflection equal to the incident angle.
The surfaces of most bodies are very rough, and the
rays are reflected in all directions, because the points
upon the surface face in so many ways. This will
be obvious to one who looks at the surface of paper or
of wood with a magnifying-glass. The smoother a surface
is made, the nearer will all the incident rays take
the same direction on reflection. Mirrors are thus
\index{Mirrors}%
made of smooth glass or metallic surfaces, and are
plane, convex, or concave; but whether they are made
with plane or curved surface, the rays reflected always
follow the above law.


\Section{REFRACTION.}
\index{Refraction}%

So long as ether waves fall perpendicularly upon any
surface of any kind of matter, the rays go straight on
into it if they be not reflected or absorbed at the surface;
there is no change in the direction, but the velocity of
transmission is less in all kinds of matter than it is in
the ether. In glass it is only about two-thirds as fast,
and in water about three-fourths. When the ray meets
the surface at an angle, it is bent out of its course more
or less, depending upon the kind of material it falls
upon, and also the angle at which it meets it. This
change of direction, when entering a new medium, is
\DPPageSep{160.png}{148}%
called refraction, and this property is possessed by all
kinds of matter, solid as well as liquid and gas. The
refraction for a given angle of incidence is more for a
liquid than for a gas, more for a solid like glass than for
water or other liquids, and more for a diamond than for
any other known substance. The same rule that obtains
when the waves enter a medium, holds when it leaves
it; the direction it will now take will depend upon the
angle the rays make with that surface and the character
of the medium into which it enters. Thus, if a
ray meets a piece of plain glass at an angle, say, of~$45°$,
some of it will be reflected, making an angle of~$90°$
with the incident ray, and some of it will be refracted
into it, making an angle with the original direction, and
continue on in a straight line until it meets the next
surface, when it will again assume its original direction:
but when the second surface is not parallel with the
first, as is the case with the prism, the direction may
depart still more from the original; and the shorter the
wave length, the more the deflection. It is this property
that is made use of in spectroscopes, microscopes,
and telescopes. A lens has one or both surfaces
curved, so as to be convex or concave, depending upon
the use it is to be put to,---a convex glass converging
the rays, and a concave one separating them,---and
almost any degree of either of these may be obtained
by proper curvature.

Both microscopes and telescopes are so common, and
descriptions of them are to be found in so many places,
that they need not be described here. The inquiry is
often made, why still more powerful microscopes and
\DPPageSep{161.png}{149}%
\index{Microscope, magnifying powers}%
telescopes are not made so as to reveal the very smallest
and the most distant thing. The utility of a
microscope depends upon how plainly it is able to
make minute objects visible; and the more a given one
magnifies an object, the smaller the portion that can be
seen and the less light is available for the purpose, and
when the objects are so small as the few thousandths
of an inch, the light waves interfere with each other at
the edges, and produce colored fringes that cannot be
got rid of altogether, and very small objects become
indistinct for that reason. Microscope lenses are
marked as $1$~inch, $\dfrac{1}{2}$~inch, $\dfrac{1}{10}$~inch, and so on, meaning
by the fraction the approximate distance it must be
brought to the object in order that the latter may be
seen. The higher the power, the shorter this distance.
A one-tenth inch objective may magnify an object a
thousand diameters and perhaps more, so that a blood
corpuscle having a diameter of only one three-thousandth
of an inch may appear about three-tenths of an
inch in diameter, and the details of its coarser structure
may be very well seen; but if there be a minute
point upon it, still indistinct because it is minute, and
a still greater magnifying power required to see it, and a
$\dfrac{1}{20}$~objective be taken, the actual magnifying power
may be five thousand diameters. But now one is
approaching the dimensions of wave lengths themselves,
and the agent necessary for observing introduces
its own complications, producing distortions and
color fringes about the point to be studied, and no way
\DPPageSep{162.png}{150}%
has been found of obviating this. Objectives have
been made having a focal length of only the $\dfrac{1}{50}$~of an
inch and one having only the~$\dfrac{1}{75}$, but no work of any
importance has ever been done with them. The best
of the microscopic work has been done with lenses that
magnify no more than one thousand diameters. It is
said that the best microscopes will show an object that
is no more than about the one hundred-thousandth of
an inch in diameter, but it appears simply as a point or
a line, and no details of its structure can be seen.
Fine rulings upon glass have been made that are known
to have this degree of fineness, because the mechanism
that rules them can be gauged to that degree; but
many persons cannot see these in a microscope, though
others can. So within the limits of the visible not a
little depends upon the acuteness of vision, and there
is a great difference among individuals in this respect.
On account of the properties of the ether waves themselves
in their relations to each other, it does not
appear probable that much improvement is possible to
the microscope. This does not imply that we may not
know more of the minute structure of bodies than we
do now, for there are other sources of knowledge of
minute quantities than simply direct eyesight, which
are just as reliable, perhaps more so. A good chemical
balance will weigh to the millionth part of the load.
Whitworth showed that it was possible to measure to
the millionth of an inch by touch. The spectroscope
will indicate the millionth of a grain by the tint of the
\DPPageSep{163.png}{151}%
gas flame, and the color of a drop of water is appreciably
changed by the one three-millionth of a grain of
fuschine. Some substances, like essential oils, sulphuretted
hydrogen, and the odors of flowers, can be
perceived when the quantity is certainly less than the
fifty-millionth of a grain.

Any day may bring tidings of new instrumentalities
that help in the solutions of the interesting questions
concerning molecular structure that are now quite out
of our reach. Let it be granted that the problems are
altogether physical ones, such as are justified by the
known mechanical relations of energy, and one may
wait with patience. Let one assume that some or any
of them are not mechanical, and he not only is in danger
of having to revise his judgment in some degree any
day, but he reasons against the significance of all the
knowledge we have of matter and its energy.

The larger a lens is the more light can go through it:
a lens two feet in diameter will let four times as much
light through it as one only one foot in diameter. As
remote objects, like the distant stars, appear dim on
account of their great distance, it becomes needful to
concentrate the light from a much larger area than that
of the pupil of the eye. If the pupil be one-tenth of an
inch in diameter, a certain amount of light from a star
may enter it. A lens one inch in diameter would concentrate
at its focus $100$~times as much, and one a
foot in diameter, $14400$~times more; and hence the
object would appear so much brighter. Along with
this apparent brightening of the star, it is apparently
brought nearer and enlarged. There are limits to the
\DPPageSep{164.png}{152}%
size and useful magnifying power of telescopes as well
as to those of microscopes. The magnifying power
of telescopes depends very largely upon the eye-pieces
used, and the shorter their focal length the more do
they magnify. The large lens, called the objective,
serves mostly to collect a large amount of light. It is to
be kept in mind that the movements of bodies are magnified
as much as their apparent dimensions, and when
there are any movements of the body surveyed, or of
the instrument itself, distinct vision becomes correspondingly
difficult.

With the telescope the chief trouble comes from
movements of the air, which are rarely of uniform quality
and motions. Not only its transparency, but its degrees
of density caused by heat and wind, are varying all the
time; and these seriously interfere with telescopic work.
If a magnifying power of say~$100$ be employed, these
disturbing causes are increased in proportion, and with a
power of~$1000$ nothing can be distinctly seen. Suppose,
however, the air be in best condition for observations,
and a power of~$1000$ be put upon the moon. As
the moon is about $240000$ miles away, this magnifying
power would have the effect of bringing it $1000$~times
nearer, or as it would appear to the eye if it were
but $240$~miles away. Now, an object $240$~miles away
can reveal no interesting details at all; anything much
less than half a mile square could not be distinguished
unless it were a very bright or very dark spot. Powers
as high as~$8000$ have been used; and such a one would
bring the surface of the moon as it would appear if it
were about thirty miles distant, which might show a
\DPPageSep{165.png}{153}%
city, a large town, a lake, and the difference between
field and woodland, yet nothing satisfactory was seen
for the reasons mentioned, so for most astronomical
work a magnifying power of only a few hundred is
used; seldom more than five hundred. When large
telescopes are set on elevated places like the Lick
Telescope on Mt.~Hamilton in California, some of the
troubles from disturbed air are obviated, and it is hoped
something more may be learned about our nearer astronomic
neighbors. But these large telescopes collect
so much more light that stars so distant as to be quite
invisible with smaller glasses become plainly visible
with them. With the unaided eye no more than $5000$
or $6000$~stars can be seen in the whole heavens, with
an opera-glass as many as $100000$ become visible, while
the Lick telescope, with an object-glass three feet in
diameter, shows nearly $100,000000$. Each increase in
the size of the telescope adds to the number of visible
stars, and one cannot but wonder if their number be
infinite, or if there be a boundary to the universe of
matter. Though the visible boundary of our universe
has been greatly extended by the invention of the telescope,
nothing has been descried anywhere but matter
and motion: there has been nothing added to our knowledge
but the sense of bigness. Instead of only a few
thousand of hot and flaming stars, there are hundreds
of millions of them, made of the same kinds of matter,
having the same kinds of motions, controlled by the
same laws, and nothing animate in any of them more
than in a bowlder in the wall. Clifford said he wished
they were farther off. The problems of astronomy are
\DPPageSep{166.png}{154}%
\index{Space, navigation of}%
interesting studies in mechanics, but are not inviting to
those most interested in life and mind. Herschel and
Chalmers and Dick and Mitchell are dead. The
knowledge already gained has destroyed both their
arguments and hopes, and has left the inhabitants of
this earth the possessors of the universe, yet unable to
take possession.

If there are inhabitants in Mars they are as unable to
traverse space as we are; and the possibility of our yet
being able to do that is not half so unlikely as it seemed
to be but a very few years ago, since it evidently requires
for accomplishment but a directed reaction against
the ether; and we already know how to produce the
reaction by electrical means; and every point in space
has the energy for transformation.

It is generally agreed that the so-called attraction of
a magnet for its armature is really due to the pressure
of the ether upon the latter, and it may be as great as
two hundred pounds to the square inch.

An electro-magnet without an armature is therefore
reacted upon by the ether to that degree. When this
reaction can in any way be neutralized at one pole and
not at the other, the ether reaction will push the magnet
backwards, and the navigation of space will at once
become mechanically possible.


\Section{THE RADIOMETER.}
\index{Radiometer}%

It is a familiar enough fact that when sunshine falls
upon a surface the latter becomes heated. In general,
the darker the color of the surface the more rapidly %[** PP: Width-dependent break]
% [Illustration]
\begin{wrapfigure}{r}{1.5in}
  \Graphic{1.5in}{167a}
  \Caption{12}{Diag.\ 12.---Radiometer.}
\end{wrapfigure}
does
the temperature rise; and some bodies, when thus exposed
\DPPageSep{167.png}{155}%
for some time, become unbearably hot. We are
able to say that the surface molecules of such a body
are in a brisk vibratory movement; that they have more
energy than other bodies with less temperature. If one
imagines the condition of things when the molecules of
the air impinge upon such a heated surface, he will understand
how they must bound away
from it with greater velocity than
they struck it with, and if with
greater velocity, then with greater
energy. As action and reaction are
equal, it must kick back upon the
surface as it leaves it, thus tending
to make the surface move in the
opposite direction; and a large number
of such impacts must give a resultant
backward pressure. If the
surface be a small one, the increased
pressure in the air in front will
travel round to the other side at
the rate of eleven hundred feet in a
second in ordinary air; so the pressure
will be equalized in a very short
interval of time. If the air be rarefied
in front of such surface to such a degree that the
free path of the molecule is many times greater than
its ordinary length, that pressure cannot get round
nearly so fast, and there will consequently be a constant
backward pressure, produced by the molecules that impinge
upon it and become heated by contact with it.
The pressure per square inch is very slight, as it is
\DPPageSep{168.png}{156}%
produced by a relatively small number of molecules;
but it may be made apparent by mounting some disks,
blackened on one side, upon a pivot in a glass bulb,
and, after exhausting a large part of the air, hermetically
sealing the bulb. Such a device is called a radiometer.
When put where sunshine, or the light from
the flame of a lamp or candle, or even the heat of the
hand, may fall upon it, the vanes begin to rotate, the
blackened side backing away from the source of the
energy. This movement was at first interpreted as
being due to the actual pressure produced by light
waves, but further investigation showed that idea to be
wrong. The movement comes from the transformation
of the motions of ether waves, first into heat, and
second into the translational mass motion observed.
The radiometer is, therefore, a machine for transforming
ether waves into visible mechanical motions.


\Section{PHOTOGRAPHY.}
\index{Photography}%

It has already been explained how heat acts upon
molecules, increasing the amplitude of the vibrations of
the atoms that make them up, and, if carried to a sufficient
degree, is able to quite destroy the molecular structure
and enable the component atoms to enter into new
combinations. The degree needed for this depends upon
the kind of molecules. Some molecules are so stable
that only the very highest temperature we can produce
can break them up. Others are so feebly cohesive that
the least touch will cause them to go to pieces, and
sometimes with explosive violence, as is the case with
what are called fulminates, compounds of nitrogen with
\DPPageSep{169.png}{157}%
silver or with mercury; and sometimes the same result
is reached by ether waves, whose number per second is
such as to set one of the ingredients into sympathetic
vibration and thus decompose the compound, doing it
at a slower rate than the others. Nearly all complex
molecules are decomposable in this way, and the process
is going on all the time in nature where there are organic
things to act upon, but the process is usually
slow.

When shingles are first laid they have a fresh surface
and new appearance, which is presently lost by
the exposure. Take a freshly planed piece of soft
pine or other white wood, and fasten to the surface a
piece of paper cut into any shape or design,---a circle,
a star, or the like,---and set the wood where the sun
can shine on it for a few days. When the design is
removed the figure will be plainly seen on the wood by
the difference in tint between its surface and that part
which the sun has shone upon. The latter is much
darker. This is an example of photographic action,
as is the color of fruit, etc.; for if a design is pasted
upon a green apple, which is red when ripe, the design
will protect the surface from the action of the light,
and will therefore appear upon the apple in a light tint.
Diagrams and letters may be fixed thus upon fruit of
any kind. Discolorations of all sorts, due to ether
waves or light, may properly be called photographic
action, both fading and darkening, as when the skin
becomes tanned. For practical purposes some compounds
of silver are generally employed, because they
are more sensitive to the action of visible waves than
\DPPageSep{170.png}{158}%
most other substances. They have the property of
being easily disorganized by waves whose length
ranges from about one forty-five-thousandth of an inch
to those in the neighborhood of the seventy-thousandth
of an inch, some of these being visible waves, the
others being too short for visibility. When a surface is
prepared with some one of the sensitive salts of silver,---generally
the iodide or the bromide,---and a picture
of an object produced by the lenses of the camera
is allowed to fall upon it, the decomposing action is
proportional to the amount of light and shade in the
different parts; and, when the plate thus exposed is
placed in certain chemical solutions called developers,
the decomposition is completed and the products dissolved
out, leaving a coating of pure silver, with a
thickness proportional to the chemical action that has
taken place. This gives, then, a correct likeness of
the picture that was in the camera. Formerly it took
a long time to produce such a picture, a person having
to sit still for half an hour or more. More and more
sensitive preparations were produced, until now a good
picture can be taken in less than the thousandth of a
second; and the practice of the art has become a great
industry. There are many preparations in common
use for taking such pictures, but nearly all of them
have silver for the chief constituent. It may be
remarked that silver compounds are remarkably unstable.
Silver is not easily oxydized\DPnote{** [sic]}, for it remains
untarnished for an indefinite time, as exemplified by
coins and jewelry. But there are plenty of other compounds
that may be used. Thus the common blue-print\DPnote{** Hyphenated across page, no other instances.}
\DPPageSep{171.png}{159}%
\index{Silver salts unstable}%
is a compound of iron. The salts of chromium
are also sensitive to such waves.

It was remarked that the salts of silver are sensitive
to ether waves between quite a wide range in wave
lengths, but the longest of them is in about the middle
of the visible spectrum. They reach from there into
the region beyond the violet. Yellow and red waves
are incapable of affecting such a preparation, while the
waves that are the most efficient for it are the blue
ones.
% [Illustration: ]
\begin{figure}[hbt]
  \begin{center}
    \Graphic{\linewidth}{171a}
  \end{center}
  \Caption{13}{Diag.\ 13.---Photographic Range for Silver Salts.}
\end{figure}

Other substances have a different range, and a curious
chemical discovery has shown that silver molecules
may be loaded; that is, may have attached to them in
a temporary way some other kinds of molecules that
render them sensitive to waves of any length. If an
ordinary photographic plate has a solar spectrum
thrown upon it, there will be no indication of action
below the green; but, if aniline be added to the sensitive
coating and the plate be then exposed in the same
way, the action will now be seen to have gone on to a
distance below even the longest red wave that can be
seen. In this way photography has shown that the
spectrum of most incandescent bodies is much longer
than the visible part of it in both directions. It was
the observation that photographic action took place
\DPPageSep{172.png}{160}%
\index{Molecules, loaded}%
most strongly in the blue part of the solar spectrum,
and in the region beyond, that led to the belief that
light waves and chemical rays were, in some way,
unlike each other. From what has been said it will be
seen that the reason for the different action was due to
the character of the material used. When a molecule
is made bigger or heavier in any way, longer waves can
affect it more; and that is the significance of the so-called
loaded molecule. In reality, the whole molecule
is made more complex and bigger, and longer waves
can shake its atoms loose.

It is to be hoped that all can understand that there
is nothing mysterious about photographic action; that
it is as simple in its mechanical principles as anything
can be. One may not be able at once to say in
any given case which atoms or which parts of a molecule
are loosened by the vibratory strains. In this one
it may be the nitrogen, in another it may be the silver,
and in still a third it may be oxygen; but in each case
the mode of action is the same, and it may be said to
be mechanical throughout.


\Section{VISION.}

Our various senses differ much in their mode of
action, and require for excitation not only each its
proper stimulant, but degrees of remoteness from
actual contact to the most distant points. Thus the
sense of touch requires absolute contact of a body: so
also does taste,---the sugar or the salt must dissolve
upon the tongue. A distance of but the tenth of an
inch between the sugar and the tongue will be absolutely
\DPPageSep{173.png}{161}%
prohibitive to the consciousness of sweetness.
The sense of smell requires the actual contact of the
gaseous molecules upon the nasal membrane, but currents
of air and gaseous diffusion secure to us this condition,
so that the emanating body itself may be at
some distance, and yet we become conscious of the
bank of violets, the cup of coffee, or the chemical laboratory.
This sense, therefore, enlarges our field, so to
speak, and permits us to be conscious of bodies out of
our immediate reach. The sense of sound still farther
enlarges the space that can react upon us. But the
loudest sounds, such as the roar of cannon and thunder,
lose their intensity shortly, and can rarely be
heard beyond a few miles. If our endowment of
senses stopped with these, we should really be quite
\index{Senses}%
limited in our possible knowledge; for as we can know
only what comes into our experience, how small the
possibilities of existence would be to us! What we
could touch, taste, smell, and hear we could know something
about, though we were unconscious of any lacking
sense. We should need some apparatus that could
make us conscious of the most distant things as well
as those close at hand. We should need just what we
have got,---the sense of sight, that extends the field of
experience and of interest to us to the boundaries
of creation. The other senses give us information of
contiguous things, but sight brings the universe itself
to our consciousness.

The sense of touch is diffused all over our bodies.
There is no such thing as an organ of touch. The
senses of taste and smell are restricted to localities and
\DPPageSep{174.png}{162}%
to organs that have other functions as well. Only sound
and sight have specific organs, having no other function
than to respond to sonorous and optical motions, and
thus they have a peculiar dignity in the physiological
mechanism; and precisely because the eye and ear have
these mechanical functions do they come into the domain
of physics. They are machines by which certain forms
of motion are transformed into others suitable for nerve
transmission to the seat of consciousness.

It has often been pointed out that the structure of
the eye is like the camera of the photographer. In each
\index{Camera}%
there is a chamber~\textit{a}, having a lens in front, which has
a length %[** PP: Width-dependent break]
% [Illustration]
\begin{figure}[hbt]
  \begin{center}
    \Graphic{\linewidth}{174a}
  \end{center}
  \Caption{14}{Diag.\ 14.}
\end{figure}
of focus adapted to the distance between it and
the back of the chamber, so that the image of objects
external to it will be produced by it upon the back of
the chamber, where there is in each a sensitive coating
so affected by the light as to make an impress. In the
camera this action has been explained as chemical
reaction when molecular dissociation results, proportionate
to the amount of light that falls upon any part
of the surface exposed.

In each there is an arrangement for altering the focal
distance of the lens. In the camera it is a ratchet-wheel
that moves the lens towards or away from the
back. In the eye there are muscles attached to the
\DPPageSep{175.png}{163}%
edge of the lens that by contracting make the pliable
lens less convex and so increase its focal length. For
the camera %[** PP: Width-dependent break]
% [Illustration]
\begin{wrapfigure}[15]{r}{2.25in}
  \Graphic{2.25in}{175a}
  \Caption{15}{Diag.\ 15.---Photographic Camera.}
\end{wrapfigure}
there is
\index{Camera}%
an exchangeable diaphragm
having perforations
of various
sizes to admit more
or less light through
the lens. In the eye
there is a colored
muscular disk called
the iris, that contracts
or expands in
an automatic way so
as to expose more or
less of the lens to
the light. The functions
of the two devices are identical.

The energy possessed by the ether waves that fall
% [Illustration: ]
\begin{figure}[hbt]
  \begin{center}
    \Graphic{\linewidth}{175b}
  \end{center}
  \Caption{16}{Diag.\ 16.}
\end{figure}
upon the sensitive photographic plate is spent in doing
\DPPageSep{176.png}{164}%
\index{Vision, phenomena of}%
the molecular work of disintegration. In the eye all
the energy is stopped at the sensitive back coating
called the retina, and must of course be accounted for
in some physical way. In the camera all the energy of
the waves is spent in precisely the same kind of a way;
that is, there is no such distinction as what is called
color in it: and color photography---that is, the direct
picture of objects in their proper, natural tints, such
as we know they have, upon the sensitive plate---has
not been accomplished, for the probable reason that the
colors of the molecules that are the result of the decomposition
of the silver compound are either transparent
or blueish black. In the eye, the distinction between
wave lengths which we denominate color sensation is
very pronounced.

The sensations are so much complicated with the
processes that induce them that it is not always easy to
keep in mind the purely physical side or the subjective
side while treating of them.

The following are some of the more common phenomena
of vision which must be taken into account in forming
any judgment or theory of it.

When a firebrand is swung round and round it
leaves an apparent luminous trail, the length of which
depends upon the rapidity of motion. This is called the
persistence of vision, and indicates that the sensation
does not cease instantly after the source has gone. If
the brand be swung round at the uniform rate of once
per second, the length of this luminous trail will be a
rough measure of the duration of the sensation after it
is once excited. Thus, if it appeared to be one-quarter
\DPPageSep{177.png}{165}%
of the circle, the sensation must last for one-fourth
a second. For impressions not very bright the sensation
lasts but about the tenth of a second. If, however,
the object looked at be very bright, like the sun, for an
instant, the sensation may last for many seconds; and,
in general, the older the person the longer does it last.

Different colors also have different degrees of persistence.
\index{Colors}%
Violet, blue, and green soonest fade out, and red
is the last to vanish for most eyes. This signifies that
wave length has in someway to do with the persistence.
When a bright colored object, like a bit of red paper,
is put upon a sheet of white paper and steadily looked
at for a few seconds, and is then suddenly removed while
the eyes are kept fixed upon the same place, the image
of the red paper will still be seen, but it will appear with
a green tint, and will fade out in a few seconds. A
green piece of paper, or any green object looked at in
the same manner, will give an image in red. Blue ones
give yellow, and yellow blue; and these tints seen in
this way are called complementary to each other, as it is
found by combining such together they produce the
sensation of white light. Whiteness is therefore a compound
sensation. Formerly, it was thought that white
was only produced by the composition of all the colors
of the spectrum in the same proportions they exist in it;
but the same sensation of whiteness can be produced
by red, green, and violet, and by blue and yellow. This
is not to be understood as applying to pigments or
paints, but to light itself.

If one looks at a strongly lighted object intently for
a few seconds, and then turns his eyes to a dimly
\DPPageSep{178.png}{166}%
\index{Vision, hallucinations of}%
\index{Vision, energy needed for}%
lighted drab surface, he will be able to see, sometimes
in a surprisingly realistic way, the same object against
the new background. If it be a person looked at,
the features may even appear in a startling way.
The size of the subjective figure will depend upon
the distance of the background, being larger the more
remote that is. Age and health have much to do
with the persistence of such sensations\DPtypo{}{.} Young and
vigorous persons seldom notice them until they
carefully look for them; while older ones, and especially
weakened ones, may be much troubled by
them. Some nervous systems react upon the eye itself,
and give rise to similar images there; and these subjective
images have not unfrequently been mistaken for
objective persons living or dead. The color a given
object appears to have is not unfrequently modified by
what colors the eye has been resting upon the instant
before, and hence two persons may look at once upon
the same picture and see it in very different tints.

As ether waves are the source of the sensation, it is
obvious that a certain number of consecutive waves
must be necessary to affect the eye; that is to say, it is
not in the least probable that a single wave of any
length could produce a sensation. How many are
needed is not known, but one can determine somewhere
near what the number must be if he knows how
brief a time is sufficient to produce a sensation. It is
said that some flashes of lightning have been found to
occur in less than a millionth of a second, and those
may produce a very strong sensation.

If there are five hundred million million vibrations per
\DPPageSep{179.png}{167}%
second, as we know there must be to give such a sensation,
in the millionth of a second there must be five
hundred millions; if the brightness were reduced ten
thousand times and it were still visible, there must
then have been not less than fifty thousand waves: and
this is equivalent to saying that the eye could perceive
light if it lasted no longer than the ten thousand
millionth part of a second, which is probably true.
But there is another condition; namely, the \emph{energy}
of the waves must be sufficient to effect a physical
change in the eye; and we know that the energy of
such ether waves varies with the square of their amplitude.
If, then, any wave whatever has not energy sufficient
to produce the necessary physical disturbance in
the eye, it could not produce vision. And this is the
most probable reason that we do not see in what we
now call darkness. It has been shown that all matter
at all temperatures is vibrating and setting up ether
waves, and also that in all liquids as well as solid
bodies there are vibrations due to their atomic and
molecular interference; and, theoretically, there must
be vibrations of all wave lengths at all times and in all
places, but at low temperatures the shorter waves,
though not absent, would have but small energy, and,
as the body becomes hot and the shorter ones acquire
more, it is done at the expense of the energy of the
longer ones, for the light given out by an incandescent
lamp increases faster than the supply of energy to produce
it. It therefore appears as a necessary conclusion
that the reason we cannot see in the dark is not so
much because the waves of proper wave length are
\DPPageSep{180.png}{168}%
\index{Vision of animals}%
\index{Vision, theory of}%
entirely absent, as that they have too little energy to
affect our eyes. Other animals, such as rats, mice,
owls, bats, and the like, can see where it appears to us
to be pitch dark. They must, therefore, have eyes
adapted for longer wave lengths than are ours, or else
the sensitiveness of their eyes exceeds ours. As
they see readily in the daylight, it is certain they are
adapted to such waves as our eyes are; and, if ours
were sufficiently sensitive, or had a greater range in
effective wave lengths, there would be no such condition
as darkness. That is the same as saying that
darkness is in us rather than being a condition external
to us.


\Section{THE THEORY OF VISION.}

When it was discovered that the sensation of whiteness
could be produced by combining three different
colors,---red, green, and violet,---it was inferred that
there were probably three sets of nerves that were spread
as a fine net-work over the retina so that either of these
rays might fall at any point in the field of vision upon
it and so produce the sensation. At the same time,
when one or two of them were absent, the other nerve
ingredient would be present to be affected; and, furthermore,
each one of these three nerves was sensitive to
quite a wide range of wave lengths, and their overlappings
gave perception without any break from the
extreme red to the extreme violet. In this way color
perception could be explained. This view was adopted
as a working hypothesis; and there was no other proposed,
although there was no evidence whatever for the
\DPPageSep{181.png}{169}%
existence of three sets of nerves having different properties.
It has, however, lately been discovered that
the retina secretes a substance called purpurine, on
\index{Purpurine}%
account of its purple tint, which is very rapidly
bleached or decomposed by the action of light. That
is to say, it possesses photographic properties in a
marked degree. This discovery has led to the view that
vision may be altogether due to photographic action,
and the older view has been about abandoned. The
details of this theory have not yet been all worked out,
but the purport of it may be briefly stated.

Given the purpurine spread over the retina: this
would be its sensitive coating corresponding to the silver
preparation upon the photographic plate. The
action of the light upon it being the same in character,
decomposes it into simpler molecular compounds. The
optic nerve is certainly spread over the retina, and the
purpurine is in its meshes, and any disturbance taking
place in this substance must correspondingly affect the
ends of the nerves imbedded in it. Given the disturbance
that can affect the optic nerves, and it is transmitted
at once to the base of the brain and there interpreted
as light sensation. The differences there might
be in the amount of disturbance would be the differences
that are called brightness or intensity. If molecules
are disintegrated, as in photographic action, there
must be a relatively large amount of free-path motion
resulting from the wave action in the eye, and the
amount of it proportional to the energy expended.
Such an effect would give a general sensation of light,
probably, also, effects of light and shade, so the forms of
\DPPageSep{182.png}{170}%
bodies would be readily enough seen. It would also
account for persistent effects; for, when molecules are
made to move fast or slow, they do not cease instantly
on the removal of the source of the motion, but they
continue to thus move until their energy has been
reduced to that of the surrounding medium. With
simple purpurine there appears to be no more possibility
of chromatic effects than there is in the common
silver preparation on the photographic plate. Suppose,
however, the purpurine to be not a simple kind of a
body, or made up of only a single kind of molecules,
but instead made up of as many as three different
kinds having as many different molecular weights, and,
therefore, capable of being reacted upon by three different
wave lengths. Call these three substances \textit{a},~\textit{b},
and \textit{c}~purpurine. Let \textit{a}~be such as red waves can
decompose, \textit{b}~such as green ones can decompose, and \textit{c}~such
as only the short purple ones can break up or
shake up. If these are uniformly mixed together and
spread over the eye, then red waves would shake up
the red constituent, but would leave the others alone;
and the same would hold true of the others. If one
has been looking at red-light wave lengths, the \textit{a}~purpurine
would be used up, but the \textit{b} and~\textit{c} would still be
present unimpaired; and now, when white light is again
looked at, the \textit{b}~and~\textit{c} would be acted on strongly because
they are present in greater quantity. The resulting
sensation would be the compound of these two
reactions, which, as is well known, is a greenish tint.
In a like manner, each of the others when used up
would leave the same field fresh with the other constituents,
\DPPageSep{183.png}{171}%
\index{Color-blindness}%
\index{Retina, its functions}%
and so give the complementary tints; and in
this way chromatic effects of all sorts can be accounted
for.

Some persons are color-blind; that is, they are
unable to distinguish some colors; and this defect is
usually for red rays. Such a color-blind person will be
unable to see the red end of the spectrum, and the
colors of it will appear to leave off in the yellow or
orange. The old explanation was that the red sensation
nerves were absent. The newer explanation is
that the \textit{a}~ingredient of the purpurine is wanting either
partially or altogether.

Of course it is to be understood that the products of
decomposition by light in the eye are removed and
fresh material secreted in its place by the organ itself
in a manner similar to the removal of waste tissue and
its repair in any other part of the system.

The function of the retina, then, would appear to be
the secretion of the sensitive substance needed for
vision, instead of itself being the sensitive substance.

Such an explanation of vision makes the eye still
more like the photographic camera than appears in its
outward form and mechanical functions. And thus one
is able to trace the forms of motion that constitute the
heat and the temperature of a body through its resultant
ether waves to the molecular break-ups at the ends
of nerve fibres, whence the characteristic motions are
transmitted to the base of the brain, to be interpreted
thus or thus, according to position, number, and energy.
We begin with motion, we end with motion at the
seat of consciousness, and there we stop. It is vibratory
\DPPageSep{184.png}{172}%
in the hot body it starts from, it is undulatory
motion in the ether, it is oscillatory in the disrupted
molecules, and a longitudinal wave in the nerve.
Whether it is discharged from further service at the
base of the brain, or is stored up in some way as experience,
no one can say; but it is certain that a relatively
large amount of molecular energy finds its way constantly
to the brain, and some of it is re-employed as
reflex action, giving rise to voluntary and involuntary
\index{Reflex action}%
muscular and secretory processes, as when one winks, or
dodges a threatening motion before the will can act, or
laughs or weeps at sights and sounds. In either case
the result is the physical expression of a physical antecedent,
with an intermediate mental quality called
emotion.

The eye may then be said to be a machine for the
transformation of ether waves into interpretable molecular
or atomic motions, and its function ceases at the
ends of the optic nerve.
%\DPPageSep{185.png}{173}%


\Chapter{VIII}{Electricity}{173}

\First{The} industrial applications of electricity are now so
extensive and varied that every one is acquainted with
them in some measure, and yet fifteen years ago there
were millions of persons in the civilized nations who
had never seen an electrical phenomenon with the exception
of lightning. The apparently capricious behavior
of lightning, together with the attractions and repulsions
exhibited by electrified bodies, were phenomena
so different in character from any other, that it came
to be looked upon as a very mysterious force. Fifty
and more years ago it was classed with heat and light
as one of the imponderables. To-day even the question
is often asked, What \emph{is} electricity? with the
emphasis on the word ``is,'' as if one knowing enough
might describe it as he might describe a genii or an
object having specific qualities that might be isolated
from everything else. Some have thought it to be a
fluid, some two fluids, some vibratory molecular motion,
some a property of matter, some a motion in the ether,
some the ether itself; and, lastly, some have concluded
that we do not and never can know its nature.
Hence, to-day there is no generally received notion
concerning its nature.
\DPPageSep{186.png}{174}%
\index{Electricity, origin of}%
\index{Electricity, thermal}%
\index{Thermodynamics, electric}%

Still, one may know a great deal about the agent
itself,---how it originates, what it will do, and its relations
to other phenomena,---and not concern himself at
all as to the nature of it. Heat and many of its laws
were well known before any one knew or even suspected
what its nature was. The law of gravitation
is known and applied on the scale of the universe without
demanding any explanation of the phenomena, and
it is equally true that our knowledge of electricity is
very extensive and accurate, and doubtless what we do
not know to-day we may know to-morrow.


\Section{ORIGIN OF ELECTRICITY.}

It is here to be assumed as known, that various
instruments, such as electrometers and galvanometers,
are employed to detect the presence of electricity, and
descriptions of them will not be given. Attention will
be paid chiefly to the conditions that are present when
electricity is generated.

\Section{1. THERMAL ORIGIN.}

When two different metals, such for instance as copper
and iron, are touched together, they are found to be
electrified; that is, an electrometer shows the presence
of electricity. A piece of copper wire twisted to a
piece of iron wire always becomes thus affected, but
the effect is so slight that only delicate and sensitive
apparatus will detect it. Wires of any of the metals
under similar circumstances exhibit the same phenomenon,
but in different degrees. This electrification is
but transient; in a few seconds it has vanished. If the
\DPPageSep{187.png}{175}%
junction of the metals is heated by the fingers, or in
any other way, the electrical condition is maintained
indefinitely. If one will imagine such a compound wire
bent into a ring so the ends nearly touch each other,
it could be shown that the ends attract each other, the
attraction being but slight. Here we are not so much
concerned about the measure of what is taking place
as with its character. If the ends of the wires be
allowed to touch, and the twisted junction be kept warm,
a current of electricity will continue to circulate through
the ring; and, if the ends be connected to a galvanometer
of sufficient delicacy, the needle would be
continuously deflected, so long as the junction was
warmer than the outer ends of the wires; and the deflection
of the needle would be found to vary with the
difference in temperature between the inner and outer
junctions. Some metals, such as bismuth and antimony,
when fastened by solder, or in any other way, give much
stronger effects with a given temperature at their junction.
Such a combination is called a thermo-electric
pair. By joining a number of such together, so that
alternate ends may be heated at once, the electrical
effect is increased proportionally: two will give twice,
and ten ten times as much, and so on. When a number
of these are nicely compacted together and provided
with binding-screws, they are called thermo-electric
piles, and are of service in some investigations. It is
not necessary, however, to have two different metals in
contact to obtain the same kind of effects. If a piece
of soft iron or platinum wire be wound into a close coil
about a lead-pencil and the ends of it connected to a
\DPPageSep{188.png}{176}%
galvanometer, a current of electricity will traverse the
circuit when one end of the coil is heated in a flame.
If the other end be heated, the current will go in the
opposite direction. The twisting of the wire into
the coil produces a strain among the molecules that
changes the physical properties to a slight extent: the
density is altered. It therefore appears that in this
case, as in the cases with two different substances, we
have two \emph{physically} \DPtypo{diferent}{different}
bodies, though of
the same element. The
facts may be generalized
by saying that, %[** PP: Width-dependent break]
%[Illustration]
\index{Thermopile}%
\begin{wrapfigure}{l}{2.5in}
  \Graphic{2.5in}{188a}
  \Caption{17}{Diag.\ 17.---Thermopile.}
\end{wrapfigure}
whenever two differently
constituted bodies
are placed in contact
with each other, electricity
is generated, and
is maintained so long
as there is a difference
in temperature between
the junction and the external
ends.

If one inquires for the
origin of such manifestation as the first case, when two
different metals are placed in contact, attention must
be directed to the actual molecular condition of the
two metals. Suppose them to have the same temperature,---as
they have different atomic weights their
vibratory rates cannot be the same,---and when the
surfaces are put in contact there must be a re-adjustment
\DPPageSep{189.png}{177}%
\index{Chemical origin of electricity}%
of their molecular motions, for each will interfere
with the other. This disturbance of molecular rates
is a disturbance in their relations of energy, and
furnishes the energy for the electrical phenomenon
that ensues. When equilibrium is restored, as it may
be shortly, there is no longer any electrical exhibit.

When heat is applied so as to keep the junction continually
hotter than the other parts, the first effect is
continuous; for as each element has its own proper
vibratory molecular rate, which is increased by the
heat, the interference is kept up and an electrical current
results, which the heat is spent to produce and
maintain. One needs to have in mind what is signified
by heat as vibratory atomic, and molecular motion, in
order to clearly perceive what is expended in the
thermo-electric pile. The face of the pile, when it is
generating a current of electricity, does not acquire
that temperature it would acquire if it was prevented
from producing a current by having the wires detached.
Hence the amplitude of vibrations is lessened by the
electrical work done, and we may say that heat has
been converted into electricity, a thermal origin.


\Section{2. CHEMICAL ORIGIN.}

When a piece of copper is dipped into a vessel of
water, and a wire leading from it is connected to a
proper electrometer, it is found to be electrified to a
certain degree. If a piece of zinc be substituted for
the copper, it too indicates a still greater degree; and
now let both be placed in the same water and connected
by a wire, and a current of electricity will flow through
\DPPageSep{190.png}{178}%
\index{Polarization of molecules}%
the wire, as in the case with the thermopile. This
current will be a transient one, or very slight, if the
water be pure; but if a little acid like sulphuric be
added to the water, the current may be relatively a
strong one. If, %[** PP: Width-dependent break]
% [Illustration]
\begin{wrapfigure}[11]{l}{1in}
  \Graphic{1in}{190a}
  \Caption{18}{Diag.\ 18.\break Galvanic Cell.}
\end{wrapfigure}
instead of the zinc and copper, any
other two metals be taken, the results will differ from
the former only in degree. Zinc and copper,
or zinc and carbon, are generally employed,
because those have been found to
give better results than other available elements;
and such a combination of metals,
with some solution, acid or alkaline, which
is capable of \DPtypo{disolving}{dissolving} one or both of the
metals, is called a galvanic battery. A single
\index{Galvanic battery}%
jar with its proper elements is called a cell; and by
the addition of cells additional effects may be produced;
that is, with two cells twice, and with ten cells
ten times the effect.

As with the thermo-pair, one may inquire what conditions
were known to be present that could furnish an
antecedent to the electrical current that results. This
is answered by pointing out, as in the other case, that
there are two substances differing in their physical qualities,
copper and water, or zinc and water, and molecular
rearrangement at their junction must necessarily
result. More than this. It is known that the zinc and
oxygen have a strong affinity for each other. The oxygen
is combined with hydrogen to form the water, and
in water the molecules are without any definite arrangement:
they face in all directions, and move about with
the greatest freedom, with but little, if any friction.
\DPPageSep{191.png}{179}%
When zinc is placed in it, the attraction of the zinc for
the oxygen part of the molecule must result in making
every water molecule in proximity to the zinc swing
round so as to present its oxygen side to it. This orientation
of the liquid molecules is called their polarization.
The attraction between the two is not quite
strong enough to disrupt the water molecule; but the
addition of sulphuric acid weakens the attraction between
the hydrogen and oxygen, and enables the oxygen
to seize a zinc atom, and both combine with the sulphuric
acid to form the sulphate of zinc. Here we
have chemical reactions such as always result in exchange
of energy; for the sulphate of zinc has less
molecular energy than the zinc, the water, and the
acid, in the same way that carbonic acid gas has less
energy than the carbon and oxygen gas that formed
it. There has been, then, a molecular change accompanied
by the development, first of heat and second
the generation of electricity; for if the electrical current
be not allowed to flow, the battery cell will itself
heat up more than it otherwise would do. There are
chemical, thermal, mechanical, and electrical phenomena
here, which may be perceived by carefully thinking
of the successive steps in the process. The distinctive
thing here is to bear in mind what the characteristic
antecedents of the electrical phenomena are. What are
the chemical, the thermal, the mechanical factors, except
special forms of exchangeable molecular motions?
So one may say that in a galvanic battery chemism or
heat has been transformed into electricity. Though
the mechanism of transformation is different, yet the
same factors appear as in the thermopile.
\DPPageSep{192.png}{180}%


\Section{3. MECHANICAL ORIGIN.}
\index{Electricity, mechanical origin}%

When a piece of glass or of wax is rubbed with a
cloth or catskin, the two substances subject to the
friction become endowed with a new property which
they do not otherwise exhibit. If a glass disk be
mounted so as to %[** PP: Width-dependent break]
% [Illustration]
\begin{figure}[hbt]
  \begin{center}
    \Graphic{\linewidth}{192a}
  \end{center}
  \Caption{19}{Diag.\ 19.---Static Electrical Machine.}
\end{figure}
be rotated, and proper connections
made to it, as in the common Static Electrical machine,
a current of electricity may be maintained by maintaining
the friction, and all the electrical phenomena may
be produced that can be with electricity from any other
source. They are identical, but the source is the friction
of dissimilar substances. It will be recalled that
dissimilarity in substance was the condition in each of
the former cases; but in this, mechanical friction is the
\DPPageSep{193.png}{181}%
\index{Electricity, magnetic origin}%
\index{Stress, magnetic}%
second factor. In the chapter on heat it was pointed
out, and it is a familiar enough fact everywhere, that
heat is always the immediate result of friction. So in
this mechanical source, with apparatus so dissimilar in
all outward form to both thermopile and galvanic battery,
we still have precisely the same molecular conditions
that were operative in them to produce electricity,---two
dissimilar substances, and heat or a kind of motion
that results at once in heat.


