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THE LIFE OF SIR ISAAC NEWTON.


      *      *      *      *      *      *

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[Illustration:

    SIR. G. KNELLER PINX.      ENG.d BY GIMBER.

    SIR ISAAC NEWTON.

    HARPER’S FAMILY LIBRARY

                               Printed by R. Miller]

      *      *      *      *      *      *


_Harper’s Stereotype Edition._

THE LIFE OF SIR ISAAC NEWTON.

by

DAVID BREWSTER, LL.D. F.R.S.

    Ergo vivida vis animi pervicit, et extra
    Processit longe flammantia mœnia mundi;
    Atque omne immensum peragravit mente amimoque.

            _Lucret._ lib. i. 1. 73.


[Illustration: The Birthplace of Newton.]


New-York:

Printed and Published by J. & J. Harper;
No. 82 Cliff-Street,
and Sold by the Booksellers Generally Throughout
the United States.

1833.




TO

THE RIGHT HONOURABLE

LORD BRAYBROOKE.


The kindness with which your lordship intrusted to me some very
valuable materials for the composition of this volume has induced me
to embrace the present opportunity of publicly acknowledging it. But
even if this personal obligation had been less powerful, those literary
attainments and that enlightened benevolence which reflect upon rank
its highest lustre would have justified me in seeking for it the
patronage of a name which they have so justly honoured.

            DAVID BREWSTER.

_Allerly, June 1st, 1831._




PREFACE.


As this is the only Life of Sir Isaac Newton on any considerable scale
that has yet appeared, I have experienced great difficulty in preparing
it for the public. The materials collected by preceding biographers
were extremely scanty; the particulars of his early life, and even
the historical details of his discoveries, have been less perfectly
preserved than those of his illustrious predecessors; and it is not
creditable to his disciples that they have allowed a whole century to
elapse without any suitable record of the life and labours of a master
who united every claim to their affection and gratitude.

In drawing up this volume, I have obtained much assistance from the
account of Sir Isaac Newton in the Biographia Britannica; from the
letters to Oldenburg, and other papers in Bishop Horsley’s edition
of his works; from Turnor’s Collections for the History of the Town
and Soke of Grantham; from M. Biot’s excellent Life of Newton in the
Biographie Universelle; and from Lord King’s Life and Correspondence of
Locke.

Although these works contain much important information respecting the
Life of Newton, yet I have been so fortunate as to obtain many new
materials of considerable value.

To the kindness of Lord Braybrooke I have been indebted for the
interesting correspondence of Newton, Mr. Pepys, and Mr. Millington,
which is now published for the first time, and which throws much light
upon an event in the life of our author that has recently acquired an
unexpected and a painful importance. These letters, when combined with
those which passed between Newton and Locke, and with a curious extract
from the manuscript diary of Mr. Abraham Pryme, kindly furnished to
me by his collateral descendant Professor Pryme of Cambridge, fill up
a blank in his history, and have enabled me to delineate in its true
character that temporary indisposition which, from the view that has
been taken of it by foreign philosophers, has been the occasion of such
deep distress to the friends of science and religion.

To Professor Whewell, of Cambridge, I owe very great obligations for
much valuable information. Professor Rigaud, of Oxford, to whose
kindness I have on many other occasions been indebted, supplied me with
several important facts, and with extracts from the diary of Hearne
in the Bodleian Library, and from the original correspondence between
Newton and Flamstead, which the president of Corpus Christi College
had for this purpose committed to his care; and Dr. J. C. Gregory, of
Edinburgh, the descendant of the illustrious inventor of the reflecting
telescope, allowed me to use his unpublished account of an autograph
manuscript of Sir Isaac Newton, which was found among the papers of
David Gregory, Savilian Professor of Astronomy at Oxford, and which
throws some light on the history of the Principia.

I have been indebted to many other friends for the communication of
books and facts, but especially to Sir William Hamilton, Bart., whose
liberality in promoting literary inquiry is not limited to the circle
of his friends.

            D. B.

_Allerly, June 1st, 1831._




CONTENTS.


                                                                    Page
  CHAPTER I.

  The Pre-eminence of Sir Isaac Newton’s Reputation—The Interest
    attached to the Study of his Life and Writings—His Birth and
    Parentage—His early Education—Is sent to Grantham School—
    His early Attachment to Mechanical Pursuits—His Windmill—His
    Water-clock—His Self-moving Cart—His Sun-dials—His Preparation
    for the University                                                17


  CHAPTER II.

  Newton enters Trinity College, Cambridge—Origin of his Propensity
    for Mathematics—He studies the Geometry of Descartes unassisted—
    Purchases a Prism—Revises Dr. Barrow’s Optical Lectures—Dr.
    Barrow’s Opinion respecting Colours—Takes his Degrees—Is
    appointed a Fellow of Trinity College—Succeeds Dr. Barrow in the
    Lucasian Chair of Mathematics                                     26


  CHAPTER III.

  Newton occupied in grinding Hyperbolical Lenses—His first
    Experiments with the Prism made in 1666—He discovers the
    Composition of White Light, and the different Refrangibility of the
    Rays which compose it—Abandons his Attempts to improve Refracting
    Telescopes, and resolves to attempt the Construction of Reflecting
    ones—He quits Cambridge on account of the Plague—Constructs
    two Reflecting Telescopes in 1668, the first ever executed—One
    of them examined by the Royal Society, and shown to the King—He
    constructs a Telescope with Glass Specula—Recent History of the
    Reflecting Telescope—Mr. Airy’s Glass Specula—Hadley’s Reflecting
    Telescopes—Short’s—Herschel’s—Ramage’s—Lord Oxmantown’s           30


  CHAPTER IV.

  He delivers a Course of Optical Lectures at Cambridge—Is elected
    Fellow of the Royal Society—He communicates to them his
    Discoveries on the different Refrangibility and Nature of Light—
    Popular Account of them—They involve him in various Controversies—
    His Dispute with Pardies—Linus—Lucas—Dr. Hooke and Mr. Huygens—
    The Influence of these Disputes on the mind of Newton             47


  CHAPTER V.

  Mistake of Newton in supposing that the Improvement of Refracting
    Telescopes was hopeless—Mr. Hall invents the Achromatic Telescope—
    Principles of the Achromatic Telescope explained—It is reinvented
    by Dollond, and improved by future Artists—Dr. Blair’s Aplanatic
    Telescope—Mistakes in Newton’s Analysis of the Spectrum—Modern
    Discoveries respecting the Structure of the Spectrum              63


  CHAPTER VI.

  Colours of thin Plates first studied by Boyle and Hooke—Newton
    determines the Law of their Production—His Theory of Fits of
    easy Reflection and Transmission—Colours of thick Plates          75


  CHAPTER VII.

  Newton’s Theory of the Colours of Natural Bodies explained—
    Objections to it stated—New Classification of Colours—Outline of
    a new Theory proposed                                             82


  CHAPTER VIII.

  Newton’s Discoveries respecting the Inflection or Diffraction of
    Light—Previous Discoveries of Grimaldi and Dr. Hooke—Labours
    of succeeding Philosophers—Law of Interference of Dr. Young—
    Fresnel’s Discoveries—New Theory of Inflection on the Hypothesis
    of the Materiality of Light                                       98


  CHAPTER IX.

  Miscellaneous Optical Researches of Newton—His Experiments on
    Refraction—His Conjecture respecting the Inflammability of the
    Diamond—His Law of Double Refraction—His Observations on the
    Polarization of Light—Newton’s Theory of Light—His “Optics”      106


  CHAPTER X.

  Astronomical Discoveries of Newton—Necessity of combined Exertion
    to the completion of great Discoveries—Sketch of the History or
    Astronomy previous to the time of Newton—Copernicus, 1473–1543—
    Tycho Brahe, 1546–1601—Kepler, 1571–1631—Galileo, 1564–1642      110


  CHAPTER XI.

  The first Idea of Gravity occurs to Newton in 1666—His first
    Speculations upon it—Interrupted by his Optical Experiments—He
    resumes the Subject in consequence of a Discussion with Doctor
    Hooke—He discovers the true Law of Gravity and the Cause of the
    Planetary Motions—Dr. Halley urges him to publish his Principia—
    His Principles of Natural Philosophy—Proceedings of the Royal
    Society on this Subject—The Principia appears in 1687—General
    Account of it, and of the Discoveries it contains—They meet with
    great Opposition, owing to the Prevalence of the Cartesian System—
    Account of the Reception and Progress of the Newtonian Philosophy
    in Foreign Countries—Account of its Progress and Establishment
    in England                                                       140


  CHAPTER XII.

  Doctrine of Infinite Quantities—Labours of Pappus—Kepler—Cavaleri—
    Roberval—Fermat—Wallis—Newton discovers the Binomial Theorem and
    the Doctrine of Fluxions in 1606—His Manuscript Work containing
    this Doctrine communicated to his Friends—His Treatise on
    Fluxions—His Mathematical Tracts—His Universal Arithmetic—His
    Methodus Differentialis—His Geometria Analytica—His Solution of
    the Problems proposed by Bernouilli and Leibnitz—Account of the
    celebrated Dispute respecting the Invention of Fluxions—Commercium
    Epistolicum—Report of the Royal Society—General View of the
    Controversy                                                      168


  CHAPTER XIII.

  James II. attacks the Privileges of the University of Cambridge--
    Newton chosen one of the Delegates to resist this Encroachment—He
    is elected a Member of the Convention Parliament—Burning of his
    Manuscript—His supposed Derangement of Mind—View taken of this
    by foreign Philosophers—His Correspondence with Mr. Pepys and
    Mr. Locke at the time of his Illness—Mr. Millington’s Letter to
    Mr. Pepys on the subject of Newton’s Illness—Refutation of the
    Statement that he laboured under Mental Derangement              200


  CHAPTER XIV.

  No Mark of National Gratitude conferred upon Newton—Friendship
    between him and Charles Montague, afterward Earl of Halifax—Mr.
    Montague appointed Chancellor of the Exchequer in 1694—He resolves
    upon a Recoinage—Nominates Mr. Newton Warden of the Mint in 1695—
    Mr. Newton appointed Master of the Mint in 1699—Notice of the
    Earl of Halifax—Mr. Newton elected Associate of the Academy of
    Sciences in 1699—Member for Cambridge in 1701—and President of
    the Royal Society in 1703—Queen Anne confers upon him the Honour
    of Knighthood in 1705—Second Edition of the Principia, edited by
    Cotes—His Conduct respecting Mr. Ditton’s Method of finding the
    Longitude                                                        223


  CHAPTER XV.

  Respect in which Newton was held at the Court of George I.—The
    Princess of Wales delighted with his Conversation—Leibnitz
    endeavours to prejudice the Princess against Sir Isaac and Locke—
    Controversy occasioned by his Conduct—The Princess obtains a
    Manuscript Abstract of his System of Chronology—The Abbé Conti
    is, at her request, allowed to take a Copy of it on the promise of
    Secrecy—He prints it surreptitiously in French, accompanied with a
    Refutation by M. Freret—Sir Isaac’s Defence of his System—Father
    Souciet attacks it, and is answered by Dr. Halley—Sir Isaac’s
    larger Work on Chronology published after his Death—Opinions
    respecting it—Sir Isaac’s Paper on the Form of the most ancient
    Year                                                             234


  CHAPTER XVI.

  Theological Studies of Sir Isaac—Their Importance to Christianity—
    Motives to which they have been ascribed—Opinions of Biot and
    La Place considered—His Theological Researches begun before his
    supposed Mental Illness—The Date of these Works fixed—Letters
    to Locke—Account of his Observations on Prophecy—His Lexicon
    Propheticum—His Four Letters to Dr. Bentley—Origin of Newton’s
    Theological Studies—Analogy between the Book of Nature and that
    of Revelation                                                    242


  CHAPTER XVII.

  The Minor Discoveries and Inventions of Newton—His Researches on
    Heat—On Fire and Flame—On Elective Attraction—On the Structure
    of Bodies—His supposed Attachment to Alchymy—His Hypothesis
    respecting Ether as the Cause of Light and Gravity—On the
    Excitation of Electricity in Glass—His Reflecting Sextant invented
    before 1700—His Reflecting Microscope—His Prismatic Reflector as
    a Substitute for the small Speculum of Reflecting Telescopes—His
    Method of varying the Magnifying Power of Newtonian Telescopes—
    His Experiments on Impressions on the Retina                     265


  CHAPTER XVIII.

  His Acquaintance with Dr. Pemberton—Who edits the Third Edition of
    the Principia—His first Attack of ill Health—His Recovery—He is
    taken ill in consequence of attending the Royal Society—His Death
    on the 20th March, 1727—His Body lies in state—His Funeral—He is
    buried in Westminster Abbey—His Monument described—His Epitaph—
    A Medal struck in honour of him—Roubiliac’s full-length Statue of
    him erected in Cambridge—Division of his Property—His Successors
                                                                     284


  CHAPTER XIX.

  Permanence of Newton’s Reputation—Character of his Genius—His
    Method of Investigation similar to that used by Galileo—Error in
    ascribing his Discoveries to the Use of the Methods recommended by
    Lord Bacon—The Pretensions of the Baconian Philosophy examined—
    Sir Isaac Newton’s Social Character—His great Modesty—The
    Simplicity of his Character—His Religious and Moral Character—
    His Hospitality and Mode of Life—His Generosity and Charity—His
    Absence—His Personal Appearance—Statues and Pictures of him—
    Memorials and Recollections of him                               292


  APPENDIX, No. I.—Observations on the Family of Sir Isaac Newton    307

  APPENDIX, No. II.—Letter from Sir Isaac Newton to Francis Aston,
    Esq., a young Friend who was on the eve of setting out on his
    Travels                                                          316

  APPENDIX, No. III.—“A Remarkable and Curious Conversation between
    Sir Isaac Newton and Mr. Conduit.”                               320




LIFE

OF

SIR ISAAC NEWTON.




CHAPTER I.

  _The Pre-eminence of Sir Isaac Newton’s Reputation—The Interest
    attached to the Study of his Life and Writings—His Birth and
    Parentage—His early Education—Is sent to Grantham School—His early
    Attachment to Mechanical Pursuits—His Windmill—His Waterclock—His
    Self-moving Cart—His Sundials—His Preparation for the University._


The name of Sir Isaac Newton has by general consent been placed at the
head of those great men who have been the ornaments of their species.
However imposing be the attributes with which time has invested the
sages and the heroes of antiquity, the brightness of their fame has
been eclipsed by the splendour of his reputation; and neither the
partiality of rival nations, nor the vanity of a presumptuous age, has
ventured to dispute the ascendency of his genius. The philosopher,[1]
indeed, to whom posterity will probably assign the place next to
Newton, has characterized the _Principia_ as pre-eminent above all the
productions of human intellect, and has thus divested of extravagance
the contemporary encomium upon its author,

    Nec fas est propius mortali attingere Divos.
                                             HALLEY.

    So near the gods—man cannot nearer go.

The biography of an individual so highly renowned cannot fail to excite
a general interest. Though his course may have lain in the vale of
private life, and may have been unmarked with those dramatic events
which throw a lustre even round perishable names, yet the inquiring
spirit will explore the history of a mind so richly endowed,—will study
its intellectual and moral phases, and will seek the shelter of its
authority on those great questions which reason has abandoned to faith
and hope.

If the conduct and opinions of men of ordinary talent are recorded for
our instruction, how interesting must it be to follow the most exalted
genius through the incidents of common life;—to mark the steps by
which he attained his lofty pre-eminence; to see how he performs the
functions of the social and the domestic compact; how he exercises his
lofty powers of invention and discovery; how he comports himself in the
arena of intellectual strife; and in what sentiments, and with what
aspirations he quits the world which he has adorned.

In almost all these bearings, the life and writings of Sir Isaac Newton
abound with the richest counsel. Here the philosopher will learn the
art by which alone he can acquire an immortal name. The moralist will
trace the lineaments of a character adjusted to all the symmetry of
which our imperfect nature is susceptible; and the Christian will
contemplate with delight the high-priest of science quitting the study
of the material universe,—the scene of his intellectual triumphs,—to
investigate with humility and patience the mysteries of his faith.

       *       *       *       *       *

Sir Isaac Newton was born at Woolsthorpe, a hamlet in the parish of
Colsterworth, in Lincolnshire, about six miles south of Grantham,
on the 25th December, O. S., 1642, exactly one year after Galileo
died, and was baptized at Colsterworth on the 1st January, 1642–3.
His father, Mr. Isaac Newton, died at the early age of thirty-six, a
little more than a year after the death of his father Robert Newton,
and only a few months after his marriage to Harriet Ayscough, daughter
of James Ayscough of Market Overton in Rutlandshire. This lady was
accordingly left in a state of pregnancy, and appears to have given
a premature birth to her only and posthumous child. The helpless
infant thus ushered into the world was of such an extremely diminutive
size,[2] and seemed of so perishable a frame, that two women who were
sent to Lady Pakenham’s at North Witham, to bring some medicine to
strengthen him, did not expect to find him alive on their return.
Providence, however, had otherwise decreed; and that frail tenement
which seemed scarcely able to imprison its immortal mind was destined
to enjoy a vigorous maturity, and to survive even the average term
of human existence. The estate of Woolsthorpe, in the manor-house of
which this remarkable birth took place, had been more than a hundred
years in the possession of the family, who came originally from Newton
in Lancashire, but who had, previous to the purchase of Woolsthorpe,
settled at Westby, in the county of Lincoln. The manor-house, of which
we have given an engraving, is situated in a beautiful little valley,
remarkable for its copious wells of pure spring water, on the west side
of the river Witham, which has its origin in the neighbourhood, and
commands an agreeable prospect to the east towards Colsterworth. The
manor of Woolsthorpe was worth only 30_l._ per annum; but Mrs. Newton
possessed another small estate at Sewstern,[3] which raised the annual
value of their property to about 80_l._; and it is probable that the
cultivation of the little farm on which she resided somewhat enlarged
the limited income upon which she had to support herself, and educate
her child.

For three years Mrs. Newton continued to watch over her tender charge
with parental anxiety; but in consequence of her marriage to the
Reverend Barnabas Smith, rector of North Witham, about a mile south
of Woolsthorpe, she left him under the care of her own mother. At the
usual age he was sent to two day-schools at Skillington and Stoke,
where he acquired the education which such seminaries afforded; but
when he reached his twelfth year he went to the public school at
Grantham, taught by Mr. Stokes, and was boarded at the house of Mr.
Clark, an apothecary in that town. According to information which
Sir Isaac himself gave to Mr. Conduit, he seems to have been very
inattentive to his studies, and very low in the school. The boy,
however, who was above him, having one day given him a severe kick
upon his stomach, from which he suffered great pain, Isaac laboured
incessantly till he got above him in the school, and from that time
he continued to rise till he was the head boy. From the habits of
application which this incident had led him to form, the peculiar
character of his mind was speedily displayed. During the hours of
play, when the other boys were occupied with their amusements, his
mind was engrossed with mechanical contrivances, either in imitation
of something which he had seen, or in execution of some original
conception of his own. For this purpose he provided himself with little
saws, hatchets, hammers, and all sorts of tools, which he acquired the
art of using with singular dexterity. The principal pieces of mechanism
which he thus constructed were a windmill, a waterclock, and a carriage
put in motion by the person who sat in it. When a windmill was erecting
near Grantham on the road to Gunnerby, Isaac frequently attended the
operations of the workmen, and acquired such a thorough knowledge of
the machinery that he completed a working model of it, which excited
universal admiration. This model was frequently placed on the top of
the house in which he lodged at Grantham, and was put in motion by
the action of the wind upon its sails. Not content with this exact
imitation of the original machine, he conceived the idea of driving it
by animal power, and for this purpose he enclosed in it a mouse which
he called the miller, and which, by acting upon a sort of treadwheel,
gave motion to the machine. According to some accounts, the mouse was
made to advance by pulling a string attached to its tail, while others
allege that the power of the little agent was called forth by its
unavailing attempts to reach a portion of corn placed above the wheel.

His waterclock was formed out of a box which he had solicited from Mrs.
Clark’s brother. It was about four feet high, and of a proportional
breadth, somewhat like a common houseclock. The index of the dialplate
was turned by a piece of wood, which either fell or rose by the action
of dropping water. As it stood in his own bedroom he supplied it every
morning with the requisite quantity of water, and it was used as a
clock by Mr. Clark’s family, and remained in the house long after its
inventor had quitted Grantham.[4] His mechanical carriage was a vehicle
with four wheels, which was put in motion with a handle wrought by the
person who sat in it, but, like Merlin’s chair, it seems to have been
used only on the smooth surface of a floor, and not fitted to overcome
the inequalities of a road. Although Newton was at this time “a sober,
silent, thinking lad,” who scarcely ever joined in the ordinary games
of his schoolfellows, yet he took great pleasure in providing them with
amusements of a scientific character. He introduced into the school
the flying of paper kites; and he is said to have been at great pains
in determining their best forms and proportions, and in ascertaining
the position and number of the points by which the string should be
attached. He made also paper lanterns, by the light of which he went
to school in the winter mornings, and he frequently attached these
lanterns to the tails of his kites in a dark night, so as to inspire
the country people with the belief that they were comets.

In the house where he lodged there were some female inmates in whose
company he appears to have taken much pleasure. One of these, a
Miss Storey, sister to Dr. Storey, a physician at Buckminster, near
Colsterworth, was two or three years younger than Newton, and to great
personal attractions she seems to have added more than the usual
allotment of female talent. The society of this young lady and her
companions was always preferred to that of his own schoolfellows, and
it was one of his most agreeable occupations to construct for them
little tables and cupboards, and other utensils for holding their dolls
and their trinkets. He had lived nearly six years in the same house
with Miss Storey, and there is reason to believe that their youthful
friendship gradually rose to a higher passion; but the smallness of her
portion and the inadequacy of his own fortune appear to have prevented
the consummation of their happiness. Miss Storey was afterward twice
married, and under the name of Mrs. Vincent, Dr. Stukely visited her
at Grantham in 1727, at the age of eighty-two, and obtained from her
many particulars respecting the early history of our author. Newton’s
esteem for her continued unabated during his life. He regularly visited
her when he went to Lincolnshire, and never failed to relieve her from
little pecuniary difficulties which seem to have beset her family.

Among the early passions of Newton we must recount his love of drawing;
and even of writing verses. His own room was furnished with pictures
drawn, coloured, and framed by himself, sometimes from copies, but
often from life.[5] Among these were portraits of Dr. Donne, Mr.
Stokes, the master of Grantham school, and King Charles I. under whose
picture were the following verses.

    A secret art my soul requires to try,
    If prayers can give me what the wars deny.
    Three crowns distinguished here, in order do
    Present their objects to my knowing view.
    Earth’s crown, thus at my feet I can disdain,
    Which heavy is, and at the best but vain.
    But now a crown of thorns I gladly greet,
    Sharp is this crown, but not so sharp as sweet;
    The crown of glory that I yonder see
    Is full of bliss and of eternity.