\Section{4. MAGNETIC ORIGIN.}

If a wire of any sort be placed across the pole of a
magnet, and held quiet there, no electrical effect will
be noted; but if the wire be moved toward or away from
the pole, it will become electrified, and if one end of it
be connected to an electrometer the movement of the
needle will indicate it. If the two ends of the wire be
connected to a galvanometer, whenever the wire is thus
moved in front of the magnet pole a current will flow
through the circuit, and the movement of the needle
this way or that will indicate the motion of approach or
recession. The strength of this current will vary with
the rapidity of the motion of translation of the wire
through the space in front of the magnet; and the wire
through which it goes becomes heated. This is the
same as saying that the mechanical motion of translation
of the wire is converted into heat in a manner as if
it had been subject to ordinary friction there; and as a
matter of fact, it is found to require more energy to
move the wire in such a space when the ends of the wire
are in contact, than it does when they are not. This
\DPPageSep{194.png}{182}%
\index{Electricity, electrical origin}%
shows that the material of the wire is subject to some
restraint under such conditions and in such positions,
and the degree of restraint depends upon the distance
it is from the magnet, as well as upon the strength of
the magnet itself. Hence the different parts of the
wire are in different physical states. And this is just
what is exhibited by the twisted wire in the case of
the thermal origin; and when motion is imparted to the
wire, the degrees of stress in it change, and a current of
electricity is the result. That such a stress is really
present in the wire can be proved in several ways,
which only need to be alluded to in this place. First,
the electrical resistance of a wire is greater when in
front of a magnet than elsewhere; and second, the
phenomenon known as Hall's, in which a current of
electricity going through a conductor is deflected from
its course in the neighborhood of a magnet. So we
have, in this magnetic origin, two bodies with different
physical constitutions and external motions impressed
upon them, which gives the electrical product
observed.


\Section{5. ELECTRICAL ORIGIN.}

Imagine two wires parallel to each other and a foot
apart. If an electrical current from any source is made
to traverse one of them, a corresponding current will
be initiated in the other, but in the contrary direction.
In a like manner if a constant current be kept in one
of the wires, and the other one be moved towards and
away from the other, currents will be set up in it.
Their direction will depend upon whether the motion
\DPPageSep{195.png}{183}%
\index{Inductive action}%
\index{Stress, electrical}%
be approach or recession. The effect is the same
whether either or both move at the same time. The
effect is similar to the one described under the head of
Magnetic Origin, showing that in some way the space %[xref]
about a wire having a current of electricity in it is substantially
similar to that about a magnet. The process
is called electro-magnetic induction in both cases, and
the explanation is the same in this as in the other. It
will be well, however, to point out that there are steps
in this process that need attention for the sake of mechanical
clearness.

Given say, an electro-magnet, through which a current
can be sent at will, and so be made magnetic,
and with the wire in front of it as before. There is
now no magnetism and no electricity in the wire.
Make the iron magnetic, and the current is at once induced
in the other. I say at once, but this does not
mean instantaneously. It takes a short time for the
effect of the magnet upon the ether to travel to the wire
and affect it. As no electricity escapes from the electro-magnetic
circuit, the electricity observed in the wire,
or second circuit, is generated in it, and the \emph{immediate}
antecedent of it was the stress in the ether which was
produced by the magnet. Hence an electrical current
can arise from a proper kind of stress in the ether, no
matter how that is produced, as one of the factors; the
other factor being motion of some sort, mechanical or
otherwise. The steps are, an electric current in a conductor,
an electro-magnetic effect of the current upon
the ether, the reaction of the ether upon the second conductor.
Let these steps be kept in mind always when
\DPPageSep{196.png}{184}%
thinking about inductive action, and there can then be
no confusion from trying to imagine how electricity
gets from one circuit to another when they are insulated
from each other.


\Section{6. PHYSIOLOGICAL ORIGIN.}

There are certain kinds of fish that are capable of
giving powerful electrical shocks to men and animals.
They are provided with special organs for this purpose,
but they have not been the subject of much study for
several good reasons. First, they are only to be found
in a few localities, and are difficult to obtain; and second,
their electrical qualities cannot be studied except
when they are alive; and when they are living and
healthy their shocks can kill both men and animals,
and few are willing to incur the risk. Both mankind and
animals in general can give rise to electrical currents.
By grasping with the thumb and finger of both hands
the terminal wires from a delicate galvanometer, a current
is indicated,---a part often due to thermo-electric
action, and a part to physiological action,---and it will
vary with the tightness of the squeeze of contact and
the person experimenting, some developing much more
relatively than others. It also varies with the parts of
the body in contact with the wires. This physiological
effect is always extremely minute, and is not to be
mentioned beside the amount necessary to effect the
remarkable things said to be done by personal electricity,
such as moving chairs, tables, etc. I do not
think any one has been found whose physiological
electricity could do so much as raise a grain the tenth
of an inch.
\DPPageSep{197.png}{185}%

The various processes continually going on in the
body, such as breathing, digestion, blood-circulation,
and muscular motions of all sorts, and under conditions
of different temperatures, different material, different
chemical reactions, are quite sufficient to account
for all that has been observed in this direction.


\Section{7. ATMOSPHERIC ORIGIN.}

The origin of lightning, so far as details go, has
\index{Lightning}%
never been satisfactorily accounted for. It is obviously
not an affair that can be investigated in any very scientific
manner, for one can never control any of the conditions
when it arises.

Some have thought it due to the condensation of
electrified vapor molecules condensing into drops of
water, the degree of electrification increasing with the
size of the drops. How the original electrification of
the molecules was produced is not explained by such.
There is no doubt but that a large amount of energy is
often involved in a stroke of lightning, judged by its
sudden destructive work. The immediate source of
this energy is the question\DPtypo{}{.} There is no doubt but
when a gas or a vapor is condensed into a liquid, a
notable amount of energy is liberated in motions of
some sort; for it requires energy to be spent upon water
to produce the vapor. This is given back when the
process is reversed. This energy has often been called
latent heat. If this process goes on faster than it can
be conducted away, it must either be transformed, or the
process must stop\DPtypo{}{.} We know, too, that heat motions
are most freely transformed into electrical by the phenomena
\DPPageSep{198.png}{186}%
\index{Electrical antecedents}%
\index{Terminology, electrical}%
of the thermopile and the galvanic battery,
and it is not improbable that this is the source of the
atmospheric electricity. It is certain that where it
originates there are two differently constituted kinds of
matter,---the air and the water; and it is equally certain
that there are some vigorous exchanges of motion, both
in the form of wind and heat, and these are the conditions
present in each of the cases where our knowledge
is most complete.

One may then fairly conclude from the analysis of
all the known sources of electrical development, that
motion of some sort is the antecedent in every case.
This motion may be the sort called mechanical, or that
called molecular or atomic, as heat, but it is always a
factor; and the amount of electrical energy developed
in every case is equal to the \emph{immediate} mechanical,
chemical, or thermal energy which disappears when it
is produced. If one admits that the quantity of energy
in phenomena is constant, that the quantity of matter
is constant, there is but one variable factor, and that is
motion. If mechanical motion is transformable into
heat, and heat into electricity, and some known form of
motion is the invariable antecedent to the production
of electricity, it does not need a very profound logician
to say, \emph{so far}, the nature of electricity is known.


\Section{ELECTRICAL TERMINOLOGY.}

Every particular science and art has some technical
terms to give precision and definiteness to its processes
and its laws, and the advances made in any science
depend very largely upon exact signification of its
\DPPageSep{199.png}{187}%
terms. The late rapid development of electrical science
is due in a large measure to terminology, adopted
about twenty-five years ago; for it enables a man not
only to know what he himself is talking about, but also
to understand others, and that was not the case before.
A system of units and names for them are matters of
the first importance. How these were derived need not
be stated here, but it is needful for every one now to understand
the significance of the more common of them.

Imagine a wire in front of you with an electrical current
traversing it from left to right. If it travels in that
direction it is because the electrical pressure is less
towards the right than in the opposite direction, just as
water flowing through a pipe towards the right travels
thus because gravitative pressure is less in that direction
than in the other. Gravitative pressure is measured
in pounds, electrical pressure is measured in \emph{volts}.

If the pressure at the left of the wire were increased
in any way, there would be an increased current of
electricity in the wire, just as there would be more water
go through the pipe if the head or gravitative pressure
were increased. The rate of water flow might be measured
as so many cubic inches or cubic feet per second.
The rate of electrical flow is measured in \emph{ampères}.

If the water pipe were a large one, and the pressure
the same, more water would flow through it than if it
were a small pipe of the same length. In like manner
a thick wire will permit more electricity to flow through
it with a given electrical pressure than a thin one. The
water pipe is said to oppose friction to the movement
of water.
\DPPageSep{200.png}{188}%

A conductor of electricity is said to offer resistance
to the flow of electricity. No name has been given to
any unit of frictional resistance, but electrical resistance
is measured in \emph{ohms}.

A definite quantity of water flowing at a given rate
will be emptied from the pipe in a second or a minute.
So will a definite quantity of electricity go through
the wire in a second or a minute. The quantity of
water thus flowing would be measured as so many cubic
feet, or so many gallons; the quantity of electricity is
measured in \emph{coulombs}, a coulomb being an ampère per
second. Where the rate of flow of an electrical current
is given in ampères, the quantity will be found by
multiplying the ampères by the number of seconds the
flow has continued. Thus a ten ampère current in an
hour will have conveyed $10 × 60 × 60 = 36000$ coulombs.

There are also measures of capacity. The cubic inch,
the cubic foot, the pint, quart, bushel, and so on, are
measures of volume or capacity: any of them may be
adopted as a unit, and when accuracy is required all are
reducible to the cubic inch as a standard. Thus in a
gallon there are $231$~cubic inches.

In electricity the unit of capacity is called a \emph{farad},
and it represents the capability of an electrical device
to receive and hold a definite amount of electricity
under the standard conditions of pressure. Thus, when
under a pressure of one volt it holds one coulomb, the
capacity of the apparatus is said to be one farad.
Actually a piece of apparatus of sufficient size to hold
that quantity has to be so enormously large that a much
smaller one was requisite for convenience, and consequently
\DPPageSep{201.png}{189}%
\index{Potential, electrical}%
the microfarad, or the one-millionth of the farad,
has been more generally adopted.

As work may be got out of a flow of water, the
amount of work depending upon the pressure and the
rate of flow, so may work be got from an electric current,
the amount depending upon the pressure, volts,
and the current, ampères. The product of these factors,
volts into ampères, is called \emph{watts}; and the mechanical
value of one watt is such that $746$~is equal to
a horse-power, which, as before stated, is $550$~foot
pounds per second. The working power of a watt is
therefore $\dfrac{550}{746} = .735$ of a foot pound per second.


\Section{OHM'S LAW.}
\index{Ohm's law}%

%[** PP: Putting upright variables in math mode]
This is simply that the current in an electric circuit
may be determined by dividing the electric pressure in
volts by the resistance in ohms. It is customary to use
symbols for each of these factors, $E$~or E.M.F. (electro-motive
force) for the pressure in volts, $R$~for the resistance
in ohms, and $C$~for the current in ampères, so Ohm's
Law when thus written reads $\dfrac{E}{R} = C$. Recurring to the
idea of a wire in front carrying a current of electricity
from the left to the right, and also the statement that
the electrical pressure is greatest at the left as the
cause of the current towards the right, it is well to
remark here that the electrical pressure at any particular
point in a circuit is sometimes spoken of as its
potential. If the potential at some other point in the
circuit be different from the first, the current will flow
\DPPageSep{202.png}{190}%
\index{Conductivity, electrical}%
from the higher towards the lower. The difference of
potentials may be measured in volts, and expressed as~$E$
in Ohm's Law.

There is a very wide difference among different substances
in their ability to transmit electricity. Some
transmit it freely, and are called good conductors; others
transmit it but slowly, and such are called poor conductors.
All solids, and liquids possess some degree of
conductivity; but some of them, such as glass, rubber,
and wax, are so poor in conductivity as to be called non-conductors.
The term non-conductor came into use
before the refined methods now in use for measuring
conductivity were known. It is now believed that
the only non-conductor of electricity is the ether. If
this be the case, then it appears that all the so-called
electrical phenomena in the ether are to be looked upon
rather as the results of electrified matter upon the
ether, than the presence of electricity in the ether, just
as radiations or ether waves are the results of actual
vibrations of atoms and molecules. Conduction, then,
is a general property of matter, and differs in degrees,
that difference depending upon both the kind of element
considered and its molecular combination. Thus,
copper is an excellent conductor; but if copper be
chemically combined with sulphur or with oxygen its
conductivity is greatly impaired.

Conduction, too, implies contact, physical contact,
as in the case of heat; hence solids and liquids may
continuously conduct electricity, while gases can conduct
no faster than their individual molecules can move
in their free-path motions, and the rate of electrical
\DPPageSep{203.png}{191}%
\index{Ether, a non-conductor}%
loss is so slow from this source, that for telegraph lines
of hundreds of miles in length it is neglected as being
of no practical consequence. Neither is moist air
much better, and for the same reason. In all cases
where dampness appears to affect the working of electrical
apparatus, the loss is due to the moisture deposited
upon the surface of the apparatus, which thus
forms a thin conductive coating. A Leyden jar may
retain its charge for months if protected from a coating
of moisture, which, of course, it could not do if
either the air or the ether were conductors in any ordinary
sense of the word.

The words conduction and conductivity represent the
property possessed by matter to become electrified by
mere contact with another body that is electrified; but
the terms do not have a very high scientific importance
now, for a much more convenient term is employed in
place, the term resistance, which is the reciprocal of
conductivity, that is, the greater the one the less the
other proportionally. The substance having the highest
degree of conductivity has the smallest degree of
resistance. Resistance is measured in ohms, and is of
two sorts; viz., specific and dimensional. Specific resistance
is that resistance which depends altogether
upon the nature of the particular element considered,
and may be determined for any element by measuring
the resistance of a cubic centimetre of it.

Tables of conductivity and of resistance of wires
are common, and the following one gives the relative
values of a few of the elements for comparison. The
standard of conductivity being silver and reckoned as~$100$.
\DPPageSep{204.png}{192}%
\index{Conductivity, electrical}%
\index{Resistance, electrical}%
The standard of resistance being a column of
mercury $106$~centimetres long and one millimetre
square, which has a resistance of one ohm. The numbers
given are the resistances in ohms and fractions of
a wire $1$~metre long ($39.37$~inches) and one millimetre
($\frac{1}{\DPtypo{15.4}{25.4}}$~of an inch) in diameter.
\begin{center}
\TableFont%
\begin{tabular}{l<{\qquad}>{\qquad}r@{}l<{\qquad}>{\qquad}r@{}l}
\scriptsize\llap{SU}BSTANCE. &
  \multicolumn{2}{c}{\scriptsize\llap{CONDU}CTI\rlap{VITY.}} &
  \multicolumn{2}{c}{\scriptsize\llap{RE}SISTA\rlap{NCE.}}
\\
Silver,       &   $100$&     &     &$.021$
\\
Copper,       &   $99.$&$9$  &     &$.021$
\\
Gold,         &   $80.$&     &     &$.027$
\\
Aluminium,    &   $56.$&     &     &$.037$
\\
Zinc,         &   $30.$&     &     &$.072$
\\
Platinum      &   $18.$&     &     &$.116$
\\
Iron,         &   $17.$&     &     &$.125$
\\
Lead,         &    $8.$&$5$  &     &$.252$
\\
German Silver,&    $8.$&     &     &$.267$
\\
Hard Carbon,  &    $1.$&     & $50$&$.00$
\\
Graphite      &    $0.$&$01$ & \multicolumn{2}{c}{Very variable.}
\\
\end{tabular}
\end{center}

The resistance of most liquids, and of such substances
as are used for insulating wires, is so very great
that they are given in units called megohms, each a
million ohms. The following represents the resistance
of a few bodies in such terms, the volume being one
cubic centimetre:---
\begin{center}
\TableFont%
\begin{tabular}{l<{\qquad\qquad}r}
\qquad\scriptsize SUBSTANCE. & \scriptsize\llap{RESISTANCE} IN \rlap{MEGOHMS.}
\\
Ice,                    &       $284.$
\\
Water at freezing-point,&       $150.$
\\
Mica,                   &        $84.$
\\
Gutta Percha,           &       $450.$
\\
Hard Rubber,            &    $28,000.$
\\
Paraffine,              &    $34,000.$
\\
Glass,                  & $3,000,000.$
\\
Air,                    &   Infinite.
\\
\end{tabular}
\end{center}
\DPPageSep{205.png}{193}%
These must be read as so many millions of ohms.
Thus, ice\DPnote{** [sic], no verb} $284$ millions. Thus can be seen within what
wide limits this electrical property of matter ranges,
and also its significance as a factor in Ohm's Law, and
why some substances can be practically used as insulators
when in reality they possess a certain degree of
conductivity. Thus, glass is called an insulator. But
if there were a difference of potential or pressure on
opposite sides of a piece of glass one centimetre thick,
equal to $3,000000$ of millions of volts, there would be
a current of one ampère passing through for
\[
\frac{3,000000,000000}{3,000000,000000} = 1
\]
In no artificial way can we produce such a voltage as
that; but it is the opinion of some physicists that the
voltage of lightning may rise as high as some thousands
of millions. Under ordinary commercial voltages of
only a few thousands, the current would be insignificant.
Suppose it were $50,000$ volts, then
\[
\frac{50,000}{3,000000,000000} = \frac{5}{300,000000} = \frac{1}{60,000000}
\]
of an ampère.

Dimensional resistance is of more practical importance,
for by making a conductor larger its resistance
becomes less. When the cross section of a wire is doubled,
the resistance is reduced one-half. When the
diameter of it is doubled, it is reduced to one-fourth,---a
relation which may be stated as follows: The resistance
of a conductor varies inversely as its cross section,
or the square of its diameter if it be a wire; so by
making a relatively poor conductor large enough, it may
\DPPageSep{206.png}{194}%
\index{Electricity, activity}%
transfer as large a current as a much better specific
conductor of smaller dimensions. In the table it is
shown that the resistance of copper to that of iron is as
$.021$ to~$.125$, or that the latter is six times the former.
If, then, the section of the iron wire be made six
times larger, it will have the same degree of conductivity
as the copper. This means that one pound of
copper is worth nearly six pounds of iron for electrical
conduction; and whether the one or the other should
be employed in a given place depends chiefly upon the
relative costs. It is a commercial rather than an electrical
question. The resistance of all conductors varies
with their length.

Temperature also affects the conductivity of nearly
all bodies. Some have their conductivity increased
by heat, as is the case with carbon; others have their
conductivity increased by cold. Thus, the conductivity
of copper at $100°$~below zero is increased nearly ten
times.

An idea of the relative magnitude of the factor of
resistance in common electrical work may be gained by
knowing that a mile of ordinary electric arc-light wire
generally has a resistance of about two ohms; telegraph
and telephone wires five or six ohms, and often
more, per mile. If there be a current of ten ampères
going through a mile of wire that has a resistance of
one ohm, then Ohm's Law enables one to determine
what is the difference in pressure between the ends;
for $\dfrac{E}{R} = C$ and $E = RC = 1 × 10 = 10\text{ volts}$. So if any
two of these factors be known, the other may be computed.
\DPPageSep{207.png}{195}%
\index{Inductive action}%
The $E$~gives the available electrical pressure;
the $R$~gives the conditions under which it can work,
and the $C$~gives their resultant, the available current,
while the product of~$EC$ gives the activity, or rate at
which energy is expended in the circuit, while if this
product be divided by~$746$, the horse-power of the circuit
will be given.

The further significance of Ohm's Law and its utility
will be given farther on, when considering the relation
of electrical energy to mechanical energy.


\Section{INDUCTION.}

It has been pointed out that the term conduction
signifies the transferrence\DPnote{** [sic]} of electricity from one body
to another by contact,---contact in the sense that the
molecules of solids and liquids are in contact when they
cohere, and when their individual vibrations cannot take
place without mutual interference. It is found that
bodies become electrified by merely being in the presence
of another body that is electrified, without material
contact, and the more perfect the vacuum between
the bodies the more freely does this phenomenon take
place. As the electrified body that thus affects other
bodies in its neighborhood does not lose any of its own
electricity, does not share it with other bodies in any
degree, and as the other bodies lose their electrification
by simply being removed to a distance, and will recover
it again by being brought back, it follows that the
action is entirely distinct from the phenomenon of electrical
conduction. A similar body electrified by conduction
will retain its condition, and distance will make
\DPPageSep{208.png}{196}%
\index{Electrical field}%
\index{Fields, electrical}%
no difference. This kind of action is called \emph{electrical
induction}. To understand what changes take place, it
will be needful to attend particularly to the factors
present. Under the head of Electrical Origin of Electricity, %[xref]
it is pointed out that an electrical current may
be induced in a circuit adjacent to another circuit in
which a current is produced in any way; and here are
similar conditions and similar phenomena. Imagine an
electrified body freely suspended in the air. If a gold-leaf
electroscope is brought within a few feet of it, its
leaves will diverge; if brought nearer they will diverge
still more; recession will cause them to collapse. This
movement of the leaves can be produced indefinitely by
changing the distance of the electrometer from the
electrified body. It is important to note here that it
requires the expenditure of energy to move the gold
leaves, though the amount may be small. If it may be
done for an indefinite number of times, then the energy
spent may be indefinitely great; and that it is not
directly derived from the electrified body itself is certain;
for the latter loses by the process none of its electricity,
and cannot lose it except by conduction. Evidently
the body has in some way modified the physical
condition of the space about it so that another body
within that space is affected somewhat as it would be if
touched by an electrified body. But the property belongs
to the space itself, and cannot be extracted from it
so long as the electrified body remains in place. This
space about an electrified body within which other bodies
assume an electrical condition is called an \emph{electrical
field}. It may extend to an indefinite distance
\DPPageSep{209.png}{197}%
\index{Electrical stress}%
\index{Stress, electrical}%
from it, and its strength has been found to vary like
gravity, being inversely as the square of the distance.
This new physical condition into which the space has
been brought by the electrified body is known to be the
effect of the latter upon the ether, and is called its electrical
\emph{stress}. It is simply the reaction of the one upon
the other, and indicates that the molecules stand in
abnormal strained positions. A mechanical idea of
what it is like may be got by pressing the hand upon
the top of a table, and then producing a twisting strain
tending to turn the table round, but without moving it.
The whole table will be subject to a stress that will react
upon the hand, a condition which will, of course, be
retained by the table as long as such pressure is kept
upon it. For the hand substitute an electrified mass of
matter, and for the table the ether in any direction
about it, and one will have a fair conception of the
electrical field. Especially so, if he will add to it that
such twisting effect can be either right-handed or left-handed,
and so produce those distinctions known as positive
and negative, which run all through electrical
phenomena.

A body brought into this distorted field of ether is
acted upon by the latter tending to twist its molecules
into new positions with reference to each other, which
is precisely the condition that brought about the original
stress, that is to say the electrical one, with this
difference, that if the original one was right-handed
the reaction of the ether would be left-handed, or
exactly opposite that of the inducing body. This is
simply because action and reaction are equal to each
other and \emph{opposite}.
\DPPageSep{210.png}{198}%
\index{Electrical waves}%

One can now understand how it can be that bodies
can be electrified by induction without loss of electrification
by the inducing body. There are three steps in
the process. 1st,~The body electrified in any known
manner. 2d,~Its resultant stress in the ether. 3d,~The
reaction of the ether upon the second body,
inductively electrifying it. Electricity has not been
conducted by the ether, but a stress has been, and
the ether stress has electrified the second body. By
periodically electrifying and delectrifying a body, a
series of stresses will be produced about it which will
travel outwards as a succession of waves, the velocity
of which is the same as that of light, $186,000$ miles
per second, and the wave length of which will depend
upon the number of electrifications per second. Suppose
a sphere, like a cannon-ball in free space, to be
connected by wire, so that by pressing a Morse telegraph
key in connection with any source of electricity
it could be charged and discharged at will. If the key
was closed regularly once a second, the wave produced
would be $186,000$ miles long. If it could be
closed $186,000$ times per second, the wave would be
one mile long. And if it could be closed so often that
the wave length should be but the one fifty-thousandth
of an inch, there is every reason to believe that the
eye would perceive the waves as light; not so much
because the waves were produced by electrical means,
as that the eye is capable of perceiving ether waves of
that length, no matter how they may originate.

The analogy between heat and electrical phenomena
in the ether is very close. The ether receives the
\DPPageSep{211.png}{199}%
energy from both sources and transforms it. The
ether is not a conductor of either heat or electricity:
it is neither heated nor electrified by them, but in each
case is simply a medium for the distribution of such
energy as gets into it according to its own laws, and
quite independent of its source. When heat gives up
its energy to ether it becomes ether waves or radiant
energy, and is no longer heat: it has been transformed.
When radiant energy falls upon other matter it is
again transformed into heat. In like manner, when
electricity gives up its energy to the ether, it becomes
radiant energy also, and when this falls upon other
matter it is again transformed into electricity. I have
been thus particular to enlarge upon induction, and
point out the factors present, in order to make it clear
how entirely distinct the electrical condition in matter
is from the electrical effect of it upon the ether. It is
from a failure to keep these distinctions in mind that
so many have been mystified by electrical phenomena,
and so many different theories have been propounded
as to its nature.

In all our experience electricity originates in matter,
and whatever the particular character of the phenomenon
\emph{in matter}, it ought to have a different and distinct
name from the effect of such phenomenon upon the
ether. If such endowment of matter be called electricity,
then it is not proper to use the same word for
its stress, or wave effect, in the ether, and this for
precisely the same reason as is allowed to hold good in
heat phenomena. Formerly ether waves were called
heat, afterwards heat waves, now radiant energy, for it
is known that there is no heat in the ether.
\DPPageSep{212.png}{200}%


\Section{EFFECTS OF AN ELECTRICAL CURRENT---1. MAGNETISM.}

If a wire through which a current of electricity is
passing be twisted into a loop or ring, it is found that
the loop acts in all ways like a magnet. Its sides have
polarity; and if it be so mounted as to be free to
assume any direction, it will move so its sides face the
north and south. If a piece of iron be placed in the
ring, the magnetic effect will be greatly strengthened.
Soft iron, however, loses its magnetic property as soon
as the current stops. A piece of steel will retain some
portion of the magnetic condition, and so is called a
permanent magnet. A given current of electricity
will make a much stronger magnet of a piece of soft
iron than it will of a piece of steel, and this is explained
by saying that the iron is more \emph{permeable} to
magnetism than steel is. Once in possession of a
magnet, one may proceed to study its physical properties
in many ways. That a magnet possesses poles;
that it can attract and hold to itself iron, steel, nickel,
cobalt, and affects other substances but slightly; that
it is attractive to unlike poles of other magnets, and
repulsive to similar poles,---and so on, are phenomena
so widely known that they need not be described here.
Only such phenomena will be considered as will be
helpful to an understanding of the constitution of a
magnet, and its relation to electricity and to the space
about it.

The magnetism of a magnet seems to reside chiefly
near its ends, for these will sustain bits of iron, but
near the middle it will not; and when a small compass-%
\DPPageSep{213.png}{201}%
needle is moved around a bar magnet, it points towards
one end or the other, except when near the middle,
where it sets itself parallel. When such a bar magnet
has a sheet of paper laid upon it, and iron filings are
sprinkled upon the paper, the filings are arranged in
curious curved lines, starting from one pole and traceable
to the other, and quite around the magnet on both
sides. This %[** PP: Width-dependent break]
% [Illustration]
\begin{figure}[hbt]
  \begin{center}
    \Graphic{3.5in}{213a}
  \end{center}
  \Caption{20}{Diag.\ 20.---Magnetic Lines.}
\end{figure}
arranging power of the magnet extends in
every direction about it, as one can satisfy himself by
trying the same experiment with the magnet turned on
different sides. If one will compare the direction of
these lines of filings with the positions of the needle,
he will see that the needle assumes the same direction
at any given place. Near the poles the lines all converge
to it, and opposite the middle the lines are parallel
with the magnet. If the magnet be of a U~or
horse-shoe form, the lines will be found still to extend
from one pole to the other, some straight, some curved
\DPPageSep{214.png}{202}%
\index{Fields, magnetic}%
outwards, but always forming a curve such as to touch
each pole of the magnet. While the filings are in the
position described, let the paper be gently tapped with
a pencil so as to jostle them slightly, and they will
begin to close up in such a way as always to shorten
themselves, and presently they will form a dense mass
between the poles, adhering to the latter as a solid
piece of iron would do.

Such phenomena show that the magnet in some way
reacts upon the space about it, so that iron and other
magnets there are affected, just as an electrified body
affects the space about it, as has been described. This
space about a magnet within which such effects are
produced is called the \emph{Magnetic field}, which may be
\index{Magnetic field}%
said to be the stress in the ether produced by a
magnet. Like the electric stress, it extends to an
indefinite distance from the magnet, and travels with
the velocity of light; so if a magnet was charged and
discharged once a second, a wave motion would be set
up: the wave length would be $186,000$ miles long, and
if it could be charged and discharged so fast that the
waves were but the one fifty-thousandth of an inch in
length, it is very probable they would be perceived as
rays of light, and the magnet would be a luminous
body. Such waves are called electro-magnetic waves.
\index{Magnetic waves}%
At present the shortest waves of this sort, that can be
artificially produced, are several inches long, but it
seems highly probable that before long some way will
be discovered of making them of the required length
for vision.

If a test-tube filled with iron filings be held near a
\DPPageSep{215.png}{203}%
delicate suspended magnetic needle it will be found to
give no indication of polarity, one part will act just
like any other part, and the magnet will be equally
attracted. Bring the test-tube against the poles of a
strong magnet for a few seconds, and then it will be
shown that the filings have become magnetic, and now
one end of the tube will attract one pole of the needle,
while the other end will repel the same end. Shake
up the filings well, and the polarity will be destroyed.

Stir up iron filings with melted wax, and pour into a
paper mould, so as to form a stick the size of the finger,
or larger. If this be tested for magnetism, it will be
found without any; but magnetize it as if it were a
piece of steel, and it will be found to retain it, becoming
a permanent magnet. If a layer of iron be electrically
deposited upon a brass wire in a magnetic field,
the wire acts like a magnet. All these phenomena go
to show that what is called polarity or magnetism is
due to the \emph{positions of the molecules}, rather than upon
some sudden endowment which the molecules receive
and may lose. Imagine every molecule of iron to be
a magnet, having its poles or faces, then if in a mass
of them, such as makes up a piece of iron or steel,
all be made to face one way and keep such position, all
will act in conjunction to give polarity to the mass.
When some molecules face one way, and others adjacent
to them face the opposite way, they will but
neutralize each other, so the external evidence of
magnetism will be destroyed. How atoms may be
magnets and exhibit polarity may be imagined by considering
the phenomena of vortex rings again. In the
\DPPageSep{216.png}{204}%
ring all the motion on one side is towards the middle
of the ring inwards, on the other side all the motion is
outwards, so the properties of the two sides are opposite.
Each such ring must have its own \emph{field}, which
may extend to an indefinite distance from it, and may
be represented roughly by the diagram in which the
curved lines show the same features before described
as belonging to a magnetic field. When two or more
\index{Magnetic field}%
are facing the same way, and are in contact, these lines
cannot re-enter the ring except by going round the
second one; and when many are in line they must go
round them all, in which case the %[** PP: Width-dependent break]
%[Illustration]
\begin{figure}[hbt]
  \begin{center}
    \begin{minipage}[b]{1.25in}
      \Graphic{1.25in}{216a}
      \Caption{21}{Diag.\ 21.---Field of a Ring.}
    \end{minipage}
%
    \begin{minipage}[b]{1.5in}
      \raisebox{12pt}{\Graphic{1.5in}{216b}}
      \Caption{22}{Diag.\ 22.---Coinciding Fields.}
    \end{minipage}
%
    \begin{minipage}[b]{1.25in}
      \Graphic{1.25in}{216c}
      \Caption{23}{Diag.\ 23.---Opposing Fields.}
    \end{minipage}
  \end{center}
\end{figure}
direction of the lines
will be precisely those observed about a straight bar
magnet.
\Pagelabel{105} %[** PP: Label to p. 105 seems to point here]

When they all face one way, as in diagram~22, the
resultant will be at~A, the sum of the outgoing movements,
and at~B, the sum of the ingoing ones, and
polarity at A and~B will be at a maximum. If they face
in different ways, each will tend to cancel the other,
and there will be no external field; as in diagram~23.
\DPPageSep{217.png}{205}%
\index{Ether pressure}%

If two such atoms be brought face to face, each will
be blowing against the other; their fields overlap, and
the stress is increased between them, and they are
crowded away from each other,---a phenomenon called
repulsion. The opposite condition obtains when they
face the same way and are near together, with the
result that the stress is lessened between them, and
they are pushed together by it; and this is called
attraction.

There has been growing the conviction for a long
time that the atoms of all substances are magnetic; but
\Pagelabel{205}%
when they combine into molecular groups they are
turned about so their magnetic fields neutralize each
other, and thus it happens that most molecular compounds
show no polarity. But every substance whatever
is attracted by a magnet, and will move up to it if
the magnet be a strong one. Brass, lead, stones, oats,
corn, and wood will all be affected alike by a strong
magnetic field, being pushed towards the magnet in the
same way as iron, though not in the same degree. The
pressure of iron against a magnet, due to the magnetic
field, may be as great as a thousand pounds per
square inch.

When a piece of iron is brought near to a magnet,
and it becomes a magnet by induction instead of by
contact, it is to be understood that its molecules are
rotated into similar positions by the action of the
magnetic field upon it, not that magnetism has gone
from the magnet to the iron; and when it requires a
pull, and therefore work, to move a piece of iron away
from a magnet, it is against the ether the work is done.
\DPPageSep{218.png}{206}%

It was stated at the outset that a loop of iron through
which an electric current is passing is a magnet, and
previous to that it was pointed out that an electric %[** PP: Width-dependent break]
%[Illustration]
\begin{wrapfigure}{l}{1.75in}
  \Graphic{1.75in}{218a}
  \Caption{24}{Diag.\ 24---Iron Filings about Electric Current.}
\end{wrapfigure}
current in a wire has a field
that extends indefinitely out
from it. If such a wire be
dipped in iron filings, they
form rings round it, showing
that the polarity is at right
angles to the wire. Now, if the wire with the iron
filings clinging about it be made into a loop, it will
be seen at once how the polarity of the different
segments is all in one direction inside the ring, and
opposite to that on the outside the ring, and the
structure will be a forcible reminder of a vortex ring.
If several similar turns be taken in the wire, and they
all be brought near together so as to form a helix, it
will also be seen that these conspire together to set a
boundary to the field on the inside, but allow indefinite
expansion to it outside; so if one should draw the lines
for it as iron filings would be arranged by it, he will
have the precise lines of a magnet, while the ring
structure will be, on a large scale, just
what was described on an atomic scale
as constituting a vortex ring magnet;
and the only thing lacking to complete
the analogy is the conception of a rotary
motion in the wire at right angles to its length.

%[Illustration][** PP: Moved down to avoid LaTeX warning]
\begin{wrapfigure}{r}{1.25in}
  \hfil\Graphic{1in}{218b}\hfil
  \Caption{25}{Diag.\ 25.---Adjacent Turns.}
\end{wrapfigure}It has been found that when a current has been
started in a conductor, a torsional impulse is given to
the latter in such a sense that if one looks along it in
\DPPageSep{219.png}{207}%
the direction of the current the twist is in the direction
of the hands of a clock. So there is direct confirmatory
experiment showing that the nature of the motion in
an electric circuit is rotary in such a way that the
whole circuit may be considered as a vortex ring; and
as it is the matter of the conductor that is thus rotated,
it follows that electrical current motion is rotary, as
heat motion is vibratory.

Allusion has been made to the opinion now current that
ether waves or light are electro-magnetic phenomena.
\index{Ether waves, their source}%
\index{Light waves}%
\index{Magnetic waves}%
How this can be may be understood by considering a
magnet of any form, with its surrounding field. If the
form of the magnet be changed, the shape of the field
will be correspondingly changed; and as this extends
out indefinitely into space, it follows that a succession
of changes of form would set up waves through the
whole of that space. Now, a magnet is an elastic body,
and if it be struck it will vibrate and produce a sound.
The vibration implies a change of form, and that in
turn a set of waves radiated into space. As the field is
an ether field, the waves will be ether waves. Now
assume that atoms are themselves elastic magnets, each
with a field indefinitely extended, and it follows that
the vibrations produced by impact, or in any other
manner, will set up corresponding waves in the ether,
the wave length depending upon the vibratory rate of
the atoms. Thus ordinary radiant energy, or light,
would consist of undulations in a magnetic field.

Of course it will be perceived that vibrations of any
electro-magnetic body, large or small, would induce
similar waves, differing only in wave length, so there
\DPPageSep{220.png}{208}%
\index{Magnetic induction}%
would be in the ether wave lengths of all dimensions,
\Pagelabel{208}%
from the shortest possible to those millions of miles
long. It is now an important physical problem how to
produce such that shall be of the dimensions capable of
affecting the eye.

\Subsection{Induction Coils.}
\index{Induction coils}%

One or more loops of iron, through which a current
of electricity is flowing, is an electro magnet. When
iron is placed in the loop, it condenses the magnetic
field, and it may be made as much as thirty times
stronger than it would be without the iron. When a
magnetic field is produced inside a loop of wire, the
reverse effect %[** PP: Width-dependent break]
%[Illustration]
\begin{wrapfigure}{l}{1.75in}
  \Graphic{1.75in}{220a}
  \Caption{26}{Diag.\ 26.---Electro-Magnetic Induction.}
\end{wrapfigure}
happens, and a
current is generated in the
opposite direction. Suppose
a short rod of iron to have a
single turn of wire at each
end about it, one of them,
as~A, to be so connected to a source of electricity
that a current through it may be produced by closing a
key, the other one to be a closed circuit, as shown. If
a current be established through~A in one direction, a
current will be induced in~B, as indicated by the arrow.
There will be in the loop of the A~circuit a certain
electro-motive force,~$E$. A nearly equal electro-motive
force will be induced in loop~B. If there were two
loops at~B instead of one, the electro-motive force would
be twice that in~A, and for $n$~turns it would be $n$~times.
The current in~B will depend upon the resistance in its
circuit; that is, it will be $\dfrac{E}{R}=C$, according to Ohm's
\DPPageSep{221.png}{209}%
Law. The size of the wire in B~circuit will not make
any difference in the value of~$E$ in it. That value will
depend only upon the magnetism of the bar, and the
magnetism in the bar will be measured by the product
of the current into the number of turns of wire in
the circuit~A. And this product is called the \emph{ampère
turns}. The ampère turns will be nearly equal in the
\index{Ampère turns}%
two circuits. This process of obtaining electrical
currents in a second circuit by two transformations is
of great use in the electrical industries, and the device
is called an induction coil or transformer. The charging
circuit is called the primary, and the discharging
one the secondary. By making circuit~A of a small
number of turns of thick wire, so as to allow strong
currents in it, and having circuit~B consist of a great
number of turns, the electro-motive force may be
raised almost indefinitely. Suppose there be $100$~turns
in the \textit{A}~circuit,\DPnote{[** Italicized in orig, not sure why]} and a hundred thousand in the \textit{B}~circuit,
then for every volt in the A~circuit there may be
nearly a thousand volts in the B~circuit; and this is the
construction in those instruments known as induction
coils, with which so called jumping sparks are produced,
and represent sometimes a million or more volts. On
the other hand, it is sometimes desirable to change a
high electro-motive force to a lower one; and this may
be done by reversing the connections and making the
primary current go through a great number of turns,
and taking the induced current from the smaller number
of turns in the other circuit. Definite reduction in
either way may be effected by making the ratio of the
number of turns in the two circuits the reduction
\DPPageSep{222.png}{210}%
\index{Electro-magnets}%
\index{Welding, electric}%
wanted. That is to say, if there are $100$~volts in
the primary circuit, and only ten are wanted, make the
secondary of one-tenth the number of turns in the primary.
If a thousand volts are wanted, make the secondary
with ten times the number of turns in the primary.
It should be remembered, also, that two turns of wire in~B
have twice the resistance of one turn, and the current
induced will be reduced to one-half. If there be one
hundred turns, it will be reduced to one-hundredth and
so on. Hence, in the large induction coils for high electro-motive
forces, the current is necessarily a small one,
while in the transformers in which the reduction is to
lower values of~$E$ than are in the primary, the current
may be very great indeed. This is the case in Thompson's
Welding Apparatus. The secondary has but a
single turn of heavy copper, while the primary has many
thousands, and the current in the secondary may be
thousands of ampères. As the heating effect is proportional
to the square of the current, it is plain that
such large currents have enormous heating power.

All such devices require either intermittent or alternating
currents to operate them, for there is no induced
current in any circuit when the inducing magnetism is
not changing. A constant magnetic field induces no
electrical changes.


\Subsection{The Electro Magnet.}\DPnote{** [sic] No hyphen}

This is generally considered as consisting of a helix
of insulated wire about a piece of soft iron, and may be
either a straight bar, or crooked in any convenient form,
its function being to produce a magnetic field when a
\DPPageSep{223.png}{211}%
current circulates in the wire, and to lose it when the
current stops. This it does only partially, for all iron
when once it has been magnetized becomes more or less
permanently magnetic; hence there is only a difference
in degree between an electro magnet and a permanent
magnet. Until within a few years the electro magnet
had its most extensive field of usefulness in telegraphy.
It was combined with a piece of soft iron near its poles
called its armature, which was so mounted that the
magnetic field made it to move towards the magnet, and
a retractile spring pulled it away when the field was
absent. The movement of the armature was employed
to receive signals. In some cases the movement recorded
itself, and sometimes its prompt motion produced
a sound, a succession of these being arranged into a
telegraphic alphabet.

If one has a good idea of a magnetic field and its
action upon a piece of iron in it, he will be able to
understand all the various combinations of forms and
functions of electro-magnetic devices, however much
they may apparently be disguised. Thus, the magnetic
telephone is an electro magnet with an armature
\index{Telephone}%
of such size and flexibility as to be capable of much
quicker movements than ordinary telegraph instrument
\index{Telegraph}%
armatures, the whole boxed so as to be convenient
to hold to the ear. A common telegraph sounder
acts in precisely the same way, though not so well, for
the armature is too heavy, and one cannot concentrate
its effects upon the ear on account of its form. An
electric bell also produces its ring by having a hammer
fixed to the armature, so as the latter moves in response
to the electric field it strikes the bell.
\DPPageSep{224.png}{212}%
\index{Motor, electric}%

An electric motor, in the largest sense, consists of a
device for transforming electric into mechanical motions;
and the relation sustained between an electro
magnet, its field and an armature, is such as to do it
directly. A telegraph sounder is thus a simple motor,
for the armature moves visibly in response to the electric
current. If a wire be wound about the armature,
there is an induced current in it, as in an induction coil,
and for the same reason; and the movements of the
armature towards and away from the poles of the electro
magnet, called sometimes the field magnet, give
rise to currents in the armature coil. If a current
from another source is sent through the armature coil,
it gives polarity to the armature itself, and the reaction
between it and the poles of the field magnet is still
stronger, and the mechanical motions are still more
energetic. The armature thus wound with wire is obviously
an electro magnet itself, and when it is so
mounted as to be capable of rotating between the poles
of a fixed electro magnet, a continuous rotation may
be kept up.

The current in the fixed magnet is steady, and therefore
maintains a steady magnetic field. The current
in the armature magnet is changed in direction by the
motion of the armature itself, and is effected by a device
called a commutator. The efficiency of such a
motor may be as high as $90$\%~or more. That is, for
every horse-power of electrical energy turned into it, it
will give back nine-tenths of a horse-power in actual
work. The small space they occupy for the working
capacity, when compared with a steam-engine for the
\DPPageSep{225.png}{213}%
\index{Efficiency of machines}%
same work, the small amount of attention they require,
and their freedom from the dirt inseparable from an
engine, commend the electric motor as a substitute
for the engine in most places where power is wanted
and an electric current can be had; for it is to be
remembered that fifty horse-power can travel through
a wire that can go through a gimlet-hole, while a steam-plant
for the same work would require a large boiler
and engine as well as a big chimney.

When the armature of a motor is made to turn by
mechanical means, the shifting positions in the magnetic
field develop electric currents in its coils. Such
an armature cannot be turned as freely when the field
magnet has a current in it as it can when it has not,
and the energy spent in making it turn appears as a
current. The device is called a dynamo, which may be
\index{Dynamo}%
said to be a machine for transforming mechanical motion
into electrical motion. The steps are mechanical
motion, magnetic field, electrical current; while in the
motor they are simply the reverse,---electric current,
magnetic field, mechanical motion.

The efficiency of a dynamo is very high indeed. It
can transform~$95$\% of the power applied to it into
electrical power, and in this particular it is one of the
most perfect machines in existence. There is absolutely
no room for any important improvement in the
dynamo as regards its efficiency. A good steam-engine
may transform ten to fifteen per cent of the energy
turned into it. A windmill may give fifty, a turbine
water-wheel ninety, but when a dynamo gives ninety-five,
it shows that the coming man has a margin of but
five per cent for improvement in its efficiency.
\DPPageSep{226.png}{214}%
\index{Energy. What determines transfer}%
\index{Fields, magnetic}%
\index{Lighting, electric}%
\index{Resistance, electrical}%

Thus the magnetic field, which is simply the ether in
\index{Magnetic field}%
an abnormal condition of stress, is the common agency
between mechanical motions and electrical phenomena,
and transfers energy one way or the other. All that
determines whether it shall be one way or the other is
simply which side has the excess of energy; for energy
of a particular sort always goes from the body having
more to one having less. Which side has the excess
is determined solely by the mechanical conditions
present.


\Subsection{Electric Lighting.}

An electric current always heats the conductor
through which it is passing. The amount of heat depends
upon the strength of the current, and varies as
the square of it. In a given circuit with a uniform current,
the current has the same value, and therefore the
same heating power, in every part of that circuit; but
the temperature to which a body will be raised by a
given current depends upon its own constitution, its
size and electrical resistance. Connect together three
wires of copper, iron, and platinum, each a foot long,
and of the same diameter, and make them a part of the
same circuit, so that the same current shall flow through
them. If the current be increased gradually, the iron
wire will grow appreciably warm, more current will
make it hot; platinum wire will be only warm;
while the copper wire will not have its temperature
much changed. Still more current will make the iron
red-hot, the platinum uncomfortably hot, and warm
appreciably the copper; and more current will fuse the
\DPPageSep{227.png}{215}%
\index{Electric lamps}%
iron, perhaps make the platinum red-hot, but the copper
may not yet be uncomfortably hot. This heating
effect in a given wire is found to be proportional to its
resistance: the iron wire having the greater resistance
is most heated, and the copper having least, is least
heated; hence to obtain a high temperature with a
given current, a conductor must be chosen that has a
relatively high resistance. Resistance, however, varies
with the cross section inversely, so a small wire must
be taken if the temperature of incandescence is to be
reached with a small current; and a current that will
raise half an inch of a wire to a white heat will raise a
mile, or any other length of the same wire, to the same
temperature; but the longer a wire is, the higher must
be the electro-motive force in order to get the same
current. For a given length of a wire the electrical
energy spent in it will be found by multiplying its resistance
by the square of the current,~\DPtypo{$RC,^2$}{$RC^2$,} which will
give the products in watts, of which $746$~equal a horsepower.
Metals are liable to fuse and become useless,
so that wires of carbon, made by heating organic fibres
in the absence of air, as in making charcoal, are substituted
for metals. They fuse only at extremely high
temperatures; and being enclosed in a vacuum in bulbs
of glass they cannot burn up as carbon does when exposed
to the air when red-hot. This is the electric incandescent
lamp. Most of them are so prepared that a
current of about three-fourths of an ampère is required
to properly light them, and this will be got when the difference
of potentials between the lamp terminals is kept
at a certain figure, so that lamps are specified by the
\DPPageSep{228.png}{216}%
number of volts they require, rather than the current;
thus there are $50$~volt lamps, $110$~volt lamps, and so on.
Now, such lamps take ordinarily about four watts for a
candle, so a twenty candle-power lamp requires eighty
watts, and that means $\dfrac{746}{80}=9.3$ such lamps to the
horse-power. Such lamps may last for a thousand or
more hours. If a stronger current be used, they shine
brighter, but their life is shortened. There is a process
of slow disintegration going on in these lamps
all the time. The surface molecules slowly evaporate
under the vigorous vibratory movements present, and
the carbon vapor thus formed sticks to the inside surface
of the bulbs, giving them the familiar blackened
appearance.


\Subsection{The Arc Light.}
\index{Arc light}%

If an electro-motive force of forty or more volts be
maintained in a circuit, and the circuit be broken at
some place and the ends separated a small fraction of
an inch, the current does not cease, and is maintained
between the ends by what is termed an arc, where the
temperature is so very great that almost all substances
are reduced to vapor at once. All metals are fused and
dissipated there. Carbon does not fuse there, but is
slowly burnt up. The ends of the carbon reach a temperature
higher than can be reached in any other
known way, and the light they then give out is called
the arc light. The rate of expenditure of energy in
that small space where the brightness is, is generally
some less than a horse-power. The current employed
\DPPageSep{229.png}{217}%
\index{Mars, signalling to}%
is about nine and a half ampères, and the electro-motive
force about forty-five volts; hence $9.5 × 45 = 427.5$
watts, and such a lamp may be equal to $800$~candles,
though they are generally rated as $2,000$ candle-power.

By increasing the current the brightness increases,
and there is no especial limit to the amount of light
that may in this way be produced. With parabolic reflectors
the light may be concentrated into a powerful
beam. The inhabitants of Mars could see such a one,
and it could be used for signalling between the two
planets if the Martians had a similar one.

Seeing that the temperature to which a given conductor
can be raised by a current is determinate, one
can arrange for heating on any scale. There is no
other reason than the relative cost of electric heating
compared with the ordinary method with fuels, why it
should not be in common use to-day. In most places
the dynamo for the production of the current would be
run by a steam-engine, requiring in its turn a furnace;
and it is cheaper to use the fuel direct for heating, than
to transform the energy so many times, each time with
some loss. A common furnace is much more economical
of energy than a steam-engine. But if ever electricity
is obtained directly from combustion in an economical
way, as there is some reason for thinking possible,
electrical heaters will displace stoves and the common
furnaces in the house. So the same current that
lights the house will serve for cooking and warmth.
\DPPageSep{230.png}{218}%
\index{Water decomposition}%


\Section{2. CHEMICAL EFFECTS.}
\index{Chemical effects}%

When a current of electricity is passed through
conducting liquids capable of being decomposed, such
as acidulated water, and solutions containing more or
less of the metallic elements, decomposition of the solution
results, with the additional curious phenomenon
that one of the elements of the decomposed compound
appears at one terminal, and the other element at the
other. Thus, if water be the liquid, hydrogen appears
at one place and the oxygen at another. If the two terminals
of an electric circuit were on opposite sides of the
Atlantic Ocean, and a current were sent through the
circuit, hydrogen would appear on one side and oxygen
on the other. The oxygen is set free at that terminal
at which the current reaches the liquid. The direction
of the current being determined in the ordinary conventional
way. Bring the wire carrying the current over
and parallel to a suspended magnetic needle. If the
current be going from south to north, the north pole will
be deflected to the west. If the current be going from
north to south, the south pole will be deflected to the
west. Hence, if one looks along a wire in the direction
of the current, oxygen will be given off at the next
terminal if it dips in water. It may be convenient to
know that when a battery is employed as a generator of
electricity, hydrogen is set free at the terminal of the
battery from which the current flows, and oxygen at
the other end of that conductor.

The decomposition of water may be taken as a type
\index{Decomposition of water}%
of electro-chemical work; hence, when the mechanical
\DPPageSep{231.png}{219}%
\index{Dissociations}%
\index{Polarization of molecules}%
conditions present where decomposition is going on are
understood, they may be applied to any other case.

Under the head Chemical Origin of Electricity it %[xref]
was pointed out that the same factors which gave rise
to the current also arranged the molecules of the liquid
so that the oxygen sides of them all faced the same way,
towards the zinc, which of course necessitates that the
hydrogen sides should all face in the opposite direction.
The other terminal of the battery tends to bring about
a similar condition of things, so that between the terminals
the molecules are all polarized or brought into an
orderly arrangement. The direction of the electric
current in such an arranged body of molecules in the
liquid is from the zinc to the oxygen---oxygen, hydrogen,
oxygen, hydrogen, and so on to the last molecule
in the line, the hydrogen face of which is against the
other terminal. So far this represents molecular arrangement,
not molecular or atomic cohesion. There
is good reason for thinking that dissociation of atoms
in such molecules is going on all the time in some
degree, on account of their incessant and vigorous vibratory
motion. Such motion must tend to disrupt
the atoms so that at any given instant there would be a
relatively large number of atoms in the liquid already
free and quite indifferent as to whether they recombine
with the same or other atoms the next instant. If there
be another agency present, like an electrical current,
adding its energy tending to disruption, not only would
a larger amount of dissociation take place, but when at
one end of the line one element of the molecule, like
oxygen, enters into a new combination which is more
\DPPageSep{232.png}{220}%
stable under the conditions present, the remaining hydrogen
will combine with the oxygen of the adjacent
molecule when that molecule is broken up, and so on
along the whole line, leaving the hydrogen of the last
liquid molecule to be freed against the other plate of
the battery. This means that there is an exchange of
partners among all the molecules of the liquid that take
part in the current, else some of both oxygen and hydrogen
would be set free elsewhere than at the terminals,
which never happens.

Now, all molecules are combinations of atoms in
definite proportions by weight, and it is therefore to be
expected when such decompositions as the above take
place the products will be found in the same proportions.
It is the necessary outcome of the operation. So for
every one part by weight of hydrogen set free, eight
parts of oxygen will be liberated; and for a like reason
twice the volume of hydrogen as of oxygen.

If a current of electricity be led through any liquid
which it can decompose, and the material of the terminals
be some substance that neither of the constituents
of the molecule can combine with, both of the elements
will be set free. Platinum is such an element; and if
terminals be made of that, and dip into a tank of water,
the current polarizes the molecules precisely as in the
battery, and decomposition takes place in the same way,---oxygen
being set free at the in-going terminal, and
hydrogen at the out-going one. If the solution contains
molecules of metallic salts of copper, nickel, iron, silver,
gold, etc., the metallic side of the molecule faces in the
direction of the current, the same as the hydrogen in
\DPPageSep{233.png}{221}%
\index{Plating, electro}%
the former case; and as a consequence, the metal is deposited
upon the out-going terminal, whatever that may
be, and the other constituent of the molecule is set free
at the in-going terminal. For example, the sulphate of
copper is a compound of copper and sulphuric acid.
Where it is subject to decomposition by an electric
current, the copper is deposited at the one terminal, and
sulphuric acid at the other. If both the terminals be
made of platinum, one will be covered with copper, and
the other will be surrounded with the acid, and all the
copper in the solution may be taken out. If the in-going
terminal be itself of copper, the sulphuric acid
set free will itself dissolve off the copper as fast as the
acid is set free, and in this way the solution will be kept
saturated. The metal may be deposited on any other
metal. It is in this manner that electro-plating of all
sorts is done. Each different metal requires different
treatment from the others as to solution, electro-motive
force, current per square inch section, and so on for the
best results. To decompose water, as much as one and
a half volts are necessary to initiate it, but copper salts
require only a small fraction of one volt. The amount
of decomposition in a given time, say a second or an
hour, depends upon the current employed. A current
of one ampère will in an hour decompose only about
fifteen and four-tenths grains of water, liberating one
and seven-tenths grains of hydrogen. The weight of
other elements set free or deposited by an ampère per
hour is determined by multiplying the weight of hydrogen
set free by the electro-chemical equivalent of the
element, and this is either equal to its atomic weight, or
\DPPageSep{234.png}{222}%
\index{Lighting, electric}%
is one-half or one-third that. Thus, the electro-chemical
equivalent of gold is $\dfrac{196.6}{3} = 65.5$, of silver $\dfrac{108}{2} =
54$\DPtypo{}{,} of copper $\dfrac{63}{2} = 31.5$, of nickel $\dfrac{57}{2} = 28.5$, and so on.
So the amount of gold that will be deposited by an
ampère in an hour is $1.7 × 65 = 111.35$ grains; of silver
$1.7 × 54 = 91.8$ grains and so on. This shows a
definite relationship between electricity and chemical
reactions.

It is to be kept in mind that when substances combine
there is always some transformation of energy,
and heat is either absorbed or given out. When
hydrogen and oxygen combine there is a large amount
given out, $61,200$ heat units for each pound of hydrogen.
When, therefore, water is decomposed so as to
set free one pound of hydrogen, the same amount of
energy must be spent to do it. The electrical energy
spent in a decomposing cell is, therefore, reducible to
the heating effect, and may be calculated as such.


\Section{3. LUMINOUS EFFECTS.}
\index{Luminous effects}%

When an electric current passes from one conductor
to another through the air an electric arc is produced,
and great heat and light are developed there. An arc
is generally about an eighth of an inch long. By
having a higher electro-motive force one may be made
several inches long. The arc itself consists of the
incandescent molecules of the air in its path mixed
with some of the disintegrated particles of the carbon
of the terminal. When an arc is formed in a partial
\DPPageSep{235.png}{223}%
\index{Geissler's tubes}%
\index{Spark, electric}%
\index{Vacuum, a non-conductor}%
vacuum the character of the phenomenon is very much
changed. Instead of being concentrated into a narrow
space, it spreads out into an oval form, the size of
which depends upon the degree of exhaustion. The
terminals may be separated to a much greater distance;
the light becomes less intense, and shows as a kind of
glowing gaseous globe, and this may extend to the
walls of the glass vessel in which it is produced.

If the vacuum be made very perfect, no current can
be got through it; for the ether is a perfect non-conductor.
Even the spark from an induction coil that
will jump several feet in the air will not jump a quarter
of an inch in a vacuum. The jumping ability of
an electric spark or current depends upon its electro-motive
force. A thousand volts will jump but
about the one-hundredth of an inch in common air,
and ten thousand volts only about one-tenth of an
inch. From such experiments it has been concluded
that a flash of lightning probably has an electric pressure
\index{Lightning}%
reckoned by hundreds of millions of volts, but
there is some doubt about the calculation for such
exceedingly high voltage. Glass tubes provided with
platinum terminals hermetically sealed, and from which
the air has been partially removed, when connected
with the high voltage terminals of an induction coil
exhibit phenomena that depend altogether upon the
degree of exhaustion in the tube. If the air pressure
%[** PP: Width-dependent break]
% [Illustration]
\begin{figure}[hbtp]
  \begin{center}
    \Graphic{4in}{236a}
  \end{center}
  \Caption{27}{Diag.\ 27.---Crookes's Tube. Long Free Path.}
\end{figure}
\index{Crookes' tubes}%
be removed to about the one-hundredth of the normal
pressure, the discharge appears as a broad band of
purplish light between the terminals; if the reduction
be to the thousandth, the light fills the tube. Still
\DPPageSep{236.png}{224}%
further reduced, the discharge appears broken up into
striæ, or bright disks, their distance apart depending
upon the degree of exhaustion, and they measure
roughly the length of the free path of the gaseous
molecules. If the exhaustion is carried to a very high
degree, this free path may be made as long as the tube,
\index{Molecules, long free path}%
or longer. This means that a molecule may move
from one end of the tube to the other without coming
into collision with another one.

When a molecule touches upon the electrified
terminal, it is impelled from it with great velocity,
quite like that exhibited in the radiometer, and probably
\DPPageSep{237.png}{225}%
\index{Heat by impact}%
for the same reason. It moves away from the
terminal in a straight line in obedience to the first
law of motion, and continues on till it strikes another
molecule, or the surface of the tube, and it shines as it
moves, on account of its vigorous internal vibrations;
for each gas gives its characteristic spectral lines when
thus made incandescent. Where they strike upon a
thin piece of platinum they may make it red-hot by
impact, and where they strike upon the
% [Illustration: ]
\begin{figure}[hbt]
  \begin{center}
    \Graphic{4in}{237a}
  \end{center}
  \Caption{28}{Diag.\ 28.---Crookes's Tube. Platinum made Red Hot by Impact.}
\end{figure}
walls of the
glass tube the latter is made luminous with a phosphorescent
glow, and may be made red-hot, and so
softened as to bring about a collapse of the tube.
These tubes are known as Crookes's Tubes, and their
phenomena are extremely interesting from the insight
they give into the behavior of matter under all sorts
of conditions. With a set of these tubes, the laws of
motion, kinetic energy, sound, heat, light, electricity,
and magnetism may be illustrated in a way unapproachable
\DPPageSep{238.png}{226}%
with any other simple and cheap apparatus. The
long free path, and inability to turn a corner when
projected from an electrified terminal, show the first
law of motion and inertia. The impact of the molecules
may make a wheel turn round,---an example of
energy as good as a windmill. The intermittent beats
upon the sides of the tube produce a sound, the pitch
of which is the same as that of the vibrations of the
induction coil. The heating of the tube and its contents
shows the transformation of free-path motion
into vibratory molecular motion. The luminousness
of the gas, and the phosphorescence of the tube, show
\index{Phosphorescence}%
the transformation of the electrical energy into the
vibratory molecular kind, at a rate capable of affecting
the eye. The phosphoresence\DPnote{** [sic]} itself showing the conditions
needed for producing it; the origination of the
motions in the tube showing the relation of electricity
to the other forms of motion developed; the deflection
of the stream of electrified molecules by a magnet
illustrating the effects of a magnetic field upon a
current of electricity. The fact that such streams of
molecules are projected from an electrified terminal
solely by impact there, is shown by their returning to
it when there is nothing in front of it to expend their
energy upon, as a ball returns to the earth when
thrown into the air, which is the case when but one
terminal is connected with the induction coil; and,
lastly, such a tube will be lighted up by being merely
in the neighborhood of an induction coil, or rather in
a varying electric field. They may be insulated and
several feet away from such induction coil or a Holtz
\DPPageSep{239.png}{227}%
or other similar machine and yet be internally lighted
every time a spark passes, which shows that the luminousness
seen in the tubes is not necessarily due to any
electrical current present, because in this case there
can be no electrical current.


\Section{THE NATURE OF ELECTRICITY.}

There have been many theories proposed to account
for electrical phenomena, yet to-day there is no one
that is generally held, even as a provisional one, among
physicists. Some have even abandoned the hope of
mankind ever being able to reach a consistent theory of
it. The case has been the same in the history of heat,
of light, and of magnetism; yet text-books of to-day do
not hesitate to state what is the nature of each of these.
Electrical phenomena have greater variety, and the
apparent dual character oftentimes present has served
to give a perplexing degree of complexity to them.
The writer has thought that a summation of the principal
factors present in electrical phenomena might be
helpful to some in their endeavor to find some physical
explanation without having to assume something \textit{sui
generis}, which has no other necessity for being except
the very dubious one of accounting for a certain phenomenon.
Caloric, light corpuscles, and vital force
were such visionary creations; but further knowledge
has enabled science to dispense with all of them, leaving
nothing in their places but what was known to
exist before; namely, matter, ether, and their motions.
Such a steady course of reduction to these factors
leaves one with the fair presumption that it will likely
\DPPageSep{240.png}{228}%
fare the same way with any other agencies that have
been imagined to account for phenomena, though the
latter may, for the time being, seem not reducible to
simple mechanics.

There are certain \textit{a~priori} reasons for thinking that
in electrical matters, as in all other physical agencies,
only matter, ether, and motion are concerned. No one
has ventured to identify ordinary matter and electricity,
which cuts down the possibility to one of the remaining
two.

If it be admitted that matter is not altered in quantity
by any process to which it may be submitted, and
also that the amount of ether and energy in the universe
are constant, it follows that all the different phenomena
exhibited by matter are due to the different
kinds of motion it may have; for \emph{motion is the only
variable factor}. On such a premise one can fairly
maintain that no matter how obscure and puzzling a
phenomenon may be, its explanation lies altogether in
its characteristic motions, and, when they are fully
made out, there will be no more to learn about it. If
so much be granted, one has got on a long way towards
the final answer to the questions, What is the nature of
heat? what is the nature of light? what is the nature
of electricity? Two of these are settled, and no one
thinks of asking as to their nature. The nature of
heat was settled by Rumford and Davy, that it is a form
of motion in matter. The nature of light was settled
by Young and Fizeau, that it is a form of motion in
the ether. What remained to be done was simply to
discover the particular kind of motion in each case.
\DPPageSep{241.png}{229}%
\index{Electricity, origin of}%
Spectrum analysis and photography have since given
us the particulars. Electricity is on precisely the same
philosophical basis; and, in the absence of evidence of
the existence of some other physical factors than matter,
the ether, and motion, one would be entitled to the philosophical
opinion that \emph{electricity must be some form of
motion}. What the particular form is may be a subject
of investigation, but not the nature of it.

It is my purpose to show, \emph{first}, that in every case
where electricity is produced motion of some sort is
antecedent to its production; \emph{second}, that in every
case the effect of electricity is to produce motion of
some sort, and that itself is annihilated in doing it in
precisely the same sense as motion of any other sort is
annihilated when it is transformed.

1. \emph{As to its origin}. When the face of the thermopile
is heated and electricity is produced, we know that
vibratory molecular motion is the condition for its appearance.

In a galvanic battery the molecular exchanges by
which zinc is dissolved and oxidized, and hydrogen is
set free, are well known, and also the heat equivalent
of such re-actions; and they are measured in heat units,
which in turn may be made the measure of the electricity
developed.

When glass or wax or other substance becomes electrified
by friction, the word itself expresses the condition
necessary for producing it. Mechanical friction
is the antecedent.

When a conductor is moved in a magnetic field and
becomes electrified, the effect depends absolutely upon
\DPPageSep{242.png}{230}%
\index{Electricity, mechanical origin}%
\index{Electricity, electrical origin}%
the motion. Stop that and all evidence of electricity
disappears.

The same thing is true when electricity is developed
by so-called induction in a field produced by a neighboring
body that is electrified in any way. The continuous
production of it implies continuous motion of one or
the other body.

In dynamos of every variety of form the mechanical
motion turned into them is the antecedent, and the
energy of the engine spent in turning the dynamo has
its full representation in the electric energy developed,
and when there is no motion there is no electricity.

In the physiological development there are always
chemical, thermal, and mechanical motions, which are
spent to produce what electrical phenomena appear,
whether in mankind or in animals.

In the air and in the earth there are changing temperatures,
condensations, etc., which signify molecular
motions.

Some crystals, like tourmaline, become electric by
heating; some, like mica, become electric by splitting;
and so on. Every one implies that some kind of motion
has to be spent to develop the electrical condition, and
in each case the particular kind of motion that has
been spent to produce it has been \emph{spent}; that is, it has
been transformed in the same sense that the translatory
motion of a bullet has been transformed into vibratory
when it strikes the target. The electricity thus appears
as the representative of the kind of motion that
has been destroyed.

Some have imagined that electricity was a kind of
\DPPageSep{243.png}{231}%
\index{Electrical effects}%
\index{Stress, electrical}%
dual matter, which was broken up by the various processes
described, or that some substance was transferred
from one place to another, so that there was
more than the normal amount in one place and less in
another. Even such conceptions do not get rid of the
idea of motion being the chief characteristic, for the
separations are the ideal embodiments of motion, and
in this case the measure of it; so nothing whatever is
gained, either in clearness or simplicity, by such invention.

2. \emph{The effects of electricity} are to bring about mechanical
motions of some sort.

The stress into which the ether is thrown by either
an electrified or magnetized body is a change of position
of adjacent parts with reference to each other,
and the fact that this stress travels with the velocity
of light shows that motion is the essence of it. The
re-action of the stress in the ether upon other matter
in it always results in the motion of the latter. If the
whole body can move, it will do so, and mechanical
motion is the immediate effect. If it cannot move as
a whole, its molecules are twisted into new positions,
so that motion, either molar or molecular, is the result.

As the electric current in a conductor always heats
the latter in every part, one has but to reflect upon the
character of heat motions to perceive that some kind
of motion must be the antecedent of it. Consider a
short portion of wire through which a current of electricity
flows. It becomes warmer and now radiates
faster into space. It is losing motion by imparting it
to the ether. Trace back the ancestry of the ether
\DPPageSep{244.png}{232}%
\index{Electrical effects, reversible}%
\index{Physical processes, reversible}%
motion, and it appears as vibratory motions of the
molecules of the conductor, thence as electrical current,
thence as armature rotations of a dynamo, thence to
the engine movements, thence to the furnace and the
chemical re-actions going on there. There is no question
as to the nature of the factors in all of these but
one. Call the chemical re-actions \textit{A}, the engine \textit{B},
the dynamo \textit{C}, the electricity \textit{D}, the heat \textit{E}, and the
ether waves \textit{F}. With the exception of \textit{D}, each one is
known to represent a certain kind of motion, molar or
molecular, and all in a consecutive series. Is it not
difficult to conceive that the step \textit{D} can be anything
different in character from the rest of the series, and,
whether understood or not, must represent some phase
of motion? To think otherwise is to think that motion
can have some other antecedent than motion. Whoever
sets himself in earnest to this problem will see
there is but one answer to it.

So heat effects, light effects, chemical effects, as
well as the direct mechanical ones shown in Crookes's
Tubes, or otherwise, will lead to precisely the same
conclusion that \emph{electricity represents an intermediate
molecular kind of motion}, having definite motions
for its antecedent, and definite motions for its consequent,
and so must itself be some peculiar form of
motion, differing from the others as they differ among
themselves, and nothing beyond that. It may also be
remarked that every form of motion which is capable,
under definite mechanical conditions, of developing
electricity, electricity is itself capable of producing.
The processes are all reversible. If heat will produce
\DPPageSep{245.png}{233}%
electricity, electricity will produce heat. If chemical
re-actions produce electricity, electricity will produce
chemical re-actions, and so on of all the rest; so if they
be reducible to motions, so must electricity.

Such considerations make logically certain what the
nature of electricity is; but they do not indicate what
the character of the motions is that gives it identity,
and distinguishes it so radically from other well-known
kinds of motion. In the chapter on ``Motion'' it is
pointed out that there are three fundamental kinds of
motions,---translatory, vibratory, and rotary,---and
that with these all the various complicated motions of
mechanical processes may be produced. It is also
pointed out that for convenience we call those motions
mechanical that are on a scale of visible magnitude,
but such as cannot be seen are called molecular and
atomic. It is plain, in this case, that the motions must
be on a molecular scale, for no motions are directly
perceived in electrical phenomena any more than in
heat phenomena; so there remains for consideration
what evidence there is for the motion being molecular
and therefore of matter, or of the ether.

It appears that when certain kinds of work, such as
friction, are spent upon a mass of ordinary matter, electricity
is developed, and we say the body is electrified.
The body in this condition at once re-acts upon the
ether about it; and it has happened that some persons
have given most attention to this effect of the electrified
body, and the phenomena that may result from it,
and have called \emph{it} electricity; while others have given
more attention to the condition of the matter that
\DPPageSep{246.png}{234}%
\index{Electricity, dual}%
\index{Ether rotations}%
induced the ether stress, and they have called \emph{that}
electricity; while the greater number have hopelessly
confused the two, calling both by the same name, just
as formerly heat and ether waves were both called
heat. It is plain that a physical condition of things in
matter requiring a name ought not to be designated by
the same term as that physical condition in the ether
which is the result of the first. One is, therefore,
justified by the logical necessity of making a distinction,
in adopting the name electricity as applicable to
one and not the other, and also in calling the phenomenon
in matter by that name and denying its applicability
to any effect of it wherever it is plain there has
been a transformation. Thus it would be as illogical
to call ether waves set up by an electrified body electrical
waves, as it would be to call the swinging of a
pendulum that was actuated by electrical attractions
electrical vibrations.

We are, therefore, now reduced to the sole consideration
as to the character of those molecular motions
which differentiate electricity from heat and free-path
motion; and here the apparent dual character, which
has been so puzzling, helps at once to an understanding
of it.

For many years it has been merely a matter of convention
that a current of electricity is said to move in
a certain direction in a wire. It has often been noticed
that there is an apparent current in both directions
from any electrical source; and one has been called a
positive, the other a negative, one; yet the current,
reckoned either way from its source, is always the
\DPPageSep{247.png}{235}%
\index{Magnetic rotation}%
\index{Rotations in ether}%
same at a given point, and has not unfrequently been
considered as made up of two currents moving in
opposite directions.

If one will take a limp rope a few feet long and tie
its ends together so as to form a ring, and, holding it
in his two hands, will begin to twist it in one direction,
he will see the twist start in opposite directions at his
hands, and each one can be traced quite round the ring,
neither interfering with the other; yet one is a right-handed
twist, the other a left-handed one; and one
might call one a positive and the other a negative current.
There will be as much twist in one part of the
rope as in any other, and the rate of rotation at the
hands will be the measure of the amount of motion,
and, consequently, of the energy that is in the circuit.
For a rope substitute a wire, and for the hands a
battery or a dynamo, and the analogy is complete,
except that no rotation is seen in the wire as a whole;
so, if there be rotations, they must be of molecules and
not of the mass. Molecular motions must, of course,
be inferential. It is so for heat. The waves called
ether waves imply vibrations of matter; and, if there
be any known rotary motions in the ether, they would
imply molecular rotations for the same reason. It is
conceded that in every electro-magnetic field the ether
is in a rotary motion, and in numerous books it is
pictured as a whirl both about a magnet and a wire
carrying an electric current. The rotation of an electric
arc in a magnetic field shows it, and the twist
given to a polarized ray of light in passing through it
also shows it; and it has been so interpreted for years.
\DPPageSep{248.png}{236}%
The twist given to a conductor through which a current
is flowing, which has been before alluded to, also
gives direct evidence of the same condition; so the
phenomena confirm the conjecture that the phenomenon
in matter which is called \emph{electricity is a phenomenon
of rotating molecules}, in the same sense as the
phenomenon called heat is a phenomenon of vibrating
molecules.

If the atoms in molecules, and the molecules themselves,
were absolutely fixed in position so as to have
no individual freedom of motion, there could be neither
vibration nor rotation; but the vibrations tend continually
to separate them, and hence between impacts
there is freedom for rotary slip, if there be any tendency
to do so. In an electro-magnetic field the ether
stress re-acts upon molecules in it so as to rotate them
upon some axis tending to set them in certain position
with reference to it. This action will be stronger upon
an atom or molecule immediately adjacent to an electrified
molecule than to one more distant, and one may
therefore infer that the process called conduction,
where heat is the immediate effect of an electric current,
is really an induction effect, and depends directly
upon the ether rather than upon the direct mechanical
effect of one molecule upon another; for such mechanical
action would make the rotation of adjacent molecules
to be opposite in direction, whereas in an electric
current all are in one direction. There is, therefore,
impact and slip, impact and slip; each impact knocking
the molecule out of the position the induction had
set it in, and each arrest of the slip resulting in increasing
\DPPageSep{249.png}{237}%
the amplitude of vibration, and hence raising
the temperature of the conductor. Hence, the explanation
of the transformation of electrical energy
into heat energy. An electric current is, therefore,
not a simple phenomenon, but is considerably complicated,
involving motions of both molecules and the
ether; the molecular motion depending directly upon
the re-action of the ether stress produced by an adjacent
molecule rather than upon mechanical contact.
The electrical condition called static being itself a
compound of abnormal molecular position and stressed
ether, is the condition which, while being propagated
in a conductor, constitutes an electric current, propagated
in the ether, constitutes an ether wave.
%\DPPageSep{250.png}{238}%


\Chapter{IX}{Chemism}{238}

\label{chap:chemism}%
\index{Chemism}%

\First{The} atomic theory of matter was held in some form
by ancient philosophers, but the reasons they assigned
for their opinion were not such reasons as have led
men of the present day to adopt that theory to the exclusion
of all others. Modern chemical analysis enables
one to reduce compound substances to their elementary
forms, and out of those to build up numerous
other substances with entirely different qualities.
Each such elementary form can be isolated, its properties
can be studied, and by compounding them one can
at will produce thousands of substances, each with its
own distinctive qualities. Some of the more thoughtful
men of all ages have pondered upon the fundamental
questions of physical science, and they have guessed
how it might be: some guessed this way, some guessed
that, and none of them gave a sufficient reason. It
would be very remarkable if, among a multitude of
guessers, some did not guess nearer right than others;
but such lucky guessing hardly entitles one to the
honor of being the founder of a philosophy that had
to wait for later men and entirely different methods to
substantiate it. And this is the real state of the case
in nearly all departments of knowledge. Ask any chemist
\DPPageSep{251.png}{239}%
\index{Atoms, chemical properties}%
to-day why he holds the atomic theory of matter, and
he will reply that he can isolate the elements, and by no
process yet discovered can they be more finely divided;
that he can measure their individual magnitude and
weigh them, prove their existence in the sun and stars;
so that the weight of evidence is exceedingly great.
He will never think of assigning any such reasons as
the early philosophers gave for their teaching. Many
of the properties of bodies of visible magnitude depend
upon the number and arrangement of the molecules
that compose them, but the properties of atoms are
fundamental and not subject to change. All substances
are identified by means of their properties, and the
chemical properties of atoms are among the most important.
Not only do atoms combine together in groups
called molecules, consisting of two or more atoms, but
they combine in definite proportions by weight, and only
so; and these proportions are called the atomic weights
of the elements, and are known for all of them; so
that molecules are compounds of definite constituents,
definite weight, and possessing definite properties. For
instance, water is made up of hydrogen and oxygen, two
parts by weight of hydrogen and sixteen of oxygen;
and as to its properties, such as density, specific gravity,
conditions at different temperatures, etc., all are familiar
with. Most of these properties of bodies are called
physical, but by chemical properties is meant the
ability of atoms to enter into definite combinations
with other atoms, to form new compounds and develop
new properties. The chemist is concerned with such
atomic exchanges, called re-actions, and notes the conditions
\DPPageSep{252.png}{240}%
\index{Affinity, chemical}%
under which they take place, and some of the
new qualities that appear, such as its physical condition,
as to being a solid, a liquid, or a gas at certain
temperatures, its crystalline form, if it has any, its
behavior with polarized light, and so on.

Underneath all chemical re-actions there lies the
question as to why atoms combine at all. At first it was
explained as due to an attractive force,---chemical attraction,
possessed by all atoms, but in different degrees
by different elements. When it became known that
this acted in definite selective ways, it was called chemical
affinity, but was still supposed to be a peculiar
force unrelated to other forces supposed to exist, such
as heat, light, electricity, and so on. In the progress of
knowledge, it became apparent that these latter phenomena
were so directly related to each other that they
were capable of being transformed one into the other,
and then the expression ``correlation of forces'' began
to be used. A further analysis showed them to differ
from each other chiefly in the character of the motion
involved in the phenomena; and so forces, as such, have
been banished from physical science, leaving not even
a single primal force; for as each one can be changed
at will into any of the others there is simply a closed
chain of phenomena, no one of which can be called an
elementary one more than any other.

Chemical phenomena have been found to be a part of
the same grand division, and the term ``chemical affinity''
has itself been in a measure supplanted by the
term ``chemism,'' which is now used to signify the
quality possessed by atoms to enter into definite combinations;
\DPPageSep{253.png}{241}%
\index{Chemism and heat}%
and its explanation is to be found by noting
the factors present when atomic and molecular exchanges
take place, and these have been found to be all
physical without exception. There is a large field
known as chemical physics with which one needs to be
acquainted in order to understand simple chemical
operations; namely, the effects of heat, light, and
electricity in bringing about chemical changes.

When hydrogen combines with oxygen to form water
the process is called a chemical one; but, as has been
pointed out in the subject ``Heat,'' there is a definite
amount of heat given out by the combination of a definite
amount of the elements; and in like manner the
dissociation of the elements in water requires the expenditure
of energy proportionate to the amount decomposed.
This too is called a chemical process, but
the conditions for doing either are purely physical, depending
absolutely upon heat. The elements cannot
combine when heat cannot be given out, and cannot be
separated except by an equal expenditure. What is
true for this example is true in degree for all other
chemical re-actions; physical energy is involved in every
change and is the condition for the change. The first
law of thermo-dynamics states the quantitative relation
between heat and mechanical work; viz., that it is measurable
in foot pounds, and is equal to $772$ foot pounds
per pound degree, and this is called a heat unit. Now,
the chemical combination of a pound of hydrogen with
oxygen gives $61,000$ heat units, and is therefore at once
measureable in foot pounds, showing a direct relation
between chemical re-actions and heat or work.
\DPPageSep{254.png}{242}%

It has also been discovered by experiment that in the
absence of heat chemical re-actions cannot go on, and
this has led chemists to the conclusion that at absolute
zero chemism does not exist. There is not only no
selective action, but no cohesion among atoms, and all
molecules would fall to pieces---that is, to atoms, quite
dissociated---at absolute zero. Instead of requiring
\index{Absolute zero}%
\Pagelabel{242}%
$61,000$ heat units to dissociate a pound of hydrogen
from water, it would not require any, for if the atoms
do not cohere, no work would need to be done in order
to separate them.\footnote
  {See Appendix, \Pageref{p.}{400}.} %[** PP: Original reads p. 399]

From this, then, it appears that chemism is determined
by heat, and does not exist in the absence of
temperature. When it is developed it manifests itself
in selective ways, and in the formation of definite compounds;
and it therefore is a proper subject of inquiry
as to how the temperature of atoms can give such selective
qualities to them. This requires a reconsideration
of the distinctive quality of heat itself. It has been
pointed out that this consists in the internal vibratory
motions of atoms and molecules, as distinguished from
translatory and rotary motions; that the evidence for
this comes, first, from the fact that a body of any size
possessing any degree of heat---that is, having a temperature
above absolute zero---is constantly exchanging
its energy with the ether, and that the rate of the exchange
depends upon the temperature; and, second, that
translatory motions of bodies in ether do not require
the expenditure of energy, or, in other words, that for
such motions the ether is frictionless. This is the
same as saying that, where the heat of a body is lost by
\DPPageSep{255.png}{243}%
\index{Atoms, vibrations of}%
radiation, it is the internal vibratory motion alone that
is lost, not its translatory velocity. Consider a body of
any magnitude whatever, having any temperature whatever,
and moving at any assignable velocity in space.
After an interval it will have lost some of its temperature
by radiation, and, if it moves long enough, it might
lose it all, reaching absolute zero; but its translatory
velocity will not therefore be reduced in any degree.
Hence, in considering the heat in a body, independent
of any other motions it may have, one has only to do
with its internal vibratory movements, and that the
temperature of a body, say an atom, is measured by
the amplitude of its vibration, and is proportional to the
square of that amplitude.

If, therefore, chemism is directly related to heat, one
must attend to what must be going on in an atom, not
groups of them.

To say that an atom vibrates is to say that it is
changing its form, and to explain how changing its form
can result in such selective properties as atoms exhibit
is to explain chemism by the mechanics of the motion
involved. Whether atoms have one form or another
will make no difference in this argument, which is that
the result is due to change of form, whatever that may
be; but, for making the subject mechanically clear, some
form may be adopted, and one can do no better than to
choose that form which now has most probability in its
favor judged by other phenomena; that is, the vortex-ring,
which has been treated under the head of ``The
Ether.''

When such a body vibrates in its simple way it
\DPPageSep{256.png}{244}%
\index{Attraction of vortex rings}%
elongates alternately on two axes at right angles to
each other; that is, the change in form is from a circle
to an ellipse, so as to assume first a horizontal, then a
vertical elliptical form, as shown in the cut. Such
%[Illustration: \textsc{Diag.~29.}]
\begin{wrapfigure}{l}{1.25in}
  \Graphic{1.25in}{256a}
  \Caption{29}{Diag.\ 29.}
\end{wrapfigure}
changes are due to the elasticity of
the ring, and are brought about in
such an atom by impact, by friction,
and by absorption of ether waves.
Whether produced in one way or
another, they represent absorbed energy
and exhibit it as heat, the temperature
of a given one depending upon the amplitude
given to it by a definite amount of energy however
applied.

Such changing forms imply nodes and loops in the
vibrating body, positions of minimum and maximum
motions; and when the vibratory rate is the fundamental
one,---that is, the lowest rate the body can have,---there
will be four of each, the nodes being the positions of
minimum change of form. Such nodes may be seen in
vibrating bodies of all sorts,---strings, bells, rods, pipes,
and rings. The size of a body makes no difference in
this characteristic, and it therefore may be affirmed of
atoms as well as of any other magnitudes.

%[Illustration: ]
\begin{wrapfigure}{r}{1.5in}
  \Graphic{1.5in}{258a}
  \Caption{30}{Diag.\ 30.}
\end{wrapfigure}
Let it be admitted that vibrating atoms can cohere
for any reason, it will be seen that an atom such as
represented could only have other atoms attached to it,
and be in a stable condition, when they were at the
nodes; and in this case four might be so attached and
no more, if they were approximately of the same size.
Such places in atoms might be called bonds: they would
\DPPageSep{257.png}{unnumbered}%
% [Illustration: ]
\begin{figure}[hp]
  \begin{center}
    \Graphic{3.75in}{257a}
  \end{center}
  \caption{Geometrical Forms of Snow Flakes.}
\index{Crystallization}%
\end{figure}
\DPPageSep{258.png}{245}%
be definite in number, position, and strength. If the
other attached atoms were themselves
vibrating, they
would each have their own
nodes; and if they were free
to turn into any position, one
might be sure that the nodes
of each would be in contact,
and that the loops of the vibratory
motions would be where
space to move in without interruption
was free. Such a combination
of atoms might be called a molecule. It would
consist of a definite number of atoms, each with its own
atomic weight; and if the strength of
the cohesion depended upon the vibratory
motion, it is easily seen that when
there was quiescence in that there
would be disruption or dissociation.
%[Illustrations]
\begin{figure}[hbt]
  \begin{center}
    \hfil
    \begin{minipage}{1.25in}
      \Graphic{1.25in}{258b}
      \Caption{31}{Diag.\ 31.}
    \end{minipage}
    \hfil
    \begin{minipage}{1.5in}
      \Graphic{1.5in}{258c}
      \Caption{32}{Diag.\ 32.}
    \end{minipage}
    \hfil
  \end{center}
\end{figure}
Moreover, when there was such a nodal
bond it would be like a hinge, and two thus united
could swing upon it; while if three were thus united
and two were to swing upwards,
they would meet at a node on
each and stick together for the
same reason the other nodes did,
thus forming a symmetrical and
stable figure against which other
similar ones could be built up,
node against node indefinitely. A
hexagonal figure would result. If four were attached
to the primary nodes, and each was to swing up ninety
\DPPageSep{259.png}{246}%
\index{Chemical field}%
\index{Fields, chemical}%
\index{Fields, mechanical}%
degrees, there would be formed a sort of cubical box
without a lid; but at the top will be presented four
open nodes, upon which the four nodes of any other
similar one might be placed: and thus could a cubical
structure be built by addition of similar forms indefinitely.
Such symmetrical forms are called crystals.

Of course all this presupposes that there is some
good mechanical reason for atomic cohesion, that is in
some way dependent upon temperature; and to make
this clear it is needful, first, to call to mind some phenomena
of a similar sort on a larger scale.