These verses were repeated to Dr. Stukely by Mrs. Vincent, who believed
them to be written by Sir Isaac, a circumstance which is the more
probable, as he himself assured Mr. Conduit, with some expression of
pleasure, that he “excelled in making verses,” although he had been
heard to express a contempt for poetical composition.

But while the mind of our young philosopher was principally occupied
with the pursuits which we have now detailed, it was not inattentive
to the movements of the celestial bodies, on which he was destined to
throw such a brilliant light. The imperfections of his waterclock had
probably directed his thoughts to the more accurate measure of time
which the motion of the sun afforded. In the yard of the house where
he lived, he traced the varying movements of that luminary upon the
walls and roofs of the buildings, and by means of fixed pins he had
marked out the hourly and half-hourly subdivisions. One of these dials,
which went by the name of _Isaac’s dial_, and was often referred to
by the country people for the hour of the day, appears to have been
drawn solely from the observations of several years; but we are not
informed whether all the dials which he drew on the wall of his house
at Woolsthorpe, and which existed after his death, were of the same
description, or were projected from his knowledge of the doctrine of
the sphere.

Upon the death of the Reverend Mr. Smith in the year 1656, his widow
left the rectory of North Witham, and took up her residence at
Woolsthorpe along with her three children, Mary, Benjamin, and Hannah
Smith. Newton had now attained the fifteenth year of his age, and had
made great progress in his studies; and as he was thought capable of
being useful in the management of the farm and country business at
Woolsthorpe, his mother, chiefly from a motive of economy, recalled
him from the school at Grantham. In order to accustom him to the art
of selling and buying, two of the most important branches of rural
labour, he was frequently sent on Saturday to Grantham market to
dispose of grain and other articles of farm produce, and to purchase
such necessaries as the family required. As he had yet acquired no
experience, an old trustworthy servant generally accompanied him on
these errands. The inn which they patronised was the Saracen’s Head at
West Gate; but no sooner had they put up their horses than our young
philosopher deserted his commercial concerns, and betook himself to
his former lodging in the apothecary’s garret, where a number of Mr.
Clark’s old books afforded him abundance of entertainment till his aged
guardian had executed the family commissions, and announced to him the
necessity of returning. At other times he deserted his duties at an
earlier stage, and intrenched himself under a hedge by the way-side,
where he continued his studies till the servant returned from Grantham.
The more immediate affairs of the farm were not more prosperous under
his management than would have been his marketings at Grantham. The
perusal of a book, the execution of a model, or the superintendence of
a waterwheel of his own construction, whirling the glittering spray
from some neighbouring stream, absorbed all his thoughts when the sheep
were going astray, and the cattle were devouring or treading down the
corn.

Mrs. Smith was soon convinced from experience that her son was not
destined to cultivate the soil, and as his passion for study, and his
dislike for every other occupation increased with his years, she wisely
resolved to give him all the advantages which education could confer.
He was accordingly sent back to Grantham school, where he continued
for some months in busy preparation for his academical studies. His
uncle, the Reverend W. Ayscough, who was rector of Burton Coggles,
about three miles east of Woolsthorpe, and who had himself studied at
Trinity College, recommended to his nephew to enter that society, and
it was accordingly determined that he should proceed to Cambridge at
the approaching term.[6]




CHAPTER II.

  _Newton enters Trinity College, Cambridge—Origin of his Propensity
    for Mathematics—He studies the Geometry of Descartes unassisted—
    Purchases a Prism—Revises Dr. Harrow’s Optical Lectures—Dr.
    Barrow’s Opinion respecting Colours—Takes his Degrees—Is appointed
    a Fellow of Trinity College—Succeeds Dr. Barrow in the Lucasian
    Chair of Mathematics._


To a young mind thirsting for knowledge, and ambitious of the
distinction which it brings, the transition from a village school
to a university like that of Cambridge,—from the absolute solitude
of thought to the society of men imbued with all the literature and
science of the age,—must be one of eventful interest. To Newton it was
a source of peculiar excitement. The history of science affords many
examples where the young aspirant had been early initiated into her
mysteries, and had even exercised his powers of invention and discovery
before he was admitted within the walls of a college; but he who was to
give philosophy her laws did not exhibit such early talent; no friendly
counsel regulated his youthful studies, and no work of scientific
eminence seems to have guided him in his course. In yielding to the
impulse of his mechanical genius, his mind obeyed the laws of its own
natural expansion, and, following the line of least resistance, it was
thus drawn aside from the strongholds with which it was destined to
grapple.

When Newton, therefore, arrived at Trinity College, he brought with
him a more slender portion of science than falls to the lot of
ordinary scholars; but this state of his acquirements was perhaps not
unfavourable to the development of his powers. Unexhausted by premature
growth, and invigorated by healthful repose, his mind was the better
fitted to make those vigorous and rapid shoots which soon covered with
foliage and with fruit the genial soil to which it had been transferred.

Cambridge was consequently the real birthplace of Newton’s genius. Her
teachers fostered his earliest studies;—her institutions sustained his
mightiest efforts;—and within her precincts were all his discoveries
made and perfected. When he was called to higher official functions,
his disciples kept up the pre-eminence of their master’s philosophy,
and their successors have maintained this seat of learning in the
fulness of its glory, and rendered it the most distinguished among the
universities of Europe.

It was on the 5th of June, 1660, in the 18th year of his age, that
Newton was admitted into Trinity College, Cambridge, during the same
year that Dr. Barrow was elected professor of Greek in the university.
His attention was first turned to the study of mathematics by a desire
to inquire into the truth of judicial astrology; and he is said to have
discovered the folly of that study by erecting a figure with the aid
of one or two of the problems of Euclid. The propositions contained in
this ancient system of geometry he regarded as self-evident truths; and
without any preliminary study he made himself master of Descartes’s
Geometry by his genius and patient application. This neglect of the
elementary truths of geometry he afterward regarded as a mistake in
his mathematical studies, and he expressed to Dr. Pemberton his regret
that “he had applied himself to the works of Descartes, and other
algebraic writers, before he had considered the elements of Euclid with
that attention which so excellent a writer deserved.[7] Dr. Wallis’s
Arithmetic of Infinites, Saunderson’s Logic, and the Optics of Kepler
were among the books which he had studied with care. On these works he
wrote comments during their perusal; and so great was his progress,
that he is reported to have found himself more deeply versed in some
branches of knowledge than the tutor who directed his studies.

Neither history nor tradition has handed down to us any particular
account of his progress during the first three years that he spent at
Cambridge. It appears from a statement of his expenses, that in 1664
he purchased a prism, for the purpose, as has been said, of examining
Descartes’s theory of colours; and it is stated by Mr. Conduit, that
he soon established his own views on the subject, and detected the
errors in those of the French philosopher. This, however, does not
seem to have been the case. Had he discovered the composition of light
in 1664 or 1665, it is not likely that he would have withheld it, not
only from the Royal Society, but from his own friends at Cambridge till
the year 1671. His friend and tutor, Dr. Barrow, was made Lucasian
Professor of Mathematics in 1663, and the optical lectures which he
afterward delivered were published in 1669. In the preface of this work
he acknowledges his obligations to his colleague, Mr. Isaac Newton,[8]
for having revised the MSS., and corrected several oversights, and
made some important suggestions. In the twelfth lecture there are
some observations on the nature and origin of colours, which Newton
could not have permitted his friend to publish had he been then in
possession of their true theory. According to Dr. Barrow, _White_ is
that which discharges a copious light equally clear in every direction;
_Black_ is that which does not emit light at all, or which does it very
sparingly. _Red_ is that which emits a light more clear than usual, but
interrupted by shady interstices. _Blue_ is that which discharges a
rarified light, as in bodies which consist of white and black particles
arranged alternately. _Green_ is nearly allied to blue. _Yellow_ is
a mixture of much white and a little red; and _Purple_ consists of a
great deal of blue mixed with a small portion of red. The blue colour
of the sea arises from the whiteness of the salt which it contains,
mixed with the blackness of the pure water in which the salt is
dissolved; and the blueness of the shadows of bodies, seen at the same
time by candle and daylight, arises from the whiteness of the paper
mixed with the faint light or blackness of the twilight. These opinions
savour so little of genuine philosophy that they must have attracted
the observation of Newton, and had he discovered at that time that
white was a mixture of all the colours, and black a privation of them
all, he could not have permitted the absurd speculations of his master
to pass uncorrected.

That Newton had not distinguished himself by any positive discovery
so early as 1664 or 1665, may be inferred also from the circumstances
which attended the competition for the law fellowship of Trinity
College. The candidates for this appointment were himself and Mr.
Robert Uvedale; and Dr. Barrow, then Master of Trinity, having found
them perfectly equal in their attainments, conferred the fellowship on
Mr. Uvedale as the senior candidate.

In the books of the university, Newton is recorded as having been
admitted sub-sizer in 1661. He became a scholar in 1664. In 1665 he
took his degree of Bachelor of Arts, and in 1666, in consequence of
the breaking out of the plague, he retired to Woolsthorpe. In 1667 he
was made Junior Fellow. In 1668 he took his degree of Master of Arts,
and in the same year he was appointed to a Senior Fellowship. In 1669,
when Dr. Barrow had resolved to devote his attention to theology, he
resigned the Lucasian Professorship of Mathematics in favour of Newton,
who may now be considered as having entered upon that brilliant career
of discovery the history of which will form the subject of some of the
following chapters.




CHAPTER III.

  _Newton, occupied in grinding Hyperbolical Lenses—His first
    Experiments with the Prism made in 1666—He discovers the Composition
    of White Light, and the different Refrangibility of the Rays which
    compose it—Abandons his Attempts to improve Refracting Telescopes
    and resolves to attempt the Construction of Reflecting ones—He
    quits Cambridge on account of the Plague—Constructs two Reflecting
    Telescopes in 1668, the first ever executed—One of them examined by
    the Royal Society, and shown to the King—He constructs a Telescope
    with Glass Specula—Recent History of the Reflecting Telescope—
    Mr. Airy’s Glass Specula—Hadley’s Reflecting Telescopes—Short’s—
    Herschel’s—Ramage’s—Lord Oxmantown’s._


The appointment of Newton to the Lucasian chair at Cambridge seems to
have been coeval with his grandest discoveries. The first of these
of which the date is well authenticated is that of the different
refrangibility of the rays of light, which he established in 1666. The
germ of the doctrine of universal gravitation seems to have presented
itself to him in the same year, or at least in 1667; and “in the year
1666 or before”[9] he was in possession of his method of fluxions, and
he had brought it to such a state in the beginning of 1669, that he
permitted Dr. Barrow to communicate it to Mr. Collins on the 20th of
June in that year.

Although we have already mentioned, on the authority of a written
memorandum of Newton himself, that he purchased a prism at Cambridge
in 1664, yet he does not appear to have made any use of it, as he
informs us that it was in 1666 that he “procured a triangular glass
prism to try therewith the celebrated phenomena of colours.”[10] During
that year he had applied himself to the grinding of “optic glasses,
of other figures than spherical,” and having, no doubt, experienced
the impracticability of executing such lenses, the idea of examining
the phenomena of colour was one of those sagacious and fortunate
impulses which more than once led him to discovery. Descartes in his
_Dioptrice_, published in 1629, and more recently James Gregory in
his _Optica Promota_ published in 1663, had shown that parallel and
diverging rays could be reflected or refracted, with mathematical
accuracy, to a point or focus, by giving the surface a parabolic, an
elliptical, or a hyperbolic form, or some other form not spherical.
Descartes had even invented and described machines by which lenses of
these shapes could be ground and polished, and the perfection of the
refracting telescope was supposed to depend on the degree of accuracy
with which they could be executed.

In attempting to grind glasses that were not spherical, Newton seems
to have conjectured that the defects of lenses, and consequently of
refracting telescopes, might arise from some other cause than the
imperfect convergency of rays to a single point, and this conjecture
was happily realized in those fine discoveries of which we shall now
endeavour to give some account.

When Newton began this inquiry, philosophers of the highest genius
were directing all the energies of their mind to the subject of light,
and to the improvement of the refracting telescope. James Gregory of
Aberdeen had invented his reflecting telescope. Descartes had explained
the theory and exerted himself in perfecting the construction of
the common refracting telescope, and Huygens had not only executed
the magnificent instruments by which he discovered the ring and
the satellites of Saturn, but had begun those splendid researches
respecting the nature of light, and the phenomena of double refraction,
which have led his successors to such brilliant discoveries. Newton,
therefore, arose when the science of light was ready for some great
accession, and at the precise time when he was required to propagate
the impulse which it had received from his illustrious predecessors.

The ignorance which then prevailed respecting the nature and origin of
colours is sufficiently apparent from the account we have already given
of Dr. Barrow’s speculations on this subject. It was always supposed
that light of every colour was equally refracted or bent out of its
direction when it passed through any lens or prism, or other refracting
medium; and though the exhibition of colours by the prism had been
often made previous to the time of Newton, yet no philosopher seems to
have attempted to analyze the phenomena.

[Illustration: _Fig. 1._]

When he had procured his triangular glass prism, a section of
which is shown at ABC, (_fig. 1_,) he made a hole H in one of his
window-shutters, SHT, and having darkened his chamber, he let in a
convenient quantity of the sun’s light RR, which, passing through
the prism ABC, was so refracted as to exhibit all the different
colours on the wall at MN, forming an image about five times as long
as it was broad. “It was at first,” says our author, “a very pleasing
divertisement to view the vivid and intense colours produced thereby,”
but this pleasure was immediately succeeded by surprise at various
circumstances which he had not expected. According to the received
laws of refraction, he expected the image MN to be circular, like the
white image at W, which the sunbeam RR had formed on the wall previous
to the interposition of the prism; but when he found it to be no less
than five times larger than its breadth, it “excited in him a more
than ordinary curiosity to examine from whence it might proceed. He
could scarcely think that the various thickness of the glass, or the
termination with shadow or darkness, could have any influence on light
to produce such an effect: yet he thought it not amiss first to examine
those circumstances, and so find what would happen by transmitting
light through parts of the glass of divers thicknesses, or through
holes in the window of divers bignesses, or by setting the prism
without (on the other side of ST), so that the light might pass through
it and be refracted before it was terminated by the hole; but he found
none of these circumstances material. The fashion of the colours was in
all those cases the same.”

Newton next suspected that some unevenness in the glass, or other
accidental irregularity, might cause the dilatation of the colours. In
order to try this, he took another prism BCB′, and placed it in such a
manner that the light RRW passing through them both might be refracted
contrary ways, and thus returned by BCB′ into that course RRW, from
which the prism ABC had diverted it, for by this means he thought
the regular effects of the prism ABC would be destroyed by the prism
BCB′, and the irregular ones more augmented by the multiplicity of
refractions. The result was, that the light which was diffused by the
first prism ABC into an oblong form, was reduced by the second prism
BCB′ into a circular one W, with as much regularity as when it did not
pass through them at all; so that whatever was the cause of the length
of the image MN, it did not arise from any irregularity in the prism.

Our author next proceeded to examine more critically what might be
effected by the difference of the incidence of the rays proceeding from
different parts of the sun’s disk: but by taking accurate measures of
the lines and angles, he found that the angle of the emergent rays
should be 31 minutes equal to the sun’s diameter, whereas the real
angle subtended by MN at the hole H was 2° 49′. But as this computation
was founded on the hypothesis, that the sine of the angle of incidence
was proportional to the sine of the angle of refraction, which from
his own experience he could not imagine to be so erroneous as to make
that angle but 31′, which was in reality 2° 49′, yet “his curiosity
caused him again to take up his prism” ABC, and having turned it round
in both directions, so as to make the rays RR fall both with greater
and with less obliquity upon the face AC, he found that the colours on
the wall did not sensibly change their place; and hence he obtained a
decided proof that they could not be occasioned by a difference in the
incidence of the light radiating from different parts of the sun’s disk.

Newton then began to suspect that the rays, after passing through the
prism, might move in curve lines, and, in proportion to the different
degrees of curvature, might tend to different parts of the wall; and
this suspicion was strengthened by the recollection that he had often
seen a tennis-ball struck with an oblique racket describe such a curve
line. In this case a circular and a progressive motion is communicated
to the ball by the stroke, and in consequence of this, the direction
of its motion was curvilineal, so that if the rays of light were
globular bodies, they might acquire a circulating motion by their
oblique passage out of one medium into another, and thus move like the
tennis-ball in a curve line. Notwithstanding, however, “this plausible
ground of suspicion,” he could discover no such curvature in their
direction, and, what was enough for his purpose, he observed that the
difference between the length MN of the image, and the diameter of the
hole H, was proportional to their distance HM, which could not have
happened had the rays moved in curvilineal paths.

These different hypotheses, or suspicions, as Newton calls them, being
thus gradually removed, he was at length led to an experiment which
determined beyond a doubt the true cause of the elongation of the
coloured image. Having taken a board with a small hole in it, he placed
it behind the face BC of the prism, and close to it, so that he could
transmit through the hole any one of the colours in MN, and keep back
all the rest. When the hole, for example, was near C, no other light
but the red fell upon the wall at N. He then placed behind N another
board with a hole in it, and behind this board he placed another prism,
so as to receive the red light at N, which passed through this hole in
the second board. He then turned round the first prism ABC so as to
make all the colours pass in succession through these two holes, and he
marked their places on the wall. From the variation of these places, he
saw that the _red_ rays at N were less refracted by the second prism
than the _orange_ rays, the _orange_ less than the _yellow_, and so on,
the _violet_ being more refracted than all the rest.

Hence he drew the grand conclusion, _that light was not homogeneous,
but consisted of rays, some of which were more refrangible than others_.

As soon as this important truth was established, Sir Isaac saw that a
lens which refracts light exactly like a prism must also refract the
differently coloured rays with different degrees of force, bringing
the violet rays to a focus nearer the glass than the red rays. This is
shown in _fig. 2_, where LL is a convex lens, and S, L, SL rays of the
sun falling upon it in parallel directions. The violet rays existing in
the white light SL being more refrangible than the rest, will be more
refracted or bent, and will meet at V, forming there a violet image of
the sun. In like manner the yellow rays will form an image of the sun
at Y, and so on, the red rays, which are the least refrangible, being
brought to a focus at R, and there forming a red image of the sun.

[Illustration: _Fig. 2._]

Hence, if we suppose LL to be the object-glass of a telescope directed
to the sun, and MM an eye-glass through which the eye at E sees
magnified the image or picture of the sun formed by LL, it cannot see
distinctly all the different images between R and V. If it is adjusted
so as to see distinctly the _yellow_ image at Y, as it is in the
figure, it will not see distinctly either the _red_ or _violet_ images,
nor indeed any of them but the yellow one. There will consequently be a
distinct yellow image, with indistinct images of all the other colours,
producing great confusion and indistinctness of vision. As soon as Sir
Isaac perceived this result of his discovery, he abandoned his attempts
to improve the refracting telescope, and took into consideration the
principle of reflection; and as he found that rays of all colours were
reflected regularly, so that the angle of reflection was equal to the
angle of incidence, he concluded that, upon this principle, _optical
instruments might be brought to any degree of perfection imaginable_,
provided a reflecting substance could be found which could polish as
finely as glass, and reflect as much light as glass transmits, and
provided a method of communicating to it a parabolic figure could be
obtained. These difficulties, however, appeared to him very great,
and he even thought them insuperable when he considered that, as any
irregularity in a reflecting surface makes the rays deviate five or
six times more from their true path than similar irregularities in a
refracting surface, a much greater degree of nicety would be required
in figuring reflecting specula than refracting lenses.

Such was the progress of Newton’s optical discoveries, when he was
forced to quit Cambridge in 1666 by the plague which then desolated
England, and more than two years elapsed before he proceeded any
farther. In 1668 he resumed the inquiry, and having thought of a
delicate method of polishing, proper for metals, by which, as he
conceived, “the figure would be corrected to the last,” he began to put
this method to the test of experiment. At this time he was acquainted
with the proposal of Mr. James Gregory, contained in his _Optica
Promota_, to construct a reflecting telescope with two concave specula,
the largest of which had a hole in the middle of the larger speculum,
to transmit the light to an eye-glass;[11] but he conceived that it
would be an improvement on this instrument to place the eye-glass at
the side of the tube, and to reflect the rays to it by an oval plane
speculum. One of these instruments he actually executed with his own
hands; and he gave an account of it in a letter to a friend, dated
February 23d, 1668–9, a letter which is also remarkable for containing
the first allusion to his discoveries respecting colours. Previous to
this he was in correspondence on the subject with Mr. Ent, afterward
Sir George Ent, one of the original council of the Royal Society, an
eminent medical writer of his day, and President of the College of
Physicians. In a letter to Mr. Ent he had promised an account of his
telescope to their mutual friend, and the letter to which we now allude
contained the fulfilment of that promise. The telescope was six inches
long. It bore an aperture in the large speculum something more than
an inch, and as the eye-glass was a plano-convex lens, whose focal
length was one-sixth or one-seventh of an inch, it magnified about
forty times, which, as Newton remarks, was more than any six-foot
tube (meaning refracting telescopes) could do with distinctness. On
account of the badness of the materials, however, and the want of a
good polish, it represented objects less distinct than a six-feet tube,
though he still thought it would be equal to a three or four feet tube
directed to common objects. He had seen through it Jupiter distinctly
with his four satellites, and also the horns or moon-like phases of
Venus, though this last phenomenon required some niceness in adjusting
the instrument.

Although Newton considered this little instrument as in itself
contemptible, yet he regarded it as an “epitome of what might be done;”
and he expressed his conviction that a six-feet telescope might be made
after this method, which would perform as well as a sixty or a hundred
feet telescope made in the common way; and that if a common refracting
telescope could be made of the “purest glass exquisitely polished,
with the best figure that any geometrician (Descartes, &c.) hath or
can design,” it would scarcely perform better than a common telescope.
This, he adds, may seem a paradoxical assertion, yet he continues, “it
is the necessary consequence of some experiments which I have made
concerning the nature of light.”

The telescope now described possesses a very peculiar interest, as
being the first reflecting one which was ever executed and directed to
the heavens. James Gregory, indeed, had attempted, in 1664 or 1665, to
construct his instrument. He employed Messrs. Rives and Cox, who were
celebrated glass-grinders of that time, to execute a concave speculum
of six feet radius, and likewise a small one; but as they had failed
in polishing the large one, and as Mr. Gregory was on the eve of going
abroad, he troubled himself no farther about the experiment, and the
tube of the telescope was never made. Some time afterward, indeed, he
“made some trials both with a little concave and convex speculum,” but,
“possessed with the fancy of the defective figure, he would not be at
the pains to fix every thing in its due distance.”

Such were the earliest attempts to construct the reflecting telescope,
that noble instrument which has since effected such splendid
discoveries in astronomy. Looking back from the present advanced state
of practical science, how great is the contrast between the loose
specula of Gregory and the fine Gregorian telescopes of Hadley, Short,
and Veitch,—between the humble six-inch tube of Newton and the gigantic
instruments of Herschel and Ramage.