It is well known that if a light body be brought near
a vibrating tuning-fork, the latter acts as if it attracted
it, for the light body will move towards the fork. The
same thing is true of other vibrating bodies, and the
explanation is that the vibratory motion reduces the
pressure about the body. Thus, suppose the hand to
move to and fro; as it moves forward the air in front
of it is somewhat condensed, while that behind it is
partially rarefied; when the hand returns the same
thing happens. The air follows up the hand because
the pressure is reduced next the hand, and if the hand
could swing back and forth, faster than the air could
return to it, there would be formed a perfect air vacuum;
and that means that the pressure would be
nothing at the hand and fifteen pounds per square
inch at a distance from it. Hence any body placed near
the hand would be subject to a pressure greater on its
remote side than on the side adjacent to the hand, and
would be pushed by it towards the hand. This would
be a phenomenon similar to attraction, the movement
\DPPageSep{260.png}{unnumbered}%
%[Illustration: ]
\begin{figure}[hp]
  \begin{center}
    \Graphic{\linewidth}{260a}

    \scriptsize CRYSTALLINE FORMS.\\[6pt]
    \begin{minipage}{\linewidth}
      The above figures illustrate very clearly the molecular arrangement in crystals of
      various kinds. \textit{A}~represents a cross section of Brazilian Topaz, as shown in polarized
      light. \textit{B}~is a hollow faced cube of salt, and \textit{C}~a similar hollow faced octahedron of
      copper sulphide. They show that the cohesive strength is greater on the edges than
      elsewhere. Some crystals, when being dissolved, leave a complete skeleton of themselves
      the last to disappear. \textit{D}~is a skeleton crystal of silver from Scotland, where the
      structure consists of a series of minute octahedral crystals adhering to each other in
      such directions as would build up a single large octahedral crystal if filled out.
    \end{minipage}
  \end{center}
\end{figure}
\DPPageSep{261.png}{247}%
\index{Crystallization}%
\index{Vibrations, sympathetic}%
towards the vibrating body being due directly to the
pressure of the medium, while the difference in the
medium would itself be directly due to the vibratory
movement. The amount of such difference in pressure
is evidently determined by the degree of vibration.
Now, if one can imagine a similar condition of things
about an atom vibrating in the ether, he can understand
how its vibratory movements might reduce the ether
pressure adjacent to it in a way proportional to the
movement, and also how at the nodes such effect would
be at a minimum, and at the loops at a maximum, so
there would be produced what is called a field. As the
condition that produced it was one of mechanical
motion, one might call the field a mechanical field, for
mechanical effects of translatory motion result from it.

When such an effect takes place among atoms one
might distinguish it as a \emph{chemical} field, for it would
bring about mutual cohesion among atoms, and the
nodes would determine the positions of stable combinations;
and a molecule so built up would require an
amount of energy spent upon it to break it up equivalent
to the energy spent, to produce the field, or, in
other words, equivalent to the heat in the atom.

It is here to be noted that when atoms combine in
this way each one retains abundant space for its heat
movements, so its temperature may be varied within
considerable limits without interfering with molecular
stability. And, if the vibratory movements continue,
then each molecule will have its own field, which will
be the resultant of all the fields of the atoms that are
combined thus to make the molecule. The field of a
\DPPageSep{262.png}{248}%
\index{Growth}%
\index{Inductive action}%
molecule will then have a form which will depend
absolutely upon the number and arrangement of the
constituent atoms, and will extend to some distance in
space beyond the geometric boundary of the molecule
itself.

The presence of such a chemical field must affect
other chemical fields in the neighboring space where
the fields overlap, hindering or facilitating the exchange
of atoms in other molecules, because lessening the
pressure holding them together. There are many
examples of this kind of action known. It is called
catalysis, which signifies the action of a given substance
\index{Catalysis}%
in bringing about chemical reactions without
itself being changed. For example, the binoxide of
manganese, when mixed with the chlorate of potash,
greatly facilitates its decomposition by heat, though
the binoxide is itself not decomposed. Pure zinc is
dissolved with difficulty by sulphuric acid; but a little
mercury or iron, or other so-called impurity, enables it
to be dissolved freely. Hydrogen and oxygen gases will
not combine when simply mixed; but a little spongy
platinum placed in the mixture will at once bring about
the combination, but will itself suffer no chemical
change. These gases will also slowly combine in the
presence of mercury when kept at the temperature of~$305°$.
In glass vessels without the mercury no combination
at that temperature occurs, but on raising the temperature
to~$448°$ it combines very slowly. In smelting
operations a flux has a similar function, and in some
cases the boundary line of such action can be observed.
Some re-actions take place at a different rate near the
\DPPageSep{263.png}{249}%
sides of the vessel that contains the solution than away
from it, and some mixtures of substances in solution
will separate from each other except within a short distance
from the surface. Such phenomena show that
the mere presence of some substances is sufficient to
profoundly affect chemical re-actions. The chemical
field of substances gives a consistent explanation of
catalysis. There is another class of phenomena well
known, but hitherto without any rational explanation;
viz., some supersaturated solutions seem unable to initiate
the process of crystallization, but the smallest crystal
of the substance starts it, and the whole body is
solidified in a few seconds. Here it is evident that the
crystal, taken as a nucleus, had a field that compelled
other and similar molecular groups to arrange themselves
in similar order. This is a phenomenon of such
importance as to warrant some attention here. When
two tuning-forks having the same pitch are separate
from each other a distance of several feet, and one of
them be made to produce a sound, the other one will be
made to sound likewise by the action of the sound
waves in the air upon it. The effect is called sympathetic
vibration. Other forks having different rates of
vibration will not be similarly affected, so the vibrations
in the air select out the particular fork having the same
rate as the one vibrating, and cause it to enter into a
similar state of vibration. So it appears with a magnet.
Any magnetic bodies in its field become magnetized
there; that is, they are brought into the same physical
state as the body that incited the field. Such physical
fields, then, are capable of compelling bodies in them
\DPPageSep{264.png}{250}%
\index{Fields, magnetic}%
\index{Magnetic field}%
\Pagelabel{252}%
to assume the same state of motion or similar position,
or both, as the body that produced the field, provided
the substance itself be constituted molecularly like the
first,---and this simply by being in proximity, not by
contact. It is a kind of induction, common through
the whole domain of physics. In the organic world of
living things the phenomenon of growth is manifested
by what are called cells, which are symmetrical groups
of molecules, as crystals are, only much more complex.
Growth consists in the formation of similar cells out of
suitable molecular constituents in the neighborhood.
Each different part of a plant or animal has a different
cell structure. If, therefore, it be conceded that each
cell has a field, which is the resultant of all the elements
that make it up, it will be seen how such field
must act upon other matter within it, compelling it to
assume a form similar to the cell that produces the
field; that is, to form a similar cell adjacent to itself.
Such formation is called growth; but the similarity in
form and function, when appearing among plants or
animals, has been considered as due to heredity, a term
that has a definite enough meaning, but which has not
been supposed to be due to mechanical necessity but
to some super-physical agency not amenable to purely
physical laws and conditions. It is possible to pursue
this much further and to show that cell structure itself
may be modified by molecular fields, and how stability
of form and function are possible with some and not
with others,---how what in natural history is called
variability, reversion, and other phenomena of the sort,
are explicable as due to the same factors that \DPtypo{organizes}{organize}
\DPPageSep{265.png}{251}%
atoms into molecules, and molecules into crystals.
Every one interested in the fundamental questions of
chemistry will be able to follow out in many ways the
mechanical conceptions here introduced, and compare
what he knows of chemical re-actions with them. It
will be especially helpful for one to draw upon paper
such ideal atomic rings with their edges touching, and
marking where the nodes must be. Such diagrams as
the one on \hyperref[fig:30]{p.~\pageref{fig:30}, fig.~30}, thus drawn, cut out, and the
parts bent up until they touch each other, will probably
surprise one at first to find how the nodes will be
brought adjacent to each other and therefore into a
stable position.

So far it has been assumed that there will be in the
ether about a vibrating atom an effect comparable with
the effect produced in air about a tuning-fork or other
vibrating body that is producing sound waves. One
might be satisfied that there was such an action, even
though he were not able to explain it, provided there
were good reason for the assumption. The case is the
same as for a magnetic field within which magnetic
phenomena take place, though a magnetic field cannot
be isolated. It is the same for the existence of the
ether itself: it is inferential, but from a large body of
phenomena of different sorts, all corroborating the hypothesis;
so one is satisfied. When a magnet acts upon
a piece of iron not in contact with itself, we explain the
action by the magnetic field; and, if a body acts chemically
upon other bodies not in immediate contact, controlling
their motions and positions, as is the case, the
same kind of an assumption is to be entertained. If a
\DPPageSep{266.png}{252}%
\index{Heat, effects}%
reasonable explanation for the existence of the field
can be offered, all the better, though no one holds more
lightly upon a magnetic field because he cannot explain
it. In the chapter on magnetism it is remarked that
there is good reason to think that atoms of all kinds
are magnets. If that be the case, then every atom has
a field of its own, wherever it may be; and it would
seem likely that this magnetic field of atoms was the
underlying factor in the so-called chemical field; and it
is therefore well to analyze the phenomena, having that
magnetic field in mind.

A single magnet of any form will have its field
under all conditions, and the \emph{shape of the field will be
determined by the form of the magnet}. If the magnet
were of sufficient size, there would be no difficulty in
locating it by its field, even though the magnet itself
could not be seen. A number of magnets arranged
promiscuously would so neutralize each other's fields
as to have no residual field, and in order to detect the
existence of magnetism it would be needful to get very
close to an individual magnet. When a steel magnet
is dissolved in an acid all evidence of the existence of
magnetism disappears, for the iron molecules are now
separated from each other and are scattered promiscuously
through the solution. Any disturbance whatever
that disarranges the magnetic arrangement of
molecules destroys the evidence of the magnetic field,
except at very short distances. When a piece of iron
is heated to redness it cannot be made magnetic in
the ordinary sense; for the vigor of the vibratory movement
continually knocks the molecules into new positions,
\DPPageSep{267.png}{253}%
and therefore changes their resultant fields,
leaving but a neutral effect upon outside bodies.

As chemical re-actions take place in liquids or gases,
and only exceedingly slow in solids, it follows that in
them one has to deal with molecules in all positions,---that
is, an entirely disordered arrangement, and such as
would exhibit no evidence of magnetic field, even though
every atom was itself a strong magnet; and this condition
of neutrality would be constant so long as the
temperature kept up so much mechanical disturbance
as to prevent any systematic arrangement. Yet it is
to be borne in mind that the magnetic field of no one
has been \DPtypo{distroyed}{destroyed}: it is as strong, as far reaching, as
ever; but it is masked by overlying fields,---that is all.
Let any one of them suffer any change at all, and the
effect of it would be felt throughout the whole space
the field would occupy if there were no other one in
its neighborhood.

Now, when the form of a magnet is changed, it
changes the form of the magnetic field---that is, the
distribution of the stress that constitutes the field; and,
when an atomic magnet vibrates, it is changing its
form; and as a result its field is changing at the same
rate. A multitude of such independent magnets, all
changing their forms and fields, would be sending out
waves into the ether; but they would be caused by and
measured by their heat motions, not by their magnetic
condition simply; and the effects of these waves at a
distance from their source would be practical uniformity
unless the waves were very long. For such short ones
as are produced by atomic and molecular vibrations
\DPPageSep{268.png}{254}%
there could be no ordinary indications of a magnetic
field such as are exhibited in the movements of bodies
of visible magnitude. Long waves of precisely the
same sort caused by motions of a slower rate might
make magnetic needles move. Thus, magnetic needles
upon the earth have been observed to move at the
same instant that solar disturbances have been witnessed
through a telescope, which indicates that the
waves were long ones, giving a magnet time to move
one way before it was impelled to move in some other
way.

This condition of practical neutrality on account of
the rapidity of the change at a distance from the magnetic
body would not hold true in close proximity to
the body itself; for the changes in the field will not
only be actually greater there, but the fact that there
are nodes and loops necessitates changes in the stress
at the surface of the atom, and renders it possible for
the actual magnetism to assert itself and act upon
another very near to it which it cannot have in any
degree a little farther away, the actual distance being
comparable with the diameter of the atom itself. Hence,
atoms close by would have certain magnetic effects
upon each other in the nature of selective effects, on
account of the uniformity of the stress at the nodes,
and the number of nodes would determine the possible
number of cohesive attachments. So one may fairly
presume that the vibratory motions such as constitute
the heat motions of atoms are the physical conditions
that underlie chemical combinations and give to them
their quantitative character, their selective property,
\DPPageSep{269.png}{255}%
\index{Sound, origin of}%
and their symmetrical form into which they arrange
themselves.

This gives a rational account of so-called chemical
attraction, and makes it clear how the laws of thermo-dynamics
are related to chemical re-actions. It reduces
the whole scheme to one of the mechanics of vibrating
magnets; and the evidence that atoms are such magnets
does not rest upon the necessity of the conception for
the hypothesis, but upon much confirmatory experiment
that has led physicists to the conclusion that
they are such, in a manner quite independent of what
phenomena might be deducible from matter with such
a constitution. In conclusion, it may be added that,
although the idea of ring-formed atoms has been
adhered to in this explanation, it is not to be understood
that the same explanation would not apply to
atoms constituted in any other manner; for all that is
implied in the above is that whatever their form and
substance they are magnets, and that they are so elastic
as to be capable of internal vibratory movements---that
is, of changing their forms in a periodic way;
and of this there appears to be no reasonable doubt.
When several such are combined together the resultant
motions and their effects become very complicated, and
therefore difficult to disentangle; but that would be no
reason for not holding a well-grounded conviction that
all chemical phenomena are truly physical, and referable
to fundamental mechanical laws, and are fully explained
when these mechanical conditions are pointed out.
%\DPPageSep{270.png}{256}%


\Chapter{X}{Sound}{256}

\First{The} term ``sound'' has two very different sign\-i\-fi\-ca\-tions,---one
a physiological one referring to a sensation
in the organ of hearing, the other the physical cause of
the sensation. When one has the sensation of sound,
of course he usually infers that it was caused by some
external physical condition that has in some way impressed
itself upon his auditory apparatus; and, to one
who has thought but little about it, it is difficult to get
rid of the idea that sound is a something which exists,
whether it be heard or not. That is, there would still
be sound though there were no ears, that a tumbling
pile of books in a deserted house would make a racket
if no one did hear it. On the other hand, one may
call that sound which is capable of being heard; and
when those conditions are investigated it is found, in
all cases, to be some kind of a mechanical impulse, or
succession of impulses, generally in the air, which may
be traced from the ear to some body which is found to
be in a state of vibration. The latter is called a
sounding body, and the air is called a sound conductor;
but these conditions are not necessary for the
sensation of sound. One may not infrequently hear
what is called ringing in the ears, that has its origin
within the head, and, perhaps, in some cases independent
\DPPageSep{271.png}{257}%
\index{Pitch}%
of any of the auditory apparatus, like some
nerve disturbance even at the base of the brain itself.
Hence there is a distinction between hearing and the
cause of hearing, and the latter does not necessarily
imply anything external to the listener. One may be
deaf so that no conditions external or internal will
produce the sensation. As the sensation itself can
give no infallible testimony as to what causes it, it has
come about that the physical conditions which may be
heard as sound have been investigated, and the science
of sound, or acoustics, has been developed quite independent
of the sense of hearing, the latter being only
a convenient instrumentality in the investigation, not
an indispensable one. In this sense sound is the
science of the vibratory movements of elastic bodies,
and one may inquire first as to the origin of such
movements. When one body strikes upon another,
motion is imparted to the latter. If enough motion is
imparted, it may move visibly, and we then call such
motion mechanical. Though it does not visibly move,
yet energy has been spent upon it in some degree, and
must be represented by some degree of motion which
at first it did not have. If a pencil be struck upon the
table, one may be as sure that energy has been spent
upon it as if it had been struck with the fist, only
less in amount.

When molecules are compressed together so as to
increase the density, and retained in such closer compactness,
heat is always the result; that is, the molecules
themselves have their amplitude of vibration
increased: but when molecules are compressed quickly,
\DPPageSep{272.png}{258}%
and the pressure be as quickly removed, the compressed
molecules at once rebound to their original
position with a velocity that depends upon the degree
of elasticity the body has, and, like a swinging pendulum,
do not stop at once when they have reached that
position, but go beyond a little, and thus oscillate back
and forth. Each molecule pushes against its neighbors,
and they upon theirs, and so on, the motion travelling
outwards from the point of disturbance in every direction,
with a velocity that is proportionate to the temperature;
that is, the vibratory rate of the molecules
themselves, which, as pointed out in the chapter on
heat, is exceedingly great.

This particular kind of movement is called longitudinal;
that is, it is to and fro in the direction in
which the disturbance travels, and depends altogether
upon the properties of the body that is struck, and not in
any degree upon the initiating cause. When the table
is struck with the pencil the sound heard is different in
quality from that given out by a similar stroke upon
the window or a tumbler. It differs also in duration.
The latter may continue to be heard for some seconds,
while the former is brief. Every elastic body has some
particular vibratory rate, which depends upon its size
and shape as well as the material it is composed of.
A stretched string or wire, a board, a lath, a bridge,
a house, for examples, all have individual rates of
motion, into which they can be brought by some well-directed,
sudden push. When a strong wind shakes a
house, the shake is the vibratory rate of the building,
and may be as low as one or two per second. In
\DPPageSep{273.png}{259}%
general, as bodies are smaller their rate of vibration
increases, until it becomes greater than thirty or forty
per second, when the effect can be heard. Stones
have an individual pitch, or rate of vibration, so that
by selection one may get a set to represent the musical
scale when struck. Smooth bits of laths of different
lengths give out their pitch when dropped upon
a table; and, with a properly graded set, tunes may be
played by dropping them successively. The rate of
vibration, or pitch, of a table is relatively high---several
hundred per second; and a pencil knock distributed
over so large a body, and by it to the floor, reduces its
strength very fast. The tumbler has its motions
symmetrical, therefore of greater amplitude, and last
longer. A tuning-fork struck and held in the fingers
near the ear will be heard for a much longer time than
if the stem be held against the table, as any one may
satisfy himself by trying. In the latter case the
motions are conducted away freely, in the former case
not so freely. In the former case the sound appears
louder to the ear, because the air, in contact with the
vibrating table, receives vibratory motions from it as
well as directly from the fork; and so the air motions
are re-enforced, and the energy is dissipated so much
the more rapidly.

The idea in all this is that, so far as sound consists
in vibratory motions, energy is involved, and is distributed
in accordance with mechanical laws; the size,
density, and elasticity of the sounding body being the
factors which determine the rate at which the distribution
can go on.
\DPPageSep{274.png}{260}%
\index{Sound, characteristics}%

If the motion be properly mechanical, any agency
that can originate such motions can give rise to sound.
One might ask himself here if it be likely that any
kind of motion, or form of energy, cannot produce it.
If it be remembered that motion is the antecedent of
motion in all known cases, one will perceive that
sound might have a variety of antecedents, as it has.
To the mechanical ones alluded to might be added
all cases of percussion, impact, friction---indeed, the
whole range of mechanical motions. Any agency that
can change the form of a body can cause sound vibrations.

That heat can directly produce sound is shown by
the roar of fire in furnaces; and tubes having a burning
gas-jet in them may give out a loud sound. In
these cases it is the body of air that is caused to
vibrate energetically\DPtypo{}{.}

When a beam of light falls upon a body that can be
heated by it there is a re-action between the surface and
the air, in which the surface is pushed slightly backwards,
as indicated by the \DPtypo{radiometre}{radiometer}. If a beam is
allowed to fall intermittently upon such a surface, it
will be thrown into vibrations as if it had been struck,
and will give out a sound, the pitch of which depends
upon the number of interruptions per second. Such a
device is called a radiophone.

A current of electricity sent through a conductor in
an interrupted manner makes the wire give out a sound.
The current heats the wire, expands it slightly, and
cools as suddenly when the current is stopped; so the
succession of currents results in sound. In like \DPtypo{manmer}{manner},
\DPPageSep{275.png}{261}%
\index{Sound, range of}%
\index{Sound, velocity of}%
a current of electricity going through an electro-magnet
causes a click at the instant of making and
breaking the current. This is occasioned by the
change in position of all the molecules. A succession
of these may keep up a continuous hum.

The electric spark itself always produces a snap of
brief duration, for short sparks from induction coils
and electric machines; but, when the spark is a long
one, like a flash of lightning, the sound may be prolonged
several seconds. Along the line of the flash
the air is greatly heated for a very brief time, and it
therefore rapidly expands. The quick cooling produces
a collapse of the heated column of air, with the consequent
noise. The duration of the thunder does not
signify that the lightning lasts such an appreciable
time, but that a part of it was a distance away, and that
time was taken for the sound to come from the more
distant place.

That chemical action can give rise to sound is proved
by the explosion of gunpowder and other explosives,
solid and liquid. In these cases a large amount of gas
is suddenly formed, and at a high temperature; it displaces
the air quickly and forms a great wave. One
may often feel the wave of compression produced by
a cannon go by him, even at the distance of several
hundred feet from it. These examples show that heat,
light, electricity, magnetism, and chemism are directly
related to mechanical motions because competent to
produce them under appropriate conditions. If motion
be the antecedent of any given motion, and any of
these may be the immediate antecedent of mechanical
\DPPageSep{276.png}{262}%
motions such as sound, what shall be said as to the
nature of each of these physical agencies?

\Section{CHARACTERISTICS OF SOUND.}

As sounds may be produced by any of the physical
agencies, it does not matter, except for convenience,
what ones are adopted. Usually mechanical motions
are most convenient, and for musical purposes either
percussion, or currents of air. We speak of high
sounds and low sounds, and we find by experiment that
those called low are produced by fewer vibrations per
second than those called high. If sounds are considered
as vibratory movements, then it is evident there is
practically an infinite range of them; for there may be
any rate, from one a year or a thousand years all the
way to such vibrations as atoms make, measured by
millions of millions per second. There is no good reason
for drawing a boundary-line at one point rather
than at another, and saying that all vibratory movements
beyond this rate are not to be considered as
sound, yet it is convenient for some purposes to confine
the range to such as can be heard.

When a succession of impulses follow each other at
such a rate as just to produce a continuous sensation of
sound, it is found to require from twenty to thirty per
second. It differs very much in individuals. In the
young it requires more, as the organ of hearing acts
more promptly than it does in the old. A less number
than these is heard as a tremble. From this as a minimum
one may go through a series, running from the
lowest sound produced by a piano---about forty per second---to
\DPPageSep{277.png}{263}%
\index{Echo}%
\index{Wave lengths of sound}%
the highest one of about $4,000$ per second.
Many insects make much higher sounds than this.
Such differences in the rate of vibration are called differences
in pitch; and, for musical purposes, a standard
of pitch has been adopted, making the middle~C of
the piano give from
%*[Illustration: ]
\begin{wrapfigure}{r}{1.25in}
  \Graphic{1.25in}{277a}
  \Caption{33}{Diag.\ 33.}
\end{wrapfigure}
$256$~to~$261$ vibrations.
The pitch of a sound may be
specified by giving its vibratory rate.
The pitch of men's voices ranges
from $100$~to~$150$ vibrations in conversation. Ordinary
whistling is produced by from $1,000$ to~$3,000$ or~$4,000$.
The squeak of bats is in the neighborhood of~$5,000$.
Beyond these figures it is difficult to hear anything,---not
because the vibratory motions are not produced, but
because they have too little energy to affect the ear.
Occasionally aurists find abnormally sensitive ears capable
of hearing sounds with a pitch as high as fifty or
sixty thousand, but ordinary persons have a limit in
the neighborhood of $20,000$; so it is customary to say
that the range of hearing of mankind is from thirty
per second to about $25,000$: but it should always be borne
in mind that the chief reason for not having a greater
range is in the difficulty of giving sufficient amplitude
to such very rapid changes. As the pitch rises the
amplitude decreases for a given amount of vibratory
energy. One might attribute the relatively low vibratory
rate of the maximum which the ear can perceive
to the lack of delicacy of the apparatus itself, which
would be true enough in an absolute sense; but the actual
sensitivity of the ear is really something wonderful,
for a piece of apparatus that is altogether mechanical
\DPPageSep{278.png}{264}%
in its mode of operation. It has been found that the
ear can hear such sounds as are produced by small
whistles at the distance of several hundred feet; and, if
the amplitude be computed,---assuming that it varies
inversely as the square of the distance---it is found to
be comparable with the diameter of a molecule, or less
than the ten-millionth of an inch. One who understands
the necessity for vibratory motions in elastic
matter will readily conclude that between the highest
number the ear can perceive, say $50,000$ per second,
and the lowest rate capable of affecting the eye ($400$
millions of millions), there is an enormous gap; and man
has no organs for perceiving the intermediate ones.

Experiments made in various ways have shown that
the velocity of sound waves in air is about eleven hundred
feet per second, and varies with the temperature,
being only $1,090$~feet at the freezing point of water,
increasing or diminishing about two feet per second for
each degree above or below that; and this is true for
sounds of all degrees of pitch. If it were not so,
music could not be heard at any distance from its
source. Suppose a tuning-fork makes one hundred
vibrations in a second. At the end of the second the
first wave would have got say eleven hundred feet
away, while the last wave would have just been completed;
or between the fork and the more distant wave
there would be a series, one hundred in all, reaching
eleven hundred feet. It follows that each wave would
be eleven feet long, or the velocity of transmission
divided by the number of vibrations. The wave length
of sounds can be measured in several ways, and of
\DPPageSep{279.png}{265}%
\index{Vibrations, sympathetic}%
\index{Vibrations, forced}%
course the product of the wave length into the number
of vibrations gives the velocity of sound in any conductor.
An idea of the actual wave length for common
sounds may be had thus: If the middle C of the piano
makes $261$ vibrations per second, and the velocity in
the air of the room be $1,140$ feet, $\dfrac{1140}{261} = 4.36\text{ feet}$,
as the length of the air wave, and for a man's voice it
will be about $\dfrac{1140}{125} = 9.1\text{ feet}$, while the highest note
on a piano will be $\dfrac{1140}{4000} = .285\text{ foot}$, or $3.4\text{ inches}$. In
water the velocity is four times greater than in air, in
wood about twelve times, and in steel about sixteen
times greater; and this will give a corresponding increase
in the wave length. This velocity of sound in
air is, roughly, about a mile in five seconds, or twelve
miles a minute; and at this rate nearly a day and a
half would be needed to go round the earth.

Air waves, like water waves, are reflected when they
come against a more solid body. Such reflections of
air waves are called echoes. The mere fact of reflection
does not change the length of the wave, as the
pitch of a sound is not altered by having its direction
changed. The law of sound reflection is the same as
that for the reflection of energy in general; viz., the
angle of reflection is equal to the angle of incidence.
Neither does reflection change the velocity of sound
waves.

The phenomena of echoes are familiar to every one,
for walls, houses, wood, and hills all echo sounds; and
one may roughly determine the distance to such an
\DPPageSep{280.png}{266}%
\index{Musical sounds}%
echoing surface. As one approaches such surface the
time between producing a sound and its return is
shortened, until, when about sixty feet from it, the two
so blend that the echo is no longer heard with distinctness.
The sound has then travelled $120$~feet.

When sounds are produced at the ends of tubes the
walls of the tube prevent, by reflection, the scattering
of the waves, and the whole motion is kept in nearly
parallel lines, and with slight loss in strength; hence the
utility of speaking-tubes. If the tube be a short one,
and stopped at one end, a new phenomenon appears
for sounds having a wave length about four times the
length of the tube. The sound is much strengthened.
A tuning-fork making say $435$~vibrations per second will
have a wave length of about thirty-one inches. If it be
held while it is vibrating over a tube or vessel of any
sort, between seven and eight inches deep, the increase
in the strength of the sound will be very marked. The
motion in the air is so much swifter than the prongs of
the fork that, while one prong is beating downwards
and thus producing a condensation in the air, the wave
reaches the bottom of the tube; there it is reflected, and
gets to the top just as the prong of the fork has returned
to its normal position. As the fork continues
upward, forming a rarefaction, the rarefaction also
travels down the tube, and is reflected so as to get
back when the prong has returned to its normal position;
so for a complete vibration of the fork the air
wave has travelled four times the length of the tube.
It is possible in this way to make quite accurate measurements
of either the wave length of a sound, its
\DPPageSep{281.png}{267}%
\index{Musical ratios}%
\index{Noise}%
velocity, or the number of vibrations a sounding body
makes per second. This phenomenon is called resonance;
and it is the chief factor in wind musical instruments,
such as flutes, organ-pipes, and the like.
Resonance in general means the ability of a body to be
thrown into sound vibrations by sound waves, and there
are two well-marked cases that need to be considered.
When the stem of a vibrating tuning-fork is held upon
a table the sound in the air is much louder, for the
whole table is made to vibrate at the same rate as the
fork. The table will resound loudly to forks of any
pitch. Such vibrations as are different in pitch from
that belonging to the body itself are called \emph{forced} vibrations.
Resonance of this sort is the function of the
sounding-boards of pianos, the bodies of violins, guitars,
and other similar instruments.

If two tuning-forks have the same pitch, and one of
them be made to sound, the other one will presently be
made to sound also, though it be several feet away from
the former one. The air waves act upon it like a
pusher upon one swinging; at each return a little more
energy is added, until the amplitude has become great
enough to make the sound audible. Such vibrations
are called \emph{sympathetic}, for they are only effective upon
bodies whose own rate of vibration is the same as that
of the sounding body. Raise the damper to the piano
and sing a sound of any particular note, then listen.
The same note will be heard prolonged by the piano.
The particular string which can give that pitch of sound
has been thrown into similar vibrations, and continues
to sound as it would if caused to in any other way.
\DPPageSep{282.png}{268}%

The air as a body is too large to have a vibratory
rate of its own, and, consequently, all sounds in it are
properly called forced vibrations; but, when it is confined
in cavities, resonance becomes apparent, and
sympathetic vibrations may be so strong as to be deafening.
That is the case often in locomotive furnace-flues
when the door is opened. One may hear it a mile
or two. The resonance of large rooms sometimes
renders it very difficult to understand a speaker in
them.

The prolonged sound of thunder has been often explained
as due in some measure to echo from the clouds,
but it is doubtful whether clouds do echo sounds. No
one ever hears the sounds of bells, whistles, or cannon,
or other strong sounds, coming from the clouds, as
would be the case if they reflected sounds appreciably.

When a single key of a piano is struck, there is produced
what is called a musical sound. There is a definite
pitch that is maintained. Strike half a dozen
adjacent keys at once, and the effect is what is called
a noise, though each component by itself would give a
pleasing sound. A load of stones when tipped from
a cart makes a great racket; yet each stone, if struck
with a hammer, may give out a distinct musical sound.
Nearly every body has its own musical pitch; but, if a
number of bodies with different unrelated pitches are
listened to at once, the effect upon the ear is a discordant
one, and is called a noise.

When, however, two or more musical sounds whose
pitches stand in a simple ratio to each other are heard
together, they blend so as to form a pleasing combinational
\DPPageSep{283.png}{269}%
\index{Musical instruments}%
sound. Thus, if one makes twice as many vibrations
per second as the other, the sound is a very
smooth musical one, and one is said to be the octave of
the other. If middle C of the piano makes $261$~vibrations,
the octave above will make~$522$, and the octave
below~$130.5$; and these may all be heard at once as a
musical sound. In music an octave is divided up into
eight parts called tones; and these are sung as \emph{do}, \emph{re},
\emph{mi}, and so on. If a string be stretched between two
points and the distance measured, the sound it will
produce may be called \emph{do} of the scale. If the string
be now shortened by a bridge so as to produce the note
\emph{re}, and the length of the string be again measured, its
length will be found to be eight-ninths of the length
of the first, the note \emph{mi} will be four-fifths, \emph{fa} three-fourths,
\emph{sol} two-thirds, \emph{la} three-fifths, \emph{si} eight-fifteenths,
and the next \emph{do} one-half. As the number of vibrations
a stretched string will make is inversely as its length,
it follows that these fractions inverted will represent
the relative number of vibrations produced by each
member of the musical scale when compared with the
beginning or fundamental one. The following shows
the letters of the musical scale, with their ratios and
vibration numbers for the middle octave of the piano.

\begin{center}
\TableFont%
\begin{tabular}{cccccccc}
C & D & E & F & G & A & B & C \\[1ex]
& $\dfrac{9}{8}$ & $\dfrac{5}{4}$ & $\dfrac{4}{3}$ & $\dfrac{3}{2}$ & $\dfrac{5}{3}$ & $\dfrac{15}{8}$ & $\dfrac{2}{1}$ \\[2ex]
261 & 293.62 & 326.25 & 348 & 391.5 & 435 & 489.37 & 522
\end{tabular}
\end{center}

The meaning of this is that $\dfrac{9}{8}×261 = 293.62$, and
so on, so that the notes of the musical scale stand in
\DPPageSep{284.png}{270}%
\index{Sound, vocal}%
\index{Voice}%
simple ratios to each other; and, if one has the vibration
rate of any one of them, he can compute any
others. Of course any octave above this one will have
simple multiples of these numbers for their vibration
numbers.

But these numbers signify more than simply this:
they signify that, when a second one is sounding with
C, it will make the number of vibrations represented by
the numerator of the fraction; while C is making the
number indicated by the denominator. Thus, G makes
three vibrations while C makes two. The sounds are
concordant one-third of the time, and the effect is a
pleasing tone. On the other hand, D makes nine while
C makes eight, and the two are in accord but one-eighth
of the time; and the effect is displeasing, and is called
discordant. The smaller the ratio the more musical
and harmonious the sounds; and music is made up of a
succession of sounds standing in such relations to each
other, and, when different ratios are employed, it is only
for contrast, and return is quickly made to these ratios.
The ear will not long tolerate a departure from them.

It has been stated that sympathetic vibrations would
cause a given body to vibrate. Press down gently a
base C on a piano, so as not to make it sound. Now
strike the C above it, holding down the key for a second
or two. On letting up the latter the sound of the
latter will continue to be heard, but coming from the
lower key, as can be learned by letting up the key, when
it will cease to be heard. If the G above the struck C
be now struck with the same low C held down, the
sound of the G will be heard from the base string, and
\DPPageSep{285.png}{271}%
so one may go up, finding eight or ten strings, each one
of which will make the low C string vibrate, giving out
the sound of the higher string. It is found that each
one of the strings able to do this has a vibration number
which is a simple multiple of the lowest one. The first
one is the octave, making twice the number; the second
one is the fifth of that octave, making three times the
number; and so on, to the upper limit of the piano.

This means that a piano string is capable of vibrating
in a number of rates,---two, three, four, and so on, times
its own lowest rate, which is always called its pitch.
It is also found that this process is reversible; that is,
if each one of these keys in turn be held down and the
lowest one struck, they will each be set vibrating; and
this shows that the struck string vibrates itself in the
several different pitches represented by the multiples
of its fundamental rate. The sound of a piano string is
therefore a compound sound. In such a compound
sound the lowest one is called the fundamental, and the
others the over-tones, or harmonics. Some of these
harmonic sounds are likely to be stronger than others;
and some may even be so much more energetic than
the fundamental as to nearly drown the latter, so as to
make the pitch of the string to appear an octave or
more higher than it really is. The number and relative
strength of the harmonics in a compound sound make
the difference in the quality of sounds. In all such
instruments as pianos, violins, guitars, and the like
string instruments, the number and strength of the
over-tones depend in a large measure upon how and
where the strings are struck and made to sound. A
\DPPageSep{286.png}{272}%
\index{Ear}%
piano string plucked near its middle point gives a different
sound from what it will give if plucked near one
end, and different in each case if plucked by the fingernail
and by the finger. So the quality of sound can be
much modified by mechanically varying these factors.

In other musical instruments the sounds are also
compound in a similar way, differing in the number and
strength of the higher harmonics. Some have the
even harmonics, as the second, fourth, sixth, and so on,
stronger; some have the odd ones---first, third, fifth,
etc.---stronger; some have few, and some many. A
flute has but one or two, a violin has twenty; and thus
the character of the sounds of musical instruments is
explained.

As for the voice, the sound is produced by the vibrations
of what are called the vocal chords, which are
fixed at the junction of the trachea and æsophagus, and
through which all the air to and from the lungs has to
go. These chords are modified in tension by muscles
at will, and so change the pitch of the vibrations. The
cavities of the throat, the mouth, and nose act as resonators
for these sounds and seem to strengthen some
of the constituents, thus giving prominence to certain
ones to the exclusion of others. That the mouth acts
this way may be observed by pursing the lips as if to
produce the various sounds of ah, oo, o, snapping one
cheek with the finger. These sounds will result;
while, with a little trial, one may thus snap a tune
which may be heard through a room, merely altering
the size of the mouth cavity. The cavity of the nose
is as important as that of the mouth. When this cavity
\DPPageSep{287.png}{273}%
\index{Corti's fibres}%
\index{Fibres of Corti}%
is small and narrow, there is produced what is called
a nasal sound. When this is prominent, and is not the
result of a cold, as is sometimes the case, the trouble
is a physiological one, due to the bad shape of the
resonating cavities rather than to careless habits, as is
often assumed by some teachers of expression. Some
different pitch of the voice in ordinary speaking might
be adopted, and thus in some measure prevent the disagreeableness
of the nasal sounds, but no amount of
painstaking can altogether prevent it. That structure
and its acoustic effects are an inheritance in some parts
of the world, as are crooked noses, thick lips, black
eyes, and broad heads in other and different parts of
the world, and is no more to be legislated away than
are these other physiological peculiarities. Neither is
it a proper subject of ridicule, more than lameness or
defective vision.

If the bell of a locomotive be rung while it is swiftly
approaching one, the pitch of the sound rises until the
engine has reached the observer. As it retreats the
pitch lowers, and the difference in pitch becomes
greater as the velocity of the engine is greater. The
explanation of the phenomenon is, that one judges of
the pitch of a sound by the number of vibrations that
reach the ear per second. Suppose an observer be
distant eleven hundred feet from a source of sound of
one hundred vibrations per second. If both observer
and source remained in place, one hundred vibrations
per second would reach the ear of the observer, and
there would be one hundred more on the way to his
ear. If the observer should continue to go that whole
\DPPageSep{288.png}{274}%
distance of eleven hundred feet to the source of the
sound in one second, he would not only receive all he
would by standing still, but in addition all that were
on the way to him,---two hundred vibrations in all,---or
just twice the number that would reach him if he
remained in place. Now, twice a given number of
vibrations represents a difference in pitch of an octave.
The sound he would hear would be an octave higher
than the sounding body was actually making. Any
less velocity than that supposed would make a corresponding
less difference in pitch, but such velocities as
railway trains have may make a difference in the pitch
of more than a musical tone. Of course, if the sounding
body and listener be separating, a less number of
vibrations will reach his ear, and the pitch will be correspondingly
lowered. One may roughly determine
the velocity of a train of cars by noting the change in
pitch of bell or whistle. Thus, if the difference be,
say a musical semitone,---one-sixteenth,---then the
speed of the train is one-sixteenth the velocity of sound
in air, one-sixteenth of $1,125$~feet, which gives seventy\DPtypo{-}{ }feet
per second, or forty-seven miles an hour.

The ear is a complicated structure of tubes, muscles,
cartilages, bones, fibres, and nerves. The external
part, or conch, is of but little service in hearing in man,
for it cannot be directed, as can the ears of horses and
cattle. If it stands out from the head so as to have
some use as a collector, it is supposed to be in abnormal
position; but it is not much needed in any case.
The orifice of the ear is known as the tympanum, a
tube a little over an inch in depth and about a quarter
\DPPageSep{289.png}{275}%
\index{Life}%
of an inch in diameter. At the inner end it is covered
with a thin membrane called the drum of the ear. On
the inner side of this membrane, there is attached to
the middle of it a bone fixed to a kind of hinge, so that
any movement of the drum of the ear, in or out, makes
this bone to move in a similar way. Then follows a
network of bones and cartilages, and a set of fibres
known as Corti's, of different lengths, and whose function
has been supposed to be for sympathetic vibrations.
%[Illustration: ]
\begin{figure}[hbt]
  \begin{center}
    \Graphic{3.5in}{289a}
  \end{center}
  \Caption{34}{Diag.\ 34.---The Ear.}
\end{figure}
There are in the neighborhood of $4,000$ of these
fibres, each one adapted to vibrate at a different pitch.
Then follow the nerve terminals and the acoustic
nerve itself, which goes to the base of the brain, where
its function as an acoustic instrument ends with the
delivery of its peculiar motions, interpreted by consciousness
as sound.

It is easily seen that the whole structure is one
adapted to receive vibratory motions from the air,
within prescribed limits, and transmit them inwards
\DPPageSep{290.png}{276}%
\index{Life, definitions of}%
where they can be interpreted. The tube itself possesses
resonating properties like any other tube. The
membrane is shaken to and fro by sound vibrations,
and this movement is handed on to each distinct part
until the nerve itself is shaken. From beginning to
end, it is only the transfer of a particular kind of
motion,---what is called mechanical,---perhaps transforming
it from longitudinal to transverse vibrations.
That it is so extremely sensitive as to be affected appreciably
by motions so slight as the ten-millionth of an
inch is a marvel, and shows that mechanical motions of
translation, though on a scale of molecular magnitudes,
is able, through the proper avenue, to affect the mind
and develop consciousness, which experience enables
the individual to interpret by direct inference.

Let one reflect upon the facts furnished in great
abundance by physical science,---that all the data which
comes to the mind through consciousness, and which
furnishes what is called experience, is simply motion
of some sort. Touch, producing pressure upon the
surface of the body, finds a suitable nerve to transmit
to the base of the brain that kind of a disturbance;
sight, another kind of disturbance to the optic nerve,
transmitted to the same place; hearing, still another
kind of motion given to another kind of nerve running
to the same headquarters. So, by means of motions
of various sorts man determines his place in the
universe, and learns how he may adjust himself to it.
%\DPPageSep{291.png}{277}%


\Chapter{XI}{Life}{277}

\First{Any} scheme of physics which fails to present that
great body of physical phenomena exhibited by living
things, both vegetable and animal, must be incomplete.
Many of these phenomena have seemed to be so remote
from ordinary mechanical operations that, in the
absence of definite knowledge concerning them, their
origin, factors, and relations to subsequent phenomena,
it is not to be wondered at that they were long thought to
be due to some peculiar force residing in a living thing,
\index{Force, vital}%
\index{Vital force}%
\Pagelabel{277}% [** PP: Note to p. 277 clearly points here]
\Pagelabel{279}%
which was not to be attributed to the general endowments
of matter, but only to be found in certain organized
forms of matter, which organization it had itself
built up as a \emph{habitat}. It was conceived to exist apart
from any material organization as a kind of entity.
The difference between a living and a dead animal was
thought to be simply one of the presence or absence
of that entity called life. It was thought to be able to
effect changes in matter which the ordinary physical
and chemical forces could not possibly do; and many
of the chemical products of living things were supposed
to be formed only through its agency; and still
more than that: it was held to be capable of ``suspending
the action of chemical laws.'' That the stomach
\DPPageSep{292.png}{278}%
\index{Cell structure}%
\index{Protoplasm}%
itself was not digested by the gastric juice it secreted
was held to be proof of its control over chemical
operations.

There have been many attempts to define life, but
the efforts have not been very successful. Thus Kant
defines it as ``an internal principle of action;'' Treviranus,
``the constant uniformity of phenomena under
diversity of external influences.'' Bichat, ``Life is the
sum of the functions by which death is resisted.''
Duges calls life ``the special activity of organized
beings.'' De~Blainville's and Compte's definition runs
thus: ``Life is the twofold internal movement of composition
and decomposition, at once general and continuous;''
and Spencer's is ``the continuous adjustment
of internal relations to external relations.'' It will be
observed that in all of these what is described is a
series of processes, or a body of functions belonging to
certain structures, rather than an entity,---a description
of what life does rather than what it is.