The success of this first experiment inspired Newton with fresh zeal,
and though his mind was now occupied with his optical discoveries,
with the elements of his method of fluxions, and with the expanding
germ of his theory of universal gravitation, yet with all the ardour
of youth he applied himself to the laborious operation of executing
another reflecting telescope with his own hands. This instrument,
which was better than the first, though it lay by him several years,
excited some interest at Cambridge; and Sir Isaac himself informs us,
that one of the fellows of Trinity College had completed a telescope
of the same kind, which he considered as somewhat superior to his own.
The existence of these telescopes having become known to the Royal
Society, Newton was requested to send his instrument for examination
to that learned body. He accordingly transmitted it to Mr. Oldenburg
in December, 1671, and from this epoch his name began to acquire that
celebrity by which it has been so peculiarly distinguished.

On the 11th of January, 1672, it was announced to the Royal Society
that his reflecting telescope had been shown to the king, and had
been examined by the president, Sir Robert Moray, Sir Paul Neale, Sir
Christopher Wren, and Mr. Hook. These gentlemen entertained so high an
opinion of it, that, in order to secure the honour of the contrivance
to its author, they advised the inventor to send a drawing and
description of it to Mr. Huygens at Paris. Mr. Oldenburg accordingly
drew up a description of it in Latin, which, after being corrected
by Mr. Newton, was transmitted to that eminent philosopher. This
telescope, of which the annexed is an accurate drawing, is carefully
preserved in the library of the Royal Society of London, with the
following inscription:—

  “_Invented by Sir Isaac Newton and made with his own hands, 1671._”

[Illustration: _Fig. 3._

_Sir Isaac Newton’s Reflecting Telescope._]

It does not appear that Newton executed any other reflecting telescopes
than the two we have mentioned. He informs us that he repolished and
greatly improved a fourteen-feet object-glass, executed by a London
artist, and having proposed in 1678 to substitute glass reflectors in
place of metallic specula, he tried to make a reflecting telescope
on this principle four feet long, and with a magnifying power of
150. The glass was wrought by a London artist, and though it seemed
well finished, yet, when it was quicksilvered on its convex side, it
exhibited all over the glass innumerable inequalities, which gave an
indistinctness to every object. He expresses, however, his conviction
that nothing but good workmanship is wanting to perfect these
telescopes, and he recommends their consideration “to the curious in
figuring glasses.”

For a period of fifty years this recommendation excited no notice.
At last Mr. James Short of Edinburgh, an artist of consummate skill,
executed about the year 1730 no fewer than six reflecting telescopes
with glass specula, three of fifteen inches, and three of nine inches
in focal length. He found it extremely troublesome to give them a true
figure with parallel surfaces; and several of them when finished turned
out useless, in consequence of the veins which then appeared in the
glass. Although these instruments performed remarkably well, yet the
light was fainter than he expected, and from this cause, combined with
the difficulty of finishing them, he afterward devoted his labours
solely to those with metallic specula.

At a later period, in 1822, Mr. G. B. Airy of Trinity College, and
one of the distinguished successors of Newton in the Lucasian chair,
resumed the consideration of glass specula, and demonstrated that the
aberration both of figure and of colour might be corrected in these
instruments. Upon this ingenious principle Mr. Airy executed more
than one telescope, but though the result of the experiment was such
as to excite hopes of ultimate success, yet the construction of such
instruments is still a desideratum in practical science.

Such were the attempts which Sir Isaac Newton made to construct
reflecting telescopes; but notwithstanding the success of his labours,
neither the philosopher nor the practical optician seems to have had
courage to pursue them. A London artist, indeed, undertook to imitate
these instruments; but Sir Isaac informs us, that “he fell much short
of what he had attained, as he afterward understood by discoursing
with the under workmen he had employed.” After a long period of fifty
years, John Hadley, Esq. of Essex, a Fellow of the Royal Society, began
in 1719 or 1720 to execute a reflecting telescope. His scientific
knowledge and his manual dexterity fitted him admirably for such a
task, and, probably after many failures, he constructed two large
telescopes about five feet three inches long, one of which, with a
speculum six inches in diameter, was presented to the Royal Society in
1723. The celebrated Dr. Bradley and the Rev. Mr. Pound compared it
with the great Huygenian refractor 123 feet long. It bore as high a
magnifying power as the Huygenian telescope: it showed objects equally
distinct, though not altogether so clear and bright, and it exhibited
every celestial object that had been discovered by Huygens,—the five
satellites of Saturn, the shadow of Jupiter’s satellites on his disk,
the black list in Saturn’s ring, and the edge of his shadow cast on the
ring. Encouraged and instructed by Mr. Hadley, Dr. Bradley began the
construction of reflecting telescopes, and succeeded so well that he
would have completed one of them, had he not been obliged to change his
residence. Some time afterward he and the Honourable Samuel Molyneux
undertook the task together at Kew, and attempted to execute specula
about twenty-six inches in focal length; but notwithstanding Dr.
Bradley’s former experience, and Mr. Hadley’s frequent instructions,
it was a long time before they succeeded. The first good instrument
which they finished was in May, 1724. It was twenty-six inches in focal
length; but they afterward completed a very large one of eight feet,
the largest that had ever been made. The first of these instruments was
afterward elegantly fitted up by Mr. Molyneux, and presented to his
majesty John V. King of Portugal.

The great object of these two able astronomers was to reduce the
method of making specula to such a degree of certainty that they
could be manufactured for public sale. Mr. Hauksbee had indeed made a
good one about three and a half feet long, and had proceeded to the
execution of two others, one of six feet, and another of twelve feet
in focal length; but Mr. Scarlet and Mr. Hearne, having received all
the information which Mr. Molyneux had acquired, constructed them
for public sale; and the reflecting telescope has ever since been an
article of trade with every regular optician.

As Sir Isaac Newton was at this time President of the Royal Society,
he had the high satisfaction of seeing his own invention become an
instrument of public use, and of great advantage to science, and
he no doubt felt the full influence of this triumph of his skill.
Still, however, the reflecting telescope had not achieved any new
discovery in the heavens. The latest accession to astronomy had been
made by the ordinary refractors of Huygens, labouring under all the
imperfections of coloured light; and this long pause in astronomical
discovery seemed to indicate that man had carried to its farthest
limits his power of penetrating into the depths of the universe.
This, however, was only one of those stationary positions from which
human genius takes a new and a loftier elevation. While the English
opticians were thus practising the recent art of grinding specula, Mr.
James Short of Edinburgh was devoting to the subject all the energies
of his youthful mind. In 1732, and in the 22d year of his age, he
began his labours, and he carried to such high perfection the art of
grinding and polishing specula, and of giving them the true parabolic
figure, that, with a telescope fifteen inches in focal length, he
read in the Philosophical Transactions at the distance of 500 feet,
and frequently saw the five satellites of Saturn together,—a power
which was beyond the reach even of Hadley’s six-feet instrument. The
celebrated Maclaurin compared the telescopes of Short with those made
by the best London artists, and so great was their superiority, that
his small telescopes were invariably superior to larger ones from
London. In 1742, after he had settled as an optician in the metropolis,
he executed for Lord Thomas Spencer a reflecting telescope, twelve
feet in focal length, for 630_l._; in 1752 he completed one for the
King of Spain, at the expense of 1200_l._; and a short time before
his death, which took place in 1768, he finished the specula of the
large telescope which was mounted equatorially for the observatory of
Edinburgh by his brother Thomas Short, who was offered twelve hundred
guineas for it by the King of Denmark.

Although the superiority of these instruments, which were all of the
Gregorian form, demonstrated the value of the reflecting telescope, yet
no skilful hand had yet directed it to the heavens; and it was reserved
for Dr. Herschel to employ it as an instrument of discovery, to exhibit
to the eye of man new worlds and new systems, and to bring within
the grasp of his reason those remote regions of space to which his
imagination even had scarcely ventured to extend its power. So early as
1774 he completed a _five_-feet Newtonian reflector, and he afterward
executed no fewer than _two hundred_ 7 feet, _one hundred and fifty_
10 feet, and _eighty_ 20 feet specula. In 1781 he began a reflector
thirty feet long, and having a speculum thirty-six inches in diameter;
and under the munificent patronage of George III. he completed,
in 1789, his gigantic instrument forty feet long, with a speculum
_forty-nine and a half_ inches in diameter. The genius and perseverance
which created instruments of such transcendent magnitude were not
likely to terminate with their construction. In the examination of
the starry heavens, the ultimate object of his labours, Dr. Herschel
exhibited the same exalted qualifications, and in a few years he rose
from the level of humble life to the enjoyment of a name more glorious
than that of the sages and warriors of ancient times, and as immortal
as the objects with which it will be for ever associated. Nor was it
in the ardour of the spring of life that these triumphs of reason were
achieved. Dr. Herschel had reached the middle of his course before his
career of discovery began, and it was in the autumn and winter of his
days that he reaped the full harvest of his glory. The discovery of a
new planet at the verge of the solar system was the first trophy of his
skill, and new double and multiple stars, and new nebulæ, and groups of
celestial bodies were added in thousands to the system of the universe.
The spring-tide of knowledge which was thus let in upon the human mind
continued for a while to spread its waves over Europe; but when it sank
to its ebb in England, there was no other bark left upon the strand but
that of the Deucalion of Science, whose home had been so long upon its
waters.

During the life of Dr. Herschel, and during the reign, and within the
dominions of his royal patron, four new planets were added to the solar
system, but they were detected by telescopes of ordinary power; and we
venture to state, that since the reign of George III. no attempt has
been made to keep up the continuity of Dr. Herschel’s discoveries.

Mr. Herschel, his distinguished son, has indeed completed more
than one telescope of considerable size; Mr. Ramage, of Aberdeen,
has executed reflectors rivalling almost those of Slough;—and Lord
Oxmantown, an Irish nobleman of high promise, is now engaged on an
instrument of great size. But what avail the enthusiasm and the efforts
of individual minds in the intellectual rivalry of nations? When the
proud science of England pines in obscurity, blighted by the absence
of the royal favour, and of the nation’s sympathy;—when its chivalry
fall unwept and unhonoured;—how can it sustain the conflict against the
honoured and marshalled genius of foreign lands?




CHAPTER IV.

  _He delivers a Course of Optical Lectures at Cambridge—Is elected
    Fellow of the Royal Society—He communicates to them his Discoveries
    on the different Refrangibility and Nature of Light—Popular Account
    of them—They involve him in various Controversies—His Dispute with
    Pardies—Linus—Lucas—Dr. Hooke and Mr. Huygens—The Influence of
    these Disputes on the Mind of Newton._


Although Newton delivered a course of lectures on optics in the
University of Cambridge in the years 1669, 1670, and 1671, containing
his principal discoveries relative to the different refrangibility of
light, yet it is a singular circumstance, that these discoveries should
not have become public through the conversation or correspondence of
his pupils. The Royal Society had acquired no knowledge of them till
the beginning of 1672, and his reputation in that body was founded
chiefly on his reflecting telescope. On the 23d December, 1671, the
celebrated Dr. Seth Ward, Lord Bishop of Sarum, who was the author of
several able works on astronomy, and had filled the astronomical chair
at Oxford, proposed Mr. Newton as a Fellow of the Royal Society.
The satisfaction which he derived from this circumstance appears to
have been considerable; and in a letter to Mr. Oldenburg, of the 6th
January, he says, “I am very sensible of the honour done me by the
Bishop of Sarum in proposing me a candidate; and which, I hope, will
be further conferred upon me by my election into the Society; and if
so, I shall endeavour to testify my gratitude, by communicating what
my poor and solitary endeavours can effect towards the promoting your
philosophical designs.” His election accordingly took place on the
11th January, the same day on which the Society agreed to transmit a
description of his telescope to Mr. Huygens at Paris. The notice of his
election, and the thanks of the Society for the communication of his
telescope, were conveyed in the same letter, with an assurance that
the Society “would take care that all right should be done him in the
matter of this invention.” In his next letter to Oldenburg, written
on the 18th January, 1671–2, he announces his optical discoveries in
the following remarkable manner: “I desire that in your next letter
you would inform me for what time the Society continue their weekly
meetings; because if they continue them for any time, I am purposing
them, to be considered of and examined, an account of a philosophical
discovery which induced me to the making of the said telescope; and
I doubt not but will prove much more grateful than the communication
of that instrument; being in my judgment the oddest, if not the most
considerable detection which hath hitherto been made in the operations
of nature.”

This “considerable detection” was the discovery of the different
refrangibility of the rays of light which we have already explained,
and which led to the construction of his reflecting telescope. It
was communicated to the Royal Society in a letter to Mr. Oldenburg,
dated February 6th, and excited great interest among its members. The
“solemn thanks” of the meeting were ordered to be transmitted to its
author for his “very ingenious discourse.” A desire was expressed to
have it immediately printed, both for the purpose of having it well
considered by philosophers, and for “securing the considerable notices
thereof to the author against the arrogations of others;” and Dr. Seth
Ward, Bishop of Salisbury, Mr. Boyle, and Dr. Hooke were desired to
peruse and consider it, and to bring in a report upon it to the Society.

The kindness of this distinguished body, and the anxiety which they
had already evinced for his reputation, excited on the part of Newton
a corresponding feeling, and he gladly accepted of their proposal to
publish his discourse in the monthly numbers in which the Transactions
were then given to the world. “It was an esteem,” says he,[12] “of the
Royal Society for most candid and able judges in philosophical matters,
encouraged me to present them with that discourse of light and colours,
which since they have so favourably accepted of, I do earnestly desire
you to return them my cordial thanks. I before thought it a great
favour to be made a member of that honourable body; but I am now more
sensible of the advantages; for believe me, sir, I do not only esteem
it a duty to concur with you in the promotion of real knowledge; but a
great privilege, that, instead of exposing discourses to a prejudiced
and common multitude, (by which means many truths have been baffled and
lost), I may with freedom apply myself to so judicious and impartial
an assembly. As to the printing of that letter, I am satisfied in
their judgment, or else I should have thought it too straight and
narrow for public view. I designed it only to those that know how to
improve upon hints of things; and, therefore, to spare tediousness,
omitted many such remarks and experiments as might be collected by
considering the assigned laws of refractions; some of which I believe,
with the generality of men, would yet be almost as taking as any I
described. But yet, since the Royal Society have thought it fit to
appear publicly, I leave it to their pleasure: and perhaps to supply
the aforesaid defects, I may send you some more of the experiments to
second it (if it be so thought fit), in the ensuing Transactions.”

Following the order which Newton himself adopted, we have, in the
preceding chapter, given an account of the leading doctrine of the
different refrangibility of light, and of the attempts to improve the
reflecting telescope which that discovery suggested. We shall now,
therefore, endeavour to make the reader acquainted with the other
discoveries respecting colours which he at this time communicated to
the Royal Society.

[Illustration: _Fig. 4._]

Having determined, by experiments already described, that a beam of
white light, as emitted from the sun, consisted of seven different
colours, which possess different degrees of refrangibility, he measured
the relative extent of the coloured spaces, and found them to have
the proportions shown in _fig. 4_, which represents the _prismatic_
spectrum, and which is nothing more than an elongated image of the sun
produced by the rays being separated in different degrees from their
original direction, the _red_ being refracted _least_, and the _violet
most_ powerfully.

If we consider light as consisting of minute particles of matter,
we may form some notion of its decomposition by the prism from the
following popular illustration. If we take steel filings of seven
different degrees of fineness and mix them together, there are two ways
in which we may conceive the mass to be decomposed, or, what is the
same thing, all the seven different kinds of filings separated from
each other. By means of seven sieves of different degrees of fineness,
and so made that the finest will just transmit the finest powder and
detain all the rest, while the next in fineness transmits the two
finest powders and detains all the rest, and so on, it is obvious that
all the powders may be completely separated from each other. If we
again mix all the steel filings, and laying them upon a table, hold
high above them a flat bar magnet, so that none of the filings are
attracted, then if we bring the magnet nearer and nearer, we shall come
to a point where the finest filings are drawn up to it. These being
removed, and the magnet brought nearer still, the next finest powders
will be attracted, and so on till we have thus drawn out of the mass
all the powders in a separate state. We may conceive the bar magnet to
be inclined to the surface of the steel filings, and so moved over the
mass, that at the end nearest to them the heaviest or coarsest will
be attracted, and all the remotest and the finest or lighter filings,
while the rest are attracted to intermediate points, so that the seven
different filings are not only separated, but are found adhering in
separate patches to the surface of the flat magnet. The first of these
methods, with the sieves, may represent the process of decomposing
light, by which certain rays of white light are absorbed, or stifled,
or stopped in passing through bodies, while certain other rays are
transmitted. The second method may represent the process of decomposing
light by refraction, or by the attraction of certain rays farther from
their original direction than other rays, and the different patches of
filings upon the flat magnet may represent the spaces on the spectrum.

When a beam of white light is decomposed into the seven different
colours of the spectrum, any particular colour, when once separated
from the rest, is not susceptible of any change, or farther
decomposition, whether it is refracted through prisms or reflected from
mirrors. It may become fainter or brighter, but Newton never could, by
any process, alter its colour or its refrangibility.

Among the various bodies which act upon light, it is conceivable
that there might have been some which acted least upon the violet
rays and most upon the red rays. Newton, however, found that this
never took place; but that the same degree of refrangibility always
belonged to the same colour, and the same colour to the same degree of
refrangibility.

Having thus determined that the seven different colours of the spectrum
were original or simple, he was led to the conclusion that _whiteness_
or white light is a compound of all the seven colours of the spectrum,
in the proportions in which they are represented in _fig. 4_. In order
to prove this, or what is called the recomposition of white light out
of the seven colours, he employed three different methods.

[Illustration: _Fig. 5._]

When the beam RR was separated into its elementary colours by the prism
ABC, he received the colours on another prism BCB′, held either close
to the first or a little behind it, and by the opposite refraction of
this prism they were all refracted back into a beam of white light BW,
which formed a white circular image on the wall at W, similar to what
took place before any of the prisms were placed in its way.

The other method of recomposing white light consisted in making the
spectrum fall upon a lens at some distance from it. When a sheet of
white paper was held behind the lens, and removed to a proper distance,
the colours were all refracted into a circular spot, and so blended as
to reproduce light so perfectly white as not to differ sensibly from
the direct light of the sun.

The last method of recomposing white light was one more suited to
vulgar apprehension. It consisted in attempting to compound a white by
mixing the coloured powders used by painters. He was aware that such
colours, from their very nature, could not compose a pure white; but
even this imperfection in the experiment he removed by an ingenious
device. He accordingly mixed one part of _red lead_, four parts of
_blue bice_, and a proper proportion of _orpiment_ and _verdigris_.
This mixture was _dun_, like wood newly cut, or like the human skin. He
now took one-third of the mixture and rubbed it thickly on the floor
of his room, where the sun shone upon it through the opened casement,
and beside it, in the shadow, he laid a piece of white paper of the
same size. “Then going from them to the distance of twelve or eighteen
feet, so that he could not discern the unevenness of the surface of
the powder nor the little shadows let fall from the gritty particles
thereof; the powder appeared intensely white, so as to transcend even
the paper itself in whiteness.” By adjusting the relative illumination
of the powders and the paper, he was able to make them both appear of
the very same degree of whiteness. “For,” says he, “when I was trying
this, a friend coming to visit me, I stopped him at the door, and
before I told him what the colours were, or what I was doing, I asked
him which of the two whites were the best, and wherein they differed!
And after he had at that distance viewed them well, he answered, that
they were both good whites, and that he could not say which was best,
nor wherein their colours differed.” Hence Newton inferred that perfect
whiteness may be compounded of different colours.

As all the various shades of colour which appear in the material world
can be imitated by intercepting certain rays in the spectrum, and
uniting all the rest, and as bodies always appear of the same colour
as the light in which they are placed, he concluded, that the colours
of natural bodies are not qualities inherent in the bodies themselves,
but arise from the disposition of the particles of each body to stop or
absorb certain rays, and thus to reflect more copiously the rays which
are not thus absorbed.

No sooner were these discoveries given to the world than they were
opposed with a degree of virulence and ignorance which have seldom
been combined in scientific controversy. Unfortunately for Newton, the
Royal Society contained few individuals of pre-eminent talent capable
of appreciating the truth of his discoveries, and of protecting him
against the shafts of his envious and ignorant assailants. This eminent
body, while they held his labours in the highest esteem, were still
of opinion that his discoveries were fair subjects of discussion,
and their secretary accordingly communicated to him all the papers
which were written in opposition to his views. The first of these
was by a Jesuit named Ignatius Pardies, Professor of Mathematics at
Clermont, who pretended that the elongation of the sun’s image arose
from the inequal incidence of the different rays on the first face
of the prism, although Newton had demonstrated in his own discourse
that this was not the case. In April, 1672, Newton transmitted to
Oldenburg a decisive reply to the animadversions of Pardies; but,
unwilling to be vanquished, this disciple of Descartes took up a fresh
position, and maintained that the elongation of the spectrum might be
explained by the diffusion of light on the hypothesis of Grimaldi,
or by the diffusion of undulations on the hypothesis of Hook. Newton
again replied to these feeble reasonings; but he contented himself
with reiterating his original experiments, and confirming them by more
popular arguments, and the vanquished Jesuit wisely quitted the field.

Another combatant soon sprung up in the person of one Francis Linus,
a physician in Liege,[13] who, on the 6th October, 1674, addressed a
letter to a friend in London, containing animadversions on Newton’s
doctrine of colours. He boldly affirms, that in a perfectly clear sky
the image of the sun made by a prism is never elongated, and that the
spectrum observed by Newton was not formed by the true sunbeams, but by
rays proceeding from some bright cloud. In support of these assertions,
he appeals to frequently repeated experiments on the refractions and
reflections of light which he had exhibited thirty years before to
Sir Kenelm Digby, “who took notes upon them;” and he unblushingly
states, that, if Newton had used the same industry as he did, he
would never have “taken so impossible a task in hand, as to explain
the difference between the length and breadth of the spectrum by the
received laws of refraction.” When this letter was shown to Newton, he
refused to answer it; but a letter was sent to Linus referring him
to the answer to Pardies, and assuring him that the experiments on
the spectrum were made when there was no bright cloud in the heavens.
This reply, however, did not satisfy the Dutch experimentalist. On the
25th February, 1675, he addressed another letter to his friend, in
which he gravely attempts to prove that the experiment of Newton was
not made in a clear day;—that the prism was not close to the hole,—and
that the length of the spectrum was not perpendicular, or parallel to
the length of the prism. Such assertions could not but irritate even
the patient mind of Newton. He more than once declined the earnest
request of Oldenburg to answer these observations; he stated, that,
as the dispute referred to matters of fact, it could only be decided
before competent witnesses, and he referred to the testimony of those
who had seen his experiments. The entreaties of Oldenburg, however,
prevailed over his own better judgment, and, “lest Mr. Linus should
make the more stir,” this great man was compelled to draw up a long
and explanatory reply to reasonings utterly contemptible, and to
assertions altogether unfounded. This answer, dated November 13th,
1675, could scarcely have been perused by Linus, who was dead on the
15th December, when his pupil Mr. Gascoigne, took up the gauntlet,
and declared that Linus had shown to various persons in Liege the
experiment which proved the spectrum to be circular, and that Sir
Isaac could not be more confident on his side than they were on the
other. He admitted, however, that the different results might arise
from different ways of placing the prism. Pleased with the “handsome
genius of Mr. Gascoigne’s letter,” Newton replied even to it, and
suggested that the spectrum seen by Linus may have been the circular
one, formed by one reflexion, or, what he thought more probable, the
circular one formed by two refractions, and one intervening reflection
from the base of the prism, which would be coloured if the prism was
not an isosceles one. This suggestion seems to have enlightened the
Dutch philosophers. Mr. Gascoigne, having no conveniences for making
the experiments pointed out by Newton, requested Mr. Lucas of Liege to
perform them in his own house. This ingenious individual, whose paper
gave great satisfaction to Newton, and deserves the highest praise,
confirmed the leading results of the English philosopher; but though
the refracting angle of his prism was 60° and the refractions equal, he
never could obtain a spectrum whose length was more than from _three_
to _three and a half_ times its breadth, while Newton found the length
to be _five_ times its breadth. In our author’s reply, he directs his
attention principally to this point of difference. He repeated his
measures with each of the three angles of _three_ different prisms, and
he affirmed that Mr. Lucas might _make sure to find the image as long
or longer than he had yet done_, by taking a prism with plain surfaces,
and with an angle of 66° or 67°. He admitted that the smallness of
the angle in Mr. Lucas’s prism, viz. 60°, did not account for the
shortness of the spectrum which he obtained with it; and he observed
in one of his own prisms that the length of the image was greater in
proportion to the refracting angle than it should have been; an effect
which he ascribes to its having a greater refractive power. There is
every reason to believe that the prism of Lucas had actually a less
dispersive power than that of Newton; and had the Dutch philosopher
measured its refractive power instead of guessing it, or had Newton
been less confident than he was[14] that all other prisms must give
a spectrum of the same length as his in relation to its refracting
angle and its index of refraction, the invention of the achromatic
telescope would have been the necessary result. The objections of Lucas
drove our author to experiments which he had never before made,—to
measure accurately the lengths of the spectra with different prisms of
different angles and different refractive powers; and had the Dutch
philosopher maintained his position with more obstinacy, he would have
conferred a distinguished favour upon science, and would have rewarded
Newton for all the vexation which had sprung from the minute discussion
of his optical experiments.

Such was the termination of his disputes with the Dutch philosophers,
and it can scarcely be doubted that it cost him more trouble to detect
the origin of his adversaries’ blunders, than to establish the great
truths which they had attempted to overturn.

Harassing as such a controversy must have been to a philosopher
like Newton, yet it did not touch those deep-seated feelings which
characterize the noble and generous mind. No rival jealousy yet
pointed the arguments of his opponents;—no charges of plagiarism were
yet directed against his personal character. These aggravations of
scientific controversy, however, he was destined to endure; and in the
dispute which he was called to maintain both against Hooke and Huygens,
the agreeable consciousness of grappling with men of kindred powers was
painfully imbittered by the personality and jealousy with which it was
conducted.

Dr. Robert Hooke was about seven years older than Newton, and was
one of the ninety-eight original or unelected members of the Royal
Society. He possessed great versatility of talent, yet, though his
genius was of the most original cast, and his acquirements extensive,
he had not devoted himself with fixed purpose to any particular branch
of knowledge. His numerous and ingenious inventions, of which it
is impossible to speak too highly, gave to his studies a practical
turn which unfitted him for that continuous labour which physical
researches so imperiously demand. The subjects of light, however, and
of gravitation seem to have deeply occupied his thoughts before Newton
appeared in the same field, and there can be no doubt that he had made
considerable progress in both of these inquiries. With a mind less
divergent in its pursuits, and more endowed with patience of thought,
he might have unveiled the mysteries in which both these subjects were
enveloped, and preoccupied the intellectual throne which was destined
for his rival; but the infirm state of his health, the peevishness
of temper which this occasioned, the number of unfinished inventions
from which he looked both for fortune and fame, and, above all, his
inordinate love of reputation, distracted and broke down the energies
of his powerful intellect. In the more matured inquiries of his rivals
he recognised, and often truly, his own incompleted speculations; and
when he saw others reaping the harvest for which he had prepared the
ground, and of which he had sown the seeds, it was not easy to suppress
the mortification which their success inspired. In the history of
science, it has always been a difficult task to adjust the rival claims
of competitors, when the one was allowed to have completed what the
other was acknowledged to have begun. He who commences an inquiry, and
publishes his results, often goes much farther than he has announced
to the world, and, pushing his speculations into the very heart of the
subject, frequently submits them to the ear of friendship. From the
pedestal of his published labours his rival begins his researches,
and brings them to a successful issue; while he has in reality done
nothing more than complete and demonstrate the imperfect speculations
of his predecessor. To the world, and to himself, he is no doubt in the
position of the principal discoverer: but there is still some apology
for his rival when he brings forward his unpublished labours; and some
excuse for the exercise of personal feeling, when he measures the speed
of his rival by his own proximity to the goal.

The conduct of Dr. Hooke would have been viewed with some such feeling,
had not his arrogance on other occasions checked the natural current
of our sympathy. When Newton presented his reflecting telescope to
the Royal Society, Dr. Hooke not only criticised the instrument with
undue severity, but announced that he possessed an infallible method of
perfecting all kinds of optical instruments, so that “whatever almost
hath been in notion and imagination, or desired in optics, may be
performed with great facility and truth.”

Hooke had been strongly impressed with the belief, that light
consisted in the undulations of a highly elastic medium pervading
all bodies; and, guided by his experimental investigation of the
phenomena of diffraction, he had even announced the great _principle
of interference_, which has performed such an important part in
modern science. Regarding himself, therefore, as in possession of
the true theory of light, he examined the discoveries of Newton in
their relation to his own speculative views, and, finding that their
author was disposed to consider that element as consisting of material
particles, he did not scruple to reject doctrines which he believed to
be incompatible with truth. Dr. Hooke was too accurate an observer not
to admit the general correctness of Newton’s observations. He allowed
the existence of different refractions, the unchangeableness of the
simple colours, and the production of white light by the union of all
the colours of the spectrum; but he maintained that the different
refractions arose from the splitting and rarefying of ethereal pulses,
and that there are only two colours in nature, viz. _red_ and _violet_,
which produce by their mixture all the rest, and which are themselves
formed by the two sides of a split pulse or undulation.

In reply to these observations, Newton wrote an able letter to
Oldenburg, dated June 11, 1672, in which he examined with great
boldness and force of argument the various objections of his opponent,
and maintained the truth of his doctrine of colours, as independent of
the two hypotheses respecting the origin and production of light. He
acknowledged his own partiality to the doctrine of the materiality of
light; he pointed out the defects of the undulatory theory; he brought
forward new experiments in confirmation of his former results; and he
refuted the opinions of Hooke respecting the existence of only two
simple colours. No reply was made to the powerful arguments of Newton;
and Hooke contented himself with laying before the Society his curious
observations on the colours of soap-bubbles, and of plates of air, and
in pursuing his experiments on the diffraction of light, which, after
an interval of two years, he laid before the same body.

After he had thus silenced the most powerful of his adversaries, Newton
was again called upon to defend himself against a new enemy. Christian
Huygens, an eminent mathematician and natural philosopher, who, like
Hooke, had maintained the undulatory theory of light, transmitted
to Oldenburg various animadversions on the Newtonian doctrine; but
though his knowledge of optics was of the most extensive kind, yet his
objections were nearly as groundless as those of his less enlightened
countryman. Attached to his own hypothesis respecting the nature
of light, namely, to the system of undulation, he seems, like Dr.
Hooke, to have regarded the discoveries of Newton as calculated to
overturn it; but his principal objections related to the composition
of colours, and particularly of white light, which he alleged could be
obtained from the union of two colours, _yellow_ and _blue_. To and
similar objections, Newton replied that the colours in question were
not simple yellows and blues, but were compound colours, in which,
together, all the colours of the spectrum were themselves blended;
and though he evinced some strong traces of feeling at being again
put upon his defence, yet his high respect for Huygens induced him to
enter with patience on a fresh development of his doctrine. Huygens
felt the reproof which the tone of this answer so gently conveyed,
and in writing to Oldenburg, he used the expression, that Mr. Newton
“maintained his doctrine with some concern.” To this our author
replied, “As for Mr. Huygens’s expression, I confess it was a little
ungrateful to me, to meet with objections which had been answered
before, without having the least reason given me why those answers
were insufficient.” But though Huygens appears in this controversy as
a rash objector to the Newtonian doctrine, it was afterward the fate
of Newton to play a similar part against the Dutch philosopher. When
Huygens published his beautiful law of double refraction in Iceland
spar, founded on the finest experimental analysis of the phenomena,
though presented as a result of the undulatory system, Newton not only
rejected it, but substituted for it another law entirely inconsistent
with the experiments of Huygens, which Newton himself had praised, and
with those of all succeeding philosophers.

The influence of these controversies on the mind of Newton seems to
have been highly exciting. Even the satisfaction of humbling all
his antagonists he did not feel as a sufficient compensation for the
disturbance of his tranquillity. “I intend,” says he,[15] “to be no
farther solicitous about matters of philosophy. And therefore I hope
you will not take it ill if you find me never doing any thing more in
that kind; or rather that you will favour me in my determination, by
preventing, so far as you can conveniently, any objections or other
philosophical letters that may concern me.” In a subsequent letter in
1675, he says, “I had some thoughts of writing a further discourse
about colours, to be read at one of your assemblies; but find it yet
against the grain to put pen to paper any more on that subject;” and
in a letter to Leibnitz, dated December the 9th, 1675, he observes, “I
was so persecuted with discussions arising from the publication of my
theory of light, that I blamed my own imprudence for parting with so
substantial a blessing as my quiet to run after a shadow.”




CHAPTER V.

  _Mistake of Newton in supposing that the Improvement of Refracting
    Telescopes was hopeless—Mr. Hall invents the Achromatic Telescope—
    Principles of the Achromatic Telescope explained—It is re-invented
    by Dollond, and improved by future Artists—Dr. Blair’s Aplanatic
    Telescope—Mistakes in Newton’s Analysis of the Spectrum—Modern
    Discoveries respecting the Structure of the Spectrum._


The new doctrines of the composition of light, and of the different
refrangibility of the rays which compose it, having been thus
established upon an impregnable basis, it will be interesting to take a
general view of the changes which they have undergone since the time
of Newton, and of their influence on the progress of optical discovery.

There is no fact in the history of science more singular than that
Newton should have believed that all bodies produced spectra of equal
length, or separated the red and violet rays to equal distances when
the refraction of the mean rays was the same. This opinion, unsupported
by experiments, and not even sanctioned by any theoretical views,
seems to have been impressed upon his mind with all the force of an
axiom.[16] Even the shortness of the spectrum observed by Lucas did
not rouse him to further inquiry; and when, under the influence of
this blind conviction he pronounced the improvement of the refracting
telescope to be desperate, he checked for a long time the progress of
this branch of science, and furnished to future philosophers a lesson
which cannot be too deeply studied.

In 1729, about two years after the death of Sir Isaac, an individual
unknown to science broke the spell in which the subject of the spectrum
had been so singularly bound. Mr. Chester More Hall, of More Hall
in Essex, while studying the mechanism of the human eye, was led to
suppose that telescopes might be improved by a combination of lenses
of different refractive powers, and he actually completed several
object-glasses upon this principle. The steps by which he arrived at
such a construction have not been recorded; but it is obvious that
he must have discovered what escaped the sagacity of Newton, that
prisms made of different kinds of glass produced different degrees of
separation of the _red_ and _violet_ rays, or gave spectra of different
lengths when the refraction of the middle ray of the spectrum was the
same.

[Illustration: _Fig. 6._]

In order to explain how such a property led him to the construction
of a _telescope without colour_, or an _achromatic telescope_, let us
take a lens LL of _crown_ or _plate_ glass, whose focal length LY is
about twelve inches. When the sun’s rays SL, SL fall upon it, the _red_
will be refracted to R, the _yellow_ to Y, and the _violet_ to V. If we
now place behind it a concave lens _ll_ of the same glass, and of the
same focus or curvature, it will be found, both by experiment and by
drawing the refracted rays, according to the rules given in elementary
works, that the concave glass _ll_ will refract the rays LR, LR into
LS′, LS′, and the rays LV, LV into LS′, LS′ free of all colour; but as
these rays will be parallel, the two lenses will not have a focus, and
consequently cannot form an image so as to be used as the object-glass
of a telescope. This is obvious from another consideration; for since
the curvatures of the convex and concave lenses are the same, the two
put together will be exactly the same as if they were formed out of a
single piece of glass, having parallel surfaces like a watch-glass,
so that the parallel rays of light SL, SL will pass on in the same
direction LS′, LS′ affected by equal and opposite refractions as in a
piece of plane glass.

Now, since the convex lens LL separated the white light SL, SL into
its component coloured rays, LV, LV being the extreme violet, and LR,
LR the extreme red; it follows that a similar concave lens of the same
glass is capable of uniting into white light LS′, LS′ rays, as much
separated as LV, LR are. Consequently, if we take a concave lens _ll_
of the same, or of a greater refractive power than the convex one, and
having the power of uniting rays farther separated than LV, LR are, a
less concavity in the lens _ll_ will be sufficient to unite the rays
LV, LR into a white ray LS′; but as the lens _ll_ is now less concave
than the lens LL is convex, the concavity will predominate, and the
uncoloured rays LS′, LS′ will no longer be parallel, but will converge
to some point O, where they will form a colourless or achromatic image
of the sun.

The effect now described may be obtained by making the _convex_ lens LL
of _crown_ or of _plate_ glass, and the _concave_ one of _flint_ glass,
or that of which wineglasses are made. If the concave lens _ll_ has a
greater refractive power than LL, which is always the case, the only
effect of it will be to make the rays converge to a focus more remote
than O, or to render a less curvature necessary in _ll_, if O is fixed
for the focus of the combined lenses.

Such is the principle of the achromatic telescope as constructed by Mr.
Hall. This ingenious individual employed working opticians to grind
his lenses, and he furnished them with the radii of the surfaces,
which were adjusted to correct the aberration of figure as well as of
colour. His invention, therefore, was not an accidental combination of
a convex and a concave lens of different kinds of glass, which might
have been made merely for experiment; but it was a complete achromatic
telescope, founded on a thorough knowledge of the different dispersive
powers of crown and flint glass. It is a curious circumstance,
however, in the history of the telescope, that this invention was
actually lost. Mr. Hall never published any account of his labours,
and it is probable that he kept them secret till he should be able to
present his instrument to the public in a more perfect form; and it
was not till John Dollond had discovered the property of light upon
which the instrument depends, and had actually constructed many fine
telescopes, that the previous labours of Mr. Hall were laid before the
public.[17] From this period the achromatic telescope underwent gradual
improvement, and by the successive labours of Dollond, Ramsden, Blair,
Tulley, Guinand, Lerebours, and Fraunhofer, it has become one of the
most valuable instruments in physical science.

Although the achromatic telescope, as constructed by Dollond, was
founded on the principle that the spectra formed by crown and flint
glass differed only in their relative lengths, when the refraction of
the mean ray was the same, yet by a more minute examination of the
best instruments, it was found that they exhibited white or luminous
objects tinged on one side with a green fringe, and on the other with
one of a claret colour. These colours, which did not arise from any
defect of skill in the artist, were found to arise from a difference in
the extent of the coloured spaces in two equal spectra formed by crown
and by flint glass. This property was called the _irrationality_ of
the coloured spaces, and the uncorrected colours which remained when
the primary spectrum of the crown glass was corrected by the primary
spectrum of the flint glass were called the _secondary_ or _residual
spectrum_. By a happy contrivance, which it would be out of place here
to describe, Dr. Blair succeeded in correcting this secondary spectrum,
or in removing the green and claret-coloured fringes which appeared in
the best telescopes, and to this contrivance he gave the name of the
_Aplanatic Telescope_.

But while Newton thus overlooked these remarkable properties of the
prismatic spectrum, as formed by different bodies, he committed some
considerable mistakes in his examination of the spectrum which was
under his own immediate examination. It does not seem to have occurred
to him that the relations of the coloured spaces must be greatly
modified by the angular magnitude of the sun or the luminous body, or
aperture from which the spectrum is obtained; and misled by an apparent
analogy between the length of the coloured spaces and the divisions
of a musical chord,[18] he adopted the latter, as representing the
proportion of the coloured spaces in every beam of white light. Had two
other observers, one situated in Mercury, and the other in Jupiter,
studied the prismatic spectrum of the sun by the same instruments,
and with the same sagacity as Newton, it is demonstrable that they
would have obtained very different results. On account of the apparent
magnitude of the sun in Mercury, the observer there would obtain a
spectrum entirely without _green_, having _red_, _orange_, and _yellow_
at one end, the _white_ in the middle, and terminated at the other
end with _blue_ and _violet_. The observer in Jupiter would, on the
contrary, have obtained a spectrum in which the colours were much more
condensed. On the planet Saturn a spectrum exactly similar would have
been obtained, notwithstanding the greater diminution of the sun’s
apparent diameter. It may now be asked, which of all these spectra are
we to consider as exhibiting the number, and arrangement, and extent
of the coloured spaces proper to be adopted as the true analysis of a
solar ray.

The spectrum observed by Newton has surely no claim to our notice,
merely because it was observed upon the surface of the earth. The
spectrum obtained in Mercury affords no analysis at all of the incident
beam, the colours being almost all compound, and not homogeneous, and
that of Newton is liable to the same objection. Had Newton examined his
spectrum under the very same circumstances in winter and in summer, he
would have found the analysis of the beam more complete in summer, on
account of the diminution of the sun’s diameter; and, therefore, we are
entitled to say that neither the number nor the extent of the coloured
spaces, as given by Newton, are those which belong to homogeneous and
uncompounded light.

The spectrum obtained in Jupiter and Saturn is the only one where
the analysis is complete, as it is incapable of having its character
altered by any farther diminution of the sun’s diameter. Hence we
are forced to conclude, not only that the number and extent of the
primitive homogeneous colours, as given by Newton, are incorrect; but
that if he had attempted to analyze some of the primitive tints in the
spectrum, he would have found them decidedly composed of heterogeneous
rays. There is one consequence of these observations which is somewhat
interesting. A rainbow formed in summer, when the sun’s diameter is
least, must have its colours more condensed and homogeneous than in
winter, when the size of its disk is a maximum, and when the upper or
the under limb of the sun is eclipsed, a rainbow formed at that time
will lose entirely the yellow rays, and have the green and the red in
perfect contact. For the same reason, a rainbow formed in Venus and
Mercury will be destitute of green rays, and have a brilliant bow of
white light separating two coloured arches; while in Mars, Jupiter,
Saturn, and the Georgian planet, the bow will exhibit only four
homogeneous colours.

From his analysis of the solar spectrum, Newton concluded, “that to
the same degree of refrangibility ever belonged the same colour, and
to the same colour ever belonged the same degree of refrangibility;”
and hence he inferred, that _red_, _orange_, _yellow_, _green_, _blue_,
_indigo_, and _violet_ were primary and simple colours. He admitted,
indeed, that “the same colours in specie with these primary ones may
be also produced by composition. For a mixture of _yellow_ and _blue_
makes _green_, and of _red_ and _yellow_ makes _orange_;” but such
compound colours were easily distinguished from the simple colours of
the spectrum by the circumstance, that they are always capable of being
resolved by the action of the prism into the two colours which compose
them.

This view of the composition of the spectrum might have long remained
unchallenged, had we not been able to apply to it a new mode of
analysis. Though we cannot separate the _green_ rays of the spectrum
into _yellow_ and _blue_ by the refraction of prisms, yet if we
possessed any substance which had a specific attraction for _blue_
rays, and which stopped them in their course, and allowed the _yellow_
rays to pass, we should thus analyze the _green_ as effectually as
if they were separated by refraction. The substance which possesses
this property is a purplish blue glass, similar to that of which
finger-glasses are made. When we view through a piece of this glass,
about the twentieth of an inch thick, a brilliant prismatic spectrum,
we find that it has exercised a most extraordinary absorptive action
on the different colours which compose it. The _red_ part of the
spectrum is divided into _two red_ spaces, separated by an interval
entirely devoid of light. Next to the inner red space comes a space
of bright _yellow_, separated from the red by a visible interval.
After the yellow comes the _green_, with an obscure space between
them, then follows the _blue_ and the _violet_, the last of which has
suffered little or no diminution. Now it is very obvious, that in this
experiment, the blue glass has actually absorbed the _red_ rays, which,
when mixed with the _yellow_ on one side, constituted _orange_, and the
_blue_ rays, which, when mixed with the _yellow_ on the other side,
constituted _green_, so that the insulation of the _yellow_ rays thus
effected, and the disappearance of the _orange_, and of the greater
part of the _green_ light, proves beyond a doubt that the _orange_
and _green_ colours in the spectrum are compound colours, the former
consisting of _red_ and _yellow_ rays, and the latter of _yellow_ and
_blue_ rays _of the very same refrangibility_. If we compare the two
red spaces of the spectrum seen through the blue glass with the red
space seen without the blue glass, it will be obvious that the red
has experienced such an alteration in its tint by the action of the
blue glass, as would be effected by the absorption of a small portion
of yellow rays; and hence we conclude, that the red of the spectrum
contains a slight tinge of yellow, and that the yellow space extends
over more than one-half of the spectrum, including the _red_, _orange_,
_yellow_, _green_, and _blue_ spaces.

I have found also that red light exists in the yellow space, and it
is certain that in the violet space red light exists in a state of
combination with the blue rays. From these and other facts which it
would be out of place here to explain, I conclude that the prismatic
spectrum consists of three different spectra, viz. red, yellow, and
blue, all having the same length, and all overlapping each other. Hence
red, yellow, and blue rays of the very same refrangibility coexist at
every point of the spectrum; but the colour at any one point will be
that of the predominant ray, and will depend upon the relative distance
of the point from the maximum ordinate of the curve which represents
the intensity of the light of each of the three spectra.