Analogous difficulties were met in the attempts to
define other of the so-called physical forces. Thus
light was supposed to be a created something. The
corpuscular theory of it represented it as consisting
of particles of some sort that ordinary matter could
absorb and eject, and which, therefore, had an existence
independent of matter. The establishment of its
being but wave motion in the ether completely destroyed
the notion of its having an objective, independent
existence.

Heat, too, was supposed to be a kind of imponderable
matter, and certain phenomena in ordinary matter
\DPPageSep{293.png}{279}%
\index{Molecular stability}%
depended upon its presence or absence; it, therefore,
was supposed to be an entity, and to have an independent
existence. Experiment showed it to be but a
particular kind of motion, so the idea that there was
any such thing as heat was abandoned.

Electricity and magnetism were supposed to be
fluids; and some of the early terminology still survives
in popular speech to-day, as when one reads that the
electric fluid struck a tree or entered a house. Nevertheless,
nobody now believes that either of them is
a fluid, or has an existence independent of matter.

The regular movements of the planets were thought
to require intelligent directive power to keep them in
their orbits; but now the gravitative property of matter
itself is held to be quite sufficient to account for all
the observed facts, and the extra material directive
force is held to be an entirely unnecessary assumption.

The discovery of the conservation of energy, covering
every field that has been investigated, led to the
growing conviction that there are no special forces of
any kind needed to explain any phenomena. What
seemed probable forty years ago, to those who were
conversant with the facts,---that vital force as an entity
has no existence, and that all physiological phenomena
whatever can be accounted for without going beyond
the bounds of physical and chemical science,---has
to-day become the general conclusion of all students of
vital phenomena; and vital force as an entity has no
advocates in the present generation of biologists.\footnote
  {See Appendix, \Pageref{p.}{400}.}
The
term has completely disappeared from the science, and
is only to be found in historical works; and every
\DPPageSep{294.png}{280}%
phenomenon which was once supposed to be due to it
is now shown to be due to the physical properties of a
particularly complex chemical substance known as protoplasm,
which is the substance out of which all living
things, animals and plants, are formed. This protoplasm
is entirely structureless, homogeneous, and as
undifferentiated as to parts as is a solution of starch,
or the albumen of an egg. Minute portions of this
elementary life-stuff possess all the distinctive fundamental
properties that are to be seen in the largest
and most complicated living structures. It has the
power of \emph{assimilation},---that is, of organizing dead food
into matter like itself,---and, consequently, what is
called growth. It possesses the ability to move---that
is, of visible, mechanical motion, which is technically
called \emph{contractility}; and it possesses \emph{sensitivity}---that
is, ability to respond to external conditions.

It was formerly thought that the cell was the
physiological unit, a cell having walls differently constituted
from the substance enclosed, also a nucleus;
but as the microscope was improved, and anatomical
research continued, it became evident that the cell,
with its more or less complicated structure, was itself
built up by the structureless protoplasm. As before
stated, it is a highly complex substance, chemically
considered, made up of many atoms of carbon, hydrogen,
oxygen, and nitrogen, with a small number of
atoms of sulphur and phosphorus,---more than a thousand
of them in one molecule; and there appears to be
a great number of varieties of it. A small pellicle of
this substance, like a minute bit of jelly, without any
\DPPageSep{295.png}{281}%
\index{Growth of crystals}%
\index{Growth of lobster}%
\index{Matter, living}%
parts or organs, possesses its various attributes in equal
degree in every part. Any particular portion can lay
hold upon assimilable material, or digest it, or be used
as a means of locomotion; so that what are called
tissues of animals and plants are only the fundamental
properties of the protoplasm out of which they have
been built---thrown into prominence by a kind of division
of labor. The protoplasm organizes itself into
cells and tissues in the same sense as atoms organize
themselves into molecules, and molecules into crystals
of various sorts, having different properties, that depend
upon the kind of atoms, their number and
arrangement in the molecule.

The greater the number of atoms in a molecule the
less stability does it have, and especially is this the case
with molecules containing nitrogen. Many of its compounds
are so unstable as to be liable to explosive
disruption. This fact makes it easy to understand how
there exists, in a mass of such molecules no larger than
the minute ones seen in the microscope, conditions for
internal motions in the nature of explosions.

Let it be granted that atoms are in the neighborhood
of the fifty-millionth of an inch in diameter; then,
if a thousand of them are organized into a molecule, its
diameter would be about the five-millionth of an inch.
A speck of protoplasm, one ten-thousandth of an inch
in diameter, would require not less than five hundred
such molecules in a row to span it; and there would be
no less than one hundred and twenty-five millions of
such molecules in the small mass. Some of these molecules
would be less stable than others on account of
\DPPageSep{296.png}{282}%
\index{Food}%
the internal motions that all the time are present.
Physical disturbances, external to such a mass, such as
temperature, ether waves of light, and chemical re-actions
of any sort, and so on, can induce and add to the
disruption and other changes going on, and visible motions
might be expected to follow.

That such external agencies can bring about visible
motions of microscopic particles has long been known.
A few small bits of camphor dropped upon the surface
of clean water in a saucer will begin to move about in
a remarkable way. They will spin round, and travel
from place to place, and dodge each other in a manner
strongly like living things. A little gamboge, which is
a reddish-yellow gum used as a pigment, if rubbed up
in water and looked at through a microscope, will be
seen to have its particles in constant motion like animalcules.
This is known as the Brownian movement,
and is caused by temperature changes between the
particles and the water. Such phenomena are rather
extreme cases of the re-action of external molecular conditions
upon a small mass of matter, resulting in mechanical
motions. In protoplasm there is added to
these same external ones others of the nature of molecular
explosions within the mass, and together they
give rise to a number of effects, in which the transformed
energy shows itself in redistributing the molecules,
absorbing additional material, and movements of
other sorts.

Biological researches within the past few years have
added vastly to our knowledge of protoplasm and its
properties; and there is no longer any question that its
\DPPageSep{297.png}{unnumbered}%
%[Illustration: ]
\begin{figure}[hp]
  \begin{center}
    \Graphic{\linewidth}{297a}
    \label{fig:frost}
  \end{center}
\begin{minipage}{\linewidth}
\scriptsize%
The above picture is copied from a photograph. It represents the plume-like
forms assumed by water when crystallized in a basin. The similarity it presents
to vegetable forms is very striking. One may often see on frosty window-panes
fantastic imitations of organic things which forcibly suggest vitality. They are
too common to be considered coincidences.
\end{minipage}
\end{figure}
\DPPageSep{298.png}{283}%
\index{Muscles}%
qualities are the expression of the various movements,
chemical and physical, and belong to it simply as a
chemical substance. Chemists have synthetically
formed out of the various elements a vast number of
substances that were not long ago believed to be formed
only by living things; and there is but little reason to
doubt that, when they shall be able to form the substance
protoplasm, it will possess all the properties it is now
known to have, including what is called its life; and one
ought not to be surprised at its announcement any day.

Some of the phenomena exhibited by bodies called
inorganic, such as minerals of many kinds, possess
properties that are very like those supposed to belong
solely to living things. A spider or a lobster will have
a new leg or claw grow to replace one lost in any way.
In like manner a crystal will replace a corner or side or
any defacement so as to complete its symmetry before
it will begin to grow elsewhere, and this in cases where
the crystal has been defaced or incomplete for millions
of years, as is found to be the case sometimes in geological
specimens. Such phenomena have led some of
the most thoughtful and best informed naturalists to
query whether the evidence we have does not lend
much support to the theory that \emph{matter itself is alive},
and that the difference we observe in things is simply
one of degree rather than of kind. See \hyperref[fig:frost]{opposite page}.

In the brief space of this chapter, only an outline of
the relations between vital and physical phenomena can
be given, and of these, only a few of the more prominent
ones. It will suffice to show that such phenomena
as assimilation and growth, movement and irritability,
\DPPageSep{299.png}{284}%
or sensitivity, have antecedents of physical energy in
the same sense as the movements of an electric motor
have physical antecedents in electric currents, dynamos,
steam-engine, and furnace.

The food of an animal consists almost altogether in
highly complex molecular compounds. It may be said to
be matter stored with energy. A pound of bread may
have the mechanical equivalent of twelve thousand heat
units, and if burnt in an engine would be better for
heating purposes than a pound of coal. When this has
been digested, and has done its work in the body, the
excreted products are of course equal in weight to the
original pound, for no kind of a physical or chemical
process affects the quantity of matter in any degree;
but the products themselves represent much less complex
compounds, and the energy has been distributed
through the body, carrying on its various operations.
There is, first, that of ordinary movement, which can be
measured in foot-pounds, as work of any kind may be.
The blood in the arteries and veins has to depend upon
a kind of hydraulic apparatus to keep it in motion.
The temperature of the body demands a supply of heat
measurable in heat units to maintain it, while the
repair and waste going on through the whole body of
all animals implies a distribution of the material necessary
for the maintenance of the integrity of the tissues,
as well as a separation and removal of the used-up material;
that is, the material that has lost all its available
energy. The energy for doing all this of course comes
from the food, so the question is not as to its source
and quantity, but it is, How is this transformation of
\DPPageSep{300.png}{288}%
\index{Nerves, their functions}%
energy in the body effected? Is it direct, or is it indirect?
This is the same as asking as to the mechanism
in the body, by means of which energy supplied is transformed
to meet the various wants of the body.

Roughly, there are five different kinds of motion to
trace the antecedents of in the body of any of the
higher animals. First, there is the common mechanical
motions of the bony framework, which transport the
body from one place to another, or change the position
of a part with respect to the rest, as when one moves
an arm. Second, there is the motion of a muscle,
wholly different in character from the first, for the
shape of the muscle changes by contracting in length
and increasing in diameter. The muscles are so attached
to the bones that the contractions of the one
cause the others to change their positions. The muscular
contractions of the heart, arteries, and veins keep
the blood circulating; and the same is true for the processes
of digestion, breathing, etc.

Third, there is the motion constituting the temperature
of the body, which, as has been explained, is altogether
atomic and molecular in its nature, and is,
therefore, in strong contrast with the other two.

Fourth, there is a kind of motion that is going on
throughout the body of the nature of transpiration, in
which solids, liquids, and gases are passing through the
various membranes without rupturing them. In the
lungs there is an exchange of gases, oxygen going one
way and carbonic acid gas going the other. In all the
mucous-membrane-lined cavities there is more or less
liquid oozing through the walls continuously, and there
\DPPageSep{301.png}{286}%
is no tissue so dense but protoplasmic masses do not
move into or out of apparently with ease. They go
through the walls of veins and arteries as if the latter
were porous bodies, though no visible pores have ever
been discovered in them.

Fifth, there is the motion in the nerves, in the nature
of a longitudinal wave, and the velocity of which is in
the neighborhood of one hundred feet in a second,
which, though it is slow compared with sound waves or
light waves, is fast when compared with the other
motions of the body. He is a swift runner who can
run at the rate of thirty feet a second for any distance.

The contraction of a muscle is to be measured in
fractions of an inch per second. The motion of heat,
measured as a rate of conduction, is exceedingly small
in the animal body,---probably not the hundredth of an
inch per second. The transpiration, or osmotic action,
is also a relatively slow movement, so that a velocity of
one hundred feet per second, which is upwards of a mile
a minute, is really rapid.

How and why the bone moves we know: it is because
the muscle that is attached to it contracts; but how is
energy spent to make a muscle contract? As a matter
of fact, when a muscle contracts it evolves a considerable
quantity of carbonic acid gas and water; it also
becomes acid, all of which imply chemical actions, for
these are chemical products. Carbonic acid gas and
water are the chief products of the combustion of such
material as foods, for they are made of what are called
hydro-carbons (combinations of carbon, hydrogen, and
oxygen chiefly); and when these elements re-combine,
\DPPageSep{302.png}{287}%
\index{Nerves, their functions}%
forming water and carbonic acid, there is always a relatively
large but definite amount of energy given out
in the form of heat, and this effect is independent of
time or place; that is, the same amount is developed
whether the process goes on fast or slow, or whether it
takes place in a furnace, in the body, or by slow decomposition
called rotting. When it goes on faster than
the heat can be conducted or radiated away, the temperature
rises and we say the body is hot. When the heat
generated is at once employed to do work, as in a steam-engine,
the temperature of it is reduced proportional to
the work done. When this takes place in a contracting
muscle better results follow, for conduction and
radiation within a muscle can take place at only a slow
rate; so the temperature rises, and this explains the
sensation of warmth resulting from muscular exercise.
The increase in perspiration is also partly due to the
same re-action of decomposition, as water is one of the
products. When the muscle in contracting does additional
work, as in raising a weight, a corresponding
amount of decomposition takes place, and the heat is
but transient, as it is at once transformed into the
muscular motion, which is as much mechanical in its
nature as is the movement in a steam-engine.

The muscle is quite like a spiral spring, which may
contract upon itself and do work by contracting.

It is not the substance of the muscle itself that undergoes
the change of disintegration, evolving water, carbonic
acid, and other products; but there is evidence
that the muscle secretes a particular substance called
\emph{inogen}, the rapid decomposition of which causes the
\DPPageSep{303.png}{288}%
\index{Corn, life of}%
\index{Egg}%
contraction. As this substance can only be replaced at
a definite rate and in a definite amount, it is clear that
the work of a given muscle is limited by the physiological
processes that precede it. The rate of work of a
muscle is then determined by the rate at which inogen
can be secreted by the muscle, and work done beyond
that rate results in muscular exhaustion, which in its
early stages is called weariness, and requires repose for
fresh accumulation. Excessive draught upon the
muscles reduces their ability to secret inogen, and their
degeneration follows.

Muscular contraction is satisfactorily accounted for
without assuming any vital force. It has a purely
physical origin, the structure itself acting as a kind of
mechanism for transforming the chemical energy supplied
in food into the mechanical forms of energy
represented by the various movements of the body,
external and internal, which have already been mentioned.

That physical and chemical agencies bring about new
movements is of course well understood. Especially
clear is this for such nerve actions as accompany the
special sensations of sound, sight, touch, and the rest.
That the disturbance is properly described as a movement
is apparent when it is found that it has a rate of
progression, as before stated, of from one hundred to
three feet per second. Whether such movement be
similar to a sound wave in a rod or tube, or to an electric
disturbance, makes no difference so far as the transformation
and transference of energy are concerned.
For sound there is the antecedent of vibratory motions
\DPPageSep{304.png}{289}%
\index{Growth}%
in the air; for light, waves in the ether; for touch,
mechanical pressure; for taste, chemical solution; and
for smell, gaseous substances with definite constitutions
and rates of vibration. These represent the ordinary
stimulants to action of such nerves, and so are commonly
understood to be the source of disturbance; but
every one of these so-called special nerves may be
excited to action by other agencies than the common
or normal ones, and the effect is the same. Thus, the
optic nerve may be stimulated by pressure, by cutting,
pricking, thumping, and electricity, and the effect is the
sensation of light; and, in the absence of other sources
of information as to the origin of the sensation, no one
could tell which of these was the originating one.
Every one of them, however, represents some form of
energy spent upon the nerve. What is important to
note about it is this,---the nerve transmits an impulse
it receives, quite indifferent as to its source, and is
interpreted as a definite sensation, quite independent
of its origin. The latter is only an inference, and is,
therefore, liable to be \DPtypo{eroneous}{erroneous}.

But there are several other kinds of nerves, each
with some different function from the rest. Thus there
are nerves running to muscles, causing them to contract,
called motor, or efferent, nerves; secretory nerves,
to glands that cause secretions; vascular nerves, that
cause contraction or dilatation of the walls of blood-vessels;\DPnote{** Only instance,}
inhibitory nerves, that affect other nerves so
as to moderate or entirely stop their action; reflex, or
afferent, nerves, which convey disturbances to the brain
or other nerve centres, but which cause no sensation;
\DPPageSep{305.png}{290}%
and still others known to exist, but the special functions
of which are unknown.

To describe the action of any nerve is to describe
the transmission of energy in greater or less amount,
and transmission in all cases requires time. This does
not mean that the energy which does the special work
of moving muscles or the chemical transformations of
foods into tissues is transmitted by the nerves, but
that the transformations of energy already present in
each place where the work is to be done are controlled
by nervous energy in the same way as a local galvanic
circuit is controlled by a relay, or the explosion in a
mine is determined by an electric spark. The energy
available for all the purposes of an animal, including
man, exists in the material of the body. The activity
of protoplasm in the various cells transforms the various
food stuffs into the proper substances needed. The
energy is already present; it is only differently distributed
by protoplasm; and nervous action determines
what changes, if any, shall go on at a given place.

Temperature determines whether any of the physiological
process shall go on or not. Plants and animals
of a low order, such as snakes, frogs, and fishes, may be
frozen without injury. Some of the minuter forms of
life can withstand arctic winters, for there is an abundance
of insect life in those regions. On the other
hand, a temperature of~$140°$ is destructive to the life of
everything except the seeds and spores of a few microscopic
beings. Some of these have been known to
survive a temperature of~$200°$, continued for an hour
or more; but nothing has been found that can withstand
\DPPageSep{306.png}{291}%
\index{Matter, living}%
\index{Toepler-Holtz electrical machine}%
the boiling temperature of~$212°$. The retarding
influence of cold upon vital processes can be understood
by considering that special chemical compounds require
special temperatures to form; and, if energy has to be
supplied to maintain the proper temperature, so much
the less will be at disposal for other processes. If life
processes were other than physical, it might be expected
that they would not be quite so rigidly conditioned by
physical surroundings.

There is a distinction between a living plant or animal
and the seed or spore or egg out of which they
grow. Both are commonly spoken of as living things,
but the processes that constitute life in the one are not
present in the other in any degree; thus, for example,
growing corn and the grain of corn from which the
plant started. The grain of corn may be kept in a
suitable dry place for several years without any apparent
change, unless it be some loss in weight due to
evaporation from it. How long it may exist thus and
still be able to grow if planted is not known. Grains
of wheat found with Egyptian mummies buried three
thousand years ago have been said to grow, but there
is much doubt about it, and botanists do not credit
the story. A few years' keeping in moister climates
destroys their ability to grow, and farmers always
choose seed corn from last year's growth, which is an
indication that there is a process of slow deterioration
going on that ends after no long time in utter inability
to grow under any conditions. This ability to remain
for several years in a nearly stable condition is a property
of the seed that does not belong to the plant; for,
\DPPageSep{307.png}{292}%
when growth has once really begun, it must keep on
growing or die: arrest is impossible, which seems to
show that life is a process rather than a condition, and
the grain of corn is simply a combination of materials
where, under suitable conditions, life may begin.

The constitution of corn is well known; that is, the
elements out of which it is built up, and the proportionate
parts of each. Like other kinds of food, it has
carbon, hydrogen, oxygen, nitrogen, for the chief constituents,
and in addition a little sulphur, phosphorus,
iron, potassium, and a trace of some others. These,
when organized as they are in a grain of corn, form a
very complex body indeed. There are not only molecular
groups of many sorts, but these are segregated
into families, so that bodies of one constitution are all
in one locality, and bodies of other constitutions in
other separate localities, but definitely arranged so as
to be available when the life process begins. Once
formed, it appears to be as inert as a crystal of any
sort, and no change happens to it until such physical
conditions as heat and moisture are provided. These
it absorbs and transforms; a sprout appears, then a
root, each with different functions, one for absorbing
ether waves, the other for absorbing water. The
energy of ether waves is utilized in digesting carbonic
acid and building up the structure, and the
growth is simply the addition of materials gathered
in this way and elaborated into similar protoplasmic
form and structure. Growth implies transformation
of one substance into the material of another, and is
effected by means of energy from external sources.
\DPPageSep{308.png}{293}%
\index{Atoms, life associated with}%
\index{Foster, Dr.\ Michael, quoted}%
The energy of a stalk of corn may be found by using
it as fuel and finding its heat units per pound. It has
about the same value as wood. The corn itself has
somewhat higher value, which shows it to have a more
complex molecular structure, and is correspondingly
less stable.

In like manner an egg, say that of a hen, possesses a
degree of stability that does not belong to it after it
has begun to grow. It may be kept with some care
for a few months and retain its ability to develop into
a chick; yet it ultimately wholly loses its possibility,
which shows that slow changes of the nature of disintegration
are going on that cannot be arrested. The
physical condition necessary to initiate the growth of
the egg is simply one of temperature. One hundred
and four degrees continued for three weeks completes
the process. When one reflects upon the nature of
heat,---that it is but vibratory motion,---he can at once
see that energy has been supplied to a complex mass
of matter and it has been chemically transformed.
There are new chemical products and new properties
produced; and however wonderful the completed product
may be, the factors at work to produce it have been
absolutely physical from beginning to end. After
growth has once begun the process must continue, at
the peril of quick degeneration on stopping; so that an
egg, like the grain of corn, seems to be a material
structure where life may begin, rather than a living
thing itself. Such a distinction has not, however,
been made in the literature of the development of living
things. It has, perhaps, only a philosophical importance;
\DPPageSep{309.png}{294}%
but, if there are any who would still hold that
life is a something \textit{sui generis}, that may be considered
apart from some material structure and not as a transformation
process, it will be well for such to inquire
what can become of such life as a grain of corn or an
egg has when either of them is cooked, or when either
of them is left for months or years and they rot. At
first it is in the grain of corn or egg. If it be an entity
of any sort it must be somewhere else after leaving
either the one or the other. On the other supposition
the question does not arise at all, for it is plain that
disintegration destroys the molecular arrangement, and
with the destruction of that the properties of such
organizations of matter must go also; for the properties
of a mass of matter are, by general agreement, the
result of the arrangements of the matter. Woody fibre
and starch are of precisely the same chemical composition,
but the properties of the two are far from being
identical.

What, then, is the distinction between what is called
living and dead matter? One is able to transform
energy for its maintenance, and the other seems to be
wholly inert; yet, if analyzed, both may be reduced to
precisely the same amount of elements.

An analogy may make the distinction plainer. A
maker of physical instruments may make what is called
a Toepler-Holtz electrical machine. It is composed of
wood and glass and brass and tinsel and tin foil, and
possibly of other materials. Each one of these is got
at a different place from the rest, and all are assembled
in the shop of the maker. The individual parts are
\DPPageSep{310.png}{295}%
\index{Fields, physical}%
\index{Fields, thermal}%
\index{Physical fields}%
shaped in particular ways, and these are at last fixed in
their appropriate places. The machine is done; but it
has never generated an electric spark, and one could
discover no electricity about it. Indeed, there is none,
any more than when the material was unshapen and
lying upon his bench. If the proper kind of energy is
spent upon it, however, it at once becomes electrified,
and electrical energy may now be got from it in indefinite
quantity, dependent wholly upon the proper turning
of the crank. If that be turned the wrong way, or
if it be stopped, the electricity soon quite disappears.
Now, it is the function of such a machine to transform
mechanical energy into electrical, and it does this so
long as energy is furnished for transformation and the
integrity of the machine is maintained. If one weighs
the machine before it has been worked, and also while
it is electrified, he will find no difference. If the brass
buttons get off or displaced, if the belt gets broken or
the glass cracked, the machine will weigh just as much
as it did when they were in place; but the property of
the machine to transform energy will be destroyed, and
it may be as useless for the purpose as a coffee-mill
would be. One might speak of the whole machine as
an organism,---its wood and glass and brass as its molecular
composition, its function depending upon each
of these being in its appropriate place, and nothing
more. It can only exercise that function when energy
of the proper sort is turned into it. If its molecular
composition is deranged in any of a dozen different
ways, no one is surprised that it no longer responds to
the turning of the crank. If the complete and perfect
\DPPageSep{311.png}{296}%
machine be called living, then the one with its
parts disarranged so it can no longer perform its functions
might be called a dead machine.

The egg may be likened to the machine. So long as
its molecular arrangement is intact, so long it is competent
to transform the heat supplied to it and exhibit
new properties. When the molecular arrangement is
interfered with, whether from within or without, its
function as transformer ceases, and we call it dead.

It may be said, and often has been, that every living
thing has an ancestry of living things; and in human
experience it is true. It is sometimes said that one
cannot get out of a mass of matter what is not in it,
which, in this case, might imply that matter itself is
alive, as suggested a few pages back, though I have
never heard any one so conclude. If one would apply
this dictum, let him settle with himself before turning
a new electrical machine whether the electricity he is
to get from it is or is not in the machine, and how, if it
be in the machine, he can get an infinite amount from
it by simply turning the crank. He may reach the conclusion
that what can be got out of a mass of matter
depends upon its composition and structure.

In conclusion, one perhaps can do no better than to
quote the words of Dr.\ Michael Foster, Professor of
Physiology, University of Cambridge, England, as to
the properties of protoplasm. ``The more these molecular
problems of physiology are studied, the stronger
becomes the conviction that the consideration of what
we call structure and composition must, in harmony
with the modern teachings of physics, be approached
\DPPageSep{312.png}{297}%
\index{Electrical field}%
\index{Fields, electrical}%
under the dominant conception of modes of motion.
The physicists have been led to consider the qualities
of things as expressions of internal movements; even
more imperative does it seem to us that the biologist
should regard the qualities of protoplasm (including
structure and composition) as in like manner the expressions
of internal movements. He may speak of
protoplasm as a complex substance, but he must strive
to realize that what he means by that is a complex
whirl, an intricate dance, of which what he calls chemical
composition, histological structure, and gross configuration
are, so to speak, the figures; to him the
renewal of protoplasm is but the continuance of the
dance, its functions and actions the transferences of
the figures\ldots. It seems to us necessary, for a satisfactory
study of the problems, to keep clearly before
the mind the conception that the phenomena in question
are the result, not of properties of kinds of matter,
but of kinds of motion.''

If such be the case, it is clear that the solution of
every ultimate question in biology is to be found only
in physics, for it is the province of physics to discover
the antecedents as well as the consequents of all modes
of motion.
%\DPPageSep{313.png}{298}%


\Chapter{XII}{Physical Fields}{298}

\Section{I.---THE THERMAL FIELD}

\First{When} a mass of matter of any kind possesses
energy of such a kind as to be able to impart some or
all of it to the medium about it, whether that medium
be the air or the ether, which transmits or distributes
it outwards with a velocity which depends solely upon
the ability of the medium to transmit energy, and not
upon the source of it, the energy so distributed is
called radiant energy.

The term was first applied to the energy radiated by
a hot or luminous body, from which the heat was said
to be radiated away, the motions of the molecules of
the hot body being transformed into wave motions in
the ether. The wave motion thus set up is known to
be competent to set other masses of matter upon
which it falls into vibratory molecular motions, similar
to those that originated the waves. In other words,
they are capable of heating other matter. The space
within which such effects can be produced will evidently
be limited only by the distance to which the
wave motion is transmitted, and this in turn depends
upon the special medium concerned---in this case the
ether---and the uniformity of its distribution. As has
\DPPageSep{314.png}{299}%
\index{Inductive action}%
been already pointed out, the ether transmits such
wave motions in straight lines, and to an indefinite
distance,---so great at least as to require not less than
five thousand years to cross the space accessible to our
observations. As such waves of all wave lengths
travel with equal velocities, and as all known bodies
of matter are continually radiating waves of many
wave lengths, it follows that in reality every molecule
of matter sets the whole visible and invisible physical
universe in a tremor. The magnitude of this effect is
not now under consideration.

The space external to a body within which the body
can act in this physical way upon other bodies, so as to
bring them into a condition similar to its own, is called
its \emph{field}. The heat or thermal field of a mass of
matter of any size and of any temperature must,
therefore, be as extensive as the universe, unless the
ether absorbs the energy to some extent and becomes
itself heated. At present there is no evidence that
such an effect is produced. Some astronomers have
inferred that absorption takes place, else the whole
surface of the sky would be bright with the multitude
of stars that occupy it. On the other hand, if absorption
did take place in a manner at all comparable
with gaseous absorption, it would be selective in some
degree, and the more distant stars would have a color
different from those closer to us; and the colors of all
stars would depend upon their distance from us. If
such a condition had been observed, it would be conclusive
evidence of absorption in the ether, but it has
not been observed.
\DPPageSep{315.png}{300}%
\index{Earth, a magnet}%
\index{Electrical waves}%
\index{Magnetic field}%
\index{Waves, electric}%

Furthermore, the perception of light implies a definite
though a small amount of energy; and, as the
energy of ether waves from a given point upon a
surface varies inversely as the square of the distance
from the point, it follows that there must be some
distance from it where the energy upon the retina
must be too slight to affect it; and hence the inability
of the eye to perceive the light could not be
used as an argument against the existence of the waves
altogether. At the rate of $186,000$ miles per second
light travels $5,800000,000000$ (nearly six millions of
millions of miles) a year, and in five thousand years,
which is the distance of some of the more remote
stars, $29000,000000,000000$ (twenty-nine thousand
millions of millions) of miles. This, therefore, is the
known length of the radius of the thermal or light
field of a heated or luminous body; and, as such heat-producing
waves are radiated in every direction about
the body, the sphere having such a radius represents
the space within which any or every atom of matter
can affect other atoms to heat them.


\Section{II.---THE ELECTRICAL FIELD.}

The phenomenon called electrical induction, by
which one body becomes electrified by simply being
in proximity to another body which is electrified, is
another illustration of both a \emph{field} and its property,
depending altogether upon its origin. But an electric
field differs in a marked way from a thermal field.

Imagine a sphere---say a cannon-ball---to be electrified,
and be isolated a long way from any other body.
\DPPageSep{316.png}{301}%
Its effect upon the ether about it would be equal in
every direction. Practically, it would be distributed as
the thermal field would be; and, if the strength of the
field should be measured in any way, it would be found
to vary inversely as the square of the distance from
the body that produced the field. When such an electrified
body is adjacent to other bodies, as is necessarily
the case with every electrified body upon the
earth, the strength of the field at a given point is
found to depend upon the size, the nearness, and the
quality of the adjacent body. Suppose the adjacent
body were a similar cannon-ball, and its distance from
the former one foot. Then the strength of the field
would be found to be greatest between them, and to be
very weak in the space equidistant and on the opposite
side. One may get a mechanical idea of the condition
of things by imagining straight lines drawn from the
electrified body when out in space as if they were rays
of light, evenly distributed in space. When, as in the
second case, another ball is near to it, these rays crowd
around the second one and apparently are absorbed by
it; and these may now be represented by the same
lines, starting at the same places as before, but sweeping
in curves to the second, with only here and there
one to escape into the unoccupied space. The nearer
the two are together the more closely are these lines
crowded together in the space between; and, as the
number of these lines in a given area represent the
strength of the electric field, it is plain the field is
strongest where the lines are most crowded. On the
other hand, if the second ball had been made of glass,
\DPPageSep{317.png}{302}%
\index{Chemical field}%
\index{Fields, chemical}%
the field would have been changed but little, for glass
is a substance having but little absorptive power for
electric rays; that is, it is not much affected by an
electric field. When such an electrified ball is suspended
in an ordinary large room, these lines, representing
the field, are distributed about the room in a
manner that depends altogether upon the kind of
material there is in the room. The metallic objects,
such as a stove, a steam-radiator, a gas-pipe, and the
like, will divide the field between them, not equally,
for the nearer ones will have the most, and other parts
of the space in the room will have but a trace of it.
The great distinction between the electrical and the
thermal field will be apparent when one reflects upon
what the latter would be for the same cannon-ball made
hot and suspended, in the same manner, in the room.
The rays go straight in every direction, and are not
deflected by proximity to other bodies. The one is
uniform in every direction about it; the other is warped
by the presence of other bodies.

An electric field, which is merely the ether in a
condition of stress, electrifies the bodies upon which it
acts; that is to say, it produces in them a condition
similar to that of the body that produced the field. It
does not heat them: it electrifies them. The process
is ordinarily called induction. If one would follow
mentally the mechanical conditions and changes that
take place when this process of induction takes place,
let him imagine the two cannon-balls suspended in
a room a few feet apart, and one of them to be
suddenly electrified artificially in any kind of a way,
\DPPageSep{318.png}{303}%
\index{Crystallization}%
as by connecting it to a charged electrical machine for
an instant. The re-action upon the ether will at once
begin. The stress into which it will be thrown will be
propagated outwards as a wave, with the velocity of
light, and equally in every direction about it too, until
the advancing wave reaches the second ball, when the
absorption so reduces the stress that other parts of
the field can move towards it, thus distorting it; for
at the outset every part of the wave moved in a radial
line. This must be the case unless the field acted
intelligently instead of mechanically, and knew where
it was to go beforehand. Of course no one would
suppose that, but the remark is made to emphasize
the necessity for the mechanical steps in order to have
clear ideas of what has happened. The whole would
happen in so small a fraction of a second that it would
be exceedingly difficult to measure it, but the rate at
which a thing is done does not necessarily modify the
way of doing it.

\Section{III.----THE MAGNETIC FIELD.} %

The distribution of iron filings about a magnet gives
one a very definite mechanical conception of the shape
and properties of a magnetic field. It has before been
remarked that the shape of the field depended upon
the form of the magnet, and when this was altered the
field changed its form. That it too represents a condition
of the ether seems unquestionable. That it is produced
by the arrangement of the molecules of the magnet
is also certain; but that presumes that the atoms
themselves are magnets, each having its own field.
\DPPageSep{319.png}{304}%
\index{Mechanical field}%
When these atoms are either in disorder or so arranged
as to mutually cancel each other's field, there is no field
observable. When they are made to all face one way,
their individual fields will conspire to produce a resultant
field, which will be strong in proportion to the
number of such individual fields that make it up. The
nature of this magnetic field is probably a kind of
whirl or spiral movement in the ether between the
two poles of the magnet; but, as two similar adjacent
whirls or lines are mutually repulsive, they spread out
into space indefinitely, and are almost always curved.
The earth as a great magnet has such a field, the lines
reaching from the north polar regions upwards and
southwards, re-entering the earth by similar downward
sweeps in the south polar regions. How far away
from the earth some of them may extend no one
knows, but there seems to be no reason why they
should not extend as far as any ray of light. There is
good reason for thinking that the other members of the
solar system are magnets, especially as iron and nickel
are so abundant in the sun and in the meteorites that
reach us from space. If that be the case, they are all
moving in each other's magnetic fields. As the movement
of a conductor in a magnetic field produces an
electric current in the conductor, and as what are known
as earth currents, apparently due to some extra terrestrial
source, are well known, their origin is accounted
for. But, when there is iron in a magnetic field, the latter
acts upon it so as to compel it to produce a field of
its own. In other words, it makes a magnet of the iron.
The process is called magnetic induction. Like the
\DPPageSep{320.png}{305}%
other cases, it is a two-step process. There is, first, the
magnet with its molecular arrangement; second, the
action of the magnet upon the surrounding ether; and,
third, the re-action of the ether upon the second body,
making it a magnet. The heat field heats a body, the
electric field electrifies a body, the magnet field magnetizes
a body; and each of these fields may exist separately
or simultaneously, and each do its own characteristic
work, quite independent of either of the
others: so the same body may become magnetized, electrified,
and heated at the same time by the same medium,
acted upon by three different sources. The magnetic
field is more selective in its action than either of
the other two. A heat field will heat any kind of matter
in it if it be solid or liquid; an electric field will
electrify all bodies to some degree, but solid conducting
bodies to the highest degree; while the magnetic field
magnetizes only iron, nickel, and cobalt appreciably,
and the two latter but to a very small extent. The
point of chief importance here is the function of the
field itself to produce, in a certain kind of elementary
solid matter, a molecular disposition and arrangement
similar to that of the body which produced the field.

\Section{IV.--THE CHEMICAL FIELD.} %

The phenomena attendant upon the combination of
atoms into molecules, and molecules in cohering together
to form larger masses, make it certain that each
atom has a peculiar field, which, for a name, may be
called its chemical field, within which it acts upon the
\DPPageSep{321.png}{306}%
\index{Attraction, gravitative}%
\index{Gravitation}%
ether about it, and which extends to a distance from it
many times the diameter of any atom or molecule.

Chemists have concluded that there is really no distinction
between what has been called chemical attraction
and cohesive attraction; such, for instance, as enables
a drop of water to adhere to a surface, or glue to
hold wood surfaces together.

Crystals are built up of similar cohering molecules
arranged in a definite order. And these molecules exist
as independent bodies while in the solution before
being crystallized, and consequently each molecule must
have some degree of attraction for others; and this is
about the same as saying that there is an ether stress
about each one that depends upon its temperature, for
crystallization cannot take place in a solution above a
definite temperature. But one of the best evidences of
a chemical field of the sort is found in the fact that a
solution of a given crystallizable salt has its process
easily initiated by putting in a small crystal of the same
kind of a substance. Moreover, the mere presence of
certain kinds of molecules among others is sufficient to
bring about chemical changes which otherwise would
not occur; while the catalytic body, as it is called, is not
changed. This is the case with starch, which is converted
into sugar by the mere presence of sulphuric
acid, which undergoes no change. This is apparently
inexplicable, unless it is admitted that molecules of all
sorts have fields which, in one degree or another, control
chemical combinations. This has been treated of
at some length in the chapter on chemism. Its signification
here is to point out again that the field of similar
\DPPageSep{322.png}{307}%
\index{Growth}%
molecules is of such a sort as to compel within it an arrangement
of atoms into similar molecules, and molecules
into similar positions, as exhibited by crystals of
any sort. It is, therefore, another example of the property
of a physical field to bring about in a mass of matter
within it the same kind of physical phenomena as
that which induced the field.

\Section{V.--THE MECHANICAL FIELD.} %

A sounding body sets up air waves that travel outwards
radially from it in every direction to an indefinite
distance. Such periodic waves are capable of making
other bodies vibrate at the same rate as the original
body. When the second body has the same specific
rate, absorption takes place, the amplitude of vibration
increases, and the case is known as one of sympathetic
vibration. When the specific rate is different from
that of the recurring waves, there is more or less interference,
and this case is called forced vibration. In all
cases, however, the second body is made to vibrate by
the sound waves that fall upon it, whether the medium
be the air or any other substance, solid or liquid. And
the space within which such effects are produced is the
field of the first or sounding body. If one considers
simply the air as the medium of the field, it will be
perceived that sound waves travel in every direction in
it, and to distances unlimited except by the presence of
the air itself. Of course, the farther the distribution
goes on the less energy there will be to any cubic inch
or any other dimension, and there must be some limit
\DPPageSep{323.png}{308}%
\index{Thought transference}%
where the energy is too small to affect the organs of
hearing; but such a limit ought not to be considered
the actual limit of sound vibrations or the field of the
sounding body. There is no reason for doubting that
every sound vibration of every kind and degree is distributed
throughout the whole earth and its atmosphere,
and more than that: as the impact of molecules in
sound vibrations results in heating them to a higher
temperature, increased radiation into space follows, and
the consequent energy in this form must affect in some
degree every particle of matter in the universe upon
which it falls. It is plain how far-reaching almost every
act and movement of every kind must be.

A sound vibration, being a to-and-fro movement of a
mass of matter, may easily be great enough to be seen,
as in the case of a tuning-fork or a piano string; and,
therefore, it is treated as being mechanical as distinguished
from molecular: but even where the sound
vibration is too slight to be seen as an actual displacement,
it can give to another body a large amount of
visible motion, as when a suspended marble is held
against a sounding tuning-fork, or as when a paper
windmill is held over a sounding Chladni plate.

The motion of a sounding body being mechanical,
the field it produces may be called the mechanical field,
because the effect of it upon other bodies is similar in
kind to that which produced the field. There are, therefore,
five well-defined modes of physical action,---heat,
electricity, magnetism, chemism, and sound,---which, in
the past, have often been called physical forces, each
one of which affects the medium about it, producing
\DPPageSep{324.png}{309}%
\index{Hair-cloth loom}%
\index{Machines}%
either a stress or a motion, or both---conditions that
travel outwards into space indefinitely, and constitute as
many different physical fields. They may all co-exist in
the same space without interference, and each one produces
upon other bodies of matter within it the same
physical condition of motion, position, or arrangement as
that which initiated the field itself. So the established
relation deserves to be called a law better than many
relations that are called laws, but are such only within
rather narrow limits (as, for instance, the law of Charles
and \DPtypo{Boyles}{Boyle's} Law), inasmuch as this law of physical fields
is as universal as gravitation.

What is called gravitation might be included in this
list, for every particle of matter attracts every other
particle near or far; so every atom has a gravitative
field as extensive as the universe, and there is no more
interference between it and the other fields than there
is between any of them. The chief distinction between
the gravitation field and all of the others is that
they are all artificially\DPtypo{,}{} variable while gravitation is not
known to be, though some phenomena indicate the
possibility of it.

It follows, from the foregoing, that every object large
or small is continually affecting the space about it in
several different ways,---through its temperature, electric
and magnetic conditions, as well as by its various
movements; and it also follows that the shape of a body
as well as its molecular arrangement determines whether
the field shall be symmetrical or otherwise. A crystal
certainly has a symmetrical field, but it cannot be
turned over in the hand without affecting in some degree
everything outside of it.
\DPPageSep{325.png}{310}%

If it be true for certain collocations of matter that
external form and molecular arrangement determine
the existence of its field, it is difficult to imagine why
it should not hold true for all cases,---a cell structure
for instance, in which case the organization of a similar
cell in adjoining space where the proper material for
construction exists would only be in accordance with
the physical properties of fields in general; and the
phenomenon of growth would be as definitely understood
as the growth of a crystal. This is not demonstrative;
but it is in accordance with everything else we
know, and is what would be predicted by one who knew
the properties of physical fields, though he had no
knowledge of cell growths.

To take one step more, yet not to go beyond the domain
of physics: It is as certain as any physical fact
can be that every movement of an individual---change
of attitude, gesture, or expression of countenance---must
produce a corresponding change in his field, and
tend to bring about in others similar movements; and,
even if such phenomena are not observed in every one,
it is no more of an argument against the existence of
the operative conditions than is the failure to perceive
through the sense of feeling the sound vibrations produced
by a speaker's voice, when it is certain the whole
body is in a state of tremor; and the effect of sympathetic
speech is more largely physical than has been supposed.
Strong emotions, or the physical semblance of
them by skilful actors, re-act in the same physical way.
This is not saying there may not be other factors, but
the purely physical ones are present and act in the way
\DPPageSep{326.png}{311}%
\index{Motion, transformations of}%
described. The term ``sympathetic action'' was applied
to physical phenomena when it was discovered to be a
mode of action quite analogous to mental phenomena
between individuals in which similar mental states are
induced.

Lastly, so far as mental action depends upon brain
structure, any changes in the latter must produce corresponding
changes in the brain field, and there must
be a brain field if there be any truth in the foregoing;
the conclusion is inevitable. Other similar structures
must be affected in some degree by them, and whether
such induced changes be able to induce similar brain
changes with the accompanying mental phenomena or
not must evidently depend upon the possibility of
synchronous action.