[Illustration: _Fig. 7._]

This structure of the spectrum, which harmonizes with the old
hypothesis of three simple colours, will be understood from the annexed
diagram, where MN is the spectrum of seven colours, all compounded of
the three simple ones, _red_, _yellow_, and _blue_. The ordinates of
the curves R, Y, and B will express the intensities of each colour
at different points of the spectrum. At the red extremity M of the
spectrum, the pure _red_ is scarcely altered by the very slight
intermixture of yellow and blue. Farther on in the red space, the
_yellow_ begins to make the red incline to scarlet. It then exists
in sufficient quantity to form orange, and, as the red declines, the
yellow predominates over the feeble portion of red and blue which are
mixed with it. As the yellow decreases in intensity, the increasing
blue forms with it a good green, and the blue rising to its maximum
speedily overpowers the small portion of yellow and red. When the blue
becomes very faint, the red exhibits its influence in converting it
into violet, and the yellow ceases to exercise a marked influence on
the tint. The influence of the red over the blue space is scarcely
perceptible, on account of the great intensity of the blue light; but
we may easily conceive it to reappear and form the violet light, not
only from the rapid decline of the blue light, but from the greater
influence of the red rays upon the retina.

These views may, perhaps, be more clearly understood by supposing that
a certain portion of white light is actually formed at every point of
the spectrum by the union of the requisite number of the three coloured
rays that exist at any point. The white light thus formed will add to
the brilliancy without affecting the tint of the predominant colour.

In the violet space we may conceive the small portion of yellow which
exists there to form white light with a part of the blue and a part
of the red, so that the resulting tint will be violet, composed of
the blue and the small remaining portion of red, mixed with the white
light. This white light will possess the remarkable property of not
being susceptible of decomposition by the analysis of the prism,
as it is composed of red, yellow, and blue rays of the very same
refrangibility. The insulation of this white light by the absorption
of the predominant colours I have effected in the green, yellow, and
red spaces, and by the use of new absorbing media we may yet hope to
exhibit it in some of the other colours, particularly in the brightest
part of the blue space, where an obvious approximation to it takes
place.

Among the most important modern discoveries respecting the spectrum
we must enumerate that of fixed dark and coloured lines, which we owe
to the sagacity of Dr. Wollaston and M. Fraunhofer. Two or three of
these lines were discovered by Dr. Wollaston, but nearly 600 have been
detected by means of the fine prisms and the magnificent apparatus
of the Bavarian optician. These lines are parallel to one another,
and perpendicular to the length of the spectrum. The largest occupy a
space from 5″ to 10″ in breadth. Sometimes they occur in well-defined
lines, and at other times in groups; and in all spectra formed from
solar light, they preserve the same order and intensity, and the same
relative position to the coloured spaces, whatever be the nature of the
prism by which they are produced. Hence these lines are fixed points,
by which the relative dispersive powers of different media may be
ascertained with a degree of accuracy hitherto unknown in this branch
of science. In the light of the fixed stars, and in that of artificial
flames, a different system of lines is produced, and this system
remains unaltered, whatever be the nature of the prism by which the
spectrum is formed.

The most important fixed lines in the spectrum formed by light emitted
from the sun, whether it is reflected from the sky, the clouds, or
the moon, may be easily seen by looking at a narrow slit in the
window-shutter of a dark room, through a hollow prism formed of
plates of parallel glass, and filled with any fluid of a considerable
dispersive power. The slit should not greatly exceed the twentieth of
an inch, and the eye should look through the thinnest edge of the prism
where there is the least thickness of fluid. These lines I have found
to be the boundaries of spaces within which the rays have particular
affinities for particular bodies.




CHAPTER VI.

  _Colours of thin Plates first studied by Boyle and Hooke—Newton
    determines the Law of their Production—His Theory of Fits of Easy
    Reflection and Transmission—Colours of thick Plates._


In examining the nature and origin of colours as the component parts
of white light, the attention of Newton was directed to the curious
subject of the colours of thin plates, and to its application to
explain the colours of natural bodies. His earliest researches on this
subject were communicated, in his Discourse on Light and Colours,
to the Royal Society, on the 9th December, 1675, and were read at
subsequent meetings of that body. This discourse contained fuller
details respecting the composition and decomposition of light than
he had given in his letter to Oldenburg, and was concluded with nine
propositions, showing how the colours of thin transparent plates stand
related to those of all natural bodies.

The colours of thin plates seem to have been first observed by Mr.
Boyle. Dr. Hooke afterward studied them with some care, and gave a
correct account of the leading phenomena, as exhibited in the coloured
rings upon soap-bubbles, and between plates of glass pressed together.
He recognised that the colour depended upon some certain thickness of
the transparent plate, but he acknowledges that he had attempted in
vain to discover the relation between the thickness of the plate and
the colour which it produced.

Dr. Hooke succeeded in splitting a mineral substance, called mica,
into films of such extreme thinness as to give brilliant colours. One
plate, for example, gave a yellow colour, another a blue colour, and
the two together a deep purple; but, as plates which produced those
colours were always less than the 12,000th part of an inch thick,
it was quite impracticable, by any contrivance yet discovered, to
measure their thickness, and determine the law according to which the
colour varied with the thickness of the film. Newton surmounted this
difficulty by laying a double convex lens, the radius of curvature
of each side of which was fifty feet, upon the flat surface of a
plano-convex object-glass, and in this way he obtained a plate of air
or of space varying from the thinnest possible edge at the centre of
the object-glass where it touched the plane surface, to a considerable
thickness at the circumference of the lens. When light was allowed to
fall upon the object-glass, every different thickness of the plate
of air between the object-glass gave different colours, so that the
point where the two object-glasses touched one another was the centre
of a number of concentric coloured rings. Now, as the curvature of
the object-glass was known, it was easy to calculate the thickness of
the plate of air at which any particular colour appeared, and thus to
determine the law of the phenomena.

In order to understand how he proceeded, let CED be the convex surface
of the one object-glass, and AEB the flat surface of the other. Let
them touch at the point E, and let homogeneous _red_ rays fall upon
them, as shown in the figure. At the point of contact E, where the
plate of air is inconceivably thin, not a single ray of the pencil RE
is reflected. The light is wholly transmitted, and, consequently, to
an eye above E, there will appear at E a black spot. At _a_, where
the plate of air is thicker, the red light _ra_ is reflected in the
direction _aa′_, and as the air has the same thickness in a circle
round the point E, the eye above E, at _a_, will see next the black
spot E a ring of red light. At _m_, where the thickness of the air is
a little greater than at _a_, the light _r′m_ is all transmitted as at
E, and not a single ray suffers reflection, so that to an eye above E
at _m′_ there will be seen without the red ring _a_ a dark ring _m_.
In like manner, at greater thicknesses of the plate of air, there is a
succession of _red_ and dark rings, diminishing in breadth as shown in
the diagram.

[Illustration: _Fig. 8._]

When the same experiment was repeated in _orange_, _yellow_, _green_,
_blue_, _indigo_, and _violet_ light, the very same phenomenon was
observed; with this difference only, that the rings were _largest_ in
_red_ light, and _smallest_ in _violet_ light, and had intermediate
magnitudes in the intermediate colours.

If the observer now places his eye below E, so as to see the
transmitted rays, he will observe a set of rings as before, but they
will have a bright spot in their centre at E, and the luminous rings
will now correspond with those which were dark when seen by reflection,
as will be readily understood from inspecting the preceding diagram.

When the object-glasses are illuminated by _white_ light, the _seven_
systems of rings, formed by all the _seven_ colours which compose white
light, will now be seen at once. Had the rings in each colour been all
of the same diameter they would all have formed brilliant white rings,
separated by dark intervals; but, as they have all different diameters,
they will overlap one another, producing rings of various colours by
their mixture. These colours, reckoning from the centre E, are as
follows:—

1st Order. Black, blue, white, yellow, orange, red.

2d Order. Violet, blue, green, yellow, orange, red.

3d Order. Purple, blue, green, yellow, red, bluish-red.

4th Order. Bluish-green, green, yellowish-green, red.

5th Order. Greenish-blue, red.

6th Order. Greenish-blue, red.

By accurate measurements, Sir Isaac found that the thicknesses of _air_
at which the most luminous parts of the first rings were produced, were
in parts of an inch 1/178000, 3/178000, 5/178000, 7/178000, 9/178000,
11/178000. If the medium or the substance of the thin plate is water,
as in the case of the soap-bubble, which produces beautiful colours
according to its different degrees of thinness, the thicknesses at
which the most luminous parts of the rings appear are produced at
1/1·336 of the thickness at which they are produced in air, and in the
case of glass or mica at 1/1·525 of that thickness; the numbers 1.336,
1.525 expressing the ratio of the sines of the angles of incidence and
refraction in the substances which produce the colours.

From the phenomena thus briefly described, Sir Isaac Newton deduces
that ingenious, though hypothetical, property of light, called its
_fits of easy reflection and transmission_. This property consists in
supposing that every particle of light from its first discharge from
a luminous body possesses, at equally distant intervals, dispositions
to be reflected from, and transmitted through, the surfaces of bodies
upon which it is incident. Hence, if a particle of light reaches a
reflecting surface of glass when it is in its _fit of reflection_,
or in its disposition to be reflected, it will yield more readily
to the reflecting force of the surface; and, on the contrary, if it
reaches the same surface while in a _fit of easy transmission_, or in
a disposition to be transmitted, it will yield with more difficulty to
the reflecting force. Sir Isaac has not ventured to inquire into the
cause of this property; but we may form a very intelligible idea of
it by supposing, that the particles of light have two attractive and
two repulsive poles at the extremities of two axes at right angles to
each other, and that the particles revolve round their axes, and at
equidistant intervals bring one or other of these axes into the line
of the direction in which the particle is moving. If the attractive
axis is in the line of the direction in which the particle moves when
it reaches the refracting surface, the particle will yield to the
attractive force of the medium, and be refracted and transmitted; but
if the repulsive axis is in the direction of the particle’s motion when
it reaches the surface, it will yield to the repulsive force of the
medium, and be reflected from it.

The application of the theory of alternate fits of reflection and
transmission to explain the colours of thin plates is very simple.
When the light falls upon the first surface AB, Fig. 8 of the plate of
air between AB and CED, the rays that are in a fit of reflection are
reflected, and those that are in a fit of transmission are transmitted.
Let us call F the length of a fit, or the distance through which the
particle of light moves while it passes from the state of being in
a fit of reflection to the state of being in a fit of transmission.
Now, as all the particles of light transmitted through AB were in a
state of easy transmission when they entered AB, it is obvious, that,
if the plate of air at E is so thin as to be less than one-half of
F, the particles of light will still be in their disposition to be
transmitted, and consequently the light will be all transmitted, and
none reflected at the curve surface at E. When the plate becomes
thicker towards _a_, so that its thickness exceeds half of F, the
light will not reach the surface CE till it has come under its fit of
reflection, and consequently at _a_ the light will be all reflected,
and none transmitted. As the thickness increases towards _m_, the
light will have come under its fit of transmission, and so on, the
light being reflected at _a_, _l_, and transmitted at E, _m_. This
will perhaps be still more easily understood from _fig. 9_, where we
may suppose AEC to be a thin wedge of glass or any other transparent
body. When light is incident on the first surface AE, all the particles
of it that are in a fit of easy reflection will be reflected, and all
those in a fit of easy transmission will be transmitted. As the fits of
transmission all commence at AE, let the first fit of transmission end
when the particles of light have reached _ab_, and the second when they
have reached _ef_; and let the fits of reflection commence at _cd_ and
_gh_. Then, as the fit of transmission continues from AE to _ab_, all
the light that falls upon the portion _m_E of the second surface will
be transmitted and none reflected, so that to an eye above E the space
_m_E will appear black. As the fit of reflection commences at _ab_,
and continues to _cd_, all the light which falls upon the portion _nm_
will be reflected, and none transmitted; and so on, the light being
transmitted at _m_E and _pn_, and reflected at _nm_ and _qp_. Hence to
an eye above E the wedge-shaped film of which AEC is a section will
be covered with parallel bands or fringes of light separated by dark
fringes of the same breadth, and they will be all parallel to the thin
edge of the plate, a dark fringe corresponding to the thinnest edge.
To an eye placed below CE, similar fringes will be seen, but the one
corresponding to the thinnest edge _m_E will be luminous.

[Illustration: _Fig. 9._]

If the thickness of the plate does not vary according to a regular law
as in _fig. 9_, but if, like a film of blown glass, it has numerous
inequalities, then the alternate fringes of light and darkness will
vary with the thickness of the film, and throughout the whole length of
each fringe the thickness of the film will be the same.

We have supposed in the preceding illustration that the light employed
is homogeneous. If it is white, then the differently coloured fringes
will form by their superposition a system of fringes analogous to those
seen between two object-glasses, as already explained.

The same periodical colours which we have now described as exhibited
by thin plates were discovered by Newton in thick plates, and he has
explained them by means of the theory of fits; but it would lead
us beyond the limits of a popular work like this to enter into any
details of his observations, or to give an account of the numerous and
important additions which this branch of optics has received from the
discoveries of succeeding authors.




CHAPTER VII.

  _Newton’s Theory of the Colours of Natural Bodies explained—Objections
    to it stated—New Classification of Colours—Outline of a New Theory
    proposed._


If the objects of the material world had been illuminated with white
light, all the particles of which possessed the same degree of
refrangibility, and were equally acted upon by the bodies on which
they fall, all nature would have shone with a leaden hue, and all the
combinations of external objects, and all the features of the human
countenance, would have exhibited no other variety but that which
they possess in a pencil sketch or a China-ink drawing. The rainbow
itself would have dwindled into a narrow arch of white light,—the
stars would have shone through a gray sky,—and the mantle of a wintry
twilight would have replaced the golden vesture of the rising and the
setting sun. But He who has exhibited such matchless skill in the
organization of material bodies, and such exquisite taste in the forms
upon which they are modelled, has superadded that ethereal beauty which
enhances their more permanent qualities, and presents them to us in
the ever-varying colours of the spectrum. Without this the foliage of
vegetable life might have filled the eye and fostered the fruit which
it veils,—but the youthful green of its spring would have been blended
with the dying yellow of its autumn. Without this the diamond might
have displayed to science the beauty of its forms, and yielded to the
arts its adamantine virtues;—but it would have ceased to shine in the
chaplet of beauty, and to sparkle in the diadem of princes. Without
this the human countenance might have expressed all the sympathies of
the heart, but the “purple light of love” would not have risen on the
cheek, nor the hectic flush been the herald of its decay.

The gay colouring with which the Almighty has decked the pale marble
of nature is not the result of any quality inherent in the coloured
body, or in the particles by which it may be tinged, but is merely a
property of the light in which they happen to be placed. Newton was the
first person who placed this great truth in the clearest evidence. He
found that all bodies, whatever were their peculiar colours, exhibited
these colours only in white light. When they were illuminated by
homogeneous _red_ light they appeared _red_, by homogeneous _yellow_
light, _yellow_, and so on, “their colours being most brisk and vivid
under the influence of their own daylight colours.” The leaf of a
plant, for example, appeared _green_ in the white light of day, because
it had the property of reflecting that light in greater abundance than
any other. When it was placed in homogeneous _red_ light, it could no
longer appear _green_, because there was no green light to reflect; but
it reflected a portion of red light, because there was some red in the
compound green which it had the property of reflecting. Had the leaf
originally reflected a pure homogeneous green, unmixed with red, and
reflected no white light from its outer surface, it would have appeared
quite black in pure homogeneous red light, as this light does not
contain a single ray which the leaf was capable of reflecting. Hence
the colours of material bodies are owing to the property which they
possess of stopping certain rays of white light, while they reflect
or transmit to the eye the rest of the rays of which white light is
composed.

So far the Newtonian doctrine of colours is capable of rigid
demonstration; but its author was not content with carrying it thus
far: he sought to determine the manner in which particular rays are
stopped, while others are reflected or transmitted; and the result of
this profound inquiry was his theory of the colours of natural bodies,
which was communicated to the Royal Society on the 10th February,
1675. This theory is perhaps the loftiest of all his speculations; and
though, as a physical generalization, it stands on a perishable basis,
and must soon be swept away in the progress of science, it yet bears
the deepest impress of the grasp of his powerful intellect.

The principles upon which this theory is founded are the following:—

1. Bodies that have the greatest refractive powers reflect the greatest
quantity of light; and at the confines of equally refracting media
there is no reflection.

2. The least particles of almost all natural bodies are in some measure
transparent.

3. Between the particles of bodies are many pores or spaces, either
empty or filled with media of less density than the particles.

4. The particles of bodies and their pores, or the spaces between the
particles, have some definite size.

Upon these principles Newton explains the origin of _transparency_,
_opacity_, and _colour_.

_Transparency_ he considers as arising from the particles and their
intervals or pores being too small to cause reflection at their common
surfaces,[19] so that all the light which enters transparent bodies
passes through them without any portion of it being turned from its
path by reflection. If we could obtain, for example, a film of mica
whose thickness does not exceed two-thirds of the millionth part of an
inch, all the light which fell upon it would pass through it, and none
would be reflected. If this film was then cut into fragments, a number
of such fragments would constitute a bundle, which would also transmit
all the light which fell upon it, and be perfectly transparent.

_Opacity_ in bodies arises, he thinks, from an opposite cause, viz.
when the parts of bodies are of such a size as to be capable of
reflecting the light which falls upon them, in which case the light is
“stopped or stifled” by the multitude of reflections.

The _colours_ of natural bodies have, in the Newtonian hypothesis, the
same origin as the colours of thin plates, their transparent particles,
according to their several sizes, reflecting rays of one colour,
and transmitting those of another. “For if a thinned or plated body
which, being of an uneven thickness, appears all over of one uniform
colour, should be slit into threads, or broken into fragments of the
same thickness with the plate or film, every thread or fragment should
keep its colour, and consequently, a heap of such threads or fragments
should constitute a mass or powder of the same colour which the plate
exhibited before it was broken: and the parts of all natural bodies
being like so many fragments of a plate, must, on the same grounds,
exhibit the same colour.”

Such is the theory of the colours of natural bodies, stated as
clearly and briefly as we can. It has been very generally admitted
by philosophers, both of our own and of other countries, and has
been recently illustrated and defended by a French philosopher of
distinguished eminence. That this theory affords the true explanation
of certain colours, or, to speak more correctly, that certain colours
in natural bodies are the colours of thin plates, cannot be doubted;
but it will not be difficult to show that it is quite inapplicable to
that great class of phenomena which may be considered as representing
the colours of natural bodies.

The first objection to the Newtonian theory is the total absence of
all reflected light from the particles of transparent coloured media,
such as coloured gems, coloured glasses, and coloured fluids. This
objection was urged long ago by Mr. Delaval, who placed coloured fluids
on black grounds, and never could perceive the least trace of the
reflected tints. I have repeated the experiment with every precaution,
and with every variation that I could think of, and I consider it as
an established fact, that in such coloured bodies the complementary
reflected colour cannot be rendered visible. If the fluid, for example,
be _red_, the _green_ light from which the red has been separated
ought to appear either directly by looking into the coloured mass, or
ought to be recognised by its influence in modifying the light really
reflected; but as it cannot be seen, we must conclude that it has not
been reflected, but has been destroyed by some other property of the
coloured body.

A similar objection may be drawn from the disappearance of the
transmitted complementary colour in the leaves of plants and petals
of flowers. I have ascertained from numerous experiments, that the
transmitted colour is almost invariably the same with the reflected
colour, and that the same holds true with the coloured juices expressed
from them. The complementary tints are never seen, and wherever
there has been any thing like an approximation to two tints, I have
invariably found that it arose from there being two different coloured
juices existing in different sides of the leaf.

In the phenomena of the light transmitted by coloured glasses, there
are some peculiarities which, we think, demonstrate that their colours
are not those of thin plates. The light, for example, transmitted
through a particular kind of blue glass, has a blue colour of such a
peculiar composition that there is no blue in any of the orders of
colours in thin plates which has any resemblance to it. It is entirely
destitute of the red rays which form the middle of the red space in
the spectrum; so that the particles on which the colour depends must
reflect the middle red rays, and transmit those on each side of it,—a
property which cannot be deduced from the Newtonian doctrine.

The explanation of _opacity_, as arising from a multitude of
reflections, is liable to the same objection which we have urged
against the explanation of colour. In order to appreciate its weight,
we must distinguish opacity into two kinds, namely, the _opacity of
whiteness_ and the _opacity of blackness_. Those bodies which possess
the power of reflection in the highest degree, such as white metals,
chalk, and plaster of Paris, never reflect more than one-half of the
light which falls upon them. The other half of the incident light is,
according to Newton, lost by a multitude of reflections. But how is
it lost? Reflection merely changes the direction of the particles of
light, so that they must again emerge from the body, unless they are
reflected into fixed returning orbits, which detain them for ever in a
state of motion within the body. In the case of black opacity, such as
that of coal, which reflects from its first surface only 1/25th of the
white light, the difficulty is still greater, and we cannot conceive
how any system of interior reflections could so completely stifle
24/25ths of the whole incident light, without some of it returning to
the eye in a visible form.

In determining the constitution of bodies that produce _transparency_
and _blackness_, the Newtonian theory encounters a difficulty which
its author has by no means surmounted. Transparency, as we have
already seen, arises from the “particles and their interstices being
too small to cause reflections in their common surfaces,” that is,
they must be “less than any of those which exhibit colours,” or
“less than is requisite to reflect the _white_ and very faint blue
of the first order. But _this is the very same constitution which
produces blackness_ by reflection, and in order to explain the cause
of blackness by transmission, or black opacity, Newton is obliged to
introduce a new principle.

“For the production of _black_,” says he, “the corpuscles must be less
than any of those which exhibit colours. For at all greater sizes there
is too much light reflected to constitute this colour. But if they
be supposed a little less than is requisite to reflect the white and
very faint blue of the first order, they will reflect so very little
light as to appear intensely black, _and yet may perhaps variously
refract[20] it_ to and fro within themselves so long, until it happens
to be stifled and lost, by which means they will appear black in all
positions of the eye, without any transparency.”

This very remarkable passage exhibits, in a striking manner, the
perplexity in which our author was involved by the difficulties of his
subject. As the particles which produce blackness by reflection are
necessarily so small as to exclude the existence of any reflective
forces, he cannot ascribe the loss of the intromitted light, as he does
in the case of white opacity, to “a multitude of reflections;” and
therefore he is compelled to have recourse to _refracting forces_ to
perform the same office. The reluctance with which he avails himself
of this expedient is well marked in the mode of expression which he
adopts; and I am persuaded that when he wrote the above passage, he
felt the full force of the objections to this hypothesis, which cannot
fail to present themselves. As the size of the particles which produce
blackness are intermediate between those which produce transparency
and those which produce colour, approaching closely to the latter, it
is difficult to conceive why _they_ should refract the intromitted
light, while the greater and smaller particles, and even those almost
of the same size, should be destitute of that property. It is, besides,
not easy to understand how a refraction can take place within bodies
which shall stifle all the light, and prevent it from emerging. Nay, we
may admit the existence of such refractions, and yet understand how, by
a compensation in their direction, the refracted rays may all emerge
from the opaque body.

The force of these objections is tacitly recognised in Pemberton’s View
of Sir Isaac Newton’s Philosophy;[21] and as Newton not only read and
approved of that work, but even perused a great part of it along with
its author, we may fairly consider the opinion there stated to be his
own.

“For producing _black_, the particles ought to be smaller than for
exhibiting any of the colours, viz. of a size answering to the
thickness of the bubble, whereby reflecting little or no light, it
appears colourless; _but yet they must not be too small_, for that will
make them transparent _through deficiency of reflections_ in the inward
parts of the body, sufficient to stop the light from going through it;
but they must be of a size _bordering upon that_ disposed to reflect
the faint blue of the first order, which affords an evident reason why
blacks usually partake a little of that colour.” In this passage all
idea of refraction is abandoned, and that precise degree of size is
assumed for the particles which leaves a small power of reflection,
which is deemed sufficient to prevent the body from becoming
transparent; that is, sufficient to render it opaque or black.

The last objection which we shall state to this theory is one to which
we attach great weight, and, as it is founded on discoveries and views
which have been published since the time of Newton, we venture to
believe, that, had he been aware of them, he would never have proposed
the theory which we are considering.

When light falls upon a thin film such as AEC, _fig. 9_, p. 80, so
as to produce the colours of thin plates, it follows, from Sir Isaac
Newton’s theory of fits, that a portion of the light is, as usual,
reflected at the first surface AE,[22] while the light which forms the
coloured image is that which is reflected from the second surface EC,
so that all the colours of thin plates are diluted with the white light
reflected from the first surface. Now, in the modern theory, which
ascribes the colours of thin plates to the interference of the light
reflected from the second surface EC, with the light reflected from the
first surface AE, the resulting tint arises from the combination of
these two pencils, and consequently there is no white light reflected
from the surface AE. In like manner, when the thickness of the film is
such that the two interfering pencils completely destroy one another,
and produce black, there is not a ray of light reflected from the first
surface. Here, then, we have a criterion for deciding between the
theory of fits and the theory of interference; for if there is no white
light reflected from the first surface AE, the theory of fits must be
rejected. In a remarkable phenomenon of blackness arising from minute
fibres, which I have had occasion to describe, there was no perceptible
reflection from the surface of the fibres;[23] and M. Fresnel describes
an experiment made to determine the same point, and states the result
of it to have been unequivocally in favour of the doctrine of
interference.

In order to apply this important fact, let us take a piece of coal, one
of the blackest and most opaque of all substances, and which does not
reflect to the eye a single ray out of those which enter its substance.
The size of its particles is so small, that they are incapable of
reflecting light. When a number of these particles are placed together,
so as to form a surface, and other particles behind them, so as to form
a solid, they will not acquire by this process the power of reflection;
and consequently, a piece of coal so composed should be destitute of
the property of reflecting light from its first surface. But this is
not the case,—light is abundantly reflected from the first surface of
the coal, and consequently, its elementary particles must possess the
same power. Hence the blackness of coal must be ascribed to some other
cause than to the minuteness of its transparent atoms.

To transparent bodies this argument has a similar application. As their
atoms are still less than those of black bodies, their inability to
reflect light is still greater, and hence arises their transparency.
But the particles forming the surface of such bodies do reflect light,
and, therefore, their transparency must have another origin.

In the case of coloured bodies, too, the particles forming their
surfaces reflect white light like those of all other bodies, so that
these particles cannot produce colour on the same principles as those
of thin plates. In many of those cases of colour which seem to depend
upon the minuteness of the particles of the body, the reflection of
white light may nevertheless be observed, but this will be found
to arise from a thin transparent film, behind which the colorific
particles are placed.

Whatever answer may be given to these objections, we think it will
be admitted by those who have studied the subject most profoundly,
that a satisfactory theory of the colours of natural bodies is still a
_desideratum_ in science. How far we may be able to approach to it in
the present state of optics the reader will judge from the following
views.

Colours may be arranged into seven classes, each of which depends upon
different principles.

1. Transparent coloured fluids—transparent coloured gems—transparent
coloured glasses—coloured powders—and the colours of the leaves and
flowers of plants.

2. Oxidations on metals—colours of Labrador feldspar—colours of
precious and hydrophanous opal, and other opalescences—the colours of
the feathers of birds, of the wings of insects, and of the scales of
fishes.

3. Superficial colours, as those of mother-of-pearl and striated
surfaces.

4. Opalescences and colours in composite crystals having double
refraction.

5. Colours from the absorption of common and polarized light by doubly
refracting crystals.

6. Colours at the surfaces of media of different dispersive powers.

7. Colours at the surface of media in which the reflecting forces
extend to different distances, or follow different laws.

The first two of these classes are the most important. The Newtonian
theory appears to be strictly applicable to the phenomena of the
_second_ class; but those of the first class cannot, we conceive, be
referred to the same cause.

       *       *       *       *       *

The rays of solar light possess several remarkable physical properties:
They heat—they illuminate—they promote chymical combination—they effect
chymical decompositions—they impart magnetism to steel—they alter
the colours of bodies—they communicate to plants and flowers their
peculiar colours, and are in many cases necessary to the development of
their characteristic qualities. It is impossible to admit for a moment
that these varied effects are produced by a mere mechanical action,
or that they arise from the agitation of the particles of bodies by
the vibration of the ether which is considered to be the cause of
light. Whatever be the difficulties which attach to the theory which
supposes light to consist of material particles, we are compelled, by
its properties, to admit that light acts as if it were material, and
that it enters into combinations with bodies, in order to produce the
effects which we have enumerated.

When a beam of light falls upon a body, and the whole or a part of that
which enters its substance totally disappears, we are entitled to say,
that it is detained by some power exercised by the particles of the
body over the particles of light. When this light is said to be lost
by a multitude of reflections or refractions, the statement is not
only hypothetical, but it is an hypothesis incompatible with optical
principles. That the light detained within bodies has been stopped by
the attractive force of the particles seems to be highly probable,
and the mind will not feel any repugnance to admit that the particles
of all bodies, whether solid, fluid, or aëriform, have a specific
affinity for the particles of light. Considering light, therefore, as
material, it is not difficult to comprehend how it should, like other
elementary substances, enter into combination with bodies, and produce
many chymical and physical effects, but particularly the phenomena of
transparency, opacity, and colour.

In _transparent_ colourless bodies, such as water and glass, the
intromitted light experiences a considerable loss, because a certain
number of its particles are attracted and detained by the atoms of the
water or glass, and the light which emerges is colourless, because the
particles exercise a proportional action over all the simple colours
which compose white light.

When the transparent body has any decided _colour_, such as those
enumerated in Class I., then the particles of the body have exercised
a specific attraction over those rays of white light which are
complementary to those which compose the colour of the transmitted
light. If the transparent body, for example, is _red_, then its
particles have detained the green rays which entered into the incident
light, or certain other rays, which with the red are necessary to
compose white light. In compound bodies, like some of the artificial
glasses, the particles will attract and detain rays of light of
different colours, as may be seen by analyzing the transmitted light
with a prism, which will exhibit a spectrum deprived of all the rays
which have been detained. In black bodies the particles exercise a
powerful attraction over light, and detain all the intromitted rays.

When coloured bodies are opaque, so as to exhibit their colours
principally by reflection, the light which is reflected back to the
observer has received its colour from transmission through part of the
thickness of the body, or, what is the same thing, the colour reflected
to the eye is complementary to that which has been detained by the
particles of the body while the light is passing and repassing through
a thickness terminated by the reflecting surfaces; and as only a part
of this light is reflected, as in the case of leaves and flowers, the
transmitted light must have the same colour as the reflected light.

When coloured bodies exhibit two different colours complementary to
each other, the one seen by reflection and the other by transmission,
it is then highly probable that the colours are those of thin plates,
though there are still other optical principles to which they may be
referred. As the particles of bodies, and the medium which unites
them, or, as the different atoms of a compound body may have different
dispersive powers, while they exercise the same refractive force over a
particular part of the spectrum, the rays for which this compensation
takes place will be transmitted, while part of the complementary light
is reflected.[24] Or in cases where the refractive and dispersive
powers are the same, the reflective forces of the particles may vary
according to a different law, so that at the separating surfaces either
white or coloured light may be reflected.[25]

In those cases of colour where the reflected and the transmitted tints
are not complementary, as in _leaf-gold_, where the former is _yellow_
and the latter _green_;—in _leaf-silver_, where they are _white_
and _blue_, and in certain pieces of fir-wood, where the reflected
light is _whitish yellow_, and the transmitted light a _brilliant
homogeneous red_, we may explain the separation of the colours either
by the principles we have already laid down or by the doctrine of thin
plates. On the first principle, the colour of the reflected light,
which is supposed to be the same as that of the transmitted light, will
be modified by the law according to which the particles of the body
attract different rays out of the beam of white light. In pitch, for
example, the blue rays are first absorbed, so that at small thicknesses
the transmitted light is a fine yellow, while, by the action of a
greater thickness, the yellow itself is absorbed, and the transmitted
light is a bright homogeneous red. Now in leaf-gold the transmitted
colour of thinner films than we can obtain may be yellow, and,
consequently, the light reflected from the first strata of interrupting
faces will be yellow, and will determine the predominant tint of the
reflected light. On the Newtonian doctrine, Mr. Herschel has explained
it by saying, “that the transmitted rays have traversed the whole
thickness of the medium, and therefore undergo many more times the
action of its atoms than those reflected, especially those near the
first surface to which the brighter part of the reflected colour is
due.”

The phenomena of the absorption of common and polarized light, which I
have described in another place,[26] throw much light on the subject
of coloured bodies. The relation of the absorbent action to the axes
of double refraction, and, consequently, to the poles of the molecules
of the crystal, shows how the particles of light attracted by the
molecules of the body will vary, both in their nature and number,
according to the direction in which they approach the molecules; and
explains how the colour of a body may be changed, either temporarily
or permanently, by heat, according as it produces a temporary or a
permanent change in the relative position of the molecules. This is not
the place to enlarge on this subject; but we may be permitted to apply
the idea to the curious experiment of Thenard on phosphorus. When this
substance is rendered pure by repeated distillation, it is transparent,
and transmits yellow light; but when it is thrown in a melted state
into cold water, it becomes jet black. When again melted, it resumes
its original colour and transparency. According to the Newtonian
theory, we must suppose that the atoms of the phosphorus have been
diminished in size by sudden cooling,—an effect which it is not easy
to comprehend; but, according to the preceding views, we may suppose
that the atoms of the phosphorus have been forced by sudden cooling
into relative positions quite different from those which they take
when they slowly assume the solid state, and their poles of maximum
attraction, in place of being turned to one another, are turned in
different directions, and then allowed to exercise their full action in
attracting the intromitted light, and detaining it wholly within the
body.[27]

Before concluding this chapter, there is one topic peculiarly
deserving our notice, namely, the change of colour produced in bodies
by continued exposure to light. The general effect of light is to
diminish or dilute the colours of bodies, and in many cases to deprive
them entirely of their colour. Now, it is not easy to understand how
repeated undulations propagated through a body could diminish the
size of its particles, or how the same effect could be produced by a
multitude of reflections from particle to particle. But if light is
attracted by the particles of bodies, and combines with them, it is
easy to conceive that, when the molecules of a body have combined with
a great number of particles of a green colour, for example, their power
of combination with others will be diminished, and, consequently, the
number of particles of any colour absorbed or detained must diminish
with the time that the body has been exposed to light; that is, these
particles must enter into the transmitted and reflected pencils, and
diminish the intensity of their colour. If the body, for example,
absorbs red light, and transmits and reflects green, then if the
quantity of absorbed red light is diminished, it will enter into the
reflected and transmitted pencils, and, forming white light by its
mixture with a portion of the green rays, will actually dilute them in
the same manner as if a portion of white light had been added.[28]




CHAPTER VIII.

  _Newton’s Discoveries respecting the Inflection or Diffraction of
    Light—Previous Discoveries of Grimaldi and Dr. Hooke—Labours of
    succeeding Philosophers—Law of Interference of Dr. Young—Fresnel’s
    Discoveries—New Theory of Inflection on the Hypothesis of the
    Materiality of Light._


Although the discoveries of Newton respecting the _Inflection of Light_
were first published in his _Optics_ in 1704, yet there is reason to
think that they were made at a much earlier period. Sir Isaac, indeed,
informs us, in his preface to that great work, that the third book,
which contains these discoveries, “was put together out of scattered
papers;” and he adds at the end of his observations, that “he designed
to repeat most of them with more care and exactness, and to make some
new ones for determining the manner how the rays of light are bent
in their passage by bodies, for making the fringes of colours with
the dark lines between them. But I was then interrupted, and cannot
now think of taking these things into consideration.” On the 18th
March, 1674, Dr. Hooke had read a valuable memoir on the phenomena of
diffraction; and, as Sir Isaac makes no allusion whatever to this work,
it is the more probable that his “scattered papers” had been written
previous to the communication of Dr. Hooke’s experiments.

The phenomena of the inflection of light were first discovered by
Francis Maria Grimaldi, a learned Jesuit, who has described them in a
posthumous work published in 1665, two years after his death.[29]

Having admitted a beam of the sun’s light through a small pin-hole in
a piece of lead or card into a dark chamber, he found that the light
diverged from this aperture in the form of a cone, and that the shadows
of all bodies placed in this light were not only larger than might have
been expected, but were surrounded with three coloured fringes, the
nearest being the widest, and the most remote the narrowest. In strong
light he discovered analogous fringes within the shadows of bodies,
which increased in number with the breadth of the body, and became
more distinct when the shadow was received obliquely and at a greater
distance. When two small apertures or pin-holes were placed so near
each other that the cones of light formed by each of them intersected
one another, Grimaldi observed, that a spot common to the circumference
of each, or, which is the same thing, illuminated by rays from each
cone, was darker than the same spot when illuminated by either of
the cones separately; and he announces this remarkable fact in the
following paradoxical proposition, “_that a body actually illuminated
may become more dark_ by adding a _light to that which it already
receives_.”

Without knowing what had been done by the Italian philosopher, our
countryman, Dr. Robert Hooke, had been diligently occupied with the
same subject. In 1672, he communicated his first observations to the
Royal Society, and he then spoke of his paper as “containing the
discovery of a new property of light not mentioned by any optical
writers before him.” In his paper of 1674, already mentioned, and which
is no doubt the one to which he alludes, he has not only described
the leading phenomena of the inflection, or the deflection of light,
as he calls it, but he has distinctly announced the _doctrine of
interference_, which has performed so great a part in the subsequent
history of optics.[30]

Such was the state of the subject when Newton directed to it his powers
of acute and accurate observation. His attention was turned only to the
enlargement of the shadow, and to the three fringes which surrounded
it; and he begins his observations by ascribing the discovery of these
facts to Grimaldi. After taking exact measures of the diameter of the
shadow of a human hair, and of the breadth of the fringes at different
distances behind it, he discovered the remarkable fact that these
diameters and breadths were not proportional to the distances from the
hair at which they were measured. In order to explain these phenomena,
Newton supposed that the rays which passed by the edge of the hair
are deflected or turned aside from it, as if by a repulsive force,
the nearest rays suffering the greatest, and those more remote a less
degree of deflection.

[Illustration: _Fig. 10._]

Thus, if X, fig. 10, represents a section of the hair, and AB, CD, EF,
GH, &c. rays passing at different distances from X, the ray AB will be
more deflected than CD, and will cross it at _m_, the ray CD will for
the same reason cross EF at _n_, and EF will cross GH at _o_. Hence the
curve or caustic formed by the intersections _m_, _n_, _o_, &c. will
be convex outward, its curvature diminishing as it recedes from the
vertex. As none of the passing light can possibly enter within this
curve, it will form the boundary of the shadow of X.

The explanation given by Sir Isaac of the coloured fringes is less
precise, and can be inferred only from the two following queries.

1. “Do not the rays which differ in refrangibility differ also in
flexibility, and are they not, by these different inflections separated
from one another, so as after separation to make the colours in the
three fringes above described? And after what manner are they inflected
to make those fringes?

2. “Are not the rays of light in passing by the edges and sides of
bodies _bent several times backwards and forwards_ with a motion like
that of an eel? And do not the three fringes of light above mentioned
arise from three such bendings?”

The idea thus indistinctly thrown out in the preceding queries has
been ingeniously interpreted by Mr. Herschel in the manner represented
in fig. 11, where SS are two rays passing by the edge of the body
MN. These rays are supposed to undergo several bendings, as at _a_,
_b_, _c_, and the particles of light are thrown off at one or other
of the points of contrary flexure, according to the state of their
fits or other circumstances. Those that are thrown outwards in the
direction _a_A, _b_B, _c_C, _d_D, will produce as many caustics by
their intersections as there are deflected rays; and each caustic, when
received on a screen at a distance, will depict on it the brightest
part or maximum of a fringe.

[Illustration: _Fig. 11._]

In this unsatisfactory state was the subject of the inflection of light
left by Sir Isaac. His inquiries were interrupted, and never again
renewed; and though he himself found that the phenomena were the same,
“whether the hair was encompassed with air or with any other pellucid
substance,” yet this important result does not seem to have shaken his
conviction, that the phenomena had their origin in the action of bodies
upon light.

During two sets of experiments which I made on the inflection of light,
the first in 1798, and the second in 1812 and 1813, I was desirous
of examining the influence of density and refractive power over the
fringes produced by inflection. I compared the fringes formed by
gold-leaf with those formed by masses of gold,—and those produced by
films which gave the colours of thin plates with those formed by masses
of the same substance. I examined the influence of platinum, diamond,
and cork in inflecting light, the effect of non-reflecting grooves
and spaces in polished metals, and of cylinders of glass immersed in
a mixture of oil of cassia and oil of olives of the same refractive
power; and, as the fringes had the same magnitude and character under
all these circumstances, I concluded that they were not produced by any
force inherent in the bodies themselves, but arose from a property of
the light itself, which always showed itself when light was stopped in
its progress.

Dr. Thomas Young, who had supported with great ingenuity and force
of argument the undulatory theory of light, as maintained by Hooke
and Huygens, was the first who gave a plausible explanation of the
inflection of light. By interposing a small screen at B, _fig. 10_, and
intercepting the rays that passed near the hair X, he was surprised to
find that all the _fringes within the shadow disappeared_. The same
effect took place when the screen intercepted the rays on the other
side; and hence he concluded, that the rays on each side of the hair
were necessary to the production of the inner fringes, and that the
fringes were produced by the _interference_ of the rays that passed
on one side of the hair with those that passed on the other side. In
order to account for the coloured fringes without the shadow, Dr.
Young conceived that the rays which pass near the edge of the hair
interfere with others, which he supposes may be reflected after falling
very obliquely upon its edge,—a supposition which, if correct, would
certainly produce fringes very similar to those actually observed.

In pursuing these researches so successfully begun by Dr. Young,
M. Fresnel had the good fortune to explain all the phenomena of
inflection by means of the undulatory doctrine combined with the
principle of interference. In place of transmitting the light through
a small aperture, he caused it to diverge from the focus of a deep
convex lens, and instead of receiving the shadow and its fringes upon
a smooth white surface, as was done by Newton, he viewed them directly
with his eye through a lens placed behind the shadow; and by means
of a microscope he was able to measure the dimensions of the fringes
with the greatest exactness. By this mode of observation he made the
remarkable discovery, that the inflection of the light _depended on
the distance of the inflecting body from the aperture or from the
focus of divergence_;[31] the fringes being observed to dilate as
the body approached that focus, and to contract as it receded from
it, their relative distances from each other, and from the margin of
the shadow continuing invariable. In attempting to account for the
formation of the exterior fringes, M. Fresnel found it necessary to
reject the supposition of Dr. Young, that they were owing to light
reflected from the edge of the body. He not only ascertained that the
real place of the fringe was the 17/100th of a millimetre different
from what it should be on that supposition, but he found that the
fringes preserved the same intensity of light, whether the inflecting
body had a round or a sharp edge, and even when the edge was such
as not to afford sufficient light for their production. From this
difficulty the undulatory theory speedily released him, and he was led
by its indications to consider the exterior fringes, as produced by an
infinite number of elementary waves of light emanating from a primitive
wave when partly interrupted by an opaque body.

The various phenomena of inflection, which had so long resisted every
effort to generalize them, having thus received so beautiful and
satisfactory an explanation from the undulatory doctrine, they must
of course be regarded as affording to that doctrine the most powerful
support, while the Newtonian hypothesis of the materiality of light is
proportionally thrown into the shade. It is impossible, indeed, even
for national partiality to consider the views of Newton as furnishing
any explanation of the facts discovered by Fresnel; and, as no attempt
has been made by the small though able phalanx of his disciples to
stay the decision with which, on this count at least, the doctrine
of emission has been threatened, we shall venture to suggest some
principles by which the refractory phenomena may perhaps be yet brought
within the pale of the Newtonian theory.

That the particles of light, like those of heat, are endowed with a
repulsive force which prevents them from accumulating when in a state
of condensation, or when they are detained by the absorptive action
of opaque bodies, will be readily admitted. By this power a beam of
light radiating from a luminous point has, in every azimuth, the same
degree of intensity at the same distance from its centre of divergence;
but if we intercept a portion of such a beam by an opaque body, the
repulsive force of the light which formerly occupied its shadow is
withdrawn, and consequently the rays which pass near the body will be
repelled into the shadow, and will form, by their interference with
those similarly repelled on the other side, the interior fringes, which
are parallel to the edges of the body. The rays which pass at a greater
distance will in like manner be bent towards the body, but with less
force, and, interfering with those rays which retain their primitive
direction, from the state of their fits or the position of their
poles, they will form the exterior fringes. When the inflecting body
is placed near the point of divergence, the greater proximity of the
rays will produce a greater repulsive force, and consequently a greater
inflection of the passing light; while the removal of the body from the
point of divergence will be accompanied with an increased distance of
the particles, an inferior repulsive force, and a feebler inflection.
As the phenomena of inflection, considered under this aspect, arise
from a property of the light itself, it follows that they will remain
invariable, whatever be the nature or density of the body, or the form
of the edge which acts upon the passing rays.




CHAPTER IX.

  _Miscellaneous Optical Researches of Newton—His Experiments on
    Refraction—His Conjecture respecting the Inflammability of the
    Diamond—His Law of Double Refraction—His Observations on the
    Polarization of Light—Newton’s Theory of Light—His “Optics.”_


Before concluding our account of Newton’s optical discoveries, it is
necessary to notice some of his minor researches, which, though of
inferior importance in the science of light, have either exercised an
influence over the progress of discovery, or been associated with the
history of other branches of knowledge.

One of the most curious of these inquiries related to the connexion
between the refractive powers and the chymical composition of bodies.
Having measured the refractive powers and the densities of twenty-two
substances, he found that the forces which reflect and refract light
are very nearly proportional to the densities of the same bodies. In
this law, however, he noticed a remarkable exception in the case of
unctuous and sulphureous bodies, such as camphire, olive oil, linseed
oil, spirit of turpentine, and _diamond_, which have their refractive
powers two or three times greater in respect of their densities than
the other substances in the table, while among themselves their
refractive powers are proportional to their densities, without any
considerable variation. Hence he concluded that diamond “is an unctuous
substance coagulated,”—a sagacious prediction, which has been verified
in the discoveries of modern chymistry. The connexion between a high
degree of inflammability and a great refracting force has been still
more strongly established by the high refractive power which I detected
in phosphorus, and which was discovered in hydrogen by MM. Biot and
Arago.