This is not to be understood as asserting that such
thought transference as is implied in the foregoing actually
occurs. All that is asserted is that the physical
conditions necessary for such transference actually
exist, and one who was acquainted with the properties
of physical fields would certainly predict the possibility
of thought transference in certain cases.
%\DPPageSep{327.png}{312}%


\Chapter{XIII}{On Machines.---Mechanism}{312}

\index{Push and pull}%

The common notion of a machine is that it is an implement
designed for doing this or that: as, for instance,
a loom is a machine for weaving cloth or carpets; a
steam-engine is a machine for driving machinery; a
water-wheel, for utilizing the power of water; and so on.
Some of these structures, built for specific purposes, are
highly complex, and many of their parts stand in curious
relation to each other, and altogether they may be able
to produce results that seem but little short of intelligent
action. Looms weave out beautiful fabrics with
artistic designs in colors, when furnished with only the
bare threads. The hair-cloth loom draws with iron fingers
a single hair from a large bundle of hairs. If it
fails to grasp one, another and another attempt is made
until one is seized, and meanwhile the rest of the machinery
waits. If it seizes more than one, as sometimes
happens, it drops both and tries again, the rest of the
apparatus waiting as before, exhibiting a kind of deliberativeness
and consciousness of what it is about that
one hardly looks for through any combination of wheels,
ratchets, levers, and the like, such as make up a complex
machine. Every one knows that by far the larger
number of things in common use which were formerly
\DPPageSep{328.png}{313}%
made by hand tools are now made by machinery more
rapidly and oftentimes more perfect than they could be
made by hand. The parts of clocks and watches are
so made; papers are printed, folded, and directed at
the rate of ten thousand in an hour by one machine;
grass is mown, grain is cut, threshed, and winnowed by
one machine as fast as it can be driven through the
field; shoes, toys, and beautiful pictures are thus made
by the million, and there is no department of human
effort but is dependent upon mechanism of some kind.
In many cases the entire work is thus done automatically,
as when pins and needles are made from the wire,
sharpened, polished, counted, arranged in papers, and
folded ready for the market. There is no field independent
of such aids. Even music is absolutely dependent
upon it, and all that is called sentiment and feeling
in it are resolvable into degrees and directions of movements
for the production of sounds; and there are no
movements of muscles but may be duplicated by automatic
mechanism. If the effects produced by mechanism
to-day are not the effects wanted, it only shows
that the mechanism has not been perfected, not that it
cannot be done.

If one considers the almost infinite number of processes
needed for the maintenance, conveniences, comforts,
and tastes of what is called civilized life, it might
seem as if an almost unlimited number of physical conditions
would be necessary; but let such an one recall
the fact that all kinds of motions are reducible to not
more than three fundamental kinds,---translatory, vibratory,
and rotary,---and he will be prepared to trace
\DPPageSep{329.png}{314}%
\index{Lever}%
\index{Pulley}%
the most complicated movements to these elementary
forms.

In the chapter on motion, only the kinds of motion
were considered; but here it is proposed to point out
the conditions under which motion is transferred from
one place to another, and how these elementary forms
are transformed into each other. For convenience, the
term ``mechanical motion'' will be employed for all having
visible magnitude, but simply on the ground of visibility,
not because there is any other distinction between
such motions and those of a molecular or atomic kind.

When one pushes against a paper-weight on the table
and it moves in consequence, no one is surprised, for
the movement is expected. If the weight were free to
move and it did not move, no matter how strong the
push, one would have reason to be surprised, because
such a phenomenon is not in accordance with the
experience of mankind. If one billiard-ball in contact
with another one received a push in direction toward
the latter, the latter would be moved in the same direction,
and the motion of the second one would be explained
by saying it was due to the push of the first
upon it. Suppose there were ten or a hundred such
balls in a line. If the end one was pushed towards the
rest of them, they would all move, the farthest one as
much as the first, as the movement imparted by push
to the first would be handed on step by step to the last.
If the balls were glued together at their points of contact,
that would make no difference in this transfer of
motion by contact; and, if there were a thousand or a million,
or any other number, there would be no difference.
\DPPageSep{330.png}{315}%
\index{Work, measure of}%
Neither would there be any difference if the separate
balls were no bigger than molecules. A rod of wood
or metal is entirely made up of a great number of cohering
particles, and, when a push is applied to one end,
every particle is pushed as much as the end particles.
If there was a row of thin rubber balls and the end one
was thus pushed, the side would be flattened somewhat,
and the opposite side in contact with the next adjacent
ball would push against its neighbor and each be flattened,
and so on, till the last one was reached, which
would be pressed on one side but not on the other, and
would, therefore, be like a single ball pressed upon one
side. The intermediate balls would act as transferrers of
pressure from one end to the other. The rubber balls
so flattened by pressure will recover their form when
the pressure is removed, and the same may be said of
a rod of any material, the difference in this particular
being only one of degree. The same process takes
place when one pulls upon a rod. It is to be remembered,
however, that in either case the transmission of
the pull is not instantaneous for any distance, however
short. Time is requisite, and hence there is a rate of
propagation of such motion in all bodies, which depends
upon the degree of elasticity and the density of the
material; and this rate cannot be exceeded, no matter
how great the initial push or pull. This rate is about
sixteen thousand feet per second for steel and the most
elastic woods, and is about eleven hundred feet per
second for air. If one inquires what the condition is
that initiates motion in any given body, it will be found
to be a push or a pull, and either of them may be measured
\DPPageSep{331.png}{316}%
in pounds. The chief distinction between a push
and a pull lies in the relative position of the moving
power and the body being moved by it. In the push,
the body being moved leads in the line of movement;
in the pull, the moving power leads. When a locomotive
goes ahead of the train, it pulls; if the train goes
ahead, it pushes. A stiff rod or bar may be used for
either a push or a pull, but a rope can be used only for
a pull, for when pressure is applied to it longitudinally
it bends at right angles to the direction of the pressure,
and so fails to act in the right direction. A rod can
transmit a push or pull only in the direction of its
length, while a rope may rest on a pulley and the pull
may act upon any other body in the same plane the
pulley turns in. If a pressure of ten pounds be applied
as a push at one end of a rod or bar, the whole of that
pressure may be transmitted to the other end. The
same may be said of the pull either with a rod or rope,
but neither rod nor rope can possibly transmit and give
up at the one end more than is applied at the other.
For this reason, a rope hanging over a pulley will hold
equal weights on its two ends. If a ten-pound weight
be tied to one end, the pull transmitted will be ten
pounds, which may be balanced by a pull either by
weight or in any other way on the other leg of the rope.
The function of a pulley is to change the direction of
the pull: it does not alter its amount.

\Section{MECHANICAL MACHINES.}

In the older treatises on natural philosophy, there
were described several machines which were called the
\DPPageSep{332.png}{317}%
mechanical powers, because their principles were embodied
in mechanical devices for transmitting pressure
or pulls. The \emph{lever} stood first among them. It consists
of a stiff rod or bar resting upon a point of support
for it called a fulcrum, and this fulcrum may be
placed anywhere between the ends of the bar. The
advantage or disadvantage of this machine depends
upon how near the fulcrum is to the body to be moved.
A stiff rod four feet long supported at its middle would
be balanced if it were of uniform dimensions. If a
weight of ten pounds was hung at one end, an equal
weight or pull would be needed at the other end to
balance it. If one weight fell one foot, it would do ten
foot-pounds of work in raising the other ten pounds
one foot. In any case the work done, measured in
foot-pounds, will be the same at both ends of the bar or
lever.

The lever changes the direction of motion or the
amount of pressure, but does not change the amount
of work measured in foot-pounds.

The simple \emph{pulley} is a device for changing the direction
of a pull, as seen in the apparatus for raising merchandise
to higher levels in buildings; but by far the
most extensive use of it is in the transfer of a continuous
pull from one place to another through the agency
of belts of leather or other pliable material.

This combination of pulley and belt is adaptable to
many places and purposes, as well as permitting great
ranges in speeds of rotation by simply making the diameters
of the pulleys proportional to the differences in
rotation wanted. It is the chief agency in machine-%
\DPPageSep{333.png}{318}%
\index{Transformations of motion}%
shops, factories, etc., for distributing the power to the
various machines. By crossing the belt the second
pulley can be made to turn in the opposite direction.

In all the ways in which it is serviceable, it is plain
that it cannot deliver more of a push or a pull than is
given to it any more than can a lever. There is no
gain of energy or work by its use, but always some loss,
because friction uses up some of the working-power in
other than useful ways. The \emph{wedge}, the \emph{inclined plane},
and the \emph{screw} are but simple devices for utilizing push
or pull; but there are other means also employed for the
same purpose; for instance, the pressure of the air or
other gas, and steam. Windmills are made to turn by
the pressure of the wind upon the inclined blades, and,
by forcing air into pipes, an increased pressure may be
transmitted for long distances and then used. The
reason this method of using air is not in more general
use is that when the air is compressed it heats. The
heat it loses soon if conveyed in pipes very far, and as a
consequence its pressure is very much reduced, so it is
not an economical thing to do. Water-wheels utilize
the pressure of water, and the amount of work it can do
is definite and easily calculated. If at a waterfall a
hundred pounds of water falls ten feet, then it can do
$100 \times 10 = 1,000$ foot-pounds of work; that is, it can
raise $1,000$ pounds a foot high, and so on for any other
amount. A perfect water-wheel that did not let slip
by any water without its doing its work would give up
practically $1,000$ foot-pounds. Really, the best water-wheels
give but about ninety per cent of \DPtypo{the-working-power}{the working-power}
of the water. So-called water-motors are but properly
\DPPageSep{334.png}{319}%
constructed wheels enclosed in the pipe through
which water is made to flow with considerable pressure.
In the cases of air, steam, and water power there is the
condition we call a push, which may be measured in
pounds; and a push measured in pounds multiplied by
the distance in feet through which it is maintained is
the measure of work.

In each of the cases, the air, or steam, or water,
as it moves on and does its work, gives up the motion
it has; and the substance itself, being no longer of use,
is allowed to escape as a waste product. Such bodies
have been sometimes called \emph{prime-movers}.

So far has been considered only the apparatus in
common use for transferring motion of one body to
other bodies, but frequently it is important to have the
\emph{form} of the motion changed from the kind it may
chance to have at the outset to one better adapted to
the special end desired.

In a sewing-machine, for instance, the particular
movement of the needle must be vibratory. The
treadle has a similar movement, but not rapid enough;
so there is arranged between them a series of movable
parts, which not only \emph{transfers} a certain amount of
motion, but the latter is \emph{transformed} into appropriate
forms. The vibratory motion of the treadle is transformed
into the rotary motion of the balance-wheel,
this into swifter rotation of the pulley by means of a
belt; then by lever and cam the needle receives its
proper kind of motion, the shuttle a similar one at
right angles to that of the needle, and the other moving
parts such forms of motion, and rates of motion, as
\DPPageSep{335.png}{320}%
are needful for their special kinds of work. In a steam-engine
the constant pressure of the steam is made to
act upon the alternate sides of a piston, giving it a
vibratory motion, which must be transformed for most
purposes into rotary; and this is effected by means of a
crank, which is, therefore, a device for transforming vibratory
motion into rotary, or \textit{vice versa}. When the
driving-wheels of a locomotive are made to rotate, their
adherence to the track carries the whole structure forward;
that is, the rotary motion is transformed into
translatory. In the stationary engine the rotary motion
of the balance-wheel is transferred to a pulley by a
belt, and the shafting transfers this through its whole
length to other pulleys. If the reader will follow back
to its antecedents any particular motion he may think
of, he will see that the function of each movable part of
a machine of any sort is to transfer push or pull, or
transform one kind of motion into another kind. However
complex a machine may be, it does no more.

It is to be noted that \emph{what} a given thing will or may
do depends altogether upon what kind or form of
motion it has, not upon how much motion or energy
it has. For instance, a bullet might spin on some axis
on the table before one, and have great rotary velocity
and energy, yet be perfectly harmless; whereas, if it
had the same amount of energy with the motion translatory,
it might be destructive to anything it struck.

\Section{MOLECULAR MACHINES.}

If one of the functions of a machine be to transform
the kind of motion it is supplied with into some other
\DPPageSep{336.png}{321}%
kind of motion,---translatory into rotary or vibratory,
any one into either of the others,---one may be prepared
to follow mechanical processes from masses of
visible magnitude into molecular magnitudes, and thus
note the antecedents of the new phenomena that
appear.

When a gas is condensed by pressure the individual
molecules have less free space to move in, and they
consequently collide with each other more frequently.
Being elastic, their average amplitude of vibration is
increased proportionally, and a greater number of them
will strike with greater velocity upon the walls of the
containing vessel per second than before. Thus the
temperature and the pressure of the gas are increased.
We say that mechanical energy has been converted
into heat energy, or sometimes simply into heat,
though what has really happened has been the transformation
of external translational motion into internal
vibratory motion, which the elasticity and mobility
of the molecules permit. When by friction or percussion
a body is heated, the same thing precisely
has happened: translatory motion has been transformed
into vibratory, through the agency of the
molecules, which have, therefore, acted as machines for
transformation.

In like manner the reverse transformation may take
place in several ways. When the increased vibratory
motion of the molecules produces an increased pressure
upon the movable head of a piston in an engine, the
piston as a whole may move and do work. Also, when
the molecules strike harder upon one side of a surface
\DPPageSep{337.png}{322}%
than upon the other side, the surface moves toward
the side of less pressure, as with the radiometer; so
that both engine and radiometer are machines for
\index{Machines}%
transforming vibratory molecular motions into translatory
mechanical motion.

When the temperature of steam is raised to about
$5,000°$~F., the amplitude of vibration is so great that the
atoms can no longer cohere in the molecules, and they
become separated into the gases hydrogen and oxygen;
and again vibratory motion is transformed into translatory,
which in gases is called free-path.

Heat is also largely derived from the chemical properties
of coal, wood, oils, gas, and other substances
called fuel. As the heat is derived from some antecedent
condition which is not heat, it follows that the
stove or furnace is a machine for transforming into
heat motions those motions which constitute and are
the measure of chemism.

When heat is applied in any way to the face of a
thermo-pile, electricity may appear which may be made
to do work in many ways. The vibratory motion disappears
as such,---that is, it is annihilated,---while an
electric current appears as its substitute. The thermo-pile
is, therefore, a machine for the transformation of
heat into electric current. If heat be a kind of molecular
motion, then an electric current must be some
other kind of motion!

When the armature of a dynamo is turned and an
electrical current is developed, the latter is the representative
of the mechanical movement of the armature.
It takes more power to make it move at a given
\DPPageSep{338.png}{323}%
speed when it is producing a current than when it is
not. The current represents the difference. It is mechanical
motion that goes into the dynamo, and an
electrical current comes out of it; and hence a dynamo
is a machine for the transformation of mechanical into
electrical motion. One is visible, the other molecular,
as is the case when friction develops heat.

An ordinary static electrical machine possesses a
similar function.

On the other hand, a galvanic battery transforms
chemical into electrical motions; and, in every case
where electricity is developed, there is some sort of
apparatus which receives one kind of motion for transformation.
That one kind of machine will transform
mechanical motion, a second heat, a third chemical, all
into the same kind of a product, helps one to see that
the antecedents, which at first seem to be so unlike,
are really but varieties of the same condition, namely,
motion, which, when transformed by suitable machines,
might be expected to appear as a similar product of
each.

An electrical current always heats the conductor
through which it passes. It is, therefore, an antecedent
for the production of heat in the same sense as mechanical
motion is an antecedent in condensation, percussion,
and friction; and the conductor is the agency for
the transformation into the vibratory molecular form.

So far as the production of light by electricity is concerned,
whether by the incandescent or the arc system,
the function of the current is to raise the temperature
of the conductor to the proper degree for luminousness.
\DPPageSep{339.png}{324}%
The light comes from the hot molecules, not from the
electricity; but here, as in the simpler case of heating
the conductor, the conductor itself, whether it be a filament
of carbon or the tips of the carbon rods, acts as a
transformer of electrical into heat motions, and thence
to ether waves.

Ether waves may be transformed in two different
ways. First, by falling on molecules of matter; the
latter absorb them, and are heated in consequence,
which is the converse of the production of ether waves
by heated molecules. Second, by their own interferences
plane, elliptical, and spiral waves may be produced,
which resultant waves are capable of affecting matter
in different ways. One of these consequences is of so
much theoretic importance it will be well to allude
to it.

Given a flexible section of a spiral ether wave, no
matter what its origin. If its ends were to come together,
there is good reason for thinking they would
close and weld together, forming a ring, which would
then be practically a vortex ring. The ends of vortex
rings formed in the air will do thus, so if the atoms of
matter are really vortex rings, as has been supposed,
the above suggests how they may originate, or how
matter is created.

All the different kinds of phenomena which are generally
attributed to different forces one may readily
trace to these antecedents; namely, matter, ether, and
motion of various forms. The condition necessary for
a new phenomenon to appear is that the present forms
of motion in either matter or ether needs to be transformed.
\DPPageSep{340.png}{325}%
Atoms and molecules, as well as large masses
of them, which we call bodies of visible magnitude, act
as machines for the transferrence and the transformation
of motion; and one might define a machine as a \emph{collocation
of matter having for its function the transferrence or
the transformation of motion, or both}. An atom and a
molecule, then, are as much machines as a steam-engine
or a dynamo; and every molecule in the universe,
whether near or remote, is constantly receiving and
transforming energy through its individual motions.
What the particular phenomenon will be in a given
case depends upon the form of the motion received by
the mechanism and the new form which the latter has
made it to assume. As before remarked, what a given
mass of matter will do depends upon the kind of motion
it has.

So far nothing has been said about the relation of
these mechanical principles to living things,---animals
and plants; but it will be obvious to every thinking
person that unless, when matter assumes the forms exhibited
by such living things, it surrenders its mechanical
properties and relations, then such transformations
must be going on constantly in all living things. Mechanical
motions, chemical re-actions, heat, and so on,
ought to be expected from such complex machines as
animals. Foods, as fuel, air, and water, are physical
factors which imply metamorphosis; and the forms into
which the factors will be changed depend upon the
special mechanism provided. Hence, an animal is a
complex machine for the transformation of motions of
various sorts, the sum of them being what are called
the phenomena of life.
\DPPageSep{341.png}{326}%
\index{Solar system}%

The foregoing analysis shows that what have heretofore
been considered as forces in nature are non-existent;\DPnote{** Only instance.}
that all phenomena in the different fields of
physics are simply and plainly mechanical; and that
an application of the laws of motion, as presented by
Sir Isaac Newton, supplemented by the laws of ether
action, is sufficient to account for all kinds of phenomena:
and therefore the supposition of particular forces
of any kind is entirely unnecessary. What have been
called forces are but various forms of motion, of matter,
or of the ether, each embodying energy; the particular
phenomenon a given body may produce depending
upon its size and the particular quality of motions it
chances to have. Granting this, one may at once perceive
that expressions implying higher and lower forms
of force are misleading. No one is higher in dignity or
importance than any other one. Let one ask the question,
Which is higher, vibratory or translatory motion?
and he will see the absurdity of the language.

If one will bear these principles in mind, they will be
helpful in unravelling phenomena which otherwise may
appear to be very puzzling. For instance, one may frequently
come across the statement that one cannot get
out of a machine what is not in it or put into it. Is it
so? Coal is put into the furnace, and heat comes out.
Mechanical motion is put into a dynamo, and electricity
comes out. A current of electricity is turned into an
arc lamp, and light comes out. The character of the
product thus depends upon the form of the machine
and its relation to some antecedent factor. The physical
\DPPageSep{342.png}{327}%
\index{Physical universe a machine}%
knowledge we have enables us in most cases to
trace and understand the metamorphosis. In some
cases the molecular changes are not so completely
known in detail, yet the quantitative relations between
what goes in and what comes out of the machine are so
definite that one is warranted in asserting that no other
factors are present than the one considered. In one
sense the product of any machine is like its antecedent,
if both be but kinds of motion, or forms of energy as
some prefer to say; but if one assumes that these
various forms of energy differ in any way from forms
of motion, or that they have distinct individualities,
then one can get out of a machine what he does not put
into it. What seem to be more unlike than the mechanical
movements of a steam-engine and the electricity
of the dynamo? One is simplicity itself; the
nature of the other, its product, has been the despair of
philosophers for generations. The subject is of fundamental
importance chiefly because some philosophers
have evolved their schemes without duly considering
these obvious relations.

However much a given phenomenon may differ in
character from its known antecedents, no good reason
can be assigned for thinking that, when properly analyzed,
it would be found resolvable into other factors
than matter, ether, and motion. Furthermore, there is
no evidence that any one of the physical forms of
motion is or was necessarily prior to any other. As
there is no hierarchy among them, no one of them can
be called primal. A linear arrangement does not
\DPPageSep{343.png}{328}%
\index{Matter, as modes of motion}%
properly represent their mutual relations. They are
more like a closed ring of interrelations thus:---
%[Illustration: ]
\begin{center}
  \Graphic{2.5in}{343a}
  \Figlabel{35}

  {\scriptsize Diag.\ 35.---Forms of Energy.}
\end{center}

The visible universe may be considered as a vast
machine, within which motions are being exchanged
by contact and by radiation. It is not the absolute
amount of energy a body may have which determines
whether it shall give or receive, but it is the degree
it has of a given kind of energy. Thus it is the temperature
of a body that determines for it whether it
shall gain or lose heat in the presence of other bodies.
The whole tendency is towards equalization of conditions,
and for this reason some philosophers think they
foresee the end of this act in the drama of the solar
system. The possibility of the variety of phenomena
that gives interest to existence depends upon the fact
that at present matter is in an unstable condition, and,
when uniformity of condition is reached, there will be
an end to changing phenomena. Astronomers have
figured out that in five or ten millions of years the sun
\DPPageSep{344.png}{329}%
\index{Cohesion, in solids and liquids}%
\index{Matter, states of}%
will have radiated away so much of his energy that the
earth will no longer be habitable. Perhaps so; but it
is certain that the whole solar system is drifting in space
somewhere at the rate of seven hundred millions of
miles a year, and in one million of years it may reach a
region in space where the present rate of loss might be
greatly reduced. In that time it will have travelled
three times the distance to the nearest of the fixed
stars. It could hardly be where its expenditure would
be greater than now. If it should drift into one of the
great hydrogen regions such as are numerous in the
heavens, not only would the supply of energy be renewed
indefinitely, but the earth would become uninhabitable
in an hour. At any rate, there is no guarantee
in nature for permanent stability, supposing that stability
should be attained; for simple mechanical impact
between the sun and any of the millions of stars would
not only annihilate the earth as such, but would so
reduce to a nebulous mass the matter that now composes
the solar system that the whole process of world
formation would have to be gone through with again.
The sudden blazing out of stars here and there in the
heavens shows that similar physical processes are taking
place elsewhere in the universe. Such an end is
quite as probable as the refrigerating one referred to;
for there is implied in the latter not only that the present
conditions in the solar system will continue, but
that the environment of the solar system will remain
for so many millions of years what it is. The matter
is not alluded to here on account of its humanitarian
\DPPageSep{345.png}{330}%
\index{Cohesion, destroyed}%
\index{Gas, motion in}%
interest, but to point out that in either case the results
will be due to purely physical conditions. What mankind
would contemplate as a dreadful catastrophe would
be but the interaction of huge machines, where energy
was transformed on a grand scale, and no particle of
matter omitted for an instant to conform to the three
laws of motion.
%\DPPageSep{346.png}{331}%


\Chapter{XIV}{Properties of Matter as Modes of Motion}{331}

\index{Gas, free path in}%
\index{Gas, pressure in}%

In the first chapter of the book only the most
obvious qualities of matter are considered, such as
magnitude, density, inertia, and so on, the properties
which are exhibited by masses of matter of visible
magnitude and form, from which the common notions
concerning its nature and possibilities have been derived.
If one stops his inquiries concerning the properties
of matter with these, and imagines that they are
the ultimate properties, and may rightly be assumed
and asserted of the individual atoms, he will be greatly
in error; for it is not difficult to show that nearly
every property of masses cannot be true of atoms, and
that nearly if not quite all material properties of what
we call matter, are derived from antecedent conditions,
and are resolvable into them or into mere relations
which are not inherent, and may be absent. It is,
then, worth the while to study the real significance
of some of the physical terms in common use, in
order the better to eliminate from the mind unessential
qualities when thinking of the inherent qualities
of matter.

During the past ten years laboratory facilities for
physical investigations have greatly aided inquirers,
\DPPageSep{347.png}{332}%
\index{Heat, effects}%
and added much to real knowledge in this field. Some
of this knowledge is of such a character as will presently
make it needful for every one to reconstruct
his notions and explanations of physical phenomena,
in order to prevent hopeless confusion in his own
thinking.

\Section{THE STATES OF MATTER.}

Under the conditions of ordinary observations matter
is found in the solid, liquid, and gaseous states;
the solid state being that in which the molecules
cohere so strongly as not to be easily separated from
each other nor from the relative positions they have
assumed with reference to other molecules. Thus, a
piece of granite, as the type of a solid, may have its
molecules cohering to each other in certain positions,
so strongly as to require a ton's weight to pull apart
a section of one square inch.

The granite is made up of small crystals of quartz,
mica, and feldspar, each having a definite chemical
composition. The individual crystals retain their relative
places for an indefinite time, and the atoms of the
individual molecules retain their relative positions for
a like indefinitely long time, else the crystalline structure
would be lost, for crystalline structure implies
definite atomic arrangement as well as molecular
arrangement. So in solids the adjacent molecules
are in what are called stable positions, and are not
easily separated.

In a liquid there is little cohesion among the molecules,
and no stable arrangement at all. The individual
molecules move among each other without
\DPPageSep{348.png}{333}%
\index{Absolute zero}%
\index{Charles, Law of}%
\index{Chemism and heat}%
\index{Chemical reactions depend on temperature}%
\index{Gas, pressure in}%
\index{Gas, destroyed}%
\index{Matter, effect of temperature upon}%
apparent friction, and the slightest force acting upon
them makes them to turn on any axis; and there is
good reason for thinking that in a liquid like water,
the individual molecules are continuously rolling and
tossing about with perfect freedom to move in every
direction. The phenomena of diffusion exemplifies
this. There is also good reason for thinking that the
individual atoms in the water are continuously changing
partners at a rapid rate, so if there were some
means for identifying the atoms of hydrogen and oxygen
in a given molecule, they might be seen presently
all separated and forming temporary constituents of
other molecules a relatively long remove from the first
position where they were observed. When the water
is frozen, that is has become a crystalline solid, this
freedom of atomic change and molecular rotations is
no longer recognized as a property. Molecular cohesion
is now exhibited where before there was none.
There are also new qualities called crystalline, hardness,
density, and so on, which before this change did
not belong to it. The new qualities which seem to
have been developed are produced by lowering the temperature
of the water, that is, reducing the amount
of kinetic energy the molecules had; and by again
imparting a like amount to the ice \emph{both crystallization
and cohesion are destroyed}.

A gas is a body of molecules in which the individuals
are free to move in every direction unconstrained by
any degree of cohesion, and where they are in frequent
collisions, bounding away in new directions through
distances usually many times the diameter of the molecules
\DPPageSep{349.png}{334}%
themselves. Thus, in air the ordinary average
distance between impacts is nearly two hundred times
the diameter of the individual particles which, as before
stated, is in the neighborhood of one fifty-millionth of
an inch. Their continuous bumping against each other
and the walls of the containing vessel, produces what
is called the gaseous pressure. Increasing the temperature
of the gas increases the velocity of movement
in the free path, and, consequently, the momentum and
the pressure. It has been customary to say that heat
increases the elasticity of a gas, that a gas occupies
the whole space which encloses it, that a gas has a
tendency to indefinite expansion, and that the properties
of a gas are due to repulsive force among the
molecules. In a loose sense such expressions may be
allowed, but they are not to be understood as correctly
specifying the qualities of the gaseous matter. It is
not repulsion that makes a ball move which has been
struck by a bat, but impact; and that it should continue
to move on until it strikes another body, follows
from the first law of motion, as true for a molecule of
a gas as for a baseball. The direction the ball takes
depends upon where it is hit, as well as upon how hard
it is hit; the velocity it has depends upon how hard it
is hit, and there is nothing peculiar to a gaseous particle
requiring the affirmation of different properties.

Some years ago improved methods of making a
vacuum were adopted, by which one could reduce the
amount of gas in a tube to even the hundred millionth
of its ordinary amount, so that a particle might have a
relatively long free path measurable in feet instead of
\DPPageSep{350.png}{335}%
\index{Diamond, hardness of}%
\index{Hardness not atomic property}%
hundred thousandths of an inch, and the phenomena
of such rarefied gases were so new and surprising that
it was at first conjectured that a new state of matter
had been discovered, and it was called the fourth or
ultra gaseous state to distinguish it from the others;
but it was soon perceived that it was still only rarefied
gas, and that no new qualities had been developed, and
the same phenomena witnessed in the rarefied gas were
present in the denser, only disguised by the greater
number of molecules which took part. So what was
called for a short time the fourth state has been
practically abandoned.

The three states already considered are known to
depend upon temperature. Thus, if ice or iron or
many other solids be heated they become liquid; if
heated still more they become gaseous. Some solids,
like wood, when heated do not assume the liquid intermediate
form, but are at once converted into a gas;
but different substances have different temperatures at
which they change from one form to the other. Thus,
water becomes a solid at $32°$~Fah., and a gas at $212°$~Fah.
Iron becomes fluid at~$2,800°$ and gaseous at~$6,000°$. So
far, then, it appears one might as properly speak of
iron as a liquid or a gas, as of water as either, if they
both may exist in the three conditions, and no temperature
is specified. We do not do that, because when
speaking thus ordinary temperatures are implied, but
seldom or never thought of. If one had been brought
up in the sun it is probable he would never have seen
a solid, and if at the moon, he would know of neither
liquid nor gas.
\DPPageSep{351.png}{336}%
\index{Color, nature of}%

But the pressure of a gas is caused by the impact of
its molecules, and is proportionate to the temperature.
The law of Charles states what has been found to be
true within the limits of experiment; namely, that the
volume of a gas is proportionate to its absolute temperature;
that is, temperature measured from an absolute
zero, in which case, it is plainly to be seen, at
absolute zero the \emph{gaseous} volume would be nothing.
It does not imply that the matter of the gas would be
annihilated, but that the matter no longer existed in
its gaseous form; the individual molecules would no
longer have any free path motion, but would fall to
the floor of the containing vessel, and thus remain
quiescent, like so much dust. \emph{At absolute zero there
would be no gas.}

Again, in the chapter on Chemism it is shown how
chemical reactions are determined by temperature, and
cannot take place in the absence of heat. The late
experiments of Pictet and Dewar show that as temperature
is lowered chemical reactions become weaker
and weaker, until some of the elements that have very
strong affinities at ordinary temperatures, and so combine
with energy, are incapable of combining, and
appear inert at such low temperatures as can now
be artificially made without great difficulty. Their
experiments confirm the conclusions given on \Pageref{page}{242};
namely, that at absolute zero chemical affinity
does not exist. Molecules would not only fall apart,
but their individual atoms would no longer exhibit
any cohesive quality; and this, it will be perceived,
would render the existence of such a thing as either
\DPPageSep{352.png}{337}%
\index{Impenetrability}%
a liquid or a solid quite impossible, for each requires
chemical action for both molecular formations and
cohesion in any degree. Every kind of a structure
would crumble to atoms in a literal sense. Book,
tower, mountain, ocean, as well as every living organism,
would completely disintegrate, and lose every characteristic
property which had belonged to it. Hence,
such qualities of matter as would be absolutely emptied
out of it by simply reducing its temperature, cannot
be considered as essential qualities. Yet when the
atoms were thus deprived of what seems to us as all
their useful qualities, there is reason for thinking they
would still have definite form, mass, gravitation, magnetic
and electric qualities which, however, by themselves
could not make the mass of matter we call the
earth a habitable place, nor give to life a material
habitat as it now has.

It is then plainly evident that what we call solids,
liquids, and gases, with all the laws that belong to each
of them, are simply the relations of heat energy to
groups of atoms, not the properties or laws that may
be asserted of the atoms as such, and do not need to
be considered by one who is inquiring for the essential
endowments of matter.

There remains, therefore, an examination of the
other so called qualities to see if, perchance, they
too may not, in a similar manner, be resolvable into
energy relations, which, in turn, may be absent.
\DPPageSep{353.png}{338}%
\index{Elasticity}%
\index{Elasticity due to motion}%

\Section{MOLECULAR AND ATOMIC QUALITIES.}
\Subsection{(HARDNESS.)}

Substances vary greatly in what is called hardness,
and this properly serves, in many cases, to distinguish
one mineral from another. The mineralogist employs
a scale of ten, differing in degree from talc which is
the softest, to diamond which is the hardest, and with
these all other minerals are compared. But the mineralogist
tells us that this scale does not represent hardness
in any proportional way, because diamond is as
much as ten times harder than the ruby which stands
next to it in the scale; also that some diamonds are so
much harder than others, that no means has yet been
discovered for grinding and polishing them.

The diamond, however, is crystallized carbon, yet carbon
exists in another crystalline form called graphite,
or plumbago, which is soft, and may be whittled with
a knife, while coke, charcoal, and lampblack are forms
of precisely the same element, and these vary through
the whole range in hardness. What, then, does hardness
mean? Evidently it signifies the resistance
offered to the separation of molecules from each other.
It is the measure of their cohesion, and could have no
existence in a single molecule of carbon. Furthermore,
as has been pointed out, as molecular structure
can have no existence at absolute zero for lack of
energy needed for maintaining cohesion, \emph{hardness cannot
be a property of atoms at all}.
\DPPageSep{354.png}{339}%

\Subsection{COLOR.}

Color, either simple or compound, is exhibited by all
masses of matter---for white is but a mixture of wave
lengths, and no object is so black as to be invisible.
Gold is yellow, copper red, lead is bluish. The petals
of flowers, the feathers of birds, the gorgeous dyes of
the chemist, seem to impress us with an assurance that
color is a real quality of some kinds of matter, and can
be affirmed of it without any qualifications. Bodies
become visible either by their own luminousness as
when they are hot or phosphorescent, or by the light
reflected by them from some other source, as is most
commonly the case. When sunlight falls upon a rose
it is to be remembered that the sunlight is what we
call white light; it is made up of all wave lengths which
we can see. The rose petals absorb some of these
waves,---the blue, the green, and the yellow, but not
the red; these are rejected by the surface, and they
therefore are reflected away, and testify to the selective
power of the petals, \emph{not their color}, as can be found
by holding the same rose in yellow or blue light, when
it will appear black, that is, will absorb all offered to it
and reflect little or none. Again, when a body is self-luminous,
as, for example, a piece of burning sodium
which gives out a yellow light, it is to be kept in mind
that the yellow rays are produced by certain vibratory
rates which the atoms are compelled for the time
being to make, but which the atoms will not make
except on compulsion, that is, the high temperature
which the heat energy gives to it, and therefore does
\DPPageSep{355.png}{340}%
not represent what can be called the color of the body---only
an artificial state of vibration. Lastly, if all
substances whatever were at absolute zero in temperature,
they would be setting up no ether waves of any
length, and could not effect any organ of vision, and,
consequently, would not only show no color, but would
be absolutely invisible. \emph{Hence color cannot be affirmed
of atoms.}

\Subsection{IMPENETRABILITY.}

It has seemed to nearly every one who has given
thought to the subject that what is called impenetrability
must be a fundamental property of matter;
that it was axiomatic, if anything could be, that two
masses of matter could not occupy the same space
at the same time. This has been believed to be
true, not because it was demonstrable, but because
it seemed to be reasonable. Maxwell, however, calls
it a vulgar opinion. He further takes the pains to
say, If hydrogen and oxygen combine to form water,
we have no experimental evidence that the molecule
of oxygen is not in the very same place with the two
molecules of hydrogen.\footnote
  {See Art. Atom.\quad Encyc. Brit., 9th ed.}

When it is possible to make one, a mechanical model
is often of great assistance in helping one to conceive
of conditions which are more or less difficult to describe
in mere words; and a mechanical model that
embodies this possibility of the coexistence of two
atoms in precisely the same space may easily be made.
Roll up a length of wire into a loose helix or spiral of
any convenient length---say two feet long. Cut it in
\DPPageSep{356.png}{341}%
\index{Hertz waves}%
\index{Magnetic waves}%
\index{Tesla ether waves}%
two parts of equal length, and bend the ends of each
round until they touch, and fasten them thus, so as to
have two rings made of spirals of wire. Each one may
be taken as representing an atom of matter somewhat
similar to a vortex ring, which has been assumed as
\index{Vortex ring model}%
the probable form of the atoms of matter. Each has
form, size, and various other qualities, but if one of
them be pressed down upon the other it will be found
they will make room for each other, so that \emph{as rings
they both occupy precisely the same space}. This is not
given here as anything more than as, possibly, a
helpful suggestion as to how a seemingly impossible
condition may be true. Evidently in this case the
difficulty lies in the assumption that an atom of matter
is a hard, impenetrable, geometrical solid, and, as Maxwell
says, there is no proof that such is the fact.
\emph{Impenetrability is an unwarrantable assumption.}

\Subsection{ELASTICITY.}

Elasticity has been assumed to be a fundamental
property of atoms, and so not derivable from physical
conditions underlying it; but Lord Kelvin has shown
good reason for thinking that elasticity is a derived
quality, for it is possible to construct models which
exhibit the phenomenon in a high degree while they
are in motion, and not at all while they are at rest. A
number of gyroscopic disks set whirling on a circular
axis, shows this in a remarkable way, and suggests on
inspection, that something like such an arrangement
may be the complete explanation of the quality as
exhibited by atoms. A vortex ring may be considered
\DPPageSep{357.png}{342}%
\index{Inertia}%
\index{Mass}%
as a large number of revolving disks on a circular
\Pagelabel{342}% [** PP: Best guess at page anchor]
axis, which will give to the ring not only rigidity, but
stability of form, any departure from which will be
resisted by the mechanical structure, and it will return
to its original form after the deforming stress has
ceased, with a rate depending upon the rate of rotation
of the constituent
%[Illustration: ]
\begin{wrapfigure}[15]{l}{1.375in}
  \Graphic{1.375in}{357a}
  \Caption{36}{Diag.\ 36.}
\end{wrapfigure}
parts of the ring. On \Pageref{page}{40}
reference is made to the behavior of a rotating disk,
and how it simulates this property of elasticity. The
common gyroscope may be cited as exhibiting it in a
\index{Gyroscope}%
manner that depends upon the
way in which the disk is mechanically
mounted.

An ordinary whirling disk can
be freely moved only in its plane
of rotation, or planes parallel to
that. Any attempt to change
the angle of the axis is mechanically
resisted. This may be understood
by reference to diagram
where $a$~$b$ is a disk capable of
rotation on axis $c$~$d$. While rotating,
it can move freely in the
plane $a$~$b$, but any attempt to tip
the axis in any direction will be
resisted by it. Imagine, then, a large number of similar
disks, mounted on a circular axis, as in diagram~36,
each one rotating. It is plain that any attempt to tip
the ring in one direction or the other, or to change
the form of the ring itself, supposing it to be flexible,
will necessarily change the plane of some of the revolving
\DPPageSep{358.png}{343}%
disks, and will be resisted as a whole, for the
same reason that one of its parts will do the same. It
will be seen that if all these disks be rotating in the
same direction the movements will be like those of a
vortex ring. If additional disks could be inserted
upon the axis, so as to form a continuous body quite
round the circular axis, it would constitute a ring;
and if the proper rotation were set up, it would possess
all the qualities of a vortex ring, and elasticity
would be a prominent quality, as stated on \Pageref{page}{39}. It
is no longer necessary, if it ever was, to assume elasticity
as a fiat quality, imposed upon atoms which
might have existed without it; \emph{for the laws of motion,
acting in a properly constructed mechanism, are quite
sufficient to produce it}.

\Subsection{MAGNETISM.}

On \Pageref{page}{205} the statement is made that magnetic
phenomena have led to the belief that all atoms of
all kinds of matter are magnetic, and are only obscured
in ordinary matter by the molecular arrangements
which tend to neutralize the magnetic fields of the
individual atoms. Attention is again invited to the
diagrams on \Pageref{page}{105}, with the accompanying description,
in order to freshly bring to mind how vortex
motion necessarily produces what is called polarity---the
two sides of the ring have different qualities.
On one side the movements are all inwards, on the
other outwards, and from these the phenomena of
apparent attraction and repulsion necessarily follow.
But beyond this, once\DPnote{** PP: Missing "we"?} assume that individual atoms
\DPPageSep{359.png}{344}%
\index{Gravitation}%
are magnets by virtue of their constitution, and that
every magnet has a magnetic field infinite in extent,
within which it can affect other atoms, one can see
at once that every atom in creation has a magnetic
hold upon every other atom, because every one is
in the magnetic field of every other one. This effect
is not necessarily one of attraction or repulsion tending
to move one mass towards or away from another;
but, on the other hand, it tends to rotate each on an
axis so both shall face the same way. So long as
there is no change in position or in \emph{form} of such a
magnet, the magnetic field will be uniform; but if the
form be changed in any way the whole field has to
change in conformity with it, as described on \Pageref{page}{252},
and such vibrations as constitute the heat of an atom
are really the change in form of the atom, and this,
therefore, changes necessarily the whole magnetic
field of the vibrating body. These changes in the
field, which originate in this way, are what are called
ether waves. When the waves are produced slowly,
by an alternating dynamo current, or more swiftly by
some of the methods so ingeniously devised by Hertz
and Tesla, they are called electro-magnetic waves.
When produced so swiftly as to have a wave length
only the one thirty-thousandth of an inch, they have
been called heat waves; and when the waves are so
short as to be capable of affecting the retina of the
eye, they are called light waves, though there is no
distinction between any of them except in their length.
The vibrations of the atomic magnet are rapid because
it is small; the waves it produces are changes in
\DPPageSep{360.png}{345}%
\index{Gravity follows from structure}%
its magnetic field in the ether, so one may trace
back in this manner the phenomena of light, of heat,
and electricity, to the mechanical structure of atoms;
and it is mechanically intelligible too, and, like the
preceding accounts of properties, it appears \emph{that magnetic
and electric qualities are due to the peculiar kinds
of motion embodied in the atoms}, and cannot be considered
as particular endowments of a something called
matter, which it might have been without.

\Subsection{INERTIA.}

The inertness of matter has been touched upon on
\Pageref{page}{70}, and here may be added the consideration of
what interpretation could be put upon such phenomena
as are exhibited by such a device as is represented by
diagram 36, supposing it were enclosed in a box so one
could not see the mechanism? The box enclosing it
would exhibit a new quality of the nature of inertia,
by virtue of the motions within it, which it would lose
as the friction diminished the rate of motion, and
when this stopped altogether the property would no
longer be present. \emph{Hence, inertia, too, must be looked
upon as probably due to motion.}

\Subsection{MASS.}

Mass, as a property of matter, is generally defined
as the amount of matter considered, and is measured
by what is called acceleration, that is, the velocity
it acquires in a second when acted on by a constant
force or push. Amount of matter is a very indefinite
expression, but is often convenient, and seldom misleading
\DPPageSep{361.png}{346}%
\index{Atoms, as vortex rings}%
when one is considering a given weight of a
substance.

One may speak of a pound of iron or of hydrogen
as a mass of iron or of hydrogen, meaning a definite
weight made up of a very large number of molecules
of one or the other element; but if one will think of
the atoms of these, and endeavor to form an idea of
what can be the physical meaning of mass, when applied
to one of them, he will at once see that the term
carries with it no conception whatever of the physical
difference between atoms of different kinds. An
atom of iron is said to contain fifty-six times the mass
of an atom of hydrogen, while an atom of gold has
a hundred and ninety-six times the mass of the hydrogen
atom, and all the elements differ in mass in the
ratio of their atomic weights. Can any one suppose
for an instant, that an atom of gold is a hundred and
ninety-six times larger than an atom of hydrogen?
There is some evidence that atoms differ somewhat
in magnitude from each other, but none of any such
difference as is represented by their atomic weights.
Furthermore, this would imply that atoms were blocks
of some primeval stuff of uniform quality, and that
atoms of a given element were but uniform volumes
of it; and it hardly needs to be said that such a view
is negatived by all we know, for the properties of the
various elements do not vary simply with their weights,
as would be the case if they were thus constituted.
Hence, mass as applied to atoms cannot be thus conceived.
It is possible to form a conception of the
physical meaning of mass as applied to atoms or
\DPPageSep{362.png}{347}%
molecules, by recalling the phenomenon of rigidity
in position, which is the outcome of rotations, as described
on pages \Pageref{}{40}~and~\Pageref{}{342}, for the amount of effort
needed to move such a rotating body depends not
simply upon the amount of rotating material, but its
velocity of rotation; so a small amount of material
with a high speed may offer as great a resistance to
movement from its position as another much larger
amount of material with corresponding slower rate,
but otherwise the two would necessarily have great
differences in their other properties; thus their rates
of vibration would be very different, because their
degrees of elasticity would be different.

One may then assume that such differences between
\emph{the atoms of the elements as are called their masses,
are due to the relative rates of rotation}. This, of
course, on the fundamental assumption that the atoms
themselves are vortex rings such as we have argued as
being highly probable.

\Subsection{GRAVITY.}

There now remains to be considered one more
general property of atoms and all combinations of
them; namely, their gravitative property. If one be
content to say that not enough is known about it
to warrant even a tentative opinion, and, therefore,
refuses to draw any inferences from what is known
as to what gravitative property is, or is like, one
need to have no quarrel with such an one; but if,
on the other hand, one is interested in fundamental
questions, and thinks that whatever be the truth
\DPPageSep{363.png}{348}%
\index{Hertz waves}%
\index{Materialists}%
about gravitation or any other unsolved problem, when
it is known, it will be seen to be in harmony with
every other physical truth, and will, therefore, be a
consistent part of the body of physical knowledge
which we now possess, such an one will perceive that
with the banishment of the old notions concerning the
structure of matter, with its endowments of sundry
properties which might have been otherwise, or that
the matter we know might have had entirely different
properties, must also go the notion of quality endowments
in any such sense as was formerly held. He
will also have good reason for holding it altogether
probable, that if the other properties of matter are
reducible to modes of motion, so the last one in
the list will be found to be reducible to the same
factor. If the others have been interpreted thus, one
after another yielding as molecular phenomena became
better understood, he will conclude that if the problem
of gravitation has not been solved, as the others
have been, it is not because it is insoluble in itself, but
because it is inherently more difficult, or has not received
the degree of attention that has been given to
other problems since conservation has been discovered
and forms a part of every discussion.

One thing seems certain, if the vortex-ring theory
of matter be true, or anything like it, then gravity
must follow from the structure; for in the absence of
any evidence of the existence of gravitation in the
ether, no one is at liberty to postulate it there for
the sake of finding it in the atoms. It must be looked
for as due to the particular kind of motion that constitutes
\DPPageSep{364.png}{349}%
\index{Ether phenomena not explained}%
the atom, and is constant because that motion
is constant.

In the chapter on gravitation is given a mechanical
conception of gravitative conditions which, whatever
may be its inadequacy, is consistent with other physical
knowledge. Faraday, as is well known, made
several efforts to discover some relation between
gravitation and electricity, but only negative results
were reached. He was not discouraged by his lack
of success, and had planned still other experiments,
which he was not able to finish. He always worked
on some hypothesis almost always radically different
from the hypotheses of his scientific contemporaries,
and time has vindicated his rather than theirs; and
that there must be some physical relation between
the two classes of phenomena was one of his, and so
it seems to-day; for if gravity be due to the form of
motion in the atom, and if an electric current in a
circuit represents a real vortex ring, having the conductor
for its core, then it seems likely there is some
gravitative effect between such current and the earth;
but it may be so slight with a single circuit as to not
be detectable with present means, and the mutual gravitative
effects between two such circuits would be
obscured by their electro-magnetic effects.

Lastly, if the atom itself be a vortex ring, as
explained in the chapter on the ether, it follows that
in the absence of such form of motion there would
be no atom---no matter, though the substance out of
which the ring was constituted would exist, but without
any of the characteristics that we assign to matter
\DPPageSep{365.png}{350}%
\index{Laws not compulsory}%
\index{Miracles possible}%
\index{Phenomena, unexplained}%
in any of its forms. If one chooses to call a common
smoke-ring \emph{alpha}, evidently when the ring is dissipated
there is no more ring, there is no alpha, it has been
annihilated as a ring; and in like manner, one may
understand that what constitutes an atom is not so
much the substance it is composed of as the motion
involved in it. Such \emph{an atom is a particular form of
motion of the ether in the ether}, in the same sense
as what is called light is a form of motion of the
ether in the ether. One is an undulation, the other
a vortex. One we call an ether wave, the other we
call matter: both involve energy, and both have properties.
Thus, one after another of the properties of
matter are found to be resolvable into ether motions,
ether being the primal substance, and matter only one
of its manifestations.

Such a conception of matter as is here presented,
resolving as it does all its physical properties, even
itself, into modes of motion of the ether in the ether,
is not simply a new conception of matter, it is rather
a revolution in fundamental conceptions, and if trustworthy,
necessitates an abandonment of nearly every
notion concerning them which men have entertained
when thinking and discoursing upon the subject.
The mystery of phenomena is not lessened but made
greater by the discovery that everything which affects
our senses in every degree is finally resolvable into a
substance having physical properties so utterly unlike
the properties of what we call matter, that it is a misuse
of terms to call it matter.

No one in the past has been able to forecast its
\DPPageSep{366.png}{351}%
\index{Electricity, origin of}%
properties. The necessity for such a medium has not
been felt by many philosophers, and though there has
been some expectation on the part of a few, any new
\index{of}%
step has been a source of surprise. For instance, when
Hertz succeeded in producing electro-magnetic waves
in the ether only two or three feet long, it was heralded
as being a demonstration of the existence of the
ether, implying that all the phenomena of induction
and electro-magnetic waves developed by machines
vibrating up to four thousand per second in telephonic
apparatus, could have some other interpretation. The
point here emphasized is that the properties of the
ether and their relations to such physical phenomena
as have been the subjects of research are so little
known, that no one has yet ventured to embody them
in an all embracing philosophy, so as to deduce apparent
phenomena from them.

The significance of this will be apparent when one
recalls the various attempts of materialistic philosophers
to explain all sorts of phenomena as due to
matter and its properties. Some of them have been
ignorant of the existence of the ether; others have
grouped matter and ether together and called both
matter, and considered both as subject to the same
laws as are found to hold true for matter as defined
in this book. When it is apparent that such physical
views are radically unsound, that one cannot reason
from our perceptual matter to imperceptual ether,---for
it is true that there are no known nerves that
respond directly to ether action,---it will also be apparent
that any scheme of things that ignores this knowledge
\DPPageSep{367.png}{352}%
or fails to make proper distinctions here cannot
be entitled to respectful consideration. Indeed, such
physical materialism is less rational than ever, for it
ignores much knowledge now in our possession which
is as certain as any we possess, and it ignores the
trend of all the physical knowledge we have; for it
cannot be denied that the advance in knowledge which
has been so marked during the past half century has
been in the discovery of the simplicity of relations,
rather than towards ultimate explanation. It may
truly be said that, in a philosophical sense, nothing
has been explained. Familiarity with constant phenomenal
relations induces in us expectations of certain
happenings, and presently they seem obvious.
The car moves because the engine pulls it; the engine
moves because the steam pushes it; the steam
pushes because the heat pushes it; and the heat
pushes because---it is the nature of heat to do work.
In that way, every physical phenomenon runs at last
into an inexplicable, into an ether question; and the
necessity for it follows from nothing we know or can
assume. No one may assume for an instant that the
possibilities of ether phenomena are limited by such
interactions as have hitherto found expression in treatises
on physics. Indeed, there is already a body of
evidence which cannot safely be ignored, that physical
phenomena sometimes take place when all the ordinary
physical antecedents are absent, when bodies move
without touch or electric or magnetic agencies,---movements
which are orderly, and more or less subject to
volition. In addition to this is still other evidence of
\DPPageSep{368.png}{353}%
\index{Postulates of Physical Science}%
\Pagelabel{356}%
competent critical observers that the subject-matter
of thought is directly transferable from one mind to
another. Such things are now well vouched for, and
those who have not chanced to be a witness have no
\textit{a~priori} right from physics or philosophy to deny such
statements. Such facts do not in any way invalidate
physical laws, nor make it needful to modify present
statements concerning energy. Physical laws are not
compulsory; they \emph{rule} nothing; they are but statements
of our more or less uniform experience. If
these things be true, they are of more importance to
philosophy than the whole body of physical knowledge
we now have, and of vast importance to humanity;
for it gives to religion corroborative testimony of the
real existence of possibilities for which it has always
contended. The antecedent improbabilities of such
occurrences as have been called miracles, which were
very great because they were plainly incompatible
with the commonly held theory of matter and its
forces, have been removed, and their antecedent probabilities
greatly strengthened by this new knowledge;
and religion will soon be able to be aggressive with
a new weapon.
%\DPPageSep{369.png}{354}%


\Chapter{XV}{Implications of Physical Phenomena}{354}

\index{Fable, La Fontaine's}%

A physical phenomenon is a phenomenon which
involves energy. Every change of condition in matter
is brought about by the action of energy upon it in one
way or another. It may be gravitative energy or heat
or light or electric or any other; but every physical
change has a physical antecedent as well as a physical
consequent, and the explanation of any given phenomenon
consists in pointing out the precise antecedents that
brought it about. There is a common saying that like
causes produce like effects, but this is far from being
true in the popular sense. If it were true the development
of science would not be the difficult and painfully
slow process it has proved to be. Electricity may be
produced by turning a crank, by dissolving a metal, by
twisting a wire, by splitting a crystal, and in others
ways. The product is the same, but the antecedents
are so different that no one can tell by examining the
product how it was produced. If it became important
to know what caused the electrical phenomenon, it
would not be sufficient to know that electricity could
be produced in these different ways; one would need
to know the specific apparatus employed. The more
\DPPageSep{370.png}{355}%
complicated the phenomenon the more difficulty there
is in unravelling it.

So far as experiment and experience have led us, the
antecedents of every physical phenomenon are themselves
physical, and more than that, all reactions are
quantitative, that is, the product is proportional to the
antecedent, and this is sometimes embodied in what is
called the doctrine of the Conservation of Energy
which every one knows about.

The exchange relations between the different forms
of energy,---mechanical, thermal, chemical, electrical,
etc., which are so well-known, being quantitative, are
therefore mathematical. They have therefore become
a corporate part of the body of knowledge, and are no
longer subject to any questions as to their validity
under any circumstances whatever. One who should
challenge them would no more be deserving of attention
than if he should offer to prove he could square a
circle.

The fundamental postulates of physical science are
binding upon the one who understands them, for the
same reason that the multiplication table is. There
are no contingencies and no possibilities of hedging.
If any one of them could be overthrown the whole
body of science would go with it. This is said because
there are not a few who appear to think that
what is called physical science may not be so certain
as its advocates think, and that there may be factors
which have not yet been reckoned with that may quite
transform the whole scheme. Science is a consistent
body of relations, not simply a classified body of facts.
\DPPageSep{371.png}{356}%
\index{Blavatsky, Madam, pretensions of}%
\index{Guppy, Mrs.}%
\index{Power, needed for rapid movement in air}%
These relations have been discovered by experiment,
not by deduction.

Some of them are the following:---

 1. Physical changes affect only the condition of
matter, not its quantity. One cannot create or annihilate
it, nor can one element be changed into
another.

 2. Every atom is continually exchanging energy
with every other atom, the rate of the exchange depending
upon their difference in temperature.

 3. The different forms of energy are transformable
into each other, but the quantity of energy is not
altered by the transformation.

 4. Complex organic molecules differ from simpler
inorganic molecules in possessing more energy. The
differences in this respect are definite, may be measured
in foot-pounds, and are practically enormous.

5. Every physical change has a physical antecedent,
is therefore mechanical, and is conditioned by the laws
of energy.

These principles are the outcome of modern investigation,
the evidence for them is overwhelming, and
a working knowledge of them needs to be a part of
the mental equipment of every investigator, especially
of the one who takes it as his province to explain
phenomena.

Science is strong here if it is anywhere; and any
description of any event, any explanation of a genuine
phenomenon that practically ignores these, cannot be
true, and can have no claim to consideration.

Before any explanation is needed there is always the
\DPPageSep{372.png}{357}%
\index{Sound, origin of}%
\index{Spiritualistic theory}%
\index{Spirit disembodied}%
advisibility of ascertaining that the alleged event really
happened, and whatever is not professedly miraculous
must not be in discordance with the bast knowledge
we have.

With the above principles in hand one is prepared to
fairly judge as to whether a given statement is credible
or not. It is not necessary, as some seem to suppose,
that one should be able to explain a phenomenon if he
rejects the explanation of another one, or to assert with
emphasis whether a thing is possible, probable, or
impossible.

In La Fontaine's fable the philosophers were at the
theatre witnessing a play in which Ph{\oe}bus rose in the
air and disappeared overhead. They undertook to explain
the phenomenon. One says Ph{\oe}bus has an
occult quality which carries him up. Another says
he is composed of certain numbers that make him
move upward. Another says Ph{\oe}bus has a longing
for the top of the theatre, and is not easy till he gets
there. Still another says Ph{\oe}bus has not a natural
tendency to fly, but he prefers flying to leaving the
top of the theatre empty. Lastly, a more modern
philosopher thinks that Ph{\oe}bus goes up because he
is pulled up by a weight that goes down behind the
scenes. The last is an explanation. From a physical
standpoint the others are not simply inadequate explanations,
they are absolute nonsense. They make
the antecedents of a phenomenon involving energy,
factors that have no more relation to energy than has
moonshine to metaphysics. Yet there has been a large
number of men in all ages, men able in many ways
\DPPageSep{373.png}{358}%
too, who have ventured to explain phenomena in such
a \emph{non-sequitur} way, and who have spurned the mechanical
philosopher and his explanations.

In that class of phenomena called spiritualistic there
is a large body of reputed physical phenomena, vouched
for by large numbers of witnesses, such as the movements
of furniture, chairs, tables, books, pianos, etc.,
the playing upon musical instruments, guitars, accordions,
pianos, the appearance of lights, of faces, of
full forms clothed, of conversations with materialized
spirits, and so on, in great variety.

I suppose no one doubts that to move a body of any
magnitude requires the expenditure of energy, and to
do a definite amount of work requires always the same
amount of energy, yet I suspect there are many persons
who give credence to statements of occurrences
which practically deny the above proposition, thinking
it to be probable that spiritual agencies may have
control of powers that mankind knows nothing about.
This may be true enough, but the question is not as to
what this or that agency can do, but whether if spirits
do a certain kind of work it takes less energy than if a
man should do the same thing.

Whenever a weight or a resistance and a velocity
are given, it is always possible to compute the energy
spent to produce or maintain it. Let us study a case
or two. In olden times it was related that one of the
prophets was carried through the air by the hair of his
head from Babylon to Jerusalem. In later times it
was said that Mrs.\ Guppy was similarly transported
from Edinburgh to London. The distance is about $400$
\DPPageSep{374.png}{359}%
\index{Séances, phenomena at}%
miles, and if I remember rightly she made the transit
through the air in less than one hour. This makes the
velocity to be about seven miles a minute or $600$ feet
per second, which is three times faster than the highest
tornado velocity. The resistance offered by the air
to the movement of bodies in it is very well known.
Pressure in hurricanes has been observed as high as $90$
pounds per square foot, and as the pressure increases
with the square of the velocity, it follows that at $600$
feet per second the pressure per square foot would be
about $800$ pounds; and if the exposed surface of Mrs.\
Guppy was no more than six square feet, the total air
pressure must have been not less than $4,800$ pounds.
Now, the energy of this is found by multiplying the
pressure by the velocity per second.
\[
4,800 \times 600 = 2,880,000\text{ foot-pounds,}
\]
and as a horse-power is equal to $550$ foot-pounds per
second, it follows that it took not less than
\[
\dfrac{2,880,000}{550} = 5,236\text{ horse-power}
\]
to move Mrs.\ Guppy in that way at that rate.

It was reported when Madam Blavatsky was living
that she was in the habit of receiving letters from
distant correspondents, brought to her by some occult
agency and dropped upon her table. These letters
were said to have been written only a few minutes
before by persons living in the most distant parts of
the earth.

It takes but a little figuring to discover the amount
of energy necessary to do a work of this kind. Thus,
\DPPageSep{375.png}{360}%
\index{Light, a sensation}%
let the distance be $10,000$ miles, the time ten minutes.
The pressure per square foot due to such a velocity in
the air will be $17,000,000$ pounds, or $118,000$ pounds
per square inch. Assume but one square inch as the
area exposed to such a pressure, then the energy
needed to transport it with the speed of $16.6$ miles
per second, will be
\[
\dfrac{118,000 \times 5,280 \times 16.6}{550.} = 18,000,000\text{ horse-power.}
\]

Unless such packages were protected by occult
agencies also, they would be burned up before they
had gone the first mile of their journey.

The popular idea is that at death the spirit leaves
the body, but that it may, and often does, remain
in the locality, and is frequently in the presence of
its friends, unperceived by them, though occasionally
they may be seen and communed with through the
agency of certain preternaturally gifted persons called
mediums.

This proposition has so many physical data, and involves
so many physical implications, it will be worth
the while to look squarely at some of them.

1. A spirit is supposed to be a conscious entity dissociated
from matter, having ability to move at will and
to be more or less interested in what is going on in the
world, and capable of giving information on matters
remote from observation or the knowledge of men.
Suppose then such an entity, a disembodied spirit,
without a corporeal body, but anxious to be in the
neighborhood of its former friends. Seeing that it
\DPPageSep{376.png}{361}%
\index{Light, its nature}%
now has, according to this view, no longer a hold upon
matter, it has ceased to be in any way affected by
gravity and inertia, for these are attributes of matter.
Now the earth has a variety of motions in space; it
turns on its axis, so that a point on the equator is
moving at the rate of a thousand miles an hour. It revolves
about the sun at the rate of nearly seventy thousand
miles an hour, and with the sun and the rest of
the bodies that make up the solar system it is drifting
in space at the speed of sixty thousand miles an hour
or more, so that the actual line drawn in space by any
point upon the earth is a highly complex curve drawn
at the rate of upwards of a hundred and twenty-five
thousand miles in an hour. Now, any object whatever
keeping up with the earth, but without the help of
gravity, must maintain the velocity in space of not less
than a hundred and twenty-five thousand miles an hour,
and that is not all, as the movement is not in a straight
line, any such object wishing to keep in a particular
locality, say a room, would have to be on the alert constantly,
for the earth wabbles\DPnote{** [sic]} for numerous reasons and
what seems to us, who have bodies held by gravitation
to the earth, as so quiet and smooth running that we
are never conscious of the motion for an instant, is so
simply because gravity takes care of us. Once surrender
that and undertake to depend upon some supposed
private source of energy, and one would instantly
discover he had an engineering problem of a high degree
of complexity. If one assumes, as some have
done, that such spirit is composed of, or associated
with, some sort of matter, and that navigation is accomplished
\DPPageSep{377.png}{362}%
\index{Materializations and energy}%
by an act of the will, it will not change the
foregoing factors in the problem at all.

2. Suppose, as some have done, that disembodied
spirits lose their hold upon matter, and that they do
not remain at the earth. Then, if they remain at the
point where separation from the body took place, in an
hour the earth will have moved forward one hundred
and twenty-five thousand miles. But over the earth
there is certainly a death every minute all the time,
and such are left in the rear by the earth never to return
to them, for the movement of the earth is not a
circuit, but an apparently endless drift. Think of the
dead of the earth for the thousands of years since man
has lived upon it! On this view, the spirits might be
seen like the tail of a comet reaching backwards for
millions on millions of miles,---the trail of the dead.

In any view, time and space and energy cannot be
ignored or ruled out.

At \emph{séances} the reported phenomena are mostly of a
physical sort, the trance of the medium being a physico-mental
phenomenon. The phenomenon of sound implies
the expenditure of energy, it is a vibratory motion
of the air or other elastic body, and in order to produce
it some antecedent force must be spent; it may be produced
by mechanical means, or heat, or electricity, or
by the muscles. Its production does not imply any
specific method any more than articulate speech implies
a person, as Faber's talking-machine and the
phonograph prove.

Let us consider some of the more subtle phenomena
that are reported. First, as to so-called conditions.
\DPPageSep{378.png}{363}%
\index{Organic and inorganic matter, difference between}%
One of the primal ones of these for such phenomena as
the movements of bodies and materializations, is said
to be darkness. This is of so much importance that it
must be fully attended to. To one who has not paid
any attention to what has been done in molecular
science within the past fifteen or twenty years, the
phenomena of light may and probably do seem to be
due to an unique agency, as much as heat or electricity;
and therefore he looks upon light as he looks
upon the others in the hierarchy of the physical
sciences, and expects that in its absence a potent
agency or kind of energy is lacking. That this idea
and conclusion is all wrong will be apparent when it is
recognized that \emph{what we call} light is a particular sensation
in the eye, and that to produce the sensation
\emph{there is no one antecedent that is essential}. Press the
eye with the finger in the darkest night and one will
see a ring of light with great distinctness. An electric
shock, a bump upon the head, will also give one the
sensation of light, and in the absence of other aids to
a judgment no one could tell what was the antecedent
of a given light sensation.

Radiations from a luminous body, and reflections
from a non-luminous one, were not long ago thought to
consist of three different kinds of rays,---heat, light, and
actinic rays. It has been discovered that there is no
such distinction in fact. What a ray will do depends
upon what it falls upon. The same ray that falls upon
the eye and produces the sensation of light, would heat
another body, or do photographic work. The only
difference in rays is in their longer or shorter wave
\DPPageSep{379.png}{364}%
\index{Immortality}%
lengths, and the energy of a wave does not depend
upon its length. From this it follows that there is no
such thing as light as distinguished among forces or
forms of energy. \emph{Light is a sensation}, and in the absence
of eyes no such distinction could possibly be discovered.
Light, then, as a particular kind of agency
takes no part in phenomena outside of the eye. The
eye of man is adapted to respond to certain wave
lengths, the eyes of other animals are adapted to respond
to other wave lengths; and if our eyes were
adapted to perceive all wave lengths the whole universe
would be always light about us, every object,
whatever its temperature, could always be seen as
easily as we now see when the sun shines.

These facts make it quite impossible for a physicist
to understand why darkness should be an essential
condition for the occurrence of such phenomena as
are described. Again, every ray of light when traced
back leads to a vibrating molecule or atom. Indeed,
light or ether waves in general all imply vibrating
atoms or molecules; and what is called spectrum analysis
is but a development of this fundamental principle,
and not only the kind of matter, but its physical
condition is revealed. If Moses had had a spectroscope
when he saw the burning bush it might have
told him the nature of that conflagration.

So when luminous forms appear at a dark \textit{séance},
there is first the ether waves of such length as to
affect the eye; these traced to their source must
arise from vibrating molecules, that is, matter expending
energy in the production of ether waves;
\DPPageSep{380.png}{365}%
for no matter ever shines without some source of
energy.

If the matter that gives out the light be ordinary
matter, there is no difficulty in understanding it; for
matter can be made to shine in several ways,---by
impact, by high temperature, by electric vibrations,
by chemical reactions; and no one could tell from
the simple fact that the matter shone, what the origin
was. But it is said that these forms that are seen
and thus affect the eye, that are touched and thus
affect the sense of touch, that are warm and thus
testify to vibrating molecules, that speak and appeal
to the ear through air vibrations, are \emph{materializations};
meaning by that that the body with its various organs
and their functions is built up \textit{de novo} out of material
at hand, as Adam was said to be made of the dust of
the ground, and as the lion that pawed to free its
hinder parts from the soil out of which it thus grew.
What are the materials that make up a human body?
Ultimately there are carbon, hydrogen, oxygen, nitrogen,
iron, phosphorous, sulphur, potassium, sodium, and
several other ingredients of less importance. From a
hundred to a hundred and fifty or more pounds of these
are needed for one full-grown person.

Many of the materializations that have been described,
from Samuel the prophet to Katie King, have
appeared to be veritable specimens of humanity even
to avoirdupois and all that is implied in that. If the
matter of such bodies was a creation and not a collocation,
then one of the fundamental principles of
physics is simply not true; for matter can be created
\DPPageSep{381.png}{366}%
\index{Seeing, what is implied in}%
and annihilated by any spirit that knows how to find
a suitable medium. If the material is gathered from
the environment---and this sometimes is asserted---then
the difficulty is nearly as great.

One must take notice of the difference there is
between inorganic or relatively simple chemical compounds
and those that make up the bodies of living
things,---the bones, the tissues, the muscles, the nerves,
the brain, the blood. For building up a single pound
of such tissue as muscle or of fat requires the expenditure
of energy represented by about sixteen million
foot-pounds; and as in such a body as we are supposing
there could hardly be less than twenty-five or thirty
to be so reckoned, it follows that not less than four
hundred million foot-pounds of energy is necessary, a
quantity equal to upwards of twelve thousand horsepower,
if done in a minute; and if done in half a
minute, then twice that quantity. I cannot but wonder
if those who think they have witnessed such phenomena
could have been conscious of the stupendous
amount of energy which was being evolved before their
eyes. Then dematerialization involves the annihilation
of the same amount; for it is to be remembered that
organic matter differs from inorganic in the amount of
energy absorbed. There has been either the creation
and annihilation of matter or the creation and annihilation
of an enormous amount of energy, without antecedents
and with no residuals. This is not saying that
such events have not taken place, it only points out the
factors of energy which are implied if they do happen.

One who is unaware of such implications and phenomena
\DPPageSep{382.png}{367}%
\index{Hearing, what is implied in}%
may easily suppose the most improbable things
can take place. Those who are aware of such implications
cannot hear of such events without instantly perceiving
how almost infinitely improbable they are.

Reports of such phenomena have never come from
any man who understood the relations of phenomena.

Scientific men have been often told of their incompetency
to investigate so-called psychical phenomena;
but if the latter involve physical phenomena, then who
else can properly investigate them?

This paper is not to be understood as implying that
there is no relation between the living and the dead,
for the writer does not believe that doctrine; instead
of that he thinks we are very near to a discovery of a
physical basis for immortality that will transform most
all our thinking. If spiritual communication is not
accompanied with physical phenomena in the alleged
way, it does not follow that it may not happen in other
ways that do not do such violence to our fundamental
knowledge as most of the reported cases do. The universe
is large, not much of it has been explored. We
live and move and have our being in an environment
about which our knowledge is most meagre; but our
knowledge of energy we get not only from the earth,
but from the sun and most distant stars and nebulæ,
and it is not probable that any contribution whatever
will materially modify our present knowledge of it.

Thus far I have considered what is always implied
when physical phenomena are considered, especially
with reference to the antecedents; for instance, when
a steam-engine is run it implies the consumption of
\DPPageSep{383.png}{368}%
\index{Senses}%
fuel, which in turn implies molecular structure, and a
definite amount of energy in what is called its chemical
form. That energy is not created or destroyed by
any physical process, and, therefore, every exhibition of
energy, no matter where or when, is to be explained
solely by reference to the laws of energy which are
now so well known as to have passed out of the region
of conjecture or hypothesis. If there be any knowledge
which man possesses, which for certainty and
accuracy compares with mathematical knowledge, it is
the knowledge of physical relations. I traced out a
few cases in which the alleged phenomena were of
such a physical sort as to be easily handled, and
showed how one must look at their antecedents. That
such phenomena did take place was not denied. It
was simply asserted that when they did happen one
must reckon with the implications, unless he was prepared
to affirm that physical phenomena might happen
when physical laws are ignored and quite counted out.
There are yet some further implications it is well to
consider. They have to do with the objective structure
and qualities of the spiritual beings that are
supposed to bring about the phenomena we are considering,
such as moving objects, playing upon musical
instruments, writing upon slates, and so on.

As such beings are always addressed as if they were
visible personages, possessing the same organs of hearing,
seeing, and so on, as are possessed by individuals
still having a material body; and as the replies to questions
never contradict such assumptions, but, on the
contrary, are confirmatory of such assumptions, it follows
\DPPageSep{384.png}{369}%
that one may properly consider what really is
implied in the assumption that spirits have eyes and
ears, because they can see and hear. When I say \emph{I
see}, I assert not only the existence of what we call
light, but the existence of an organ called the eye, the
structure of which is adapted to be acted upon by what
we call light. Light is, as we all know, a wave-motion
in the ether. It travels at the great velocity of a hundred
and eighty-six thousand miles in a second, and the
waves are in the neighborhood of only the one fifty-thousandth
of an inch long. The eye is the only
structure in the body that can perceive these waves.
It is a kind of camera, and photographic work goes on
in the retina very much as it does in the process of
photography. Then, there is the optic nerve, which is
an essential part of the apparatus, and conveys to the
seat of consciousness the impress of the molecular
disturbances which have taken place in the eye. No
one is conscious of the phenomenon of light except
through the action of this complex mechanism. Therefore,
when one says he \emph{sees}, he means that a particular
kind of disturbance has taken place in a particular physiological
structure. The term sight is never used in a
different sense from this, except when it is avowedly
used figuratively. In the absence of ether waves there
could no more be what we call sight than if there were
no eyes; both are essential.

When, then, it is said or admitted that a spirit \emph{sees},
not in a figurative sense, but in the sense in which we
all use the term, it is implied that a spirit has eyes, a
physiological structure, acted upon by ether waves, and
\DPPageSep{385.png}{370}%
\index{Law, physical}%
\index{Specialists}%
the nervous system behind that. It has what \emph{we} call
eyes. It will not do at all to say that such spirit has
an equivalent sense, for whatever that might be it
would certainly not be \emph{sight}. One may get a very
accurate knowledge of the presence of another person
by the voice, or by the sense of touch, but it
would be a culpable misuse of language to say of such
person that he was \emph{seen}. Sound can no more affect
the eyes than light can affect the ears. This, then, is
the same as saying that a spirit has a physical structure
for seeing similarly constituted to that in man,
and, indeed, in all organizations that \emph{see}.

When I say \emph{I hear}, I mean that air vibrations have
affected my organs of hearing, the ears with the nervous
structure between the ear and the seat of consciousness.
There is implied in the statement not
only that sound vibrations of a definite sort have been
produced and are acting, but that they are acting upon
a certain physiological structure adapted to be affected
by gaseous vibrations. Vibrations in the ether cannot
affect the organ of hearing. The media are radically
different, and cannot be used as substitutes for each
other; and it is therefore wrong to say \emph{I hear}, unless
what I perceive reaches my consciousness through the
physiological mechanism called the auditory apparatus.
In a figurative sense one may say he hears as he may
say he sees.
\begin{verse}
  \small
  ``Lo, the poor Indian! whose untutored mind \\
  \PadTo{``}{}Sees God in clouds, or hears him in the wind.''
\end{verse}

But real seeing and real hearing imply certain distinct
\DPPageSep{386.png}{371}%
organs adapted to different physical conditions.
One cannot, by talking, affect one's eyes; nor will
light waves, as such, affect one's ears.

Suppose, then, in a \textit{séance}, when a spirit is addressed
thus: Will the spirit please rap upon the table? and
the answer comes at once,---a rap distinctly heard. The
question was an oral one, and was produced by physical
means, regular sound vibrations, and can be heard
by such beings as are possessed of the proper organs
to be acted upon by air vibrations, that is, ears; and
by ears I \emph{mean} ears, not substitutes of any sort. What
we call \emph{speech} is absolutely impossible in a vacuum,
as much as is sound, for speech is a succession of
sounds. There are numerous substitutes for speech,---signs
made with the fingers or lips that do not appeal
to the ear; but these are not speech. If, then, spirits
\emph{hear}, it is because they have ears, organs that can be
affected by sound vibrations in the same manner as we,
the so-called living beings, can be. Moreover, do not
all testify that they can and do both see and hear?

In like manner one may treat of the sense of feeling,
or any other sense. All imply a molecular structure, a
nervous organization, indeed, everything that goes to
make up a consciousness of the external world such as
is possessed by living beings governed by physical
laws.

It is clear that what we call pain is immediately due
to disordered nervous structure, and in the absence of
nerves could never be known. This can be tested in a
minute by any one, by simply pricking one's finger.
Does not the destruction of the nervous tissue in any
\DPPageSep{387.png}{372}%
manner end the possibility of pain? Can a spirit
then suffer physical pain without a nervous organization?
By pain I mean what all mean by the
term, the sensation which, if severe and long-continued,
results fatally to the sufferer, because the
nervous tissue is itself destroyed.

If some one having read so far, perhaps with impatience,
should say, ``All this may be as you say for living
beings, incorporated in a body of flesh and blood
and a nervous system, but we are not to suppose for
a moment that spirits are thus constituted, and if not,
then they are not to be supposed to be conditioned by
such physical laws as all common matter is conditioned
by. They have their own constitution, different enough
from ours, and one cannot reason from our condition to
theirs.'' To this I would reply, that if one cannot do
this, if a physicist must not carry his terms and conceptions
into this spiritual domain, for precisely the
same reason the spiritualist must not talk about a spirit
\emph{seeing}, \emph{hearing}, \emph{feeling}, and so on, unless he admits he
is talking loosely, and means by those terms only to
symbolize his conceptions, and has to employ such
terms as best convey the idea, which idea cannot be
physically true. Even then it is very difficult to understand
why, if the physical terminology is inappropriate,
any one should at a \textit{séance} ask such a question aloud as,
If John be present will he please rap on the table; for
this is \emph{sound} addressed to an ear---both of which are
purely physical things.

An Arab may not have any difficulty in imagining a
genie that may be summoned by rubbing a cup, to do
\DPPageSep{388.png}{373}%
wonderful things, and then vanish out of relations to
everything; but no one who has studied deeply into
the significance of physical relations can possibly admit
that affairs in nature go on in such a fast-and-loose
way.

Thus far I have considered such relations of physical
phenomena as have been found by experience to hold
good in the whole range of physics---such relations as
properly come under the domain of what is called law,
and by law I mean mathematical precision, both in the
antecedents and the results. With the exception of
the original apparition of matter and of physical energy,
there has not been found in the whole field of physics,
by any investigator of any nationality, any kind of a
phenomenon which is believed to be unexplainable on
the basis of the knowledge of physical science we
already possess. Of course, what we call explanation
is merely presenting the antecedent factors of a given
occurrence, both in quality and quantity, and a thing is
fully explained when these are given so fully as to leave
no reasonable doubt as to their sufficiency in the mind
of one who is properly well acquainted with the data;
but the data that enter into a given phenomenon are
the very things most persons know least about; and a
given explanation may be full and adequate, and yet, to
some, seem to be wholly insufficient.

In these days one often hears about \emph{specialists}---of
their limited knowledge and inadequate preparation for
giving a judgment in other fields than their own. So it
has come to be reckoned that if a man has, by study
and investigation in a given field, made himself a competent
\DPPageSep{389.png}{374}%
judge, so as to be considered an authority in
that field, he is by so much less fitted to be heard in
the settlement of some question foreign to that field;
whereas some other man who is not known to have
done anything in any field, may be called in for judgment,
to the exclusion of the former, lest his increased
knowledge in some one department should disqualify
him elsewhere.

Do we not hear that biologists are incompetent
judges of mental phenomena, that astronomers are not
competent in biological questions, and so on? If this
distinction be true to the extent generally assumed,
then philosophy itself is impossible; for if a man's
opinion can be good only in a small department of
knowledge, and he cannot adequately master more, how
shall we ever know the relationships that constitute
philosophy? The truth is, this is a one-sided affair
altogether, and holds true from but one standpoint. If
an astronomer propounds a chemical theory of the sun,
will it be needful in any degree that the chemist who
reviews the work shall have even studied astronomy
or paid the slightest attention to telescopes or solar
affairs? If chemical science is involved, it is for the
chemist to say whether what is propounded is adequate
or not. That is to say, the man who concerns himself
with the constitution of the sun must so far be a
chemist, but a man may be a chemist and never concern
himself about the sun.

Again, if a biologist who is admittedly ignorant of
chemical and physical science makes statements that
plainly contradict the laws of energy as determined in
\DPPageSep{390.png}{375}%
\index{Science, no one independent}%
chemistry and physics, and if a physicist challenges the
statements, shall the latter be silenced by calling him a
specialist who may be competent enough in his own
field, but who knows nothing of biology? Or shall he
be told that physical laws may be rigorous enough in
one mass of matter, but not in another? Is it to be
believed that physical laws thus play fast and loose?
Here the arithmetic holds good, but there all is indefinite,
and would not this be a fine example of dictation
out of one's field? Physiologists tell us that ultimately
every physiological problem reduces itself to one of
chemistry and physics.\footnote
  {See Appendix, \Pageref{p.}{400}.}
If this be so, is it not plain
that the one who treats broadly of biological problems
must either be a physicist or submit his work to the
criticism of a physicist? But a man may be a physicist
and never trouble himself about biological questions.

If a social philosopher presents a scheme for ameliorating
the evils present in society, in which scheme he
plainly ignores the laws of life as determined by biologists,---as
if such laws were not the very determining
factors which must first be reckoned with,---shall not
the biologist condemn such work? and shall he, too, be
told that however much he knows of biology, he is incompetent
in sociology? Plainly, not so. But is this
process a reversible one? Can the sociologist criticise
the biologist's work unless he be himself a biologist, or
the biologist criticise the chemist's or physicist's work
unless he be so far a chemist or physicist? He certainly
cannot; and this shows that there is a certain
relationship among these subjects in which there is an
\DPPageSep{391.png}{376}%
\index{Séances, phenomena at}%
order of dependence. In order to fully understand and
explain a sociological problem, a knowledge of psychology
is essential; a working knowledge of biology,
or the laws of life, and no adequate knowledge of this
can be had without a preparation in chemistry and
physics.

In this there is nothing new, but it is generally
ignored by most persons who treat on broad questions.
It is plain that every kind of a question is, in the last
analysis, referable to the laws of physical phenomena,
and from these there is no appeal. There are not
many who like this, it is true; but the test for truth
is not what one likes or dislikes, but whether the
proposition is in accordance with the best and most
fundamental knowledge we have. Some of those fundamental
truths discovered within the past fifty years,
and not questioned by any one who can stand an
examination on them, were given on \Pageref{page}{356}; and
whoever sees, or thinks he sees, a phenomenon which
he interprets in a way which plainly contradicts or
ignores those laws, does not so much have a contention
with any man as with science itself. If those laws are
not irrefragably true, then we have no science at all,
no philosophy, knowledge is scrappy, and what we call
the interdependence of phenomena is a myth.

Some of the phenomena alleged to happen at spiritual
\textit{séances}, such as levitation of human bodies, writing between
closed slates, the moving of matter without contact,
and so forth, are said to be as thoroughly proved
as any of the facts of the fundamental knowledge I
have treated. Such a statement cannot have come
\DPPageSep{392.png}{377}%
from any one who knows how the knowledge I spoke
of was obtained, or how it may be verified by anybody
who cares to take the pains. None of it depends in
any degree upon anybody's dictum. If any one has
doubts as to the constitution of water, he can determine
it himself in half a dozen different ways. If
he doubts that the earth is eight thousand miles in
diameter, he can measure it in several ways. If he
thinks a pound of coal does not have eleven million
foot-pounds of energy, he can himself try it and be satisfied.
Any one can satisfy himself by himself; assistance
of others is only a convenience, not a necessity,
and the fundamental statements are now believed by
so many because so many have tested them, and all
have reached the same conclusion. Furthermore, great
commercial enterprises are founded upon some of them,
as when so much limestone and coal are mixed with a
given ore of iron for its reduction. So if such alleged
facts be true, it cannot be true they are as thoroughly
proved as the ones I stated, and they will not be so
proved until each one can be verified in like manner.

There is another excellent reason for denying that
they are proved in any scientific sense. All physical
phenomena, so far as they have become a part of physical
science, have been examined and reported upon by
physicists; and both phenomena and their interpretation
have been the subject of remorseless criticism,
and have been adopted, if at all, on \emph{compulsion}; their
acceptance has been a matter of last resort. This is
true in all departments. Why should one believe that
the world turns round unless there is no other possible
\DPPageSep{393.png}{378}%
\index{Growth of crystals}%
way to explain and account for all the facts which must
be reckoned with in any explanation? The theory itself
is so remote from the common experience of mankind
that nobody suspected it for thousands of years, and it
is not at all obvious to one who is not acquainted with
phenomena out of the range of ordinary experience.
The form of the earth, the aberration of light, the
apparent change of latitude, and so forth, have to be
considered even more than the recurrence of day and
night. For most of the purposes of life it does not
matter whether it turns round or not, and most men
have no interest in the question further than that it
accords or not with their other beliefs and feelings.
But the answer to the question, ``Does it turn?'' is
not one that can be settled by submitting it to the vote
of the world. The judgment of one Galileo is worth
more than that of all the rest of the world on that
point. Once admit that no department of science is
independent of other departments, and that no phenomenon
occurs independent of relations which must
be satisfied by any attempted explanation, and it follows
that no explanation of an event should be adopted
and be considered a part of science, unless it is shown
to be in agreement with what is known. Hence, if an
event is reported which appears to be out of relation
with those established relations which there is general
agreement upon, there is the best of reasons for thinking
that either the event did not happen, or that it did
not happen as reported, especially if the one reporting
it is unacquainted with the variety of ways in which it
is possible to do the same thing. If one sees a wheel
\DPPageSep{394.png}{379}%
\index{Physicists, prepossessions}%
turning round but does not see its connections, how can
he tell whether it is turned by muscular action or water-power
or wind-power or gravity or heat or electricity
or magnetism, every one of which is capable of turning
a wheel? Even if he can see the connections, he cannot
always tell what makes the wheel go without further
investigation. Air and steam will make a water motor
go as well as water itself, and the presence of electrical
devices would not insure that the wheel was turned by
electricity, and the absence of such electrical devices
would not insure that it was not driven by electrical
agency. Hence the testimony of witnesses only, even
though they were otherwise competent, would be of
little weight in deciding what made the wheel go. If
the question were one of any importance it could be
determined only by a competent investigator with
proper appliances, and unhindered by restrictions of
any sort. One cannot trust his sense of sight implicitly.
Many persons have lost fingers because the
buzz saw looked as if it was still; and it is easy with
the zoetrope, and in other ways, to produce the impression
of movements that are not taking place; so it
might be that after all the wheel was not turning, or
even that there was no wheel at all.

Admitting, for the argument's sake, that the alleged
phenomena at \textit{séances} are real occurrences and must
be accounted for, there are certainly three different
possible ways:---

1. By more or less skilfully devised tricks, and fraudulent
only in the attempt to make others believe they
are not tricks. To be certain they are not the results
\DPPageSep{395.png}{380}%
of manipulative skill on the part of some one, only a
skilful juggler might be able to find out. It is known
that hundreds have been thus imposed upon; and skilful
jugglers, such as Hermann and Maskaline, who have
investigated many such, declare themselves satisfied
that the whole of it is trickery.

2. Suppose some of the surprising things done are
not the results of conscious duplicity, then it may be,
as most interested persons contend, the work of disembodied
spirits who, through the agency of mediums,
do apparently the most absurd and irrational things,
but are never willing or able to do the simplest reasonable
thing to satisfy a competent judge; who mutter no
end of maudlin rubbish, add nothing of wisdom or
knowledge to mankind, and justify Professor Huxley
in saying that if such is the state of the dead we have
another good reason against suicide.