There is no part of the optical labours of Newton which is less
satisfactory than that which relates to the double refraction of
light. In 1690, Huygens, published his admirable treatise on light,
in which he has given the law of double refraction in calcareous
spar, as deduced from his theory of light, and as confirmed by direct
experiment. Viewing it probably as a theoretical deduction, Newton
seems to have regarded it as incorrect, and though he has given Huygens
the credit of describing the phenomena more exactly than Bartholinus,
yet, without assigning any reason, he rejected the law of the Dutch
philosopher, and substituted another in its place. These observations
of our author form the subject of the twenty-fifth and twenty-sixth
queries at the end of his Optics, which was published fourteen years
after the appearance of Huygens’s work. The law adopted by Newton
is not accompanied with any of the experiments from which it was
deduced; and though he has given it without expressing any doubt of its
accuracy, it is, nevertheless, entirely incompatible with observation,
and has been rejected by all succeeding philosophers.

In his speculations respecting the successive disappearance and
reappearance of two of the four images which are formed when a
luminous object is viewed through two rhombs of calcareous spar, one
of which is made to revolve upon the other, Newton has been more
successful. He concluded from these phenomena that every ray of light
has two opposite sides originally endued with the property on which
the unusual refraction depends, and other two opposite sides not
endued with that property; and he suggested it as a subject for future
inquiry, whether there are not more properties of light by which the
sides of the rays differ, and are distinguished from one another. This
is the first occasion on which the idea of a _polarity_ in the rays of
light has been suggested.[32]

From the various optical inquiries in which Newton was engaged, he
was strongly impressed with the belief that light consists of small
material particles emitted from shining substances, and that these
particles could be again recombined into solid matter, so that “gross
bodies and light were convertible into one another.” He conceived also
that the particles of solid bodies and of light exerted a mutual action
upon each other, the former being agitated and heated by the latter,
and the latter being attracted and repelled by the former, with forces
depending on the inertia of the luminous particles. These forces he
regarded as insensible at all measurable distances, and he conceived
that the distances between the particles of bodies were very small when
compared with the extent of their sphere of attraction and repulsion.

With the exception of Hooke, Huygens, and Euler, almost all the
contemporaries and successors of Newton maintained the doctrine of the
materiality of light. It was first successfully assailed by Dr. Thomas
Young, and since that time it has been shaken to its foundation by
those great discoveries which have illustrated the commencement of the
present century. The undulatory theory, which has thus triumphed in
its turn, is still subject to grave difficulties, and we fear another
century must elapse before a final decision can be pronounced on this
long-agitated question.

The most important of the optical discoveries of Newton, of which
we have given a general history, were communicated to the Royal
Society in detached papers; but the disputes in which they had
involved their author made him hesitate about the publication of his
other discoveries. Although he had drawn up a connected view of his
labours under the title of “Opticks, or a Treatise on the Reflexions,
Refractions, Inflexions, and Colours of Light,” yet he resolved not to
publish this work during the life of Hooke, by whose rival jealousy
his tranquillity had been so frequently interrupted. Hooke, however,
died in 1702, and the Optics of Newton appeared in English in 1704. Dr.
Samuel Clark proposed a Latin edition of it, which appeared in 1706,
and he was generously presented by Sir Isaac with 500_l._ (or 100_l._
for each of his five children), as a token of the approbation and
gratitude of the author. Both the English and the Latin editions have
been frequently reprinted both in England and on the Continent,[33]
and there perhaps never was a work of profound science so widely
circulated.




CHAPTER X.

  _Astronomical Discoveries of Newton—Necessity of combined Exertion
    to the Completion of great Discoveries—Sketch of the History of
    Astronomy previous to the Time of Newton—Copernicus, 1473–1543—
    Tycho Brahe, 1546–1601—Kepler, 1571–1631—Galileo, 1564–1642._


From the optical labours of Newton we now proceed to the history of his
astronomical discoveries—those transcendent deductions of human reason
by which he has secured to himself an immortal name, and vindicated
the intellectual dignity of his species. Pre-eminent as his triumphs
have been, it would be unjust to affirm that they were achieved by his
single arm. The torch of many a preceding age had thrown its light
into the strongholds of the material universe, and the grasp of many
a powerful hand had pulled down the most impregnable of its defences.
An alliance, indeed, of many kindred spirits had been long struggling
in this great cause, and Newton was but the leader of their mighty
phalanx,—the director of their combined genius,—the general who won the
victory, and therefore wears its laurels.

The history of science presents us with no example of an individual
mind throwing itself far in advance of its contemporaries. It is only
in the career of crime and ambition that reckless man takes the start
of his species, and, uncurbed by moral and religious restraint, erects
an unholy dynasty upon the ruins of ancient and venerable institutions.
The achievements of intellectual power, though often begun by one
mind and completed by another, have ever been the results of combined
exertions. Slow in their growth, they gradually approximate to a more
perfect condition:—the variety in the phenomena of nature call forth a
variety of intellectual gifts;—the powers of analysis and combination
are applied to the humbler labours of observation and experiment,
and in the ordeal of rival inquiry truth is finally purified from
error. How different is it with those systems which the imagination
rears,—those theories of wild import which are directed against the
consciences and hopes of man. The fatal upas-tree distils its poison
in the spring as well as the autumn of its growth, but the fruit which
sustains life must have its bud prepared before the approach of winter,
its blossom expanded in the spring, and its juices elaborated by the
light and heat of the summer and the autumnal sun.

In the century which preceded the birth of Newton the science of
astronomy advanced with the most rapid steps. Emerging from the
darkness of the middle ages, the human mind seemed to rejoice in its
new-born strength, and to apply itself with elastic vigour to unfold
the mechanism of the heavens. The labours of Hipparchus and Ptolemy
had indeed furnished many important epochs and supplied many valuable
data; but the cumbrous appendages of cycles and epicycles with which
they explained the stations and retrogradations of the planets, and the
vulgar prejudices which a false interpretation of Scripture had excited
against a belief in the motion of the earth, rendered it difficult even
for great minds to escape from the trammels of authority, and appeal to
the simplicity of nature.

The sovereign of Castile, the generous and noble-minded Alphonso,
had long before proscribed the rude expedients of his predecessors;
and when he declared that if the heavens were thus constituted,
he could have given the Deity good advice, he must not only have
felt the absurdity of the prevailing system, but must have obtained
some foresight of a more simple arrangement. But neither he nor the
astronomers whom he so liberally protected seem to have established a
better system, and it was left to Copernicus to enjoy the dignity of
being the restorer of astronomy.

This great man, a native of Thorn in Prussia, following his father’s
profession, began his career as a doctor of medicine, but an accidental
attendance on the mathematical lectures of Brudzevius excited a love
for astronomy, which became the leading passion of his life. Quitting
a profession uncongenial to such pursuits, he went to Bologna to
study astronomy under Dominic Maria; and after having enjoyed the
friendship and instruction of that able philosopher, he established
himself at Rome in the humble situation of a teacher of mathematics.
Here he made numerous astronomical observations which served him as
the basis of future researches; but an event soon occurred which,
though it interrupted for a while his important studies, placed him in
a situation for pursuing them with new zeal. The death of one of the
canons enabled his uncle, who was Bishop of Ermeland, to appoint him to
a canonry in the chapter of Frauenburg, where, in a house situated on
the brow of a mountain, he continued, in peaceful seclusion, to carry
on his astronomical observations. During his residence at Rome his
talents had been so well appreciated, that the Bishop of Fossombrona,
who presided over the council for reforming the calendar, solicited the
aid of Copernicus in this desirable undertaking. At first he entered
warmly into the views of the council, and charged himself with the
determination of the length of the year and of the month, and of the
other motions of the sun and moon that seemed to be required; but he
found the task too irksome, and probably felt that it would interfere
with those interesting discoveries which had already begun to dawn upon
his mind.

Copernicus is said to have commenced his inquiries by an historical
examination of the opinions of ancient authors on the system of the
universe; but it is more likely that he sought for the authority of
their great names to countenance his peculiar views, and that he was
more desirous to present his own theory as one that he had received,
rather than as one which he had invented. His mind had been long
imbued with the idea that simplicity and harmony should characterize
the arrangements of the planetary system, and, in the complication and
disorder which reigned in the hypothesis of Ptolemy, he saw insuperable
objections to its being regarded as a representation of nature. In the
opinions of the Egyptian sages, in those of Pythagoras, Philolaus,
Aristarchus, and Nicetas, he recognised his own earliest conviction
that the earth was not the centre of the universe; but he appears to
have considered it as still possible that our globe might perform some
function in the system more important than that of the other planets;
and his attention was much occupied with the speculation of Martianus
Capella, who placed the sun between Mars and the moon, and made
Mercury and Venus revolve round him as a centre; and with the system
of Apollonius Pergæus, who made all the planets revolve round the sun,
while the sun and moon were carried round the earth in the centre of
the universe. The examination, however, of these hypotheses gradually
dispelled the difficulties with which the subject was beset; and after
the labours of more than thirty years, he was permitted to see the
true system of the heavens. The sun he considered as immoveable in
the centre of the system, while the earth revolved between the orbits
of Venus and Mars, and produced by its rotation about its axis all
the diurnal phenomena of the celestial sphere. The precession of the
equinoxes was thus referred to a slight motion of the earth’s axis,
and the stations and retrogradations of the planets were the necessary
consequence of their own motions combined with that of the earth about
the sun. These remarkable views were supported by numerous astronomical
observations; and in 1530 Copernicus brought to a close his immortal
work on the Revolutions of the Heavenly Bodies.

But while we admire the genius which triumphed over so many
difficulties, we cannot fail to commend the extraordinary prudence
with which he ushered his new system into the world. Aware of the
prejudices, and even of the hostility with which such a system would
be received, he resolved neither to startle the one nor provoke the
other. He allowed his opinions to circulate in the slow current of
personal communication. The points of opposition which they presented
to established doctrines were gradually worn down, and they insinuated
themselves into reception among the ecclesiastical circles by the very
reluctance of their author to bring them into notice. In the year
1534, Cardinal Schonberg, Bishop of Capua, and Gyse, Bishop of Culm,
exerted all their influence to induce Copernicus to lay his system
before the world; but he resisted their solicitations; and it was not
till 1539 that an accidental circumstance contributed to alter his
resolution. George Rheticus, professor of mathematics at Wirtemberg,
having heard of the labours of Copernicus, resigned his chair, and
repaired to Frauenberg to make himself master of his discoveries.
This zealous disciple prevailed upon his master to permit the
publication of his system; and they seem to have arranged a plan for
giving it to the world without alarming the vigilance of the church,
or startling the prejudices of individuals. Under the disguise of a
student of mathematics, Rheticus published in 1540 an account of the
manuscript volume of Copernicus. This pamphlet was received without
any disapprobation, and its author was encouraged to reprint it at
Basle, in 1541, with his own name. The success of these publications,
and the flattering manner in which the new astronomy was received by
several able writers, induced Copernicus to place his MSS. in the hands
of Rheticus. It was accordingly printed at the expense of Cardinal
Schonberg, and appeared at Nuremberg in 1543. Its illustrious author,
however, did not live to peruse it. A complete copy was handed to him
in his last moments, and he saw and touched it a few hours before his
death. This great work was dedicated to the Holy Pontiff, in order, as
Copernicus himself says, that the authority of the head of the church
might silence the calumnies of individuals who had attacked his views
by arguments drawn from religion. Thus introduced, the Copernican
system met with no ecclesiastical opposition, and gradually made its
way in spite of the ignorance and prejudices of the age.

Among the astronomers who provided the materials of the Newtonian
philosophy the name of Tycho Brahe merits a conspicuous place.
Descended from an ancient Swedish family, he was born at Knudstorp, in
Norway, in 1546, three years after the death of Copernicus. The great
eclipse of the sun which happened on the 26th August, 1560, while he
was at the University of Copenhagen, attracted his notice: and when
he found that all its phenomena had been accurately predicted, he was
seized with the most irresistible passion to acquire the knowledge of
a science so infallible in its results. Destined for the profession
of the law, his friends discouraged the pursuit which now engrossed
his thoughts; and such were the reproaches and even persecutions to
which he was exposed, that he quitted his country with the design of
travelling through Germany. At the very commencement of his journey,
however, an event occurred in which the impetuosity of his temper had
nearly cost him his life. At a wedding-feast in Rostock, a questionable
point in geometry involved him in a dispute with a Danish nobleman of
the same temperament with himself; and the two mathematicians resolved
to settle the difference by the sword. Tycho, however, seems to have
been second in the conflict, for he lost the greater part of his
nose, and was obliged to supply its place by a substitute of gold and
silver, which a cement of glue attached to his face. During his stay at
Augsburg he inspired the burgomaster of the city, Peter Hainzell, with
a love of astronomy. This public-spirited citizen erected an excellent
observatory at his own expense, and here Tycho began that distinguished
career which has placed him in the first rank of practical astronomers.

Upon his return to Copenhagen in 1570, he was received with every mark
of respect. The king invited him to court, and persons of all ranks
harassed him with their attentions. At Herritzvold, near his native
place, the house of his maternal uncle afforded him a retreat from the
gayeties of the capital, and he was there offered every accommodation
for the prosecution of his astronomical studies. Here, however, the
passion of love and the pursuits of alchymy distracted his thoughts;
but though the peasant girl of whom he was enamoured was of easier
attainment than the philosopher’s stone, the marriage produced an open
quarrel with his relations, which it required the interference of
the king to allay. In the tranquillity of domestic happiness, Tycho
resumed his study of the heavens, and in 1572 he enjoyed the singular
good fortune of observing, through all its variations, the new star
in Cassiopeia, which appeared with such extraordinary splendour as
to be visible in the daytime, and which gradually disappeared in the
following year.

Dissatisfied with his residence in Denmark, Tycho resolved to settle in
some distant country; and having gone as far as Venice in search of a
suitable residence, he at last fixed upon Basle, in Switzerland. The
King of Denmark, however, had learned his intention from the Prince
of Hesse; and when Tycho returned to Copenhagen to remove his family
and his instruments, his sovereign announced to him his resolution
to detain him in his kingdom. He presented him with the canonry of
Roschild, with an income of 2000 crowns per annum. To this he added
a pension of 1000 crowns; and he promised to give him the island of
Huen, with a complete observatory erected under his own eye. This
generous offer was instantly accepted. The celebrated observatory of
Uraniburg was established at the expense of about 20,000_l._; and in
this magnificent retreat Tycho continued for twenty-one years to enrich
astronomy with the most valuable observations. Admiring disciples
crowded to this sanctuary of the sciences to acquire the knowledge of
the heavens; and kings[34] and princes felt themselves honoured by
becoming the guests of the great astronomer of the age.

One of the principal discoveries of Tycho was that of the inequality
of the moon’s motion, called the variation. He detected, also, the
annual equation which affects the place of her apogee and nodes, and he
determined the greatest and the least inclination of the lunar orbit.
His observations on the planets were numerous and precise, and have
formed the data of the present generalizations in astronomy. Though
thus skilful in the observation of phenomena, his mind was but little
suited to investigate their cause, and it was probably owing to this
defect that he rejected the system of Copernicus. The vanity of giving
his own name to another system was not likely to actuate a mind such as
his, and it was more probable that he was led to adopt the immobility
of the earth, and to make the sun, with all his attendant planets,
circulate round it, from the great difficulty which still presented
itself by comparing the apparent diameter of the stars with the annual
parallax of the earth’s orbit.

The death of Frederick in 1588 proved a severe calamity to Tycho, and
to the science which he cultivated. During the first years of the
minority of Christian IV. the regency continued the royal patronage
to the observatory of Uraniburg; and in 1592 the young king paid a
visit of some days to Tycho, and left him a gold chain in token of his
favour. The astronomer, however, had made himself enemies at court, and
the envy of his high reputation had probably added fresh malignity to
the irritation of personal feelings. Under the ministry of Wolchendorf,
a name for ever odious to science, Tycho’s pension was stopped;—he was
in 1597 deprived of the canonry of Roschild, and was thus forced, with
his wife and children, to seek an asylum in a foreign land. His friend,
Henry Rantzau, of Wansbeck, under whose roof he found a hospitable
shelter, was fortunately acquainted with the emperor Rodolph II., who,
to his love of science, added a passion for alchymy and astrology.
The reputation of Tycho having already reached the imperial ear, the
recommendation of Rantzau was scarcely necessary to ensure him his
warmest friendship. Invited by the emperor, he repaired in 1599 to
Prague, where he met with the kindest reception. A pension of three
thousand crowns was immediately settled upon him, and a commodious
observatory erected for his use in the vicinity of that city. Here
the exiled astronomer renewed with delight his interrupted labours,
and the gratitude which he cherished for the royal favour increased
the satisfaction which he felt in having so unexpectedly found a
resting-place for approaching age. These prospects of better days were
enhanced by the good fortune of receiving two such men as Kepler and
Longomontanus for his pupils; but the fallacy of human anticipation was
here, as in so many other cases, strikingly displayed. Tycho was not
aware of the inroads which both his labours and his disappointments
had made upon his constitution. Though surrounded with affectionate
friends and admiring disciples, he was still an exile in a foreign
land. Though his country had been base in its ingratitude, it was yet
the land which he loved,—the scene of his earliest affection,—the
theatre of his scientific glory. These feelings continually preyed upon
his mind, and his unsettled spirit was ever hovering among his native
mountains. In this condition he was attacked with a disease of the most
painful kind, and though the paroxysms of its agonies had lengthened
intermissions, yet he saw that death was approaching. He implored his
pupils to persevere in their scientific labours. He conversed with
Kepler on some of the profoundest points of astronomy, and with these
secular occupations he mingled frequent acts of piety and devotion. In
this happy condition he expired without pain at the age of fifty-five,
the unquestionable victim of the councils of Christian IV.

Notwithstanding the accessions which astronomy had received from the
labours of Copernicus and Tycho, no progress was yet made in developing
the general laws of the system, and scarcely an idea had been formed
of the power by which the planets were retained in their orbits. The
labours of assiduous observers had supplied the materials for this
purpose, and Kepler arose to lay the foundations of physical astronomy.

John Kepler was born at Wiel, in Wirtemberg, in 1571. He was educated
for the church, and discharged even some of the clerical functions;
but his devotion to science withdrew him from the study of theology.
Having received mathematical instruction from the celebrated Mæstlinus,
he had made such progress in the science, that he was invited in 1594
to fill the mathematical chair of Gratz in Styria. Endowed with a
fertile imagination, his mind was ever intent upon subtle and ingenious
speculations. In the year 1596 he published his peculiar views in
a work on the Harmonies and Analogies of Nature. In this singular
production, he attempts to solve what he calls the great cosmographical
mystery of the admirable proportion of the planetary orbits; and by
means of the six regular geometrical solids,[35] he endeavours to
assign a reason why there are six planets, and why the dimensions of
their orbits and the time of their periodical revolutions were such as
Copernicus had found them. If a cube, for example, were inserted in a
sphere, of which Saturn’s orbit was one of the great circles, it would,
he supposed, touch by its six planes the lesser sphere of Jupiter;
and, in like manner, he proposes to determine, by the aid of the other
geometrical solids, the magnitude of the spheres of the other planets.
A copy of this work was presented by its author to Tycho Brahe, who had
been too long versed in the severe realities of observation to attach
any value to such wild theories. He advised his young friend “first to
lay a solid foundation for his views by actual observation, and then,
by ascending from these, to strive to reach the causes of things;”
and there is reason to think that, by the aid of the whole Baconian
philosophy, thus compressed by anticipation into a single sentence, he
abandoned for a while his visionary inquiries.

In the year 1598 Kepler suffered persecution for his religious
principles, and was compelled to quit Gratz; but though he was recalled
by the States of Styria, he felt his situation insecure, and accepted
of a pressing invitation from Tycho to settle at Prague, and assist
him in his calculations. Having arrived in Bohemia in 1600, he was
introduced by his friends to the Emperor Rodolph, from whom he ever
afterward received the kindest attention. On the death of Tycho in
1601, he was appointed mathematician to the emperor,—a situation in
which he was continued during the successive reigns of Matthias and
Ferdinand; but what was of more importance to science, he was put in
possession of the valuable collection of Tycho’s observations. These
observations were remarkably numerous; and as the orbit of Mars was
more oval than that of any of the other planets, they were peculiarly
suitable for determining its real form. The notions of harmony and
symmetry in the construction of the solar system, which had filled
the mind of Kepler, necessarily led him to believe that the planets
revolved with a uniform motion in circular orbits. So firm, indeed,
was this conviction, that he made numerous attempts to represent the
observations of Tycho by this hypothesis. The deviations were too
great to be ascribed to errors of observation; and in trying various
other curves, he was led to the discovery that Mars revolved round
the sun in an elliptical orbit, in one of the foci of which the sun
itself was placed. The same observations enabled him to determine the
dimensions of the planet’s orbit, and by comparing together the times
in which Mars passed over different portions of its orbit, he found
that they were to one another as the areas described by the lines
drawn from the centre of the planet to the centre of the sun, or, in
more technical terms, that the radius vector describes equal areas
in equal times. These two remarkable discoveries, the first that were
ever made in physical astronomy, were extended to all the other planets
of the system, and were communicated to the world in 1609, in his
“Commentaries on the Motions of the Planet Mars, as deduced from the
observations of Tycho Brahe.”

Although our author was conducted to these great laws by the patient
examination of well-established facts, his imagination was ever
hurrying him among the wilds of conjecture. Convinced that the mean
distances of the planets from the sun bore to one another some
mysterious relation, he not only compared them with the regular
geometrical solids, but also with the intervals of musical tones; an
idea which the ancient Pythagoreans had suggested, and which had been
adopted by Archimedes himself. All these comparisons were fruitless;
and Kepler was about to abandon an inquiry of about seventeen years’
duration, when, on the 8th March, 1618, he conceived the idea of
comparing the powers of the different members which express the
planetary distances, in place of the numbers themselves. He compared
the squares and the cubes of the distances with the same powers of the
periodic times; nay, he tried even the squares of the times with the
cubes of the distances; but his hurry and impatience led him into an
error of calculation, and he rejected this law as having no existence
in nature! On the 15th May, his mind again reverted to the same
notion, and upon making the calculations anew, and free from error, he
discovered the great law, that the squares of the periodic times of any
two planets are to one another as the cubes of their distances from the
sun. Enchanted with this unexpected result, he could scarcely trust his
calculations; and, to use his own language, he at first believed that
he was dreaming, and had taken for granted the very truth of which he
was in search. This brilliant discovery was published in 1619, in his
“Harmony of the World;” a work dedicated to James VI. of Scotland. Thus
were established what have been called the three laws of Kepler,—the
motion of the planets in elliptical orbits,—the proportionality between
the areas described and their times of description,—and the relations
between the squares of the periodic times and the cubes of the
distances.