3. There are a small number who think some of the
\emph{phenomena} to be genuine, but who attribute them not
to spirits, but to some obscure physical force not yet
understood, and but little investigated. This is the
attitude of Professor Crookes, and of the Milan experimenters.

As to the class that is satisfied with the spiritistic
interpretation, it may be remarked that such an explanation
is in accordance with the attempts of the race
to give a rational explanation of all kinds of phenomena.
In the absence of proper knowledge, what
seems simpler or more natural than to assume some intelligent
agency as the cause of any obscure event?
This it was that peopled the mountains, glens, trees,
\DPPageSep{396.png}{381}%
\index{Knowledge, rapid growth of}%
and rivers with unseen beings, watchful and interested
in the affairs of men. The more ignorant, the closer
was the fetich; the more enlightened, the higher these
agencies retreated into the sky, useful now chiefly for
literary and artistic purposes. For some reason it has
always been discreditable to be without some theory
for all sorts of occurrences, and even to-day, in the
most enlightened communities, a man is liable to be
denounced for his stupidity or his cowardice if he says,
about some matters, I don't know. It is said, however,
that some of the phenomena at \textit{séances} bear the marks
of intelligence such as do not belong to natural occurrences,
and that it is a fair inference that other minds
than the witnesses are present. When Kepler discovered
that the planets moved in elliptical orbits
instead of circular ones as had been supposed, he felt
bound to give some reasonable explanation of the facts.
He knew of nothing but intelligence that could maintain
such motions, and he therefore supposed that each
planet must have some guiding spirit. When the law
of gravitation was applied, it was found that a circular
orbit was the only unstable orbit in the system, and
that gravity alone was sufficient to account for the
order, the harmony, and all the variety of motions; so
the spirits were dismissed from further duty. When a
spider has a leg grow to replace one that has been lost,
it has been held to be due to intelligent action superior
to ordinary chemical and physical action. When a
crystal of quartz is seen to replace a part accidentally
lost, so as to complete its symmetry before it begins to
grow elsewhere, it appears as if mind was at work here
\DPPageSep{397.png}{382}%
quite as much as in the other case, only in the latter most
persons are content not to follow the implications, for
they quickly see the philosophical rocks ahead. The
real truth is that the further one pursues the causes
of phenomena the more clearly does it appear unlikely
that disembodied intelligence is behind any particular
phenomena.

Among all those who make up the great class of
believers in the spiritualistic theory of physical phenomena,
there is not a single physicist; that is, not one
to whom one would go for an explanation of any complicated
physical process. It is assumed that he is no
better qualified to investigate \textit{séance} phenomena than
others who do not know what to expect and look out
for in simpler cases, and that he is unreasonable if he
does not accept the statements of untrained observers
as being as good as his own observations.

It is true that he has some prepossessions. He does
not believe the multiplication table should be trifled
with. He knows that most things may be done in
many different ways, independent of appearances. He
knows a man may sometimes not perceive what is
plainly before his eyes, simply because he was not
looking for it. He deems it right to exhaust the
possibilities of the known before summoning some
unknown and hypothetical factors in any given case.
He knows it to be well-nigh impossible for a man to
give an entirely accurate account to-day of what occurred
yesterday. He knows that a photograph is a
better witness of an event, and that a stenographic
report of statements made is more reliable than any
\DPPageSep{398.png}{383}%
\index{Miracle defined}%
man's memory. He knows that the interpretations of
events by mankind have never been true interpretations,
and that the general beliefs of mankind have
never been confirmed by science in any particular, and
that, so far as anything has been settled, it has been
decided against the opinions and judgment of mankind
and its leaders. He is aware that his key has unlocked
every one of the doors in Doubting Castle that have
been unlocked, and therefore he believes that the
implications of physical science as a whole are against
any generally received interpretation of any event that
has not been subjected to its scrutiny.
%\DPPageSep{399.png}{384}%


\Chapter[The Relations of Physical and Psychical Phenomena]%
{XVI}{The Relations of Physical and Psychical
Phenomena\protect\footnotemark}{384}

\footnotetext{Read before the Psychical Congress, Chicago, August, 1893.}%

% Set manually
\SetRunningHeads{MATTER, ETHER, AND MOTION}{Physical and Psychical Phenomena}%

\First{Knowledge} has grown apace within the past fifty
years. It is generally admitted that more has been
acquired in this time than in all the preceding centuries.
Furthermore, the knowledge thus acquired has
not been simply an addition to the mental possessions
of former days; it has instead been of such a kind as
to completely overthrow nearly all former notions of
nature and its mode of operations, and the new product
can hardly be allowed to be an outcome of the work of
earlier men. It is in the nature of a catastrophe where
old continents have sunk and new ones have arisen
from old ocean beds.

This generation lives in a new world, with new environments,
new ideas, new explanations, new philosophy,
new ideals, and new beliefs. We have new astronomy,
new chemistry, new physics, new psychology, new natural
history, and everybody is on the \textit{qui vive} to know
what can possibly come next. This does not mean
that nature goes on in a different way from what it had
hitherto done, but that we have mentally grasped a new
\DPPageSep{400.png}{385}%
\index{Mental processes imply physical conditions}%
and transforming idea. We have reached an elevation
from which it is possible to survey a broader field, and
can interpret phenomena better because their relations
are better perceived, and because of this it is seen that
the old interpretations were all wrong, and, indeed,
were worthless, because not true. While all this is
granted readily by most thoughtful persons, there are
not a few who recognize the changed opinions in the
various sciences and philosophy in general, who are not
at all persuaded but what the present philosophy of
things, which is dubbed evolution, is only a passing
phase and may itself presently give way to some
new and possibly truer conceptions, being content to
be mildly agnostic on such matters, and willing to wait
with patience for more light. There are some who
think the new philosophy does not take account of all
the known factors, if, by chance, there may not be
unknown factors of as much or more importance than
any which have been included, and which a final philosophy
of things will certainly include; and such object
strenuously to the limitations which the current philosophy
seems to set to knowledge and to the ideals
of the race.

The man of science hears rumors of phenomena
which are said to be as certain as any in his own field,
which he has never investigated, and which cannot
come into his category of related things. Some of
these reported happenings are as marvellous as any
miracles that have been recorded. Persons of undoubted
probity have reported phenomena taking place
in their presence which, if true, give credence to many
\DPPageSep{401.png}{386}%
things for which in the past men and women have been
burned to death as wizards and witches. Thus, I have
an acquaintance, an eminent man not given to romancing,
who assures me he has seen, in undimmed light, a
chair ten feet from any person rise as if some one had
hold of its back and come and set itself down by his
side. Something of the same kind is said to have taken
place in the Milan experiments of last fall. Mr.\
William Crookes tells us that the weight of a body has
been changed to be more or less according to an effort
of the will of Mr.\ Home, and likewise in Milan the
weight of the medium varied as much as fifty pounds.

Now, there have been numerous attempts to define a
miracle for the purposes of philosophy, and usually it
is not the thing accomplished so much as the means
adopted for doing it. The antecedents of the event
are supposed to be other than the usual ones which
might do the same thing. Thus, a chair may be moved
by a person who lifts it and carries it to a new place;
but the chair may be pushed by a stick or pulled by a
string to a new place, while no one touched it, and all
who have been to see Hermann, and other magicians,
have seen things move about in a surprising manner
when no one touched them. In such cases it is
believed that none but well-known means are skilfully
used to produce such displacements, and that any one
might learn the art if it were worth his while. In other
words, no one thinks he is looking at a miraculous
event at a magician's show, no matter how surprising
the thing done; but if any person should be able to
make a chair, or an object, move from one place to
\DPPageSep{402.png}{387}%
\index{Consciousness implies energy}%
\index{Mind and energy}%
another without the mechanical adjuncts of some sort
which are needed by others, by an act of will rather
than by the employment of what we call energy, such
a person is able to work what has always been called a
``miracle.'' His method of doing that thing is a super-natural\DPnote{** Only instance.}
method, which is not the gift of every one even
in the slightest degree; for any one can try and satisfy
himself as to whether he can, by any simple act of will,
make the tiniest mote in a sunbeam or the most delicately
poised needle move in the slightest degree.
This is the common experience; and because it has
been found by experience that matter never moves
except when some other body has previously acted
upon it with a push or a pull, it has come about that
we have reduced the experience to the statements
embodied in so-called laws of motion, have found them
to be justified and without any exception so far as
investigation has gone, and this, too, by a multitude of
persons for two hundred years. As modern science
rests upon a mechanical basis, as it is concerned altogether
with the phenomena of matter and the relations
of the phenomena, and as these have been found in
every case that has been fully investigated to conform
to mathematical laws rigorously, not partly or dubiously,
is it not much more probable that any other phenomenon,
no matter what, that involves matter and its
changes, does conform strictly to the general laws,
than that these laws are sometimes inoperative?

Probably the whole thing resolves itself into this:
Are the fundamental properties of matter variable?
Some of the phenomena alleged to happen at \textit{séances}
\DPPageSep{403.png}{388}%
imply that they are. How strong the case is against
such assumption, I think is not perceived by many persons
who give credence to the happenings, but who are
not well equipped with physical knowledge. Many persons
seem willing enough to admit physical laws and
physical processes in what they take to be the field of
physics, but they hold that there are other fields just as
certain, and among such, mind, that controls matter and
its forces, and to which it is not necessarily subject;
that it is perfectly philosophical to think that mind may
exist independent of matter and its relations, and be
able in this condition to control phenomena.

Let us examine this. Assume that every physical
process in the world should be suddenly stopped, so
there should be no change. That would mean that all
motions were stopped. There would at once be neither
day nor night, for these are due to the earth's rotation;
no light, for light is a wave motion; there would
be no heat, for heat is a vibratory motion; there
would be no chemical changes, for they depend upon
heat; there would be neither solid nor liquid nor
gas, for each depends upon conditions of temperature,
that is, of heat, which is assumed to be absent; there
would be no sight, for that implies wave motions; nor
sound, for that implies air waves; nor taste, for that
implies chemical action; nor smell, for like reason; nor
touch, for that implies pressure---the result of motion.
The heart would cease to beat, the blood to flow, and
consciousness would be stopped. Every one of the
senses would be obliterated or annihilated; nothing
would happen, because there would be no change anywhere.
\DPPageSep{404.png}{389}%
Every phenomenon in the world of sensation
would be stopped, because every phenomenon in the
physical world had stopped; which is the same as saying
that all we call sensations are absolutely dependent
upon physical changes, going on all the time independent
of our will or choice, and which cannot be controlled
in the slightest degree by anybody. Every
phenomenon of every kind, then, consists in, as well
as is dependent upon, matter and its motion, and there
is in the whole range of experience no example of any
kind of a phenomenon where matter, ordinary matter,
is not the conditioning factor. There is no known case
where force or energy is changed in degree or direction
or kind but through the agency of matter. Every kind
of a change implies matter that has thus acted. What
is called the correlation of forces means that one kind
is convertible into some other kind of energy, as heat
into mechanical energy in the steam engine. But the
engine, a material structure, is essential for the change.
What is called the conservation of energy means that
in all the exchanges energy may undergo, as heat into
light, or work of any kind, the quantity of it does not
vary. The matter, as such, does not add to, or subtract
from it; hence only a material body can possess energy,
and a second material structure is necessary in order
that the energy of the first should be changed into any
other form. So it appears there must be at least two
bodies before anything can possibly happen.

This all means that what we call energy is embodied
only in matter, and that what we call phenomena is but
the exchange of energy between different masses of
\DPPageSep{405.png}{390}%
\index{Mind and matter}%
matter; also that these exchanges take place with
mathematical precision, else prediction would be impossible,
and computation a waste of time.

Now, assume that the physical structure of an individual
was kept intact, and that every atom and molecule
in the body maintained its relative position after all
motions had ceased. Assume, too, that the mind or
soul, or whatever one chooses to call the conscious
individuality, was present and capable as ever of acting
upon the material structure; can a single atom be
moved in the slightest degree? If any be moved, then
energy has been expended, energy which must have existed
elsewhere or have been created \textit{de novo}. For conscious
perception, whether sight or sound or any other,
motions embodying energy are essential, as pointed out;
and hence, to produce any perception, some motions
would necessarily have to be initiated, and to initiate
them energy from some source must be supplied.
All the energy the matter had has been destroyed
according to the assumption; so, if any movement has
begun, it must have been created or produced from some
other unthinkable condition which was not energy, in
some such sense as matter is supposed to have been
created, in which something is made out of nothing.
The demand is for creative power. Admit for the
argument's sake that it is done, and matter begins to
move in any kind of a way; so far it possesses energy,
physical energy as embodied in matter. Call the
amount of it ``A.'' Now, if the original condition of
things was established, so far as the amount of energy
was concerned, which may be called ``B,'' then the
\DPPageSep{406.png}{391}%
\index{Phenomena, unexplained}%
\index{Psychics}%
whole amount of energy is ``A plus B.'' It will make
no difference in this sum if one supposes that the
original motions and energy were not interrupted; for
if, on account of mind action, any particle moves more
or less than it would have done with its original supply,
then something has been added to the store of energy
in matter, and what is called the conservation of energy
is not true.

Until all phenomena have been examined, there will be
obscure happenings and things to be explained by some
one who can; but it is no final explanation of anything
to say, ``A man did it,'' or ``An intelligence did it.''
What kind of changes, that is, what kind of phenomena,
the forms of energy we are now acquainted with are
capable of producing no one can now limit, certainly
not one who has not been to the pains to understand
how the simple ones take place. I have often been
told that things cannot move in certain ways, or certain
things cannot be done except by intelligent action
or guidance; but it may be remembered that Kepler
thought guiding spirits were needful for making the
planets move in their elliptical orbits. If one must
explain an obscure phenomenon, is it not wisest to explain
it in accordance with what we know rather than in
accordance with what we do not know? It is better for
one to acknowledge his ignorance of the cause of it, than
to go romancing for a reason, and repudiate all we really
do know and its implications. A juggler may do the
most surprising things before one's eyes, but if one
cares to inquire into the antecedents of anything done
he will have no difficulty in tracing it as far as the
\DPPageSep{407.png}{392}%
\index{Thought transference}%
breakfast. What is meant is, the juggler does nothing
which does not require energy,---energy of the ordinary
sort, in the same sense as if it had been required
for sawing wood or walking up the street. As for consciousness,
dexterity, and all that is implied in both, I
pointed out a little way back there could be neither in
the absence of those changes which constitute physical
phenomena; and that not only life itself, but consciousness
as we know it, would be impossible without the
exchanges in the energy embodied in the cellular structure
of the brain. In the light of what has been accomplished
in the direction of physiological psychology, it
is entirely unwarrantable to assume that even thinking
can go on in the absence of physical changes of measurable
magnitude; and this is the same as saying that
what we call intelligent action is physical at its basis.

There is such a formal agreement as well as actual
connection between conscious life and the life of the
brain, that it is not to be supposed any one who has properly
attended to the facts will venture to deny them.
Argue as one will, it is true there is no experimental
knowledge that is a part of science, of consciousness
separable from a material structure called brain, in which
physiological changes take place as the conditions for
thinking as well as for acting. This is the only known
relation of mind and body. However this association of
such apparently different provinces is to be explained,
it is still true that for every phenomenon in consciousness
there is a corresponding phenomenon in matter.
Psychologists have pointed out that the phenomena indicate
an identity at bottom between the activity of
\DPPageSep{408.png}{393}%
consciousness and cerebral activity. To follow this out
into particulars would be interesting and perhaps profitable
to most; but the significance of it here is that even
in the psychological field, where the opportunities for investigation
are right at hand and most is known, there
is no evidence for consciousness apart from a material
structure, or that the law of conservation of energy does
not hold as strictly true here as elsewhere in physics.
So there is no experimental reason for assuming the
existence of incorporeal intelligences. There is no
psychological question that is not at the same time a
physiological question.

Experimentally it appears that the association of mind
with matter and energy is not of such a nature that one
is at liberty to assume their dissociation, any more than
one is at liberty to assume gravitation or magnetism as
independent existing somethings controlling matter according
to certain laws. So any hypothesis invented to
account for an occurrence that is not yet explained ought
not to be in contradiction to everything else we know,
and ought not to be entertained except as a last resort;
and the hypothesis of disembodied intelligences acting
now in and now out of the field of material things is
such an one. If such phenomena really happen at
\textit{séances} as are alleged, then we have to do with affairs
strictly within the line of physics, whether such phenomena
are so-called mental or so-called physical. It is
useless to affirm that the two are such radically different
phenomena that the methods of the latter are not
appropriate in the former; and the extensive laboratories
for physiological psychology, which are now
\DPPageSep{409.png}{394}%
being established in all the larger institutions of
learning, is a sufficient denial of the proposition.

The term psychics is intended to denote something
different from the phenomena of psychology as manifested
in a given organism. It is supposed to relate to
the sympathetic relation of one mind to that of another
quite apart from the ordinary physical relations, that is,
from the senses. As for the mind-reading as exhibited
some years ago by Brown and others, I believe it is now
agreed that it is due to the sense of touch, and cannot
be done without contact. In hypnotic work there has
to be ``suggestion,'' and most of the very remarkable
cases, such as those in France last winter, have been
shown to be gross frauds. But let it be granted that
some of it is genuine, that it is possible in some cases
to impart information and discover the thoughts of
another without the common resources, it does not
then follow that the method is extra-physical. If only
here and there is to be found an individual called a
psychic, who is thus sensitive, and it is not a race
endowment, one no more need to summon a mysterious
supernormal agency to account for it, than such is
needed for the work of Newton or Mozart. Because a
phenomenon has not been explained, and no one knows
how to explain it, is no reason at all for supposing there
is anything mysterious about it. There are any number
of phenomena throughout nature that have not
been explained, and no one knows how to explain on
the basis of what is known. Such, for instance, is the
whirlwind that crosses the field, raising dust and leaves
into the air. No one has explained the soaring of birds,
\DPPageSep{410.png}{395}%
no one knows what goes on in an active nerve, or why
atoms are selective in their associates. Ignorance is
not a proper basis for speculation; and if one must have
a theory, let it be one having some obvious continuity
with our best physical knowledge.

What is here given is not intended to be a denial that
such phenomena as thought-transference, or even the
most surprising things such as those described in the
Milan experiments, take place. It is only intended to
emphasize the probability that whatever happens has a
physical basis, and is therefore explained only when
these physical relations are known.
\DPPageSep{411.png}{unnumbered}%
%[Blank Page]


\Appendix
\DPPageSep{412.png}{397}%

\Note{Note to \Pageref{Page}{57}.}
\Pagelabel{400}%

\First{As} to whether it is considered as known that the sum of
the interior angles of a plane triangle are exactly equal to
one hundred and eighty degrees: ``Suppose that three points
are taken in space, distant from one another as far as the
sun is from $\alpha$~Centauri; and that the shortest distance between
these points is drawn so as to form a triangle. And suppose
the angles of this triangle to be very accurately measured
and added together; this can at present be done so accurately
that the error shall certainly be less than one minute,
less therefore than the five-thousandth part of a right angle.
Then I do not know that this sum would differ at all from
two right angles; but I also \emph{do not know that the difference
would be less than ten degrees}, and I have reasons for not
knowing.''
\AppendixCite{W.~K. Clifford:}{Aims and Instruments of Scientific Thought.}

``If the Euclidian\DPnote{** [sic]} assumptions are true, the constitution
of parts of space at an infinite distance is as well known as
the geometry of any portion of this room. So that here we
have real knowledge of something at least that concerns the
cosmos; something that is true throughout the immensities
and the eternities. That something Lobotchewski\DPnote{** [sic]} and his
successors have taken away.''
\AppendixCite{W.~K. Clifford:}{Philosophy of the Pure Sciences.}
\DPPageSep{413.png}{398}%

``In this case the universe as known becomes a valid conception,
for the extent of space is a finite number of cubic
miles. If you were to start in any direction whatever, and
move in a perfectly straight line according to the definition
of Liebnitz,\DPnote{** [sic]} after travelling a most prodigious distance \ldots
you would arrive at---this place.''
\AppendixRef{\textsc{Ibid.}}

``It must remain an open question whether, if we had
large enough triangles, the sum of the three angles would
still be two right angles.''
\AppendixRef{\textit{Enc.\ Brit.\ 9th~ed., Art.\ Measurement.}}

``It is true that according to the axioms of geometry, the
sum of the three angles of a triangle are precisely one hundred
and eighty degrees; but these axioms are now exploded,
and geometers confess that they, as geometers, know not the
slightest reason for supposing them to be precisely true.
That they are exactly that amount is what nobody can be
justified in concluding.''
\AppendixCitePage{C.~S. Peirce:}{Monist,}{vol.~i.\ No.~2, p.~174.}

``All that we need do is to call the attention of those who
busy themselves with mental philosophy to this generalization
of geometry as one of the results of modern mathematical
research which they cannot afford to overlook.''
\AppendixCite{George Chrystal,}{in Enc.\ Brit., Art.\ Parallels.}

Such as care to look into the matter further will find
the subject treated in an untechnical way in the works of
W.~K.~Clifford, in the chapters on the ``Theories of the
Physical Forces,'' ``Aims and Instruments of Scientific
Thought,'' and especially the ``Philosophy of the Pure Sciences.''
There is much on it in the \textit{American Journal of
Mathematics}, vols. \i.~and~ii., also in the ``Proceedings of the
Royal Society,'' Edinburgh, vol.~x., 1879, and in article
``Measurement,'' \textit{Enc.~Brit.}
\DPPageSep{414.png}{399}%

\Note{Note to \Pageref{Page}{208}.}
\Pagelabel{402a}%

In 1881 the author discovered how electric ether waves
could be produced and identified, where the vibratory rates
were as high as $4000$ or more per second, by employing
static telephones detached and removed many feet from
the inducing electric current. These gave a wave length
of $\frac{186000}{4000} = 46+$ miles long. Hertz, Tesla, and others have
since then described methods of producing them so short
as to be but a few feet long. When they have thus been
mechanically shortened so as to be but the one forty-thousandth
of an inch in length, they will be seen by the eye as
red light.

\Note{Note to \Pageref{Page}{242}.}
\Pagelabel{402b}%

See Maxwell's ``Theory of Heat,'' pp.~160, 161.

\settowidth{\TmpLen}{$\dfrac{H}{S} = \dfrac{h}{T}$.}
\begin{wrapfigure}[2]{l}{\TmpLen+\parindent}
\hfill\smash{$\dfrac{H}{S} = \dfrac{h}{T}$.}
\end{wrapfigure}
\noindent $S$~and~$T$ are the absolute temperatures of the
hot and cold bodies in Carnot's engine. $H$
and $h$ are the quantities of heat taken up and given out.
When $T = 0°$, $h = 0$, when $h$ is the equivalent of the work
done. As this is $0$ at absolute zero, no work could be done
in changing the volume of a substance at that temperature.
There can be no cohesion among the molecules or atoms, for
this would require that work should be done to separate
them. It is the temperature of \emph{dissociation}.

This conclusion is one to which chemists and physicists
have been led by their researches. For example, Dr.\ Lothar
Meyer says, ``At the lowest temperature to which we can
attain, the majority of chemical reactions studied under
these conditions have been found to cease or to proceed
very slowly, so that it would appear to be very probable that
at the absolute zero, viz., $273°$, a temperature much below
the lowest yet attained, chemical action would cease altogether
from the absence of any form of heat motion whatsoever;
so without heat there would be no exertion of the
so-called chemical affinity.''
\AppendixRef{\textit{Modern Theories of Chemistry}, §~211.}
\DPPageSep{415.png}{400}%

\Note{Note to \Pageref{Page}{277}.}
\Pagelabel{403}%

The hypothesis of a ``vital principle'' is now as completely
discarded as the hypothesis of phlogiston in chemistry.
No biologist with a reputation to lose would for a
moment think of defending it.
\AppendixCitePage{John Fiske:}{Cosmic Philosophy,}{vol.~i.\ p.~422.}

``We can demonstrate the infinitely manifold and complicated
physical and chemical properties of the albuminous
bodies to be the real cause of organic or vital phenomena.''
\AppendixCitePage{Haeckel:}{History of Creation,}{vol.~i.\ p.~330.}

``The aim of modern physiology is to conceive all organic
processes as physical or chemical.''
\AppendixCitePage{Höffding:}{Outlines of Psychology,}{p.~57.}

``Physiologists must expect to meet with an unconditional
conformity to law of the forces of nature in their inquiries
respecting the vital processes. They will have to apply
themselves to the investigation of the physical and chemical
processes going on within the organism.''
\AppendixCitePage{Helmholtz:}{Scientific Lectures,}{p.~384.}

``A vital element, i.e., an element peculiar to organisms,
no more exists than does a vital force working independently
of natural and material processes.''
\AppendixCitePage{Claus \& Sedgwick:}{Zoölogy,}{part~i.\ p.~10.}

``In Physiology the word life is understood to mean the
chemical and physical activities of the parts of which the
organism consists.''
\AppendixCitePage{B. Sanderson:}{Nature,}{vol.~xlviii., p.~613.}

``Modern physiology interprets the phenomena of organic
life by means of physical and chemical laws. An appeal to
`vital force' or to the intervention of mind, it does not
recognize as an explanation of an organic phenomenon.''
\AppendixCitePage{Höffding:}{Outlines of Psychology,}{p.~10.}
\DPPageSep{416.png}{401}%

``Physiology thus appears as a branch of applied physics,
its problems being a reduction of vital phenomena to general
physical laws and thus ultimately to the fundamental laws
of mechanics.''
\AppendixCitePage{Wundt:}{Lehrbuch der Physiologie,}{p.~2.}

``It must not be supposed that the differences between
living and not living matter are such as to justify the
assumption that the forces at work in the one are different
from those to be met with in the other.''
\AppendixCitePage{Huxley:}{Art.\ Biology, Enc.\ Brit.,}{p.~681.}

``Zoölogy, the science which seeks to arrange and discuss
the phenomena of animal life and form as the outcome
of the operation of the laws of physics and chemistry.''
\AppendixCitePage{Lankester:}{Art.\ Zoölogy, Enc.\ Brit.,}{p.~803.}

``If corporal functions are mediated by immaterial
agencies, physiological science is impossible.''
\AppendixCitePage{G.~Stanley Hall:}{Amer.\ Jour.\ Psychology,}{vol.~iii.\ p.~74.}

``It has not occurred to me that any one now uses the
term `vital force' in any other way than as a convenient
method of expressing the sum total of the physical and
chemical activities of organisms.''
\AppendixCite{Prof.\ E.~L. Mark,}{Harvard University.}

``These phenomena of life, though they may not as yet be
physically and chemically explained, are certainly not to be
referred to the working of any special \emph{vital force} peculiar
to organisms\ldots. We have to do here with the same
forces and the same substances that we meet with elsewhere
in nature.''
\AppendixCitePage{Lang:}{Textbook of Comp.\ Anat.,}{London, 1891, p.~2.}

``Modern science has allowed the vitalistic theory (\textit{vitalismus})
to drop; instead of by means of a special vital force,
it explains irritability as a very complex chemico-physical
phenomenon. It is only distinguished from other chemico-physical
\DPPageSep{417.png}{402}%
phenomena of inorganic nature by degree, namely,
that the external stimuli come in contact with a substance
of complicated structure, an organism, and correspondingly
produce in it also a series of complicated processes.''
\AppendixCitePage{O.~Hertwig:}{Die Zelle und die Gewebe,}{p.~75, 1893.}

``I know of no authority in recent years which recognizes
a distinct vital force; all students of nature, so far as I am
aware, explain all the phenomena of life by means of physical
and chemical forces.\DPtypo{}{''}
\AppendixCite{Prof.\ J.~S. Kingsley,}{Tufts College.}

%\DPPageSep{418.png}{403}%
% [** PP: Not small-capping first index entry]

\normalsize
\clearpage
\fancyhf{}
\cleardoublepage

\IndexBookmark
\fancyhead[C]{\textsc{INDEX}}
\printindex

\iffalse
Action at a distance 88

Absolute zero 242, 336

Affinity, chemical 240

Albumen, size of molecule 15

Ampère turns 209

Arcturus 145

Arc light 216

Atmosphere, height of 26

Atoms 10, 18, 19

Atoms, unalterable 21, 22

Atoms, life associated with 24, 296

Atoms, chemical properties 239

Atoms, as vortex rings 349

Atoms, vibrations of 243

Attraction, gravitative 83, 309

Attraction of vibrating fork 87

Attraction of disks 94

Attraction depends upon distance 85

Attraction of vortex rings 95, 244
% \indexspace

Blavatsky, Madam, pretensions of 359

Bonnenburger's apparatus 40

Boiling-point pressure 125
% \indexspace

Cause and effect 75

Camera 162, 163

Catalysis 248

Cell structure 280

Charles, Law of 336

Chemism 238

Chemism and heat 241, 336

Chemical field 247, 305

Chemical effects 218

Chemical origin of electricity 177

Chemical reactions depend on temperature 336

Cohesion, in solids and liquids 332

Cohesion, destroyed 333

Colors 165

Color-blindness 171

Color, nature of 339

Combustion 103

Conductivity, electrical 190, 192

Consciousness implies energy 390

Corti's fibres 275

Corn, life of 291

Crookes' tubes 224

Crystallization 245, 249, 306
% \indexspace

Decomposition of water 218

Density 6

Diamond, hardness of 338

Dissociations 131, 219

Dispersion 138

Dynamo 213
% \indexspace

Ear 274

Earth, velocity of, in space 34

Earth, diameter of 55
%\DPPageSep{419.png}{404}%

Earth, a magnet 303

Earth, curvature 69

Earth, solidity of 126

Egg 291

Echo 265

Efficiency of machines 213

Elasticity 341

Elasticity due to motion 39, 341

Elements 136

Energy, factors of 70, 77

Energy in the ether 79, 105

Energy. What determines transfer 214

Energy, unknown, preface.

Electricity, origin of 174, 229, 354

Electricity, thermal 174

Electricity, mechanical origin 180, 230

Electricity, magnetic origin 181

Electricity, electrical origin 182, 230

Electrical antecedents 186

Electrical effects 231

Electrical effects, reversible 232

Electricity, dual 234

Electricity, activity 194

Electrical field 196, 300

Electrical stress 197

Electrical waves 198, 303

Electro-magnets 81, 210

Electric lamps 215

Energy of translation 64

Energy of vibration 66

Energy of rotation 68

Ether 26, 32, 34, 80

Ether, a non-conductor 191

Ether waves 134

Ether wave qualities 134

Ether phenomena not explained 352

Ether waves, their source 135, 207

Ether pressure 205

Ether rotations 234

Explosion products 71
% \indexspace

Fable, La Fontaine's 357

Falling bodies 60

Falling bodies, energy of 60

Fibres of Corti 275

Fields, physical 298

Fields, chemical 247, 305

Fields, electrical 196, 300

Fields, magnetic 202, 214, 252

Fields, mechanical 247

Fields, thermal 298

Flames 137

Foot-pound 60, 62

Food 284

Foster, Dr.\ Michael, quoted 296

Force, vital 279

Friction, its effects 23, 34

Fuels 103
% \indexspace

Galvanic battery 178

Gas, motion in 333

Gas, free path in 334

Gas, pressure in 334, 336

Gas, destroyed 336

Gaseous absorption 142

Geometry 56, 57 % Appendix.

Geometry@{Appendix.}

Geissler's tubes 223

Goose, work in flying 65

Gravitation 82, 90, 309, 347

Gravitation, law of 84

Gravity, specific 7

Gravity follows from structure 348

Growth 250, 292, 310

Growth of crystals 283, 381

Growth of lobster 283

Gunpowder 103

Guppy, Mrs. 359

Gyroscope 342
% \indexspace

Hair-cloth loom 312

Hardness not atomic property 338
%\DPPageSep{420.png}{405}%

Hearing, what is implied in 370

Hertz waves 344, 351

Helmholtz 35

Heat, mechanical origin of 99

Heat, chemical origin of 102

Heat, electrical origin of 104

Heat, radiational origin of 105

Heat, mechanical equivalent 109

Heat unit 112

Heat, effects 123, 254, 335

Heat by impact 225

Heat of the sun, origin of 119

Heat, nature of 115, 118

Hypothesis, needful 94

Hypothesis, gravitation 90

Hydrogen vibrations 116
% \indexspace

Impenetrability 340

Immortality 24, 367

Inertia 70, 345

Induction coils 208

Inductive action 183, 195, 250, 302
% \indexspace

Joule 110

Jupiter, temperature of 144
%[**missing \indexspace]

Kepler, the guesser 90

Kinetics 46

Kinematics 46

Knowledge, rapid growth of 384
% \indexspace

Laws not compulsory 353

Law, physical 373

Lever 317

Life 277 % Appendix.

Life@{Appendix.}

Life, definitions of 278

Light, a sensation 135, 363

Light, energy of 80

Light, its velocity 26, 28

Light, its nature 27, 80, 134, 364

Light waves 207

Lightning 185, 223

Lighting, electric 214, 222

Luminous effects 222
% \indexspace

Matter, living 283, 294

Matter, characteristic property 4

Matter, its definition 4

Matter, divisibility of 8

Matter, effect of temperature upon 132, 336

Matter, as modes of motion 331

Matter, states of 332

Mass 345

Materialists 351

Materializations and energy 365

Mars, atmosphere of 144

Mars, signalling to 217

Machines 312, 325

Magnetic field 202, 204, 214, 252, 303

Magnetic induction 208

Magnetic rotation 235

Magnetic waves 81, 202, 207, 344

Magnet, electro 81

Mathematics 89

Mechanical field 307

Medium, necessity for 29

Mental processes imply physical conditions 388

Meteors 21, 26, 64

Mercury 55

Miracles possible 353

Miracle defined 386

Mind and energy 390

Mind, a material habitat for 24

Mind and matter 24, 393

Mirrors 147

Microscope, magnifying powers 15, 149

Molecules, size of 13, 18, 46

Molecules, loaded 160

Molecules, long free path 224
%\DPPageSep{421.png}{406}%

Molecules, number of, in universe 124

Motion, kinds of 46, 48, 49, 145

Motion, velocity of 50

Motion, transformations of 314

Motion, molecular and atomic 49

Motion, laws of 70, 73

Motion, antecedent of 72

Molecular fatigue 78

Molecular stability 281

Momentum 74

Motor, electric 212

Muscles 286

Muscular work 67

Musical sounds 268

Musical ratios 269

Musical instruments 271
% \indexspace

Newton, Sir Isaac 30, 82, 83, 88

Nerves, their functions 288, 290

Nebula theory 97

Neptune, discovery of 89

Noise 269
% \indexspace

Ohm's law 189

Organic and inorganic matter, difference between 366
% \indexspace

Phenomena, nature of 59

Phenomena, unexplained 353, 394

Phenomena physical, implications

of 354

Photography 156

Phosphorescence 226

Physical fields 298

Physical universe a machine 330

Physical processes, reversible 232

Physicists, prepossessions 382

Pitch 259

Plating, electro 221

Polarization of molecules 178, 219

Postulates of Physical Science 356

Power, needed for rapid movement in air 359

Potential, electrical 189

Principia 31, 70

Prism 138

Protoplasm 280

Psychics 394

Pulley 317

Purpurine 169

Push and pull 315
% \indexspace

Radiometer 154

Reflection 147

Retina, its functions 171

Reflex action 172

Refraction 138, 147

Resistance, electrical 192, 214

Rotations in ether 235
% \indexspace

Satellite 69

Saturn, temperature of 144

Science, no one independent 378

Senses 161, 371

Séances, phenomena at 362, 379

Seeing, what is implied in 369

Sirius 145

Silver salts unstable 159

Soap-bubbles 10

Sound, origin of 257, 360

Sound, characteristics 262

Sound, range of 263

Sound, velocity of 263

Sound, vocal 272

Solar system 329

Space 58

Space, navigation of 154

Specialists 373

Spiritualistic theory 360

Specific gravity 7

Specific heat 130

Spectroscope 139

Spectrum analysis 140
%\DPPageSep{422.png}{407}%

Spectrum, solar 138, 142

Spark, electric 223

Spirit disembodied 360

Stress in ether 93

Stress in glass 92

Stress, electrical 183, 197, 231

Stress, magnetic 181

Steam-engine 113

Steam-engine, efficiency of 114

Stars, their number 18

Stars, their distance 19, 28

Stars, their motions 145

Sun, its distance 28, 56

Sun, its magnitude 122

Sun, its heat 122

Sun, its age 122

Sun, its structure 143
% \indexspace

Temperature 106

Temperature, table 108

Temperature, maximum 127

Terminology, electrical 186

Telegraph 211

Telephone 211

Thermometer 107

Tesla ether waves 344

Thermometer, air 109

Thomson, Sir Wm. 35

Thermodynamics 112

Thermopile 176

Thermodynamics, electric 174

Thought transference 395, 311

Toepler-Holtz electrical machine 294

Top, sleep of 72

Transparency 146

Transformations of motion 321
% \indexspace

Universe, its size 28

Universe, atoms in 20
% \indexspace

Vacuum, a non-conductor 223

Vacuum 47

Venus 55

Velocities 50, 54, 56

Vibrations per second 52, 53

Vibrations, gaseous 116

Vibrations, sympathetic 249, 267

Vibrations, forced 267

Vital force 279 % Appendix.

Vital force@{Appendix.}

Vision, phenomena of 164

Vision, hallucinations of 166

Vision, energy needed for 166

Vision of animals 168

Vision, theory of 168

Voice 272

Vortex ring theory of matter 94

Vortex ring model 342

Vortex rings in air 35

Vortex rings, properties of 37, 72

Volcanoes 127
% \indexspace

Wave lengths of sound 265

Waves, electric 303

Water decomposition 218

Weight 61

Weights, standards of 60

Welding, electric 210

Work, standard of 60

Work, measure of 62, 64, 318

Work, muscular 67
\fi

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%\DPPageSep{423.png}{I}%
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\fancyhead[C]{\textit{Books Upon Various Subjects}}
\thispagestyle{empty}

\begin{center}
\textsf{\Large LEE AND SHEPARD}\\[12pt]
\textsf{\large 10~MILK STREET BOSTON}\\[8pt]
\tb\\[12pt]
{\Large List of Books upon Various Subjects}\\[8pt]
\tb
\end{center}

\Entry{QUABBIN}

\Subentry
Sketches in a Small Town \quad With Outlooks upon Puritan Life \quad By \Au{Francis~H.
Underwood}~LL.D. author of ``Handbooks of English Literature''
``Man Proposes'' ``Lord of Himself'' etc. Fully illustrated
Cloth \$1.75

\begin{Descrip}
This work purports to give an account of the progress of a small New England town;
but it is of wider and deeper import; namely, a view of the development of the narrow
and sombre Puritan into the variously gifted and accomplished ``Yankee'' of to-day. It
concerns the state of literature and art in the early part of the present century, and shows
how the fairer conditions of modern times came into being.

In plan it is wholly unlike any modern book. It is not a town history, nor an historical
essay, nor a collection of reminiscences. Its chapters are mostly picturesque descriptions
of the old times, and show the ``rude forefathers'' at home, at church, at town-meetings, at
road-making, and in other scenes of their daily life. There are sketches of the successive
ministers, the schools, the quiltings, sleigh-rides, and other rustic gatherings,---of the
homely speech and manners, and of the complexities of Yankee character.

It is believed that these graphic, tender, and humorous pictures will appeal to the hearts
and memories of New England people, and to their descendants along the line of migration
westward to the Mississippi and beyond.

The illustrations are from photographs taken from beautiful scenes in ``Quabbin.''
\end{Descrip}

\clearpage
\Entry{UNIVERSAL PHONOGRAPHY or Short-hand by the ``Allen
Method''}

\Subentry
A self-instructor, whereby more speed than long-hand writing is gained at
the first lesson, and additional speed at each subsequent lesson \quad By \Au{G.~G.
Allen}, Principal of the Allen Stenographic Institute Boston \quad 50~cents

\begin{Descrip}
There is scarcely any requirement so helpful to the student, scholar, scientist, or professional
man as short-hand writing. Heretofore all methods have required so long a
time before one could become so proficient as to make it of any advantage, that men in
middle life, or busy men, have not been able to give the time to learn it; but by the ``Allen
Method'' one can almost in ``the idle moments of a busy life,'' certainly in an hour a day
for two or three months, become so expert as to report a lecture \textit{verbatim}.
\end{Descrip}
%\DPPageSep{424.png}{II}%
%Font size changes on this page
\Entry{MATTER, ETHER, AND MOTION}

\Subentry
The Factors and Relations of Physical Science \quad By \Au{Prof.\ A.~E. Dolbear}
Tufts College author of ``The Telephone'' ``The Art of Projecting''
etc. \quad Cloth~\$2.00

\begin{Descrip}
``Matter, Ether, and Motion,'' the Factors and Relations of Physical Science, by A.~E.
Dolbear,~Ph.D\@. The author in this treatise presents to his readers the principles of physical
science. The chapters are arranged as Matter, Ether, Motion, Energy, Gravitation,
Heat, Ether Waves, Electricity, Chemism, Sound, Life, Physical Fields, Machines and
Mechanism. This is a tolerably comprehensive table, and introduces the student to the
principles on which, so far as at present known, the action of the universe seems to
depend.

Altogether this little treatise gives an insight into matters outside the common range of
serious study, and yet places the subject within reach of the student seeking for knowledge.
Although dealing with abstruse scientific topics, the style is lucid, and the matter intelligible
to ordinary thinkers and readers in search of information.---\textit{New York Commercial
Advertiser}.
\end{Descrip}


\Entry{THE TELEPHONE}

\Subentry
An account of the phenomena of electricity, magnetism, and sound as involved
in its action; with directions for making a speaking telephone \quad
By \Au{Prof.\ A.~E. Dolbear} of Tufts College \quad 50~cents

\begin{Descrip}
An interesting little book upon this most fascinating subject, which is treated in a very
clear and methodical way. First we have a thorough review of the discoveries in electricity,
then of magnetism, then of those in the study of sound,---pitch, velocity, timbre, tone,
resonance, sympathetic vibrations, etc. From these the telephone is reached, and by them
in a measure explained.---\textit{Hartford Courant}.
\end{Descrip}


\Entry{THE ART OF PROJECTING}

\Subentry
By \textsc{Prof.\ A.~E. Dolbear}~Ph.D. (Tufts College) \quad New Edition revised
with additions \quad $125$~illustrations \quad Cloth~\$2.00

\begin{Descrip}
A Manual of Experimentation in Physics, Chemistry, and Natural History with the Porte
Lumière and the Magic Lantern; also with Electric Lights and Lamps and the Production
and Phenomena of Vortex Rings.
\end{Descrip}


\Entry{WHAT IS TO BE DONE--(Emergency Handbook)}

\Subentry
A Handbook for the Nursery with Useful Hints for Children and Adults \quad
By \Au{Robert~B. Dixon}~M.D. Surgeon of the Fifth Massachusetts Infantry,
Physician to the Boston Dispensary \quad Cloth 50~cents; paper 30~cents

\begin{Descrip}
Dr.\ Dixon, in this little ``Emergency Handbook,'' gives simple directions what to do
in a number of the most common cases that arise, either in home treatment of slight accidents,
or indispositions, or in the case of patients in more serious cases, until the arrival of
the physician. The book is worth its weight in gold, and ought to have a place in every
family library.---\textit{Providence Press}.
\end{Descrip}


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% End of the Project Gutenberg EBook of Matter, Ether, and Motion, Rev. ed.,
% enl., by Amos Emerson Dolbear                                           %
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 31428-t.out
 31428-t.out
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./images/048a.png
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 31428-t.ind
 ***********

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PDF statistics:
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 415 words of extra memory for PDF output out of 10000 (max. 10000000)