The relation of the movements of the planets to the sun, as the general
centre of all their orbits, could not fail to suggest to Kepler that
some power resided in that luminary by which these various motions
were produced; and he went so far as to conjecture that this power
diminishes as the square of the distance of the body on which it was
exerted; but he immediately rejects this law, and prefers that of
the simple distances. In his work on Mars, he speaks of gravity as a
mutual and corporeal affection between similar bodies. He maintained
that the tides were occasioned by the moon’s attraction, and that the
irregularities of the lunar motions, as detected by Tycho, were owing
to the joint actions of the sun and the earth; but the relation between
gravity, as exhibited on the earth’s surface, and as conducting the
planets in their orbits, required more patience of thought than he
could command, and was accordingly left for the exercise of higher
powers.

The misery in which Kepler lived forms a painful contrast with the
services which he performed to science. The pension on which he
subsisted was always in arrears, and though the three emperors whose
reigns he adorned directed their ministers to be more punctual in its
payment, the disobedience of their commands was a source of continued
vexation to Kepler. When he retired to Sagan, in Silesia, to spend
in retirement the remainder of his days, his pecuniary difficulties
became still more harassing. Necessity at last compelled him to apply
personally for the arrears which were due; and he accordingly set out
in 1630 for Ratisbon; but in consequence of the great fatigue which so
long a journey on horseback produced, he was seized with a fever, which
carried him off on the 30th November, 1630, in the 59th year of his age.

While Kepler was thus laying the foundation of physical astronomy,
Galileo was busily employed in extending the boundaries of the solar
system. This distinguished philosopher was born at Pisa in 1564.
He was the son of a Florentine nobleman, and was educated for the
medical profession; but a passion for geometry took possession of his
mind, and called forth all his powers. Without the aid of a master,
he studied the writings of Euclid and of Archimedes; and such were
his acquirements, that he was appointed by the Grand-duke of Tuscany
to the mathematical chair of Pisa in the twenty-fifth year of his
age. His opposition to the Aristotelian philosophy gained him many
enemies, and at the end of three years he quitted Pisa, and accepted
of an invitation to the professorship of mathematics at Padua. Here
he continued for eighteen years adorning the university by his name,
and diffusing around him a taste for the physical sciences. With
the exception of some contrivances of inferior importance, Galileo
had distinguished himself by no discovery till he had reached the
forty-fifth year of his age. In the year 1609, the same year in which
Kepler published his celebrated commentary on Mars, Galileo paid a
visit to Venice, where he heard, in the course of conversation, that a
Dutchman of the name of Jansens had constructed and presented to Prince
Maurice an instrument through which he saw distant objects magnified
and rendered more distinct, as if they had been brought nearer to the
observer. This report was credited by some and disbelieved by others;
but, in the course of a few days, Galileo received a letter from James
Badovere at Paris, which placed beyond a doubt the existence of such
an instrument. The idea instantly filled his mind as one of the utmost
importance to science; and so thoroughly was he acquainted with the
properties of lenses, that he not only discovered the principle of its
construction, but was able to complete a telescope for his own use.
Into one end of a leaden tube he fitted a spectacle-glass plane on one
side and convex on the other, and in the other end he placed another
spectacle-glass concave on one side and plane on the other. He then
applied his eye to the concave glass, and saw objects “pretty large
and pretty near him.” They appeared three times nearer, and nine times
larger in surface, than to the naked eye. He soon after made another,
which represented objects above sixty times larger; and, sparing
neither labour nor expense, he finally constructed an instrument so
excellent, as “to show things almost a thousand times larger, and above
thirty times nearer to the naked eye.”

There is, perhaps, no invention that science has presented to man so
extraordinary in its nature, and so boundless in its influence, as
that of the telescope. To the uninstructed mind, the power of seeing
an object a thousand miles distant, as large and nearly as distinct
as if it were brought within a mile of the observer, must seem almost
miraculous; and to the philosopher, even, who thoroughly comprehends
the principles upon which it acts, it must ever appear one of the most
elegant applications of science. To have been the first astronomer in
whose hands such a gift was placed was a preference to which Galileo
owed much of his future reputation.

No sooner had he completed his telescope than he applied it to the
heavens, and on the 7th January, 1618, the first day of its use, he
saw round Jupiter three bright little stars lying in a line parallel
to the ecliptic, two to the east, and one to the west of the planet.
Regarding them as ordinary stars, he never thought of estimating their
distances. On the following day, when he accidentally directed his
telescope to Jupiter, he was surprised to see the three stars to the
west of the planet. To produce this effect it was requisite that the
motion of Jupiter should be direct, though, according to calculation,
it was actually retrograde. In this dilemma he waited with impatience
for the evening of the 9th, but unfortunately the sky was covered with
clouds. On the 10th he saw only two stars to the east—a circumstance
which he was no longer able to explain by the motion of Jupiter. He was
therefore compelled to ascribe the change to the stars themselves; and
upon repeating his observations on the 11th, he no longer doubted that
he had discovered three planets revolving round Jupiter. On the 13th
January he for the first time saw the fourth satellite.[36]

This discovery, though of the utmost importance in itself, derived an
additional value from the light which it threw on the true system of
the universe. While the earth was the only planet enlightened by a
moon, it might naturally be supposed that it alone was habitable, and
was therefore entitled to the pre-eminence of occupying the centre of
the system; but the discovery of four moons round a much larger planet
deprived this argument of its force, and created a new analogy between
the earth and the other planets. When Kepler received the “Sidereal
Messenger,” the work in which Galileo announced his discovery in 1610,
he perused it with the deepest interest; and while it confirmed and
extended his substantial discoveries, it dispelled at the same time
some of those harmonic dreams which still hovered among his thoughts.
In the “Dissertation” which he published on the discovery of Galileo,
he expresses his hope that satellites will be discovered round Saturn
and Mars,—he conjectures that Jupiter has a motion of rotation about
his axis,—and states his surprise, that, after what had been written on
the subject of telescopes by Baptista Porta, they had not been earlier
introduced into observatories.

In continuing his observations, Galileo applied his telescope to
Venus, and in 1610 he discovered the phases of that planet, which
exhibited to him the various forms of the waxing and the waning moon.
This fact established beyond a doubt that the planet revolved round
the sun, and thus gave an additional blow to the Ptolemaic system. In
his observations on the sun, Galileo discovered his spots, and deduced
from them the rotation of the central luminary. He observed that
the body of Saturn had handles attached to it; but he was unable to
detect the form of its ring, or render visible its minute satellites.
On the surface of the moon he discovered her mountains and valleys,
and determined the curious fact of her libration, in virtue of which
parts of the margin of her disk occasionally appear and disappear. In
the Milky Way he descried numerous minute stars which the unassisted
eye was unable to perceive; and as the largest fixed stars, in place
of being magnified by the telescope, became actually minute brilliant
points, he inferred their immense distance as rendered necessary by the
Copernican hypothesis. All his discoveries, indeed, furnished fresh
arguments in favour of the new system; and the order of the planets and
their relation to a central sun may now be considered as established by
incontrovertible evidence.

While Galileo was occupied with these noble pursuits at Pisa, to which
he had been recalled in 1611, his generous patron, Cosmo II. Grand-duke
of Tuscany, invited him to Florence, that he might pursue with
uninterrupted leisure his astronomical observations, and carry on his
correspondence with the German astronomers. His fame had now resounded
through all Europe;—the strongholds of prejudice and ignorance
were unbarred;—and the most obstinate adherents of ancient systems
acknowledged the meridian power of the day-star of science. Galileo
was ambitious of propagating the great truths which he contributed so
powerfully to establish. He never doubted that they would received
with gratitude by all,—by the philosopher as the consummation of
the greatest efforts of human genius,—and by the Christian as the
most transcendent displays of Almighty power. But he had mistaken
the disposition of his species, and the character of the age. That
same system of the heavens which had been discovered by the humble
ecclesiastic of Frauenberg, which had been patronised by the kindness
of a bishop, and published at the expense of a cardinal, and which
the pope himself had sanctioned by the warmest reception, was, after
the lapse of a hundred years, doomed to the most violent opposition,
as subversive of the doctrines of the Christian faith. On no former
occasion has the human mind exhibited such a fatal relapse into
intolerance. The age itself had improved in liberality;—the persecuted
doctrines themselves had become more deserving of reception;—the light
of the Reformed faith had driven the Catholics from some of their most
obnoxious positions;—and yet, under all these circumstances, the church
of Rome unfurled her banner of persecution against the pride of Italy,
against the ornament of his species, and against truths immutable and
eternal.

In consequence of complaints laid before the Holy Inquisition, Galileo
was summoned to appear at Rome in 1615, to answer for the heretical
opinions which he had promulgated. He was charged with “maintaining
as true the false doctrine held by many, that the sun was immoveable
in the centre of the world, and that the earth revolved with a
diurnal motion;—with having certain disciples to whom he taught the
same doctrine;—with keeping up a correspondence on the subject with
several German mathematicians;—with having published letters on the
solar spots, in which he explained the same doctrine as true;—and
with having glossed over with a false interpretation the passages of
Scripture which were urged against it.” The consideration of these
charges came before a meeting of the Inquisition, which assembled on
the 25th February, 1616; and the court, declaring their disposition to
deal gently with the prisoner, pronounced the following decree:—“That
Cardinal Bellarmine should enjoin Galileo to renounce entirely the
above-recited false opinions; that, on his refusal to do so, he
should be commanded by the commissary of the Inquisition to abandon
the said doctrine, and to cease to teach and defend it; and that, if
he did not obey this command, he should be thrown into prison.” On
the 26th of February Galileo appeared before Cardinal Bellarmine,
and, after receiving from him a gentle admonition, he was commanded
by the commissary, in the presence of a notary and witnesses, to
desist altogether from his erroneous opinions; and it was declared
to be unlawful for him in future to teach them in any way whatever,
either orally or in his writings. To these commands Galileo promised
obedience, and was dismissed from the Inquisition.

The mildness of this sentence was no doubt partly owing to the
influence of the Grand-duke of Tuscany, and other persons of rank and
influence at the papal court, who took a deep interest in the issue
of the trial. Dreading, however, that so slight a punishment might
not have the effect of putting down the obnoxious doctrines, the
Inquisition issued a decree denouncing the new opinions as false and
contrary to the sacred writings, and prohibiting the sale of every book
in which they should be maintained.

Thus liberated from his persecutors, Galileo returned to Florence,
where he pursued his studies with his wonted diligence and ardour. The
recantation of his astronomical opinions was so formal and unreserved,
that ordinary prudence, if not a sense of personal honour, should
have restrained him from unnecessarily bringing them before the
world. No anathema was pronounced against his scientific discoveries;
no interdict was laid upon the free exercise of his genius. He was
prohibited merely from teaching a doctrine which the church of Rome
considered to be injurious to its faith. We might have expected,
therefore, that a philosopher so conspicuous in the eyes of the world
would have respected the prejudices, however base, of an institution
whose decrees formed part of the law of the land, and which possessed
the power of life and death within the limits of its jurisdiction.
Galileo, however, thought otherwise. A sense of degradation[37] seems
to have urged him to retaliate, and before six years had elapsed, he
began to compose his “Cosmical System, or Dialogues on the two greatest
Systems of the World, the Ptolemean and the Copernican,” the concealed
object of which is to establish the opinions which he had promised
to abandon. In this work the subject is discussed by three speakers,
Sagredo, Salviatus, and Simplicius, a peripatetic philosopher, who
defends the system of Ptolemy with much skill against the overwhelming
arguments of the rival disputants. Galileo hoped to escape notice by
this indirect mode of propagating the new system, and he obtained
permission to publish his work, which appeared at Florence in 1632.

The Inquisition did not, as might have been expected, immediately
summon Galileo to their presence. Nearly a year elapsed before they
gave any indication of their design; and, according to their own
statement, they did not even take the subject under consideration till
they saw that the obnoxious tenets were every day gaining ground, in
consequence of the publication of the Dialogues. They then submitted
the work to a careful examination, and having found it to be a direct
violation of the injunction which had been formerly intimated to
its author, they again cited him before their tribunal in 1633. The
venerable sage, now in his seventieth year, was thus compelled to
repair to Rome, and when he arrived he was committed to the apartments
of the Fiscal of the Inquisition. The unchangeable friendship, however,
of the Grand-duke of Tuscany obtained a remission of this severity, and
Galileo was allowed to reside at the house of the Tuscan ambassador
during the two months which the trial occupied. When brought before the
Inquisition, and examined upon oath, he acknowledged that the Dialogues
were written by himself, and that he obtained permission to publish
them without notifying to the person who gave it that he had been
prohibited from holding, defending, or teaching the heretical opinions.
He confessed also that the Dialogues were composed in such a manner,
that the arguments in favour of the Copernican system, though given as
partly false, were yet managed in such a manner that they were more
likely to confirm than overturn its doctrines; but that this error,
which was not intentional, arose from the natural desire of making an
ingenious defence of false propositions, and of opinions that had the
semblance of probability.

After receiving these confessions and excuses, the Inquisition allowed
Galileo a proper time for giving in his defence; but this seems to
have consisted solely in bringing forward the certificate of Cardinal
Bellarmine already mentioned, which made no allusion to the promise
under which Galileo had come never to defend, nor teach in any way
whatever, the Copernican doctrines. The court held this defence to be
an aggravation of the crime rather than an excuse for it, and proceeded
to pronounce a sentence which will be ever memorable in the history of
the human mind.

Invoking the name of our Saviour, they declare, that Galileo had made
himself liable to the suspicion of heresy, by believing the doctrine,
contrary to Scripture, that the sun was the centre of the earth’s
orbit, and did not move from east to west; and by defending as probable
the opinion that the earth moved, and was not the centre of the world;
and that he had thus incurred all the censures and penalties which were
enacted by the church against such offences;—but that he should be
absolved from these penalties, provided he sincerely abjured and cursed
all the errors and heresies contained in the formula of the church,
which should be submitted to him. That so grave and pernicious a crime
should not pass altogether unpunished, that he might become more
cautious in future, and might be an example to others to abstain from
such offences, they decreed that his Dialogues should be prohibited
by a formal edict,—that he should be condemned to the prison of the
Inquisition during pleasure,—and that, during the three following
years, he should recite once a week the seven penitential psalms.

This sentence was subscribed by seven cardinals; and on the 22d
June, 1633, Galileo signed an abjuration humiliating to himself and
degrading to philosophy. At the age of seventy, on his bended knees,
and with his right hand resting on the Holy Evangelists, did this
patriarch of science avow his present and his past belief in all
the dogmas of the Romish Church, abandon as false and heretical the
doctrine of the earth’s motion and of the sun’s immobility, and pledge
himself to denounce to the Inquisition any other person who was even
suspected of heresy. He abjured, cursed, and detested those eternal
and immutable truths which the Almighty had permitted him to be the
first to establish. What a mortifying picture of moral depravity and
intellectual weakness! If the unholy zeal of the assembly of cardinals
has been branded with infamy, what must we think of the venerable
sage whose gray hairs were entwined with the chaplet of immortality,
quailing under the fear of man, and sacrificing the convictions of his
conscience and the deductions of his reason at the altar of a base
superstition? Had Galileo but added the courage of the martyr to the
wisdom of the sage,—had he carried the glance of his indignant eye
round the circle of his judges,—had he lifted his hands to heaven, and
called the living God to witness the truth and immutability of his
opinions, the bigotry of his enemies would have been disarmed, and
science would have enjoyed a memorable triumph.

The great truths of the Copernican system, instead of being considered
as heretical, had been actually adopted by many pious members of the
Catholic church, and even some of its dignitaries did not scruple
to defend it openly. Previous to the first persecution of Galileo
in 1615, a Neapolitan nobleman, Vincenzio Caraffa, a person equally
distinguished by his piety and birth, had solicited Paul Anthony
Foscarinus, a learned Carmelite monk, to illustrate and defend the
new system of the universe. With this request the ecclesiastic
speedily complied; and in the pamphlet which he completed on the 6th
January, 1615, he defends the Copernican system with much boldness and
ingenuity; he reconciles the various passages of Scripture with the new
doctrine, and he expresses the hope that such an attempt, now made for
the first time, will prove agreeable to philosophers, but particularly
to those very learned men, Galileo Galilei, John Kepler, and all the
members of the Lyncean Academy, who, he believes, entertain the same
opinion. This remarkable production, written from the convent of the
Carmelites at Naples, is dedicated to the very Reverend Sebastian
Fantoni, general of the order of Carmelites, and was published at
Florence, with the sanction of the ecclesiastical authorities, in 1630;
three years before the second persecution of Galileo.

It would be interesting to know the state of public feeling in Italy
when Galileo was doomed to the prisons of the Inquisition. No appeal
seems to have been made against so cruel a sentence; and neither
in remonstrance nor in derision does an individual voice seem to
have been raised. The master spirits of the age looked with sullen
indifference on the persecution of exalted genius; and Galileo lay in
chains, deserted and unpitied. This unrebuked triumph of his enemies
was perhaps favourable to the object of their vengeance. Resistance
might have heightened the rigour of a sentence, which submission seems
to have alleviated. The interference of some eminent individuals of
Rome, among whom we have no doubt that the Grand-duke of Tuscany was
the most influential, induced Pope Urban VIII., not only to shorten
the period, but to soften the rigour of Galileo’s imprisonment. From
the dungeon of the Inquisition, where he had remained only four days,
he was transported to the ambassador’s palace in the Garden de Medici
at Rome; and when his health had begun to suffer, he was permitted
to leave the metropolis; and would have been allowed to return to
Florence, but as the plague raged in that city, he was sent, in July,
1633, to the archiepiscopal palace of Sienna, the residence of the
Archbishop Piccolimini, where he carried on and completed his valuable
investigations respecting the resistance of solids. Here he continued
five months, when, in consequence of the disappearance of the plague at
Florence, he was allowed to retire to his villa at Bellosguardo, and
afterward to that of Arcetri in the vicinity of Florence.

Though Galileo was now, to a certain degree, liberated from the power
of man, yet the afflicting dispensations of Providence began to fall
thickly around him. No sooner had he returned to Arcetri, than his
favourite daughter, Maria, was seized with a dangerous illness, which
soon terminated in her death. He was himself attacked with hernia,
palpitation of the heart, loss of appetite, and the most oppressive
melancholy; and though he solicited permission to repair to Florence
for medical assistance, yet this deed of mercy was denied him. In 1638,
however, the pope permitted him to pay a visit to Florence, and his
friend, Father Castelli, was allowed to visit him in the company of an
officer of the Inquisition. But this indulgence was soon withdrawn, and
at the end of a few months he was remanded to Arcetri. The sight of his
right eye had begun to fail in 1636, from an opacity of the cornea. In
1637 his left eye was attacked with the same complaint; so that in a
few months he was affected with total and incurable blindness. Before
this calamity had supervened, he had noticed the curious phenomenon of
the moon’s libration, in consequence of which, parts of her visible
disk that are exposed to view at one time are withdrawn at another. He
succeeded in explaining two of the causes of this curious phenomenon,
viz. the different distances of the observer from the line joining the
centre of the earth and the moon, which produces the diurnal libration,
and the unequal motion of the moon in her orbit, which produces the
libration in longitude. It was left, however, to Hevelius to discover
the libration in latitude, which arises from the inclination of her
axis being a little less than a right angle to the ecliptic; and to
Lagrange to discover the spheroidal libration, or that which arises
from the action of the earth upon the lunar spheroid.

The sorrows with which Galileo was now beset, seemed to have disarmed
the severity of the Inquisition. He was freely permitted to enjoy the
society of his friends, who now thronged around him to express their
respect and their sympathy. The Grand-duke of Tuscany was his frequent
visiter, and Gassendi, Deodati, and our countryman Milton went to Italy
for the purpose of visiting him. He entertained his friends with the
warmest hospitality, and though simple and abstemious in his diet, yet
he was fond of good wine, and seems even in his last days to have paid
particular attention to the excellence of his cellar.

Although Galileo had nearly lost his hearing as well as his sight, yet
his intellectual faculties were unimpaired; and while his mind was
occupied in considering the force of percussion, he was seized with
fever and palpitation of the heart, which, after two months’ illness,
terminated his life on the 8th of January, 1642.

Among the predecessors of Newton in astronomical research we must not
omit the names of Bouillaud (Bullialdus), Borelli, and Dr. Hooke.
Ismael Bouillaud, a native of Laon in France, and the author of several
valuable astronomical works, has derived more reputation from a single
sentence in his _Astronomica Philolaica_, published in 1645, than from
all the rest of his labours. He was not a believer in the doctrine
of attraction, which, as we have already seen, had been broached by
Copernicus, and discovered by Kepler; but in speaking of that power as
the cause of the planetary motions, he remarks, “that if attraction
existed, it would decrease as the square of the distance.” The
influence of gravity was still more distinctly developed by Borelli,
a Neapolitan philosopher, who published in 1666 a work on Jupiter’s
satellites.[38] In this work he maintains, that all the planets perform
their motions round the sun according to a general law; that the
satellites of Jupiter and of Saturn move round their primary planets
in the same manner as the moon does round the earth, and that they all
revolve round the sun, which is the only source of any virtue, and that
this virtue attaches them, and unites them so that they cannot recede
from their centre of action.[39]

Our countryman Dr. Robert Hooke seems to have devoted much of
his attention to the cause of the planetary motions. On the 21st
March, 1666, he read to the Royal Society an account of a series of
experiments for determining if bodies experience any variation in
their weight at different distances from the centre of the earth. His
experiments, as Hooke himself saw, were by no means satisfactory,
and hence he was led to the ingenious idea of measuring the force of
gravity by observing, at different altitudes, the rate of a pendulum
clock. About two months afterward, he exhibited to the Society an
approximate representation of the forces which retain the planets
in their orbits, in the paths described by a circular pendulum
impelled with different degrees of force; but though this experiment
illustrated the production of a curvilineal motion, by combining a
tangential force with a central power of attraction, yet it was only
an illustration, and could not lead to the true cause of the planetary
motions. At a later period, however, viz. in 1674, Hooke resumed the
subject in a dissertation entitled “An Attempt to prove the Motion of
the Earth from Observation,” which contains the following remarkable
observations upon gravity:—

“I shall hereafter explain a system of the world differing in
many particulars from any yet known, answering in all things to
the common rules of mechanical motions. This depends upon three
suppositions:—first, that all celestial bodies whatsoever have an
attraction or gravitating power towards their own centres, whereby
they attract, not only their own parts, and keep them from flying
from them, as we may observe the earth to do, but that they also do
attract all the other celestial bodies that are within the sphere of
their activity, and consequently, that not only the sun and moon have
an influence upon the body and motion of the earth, and the earth upon
them, but that Mercury, Venus, Mars, Jupiter, and Saturn, also, by
their attractive powers, have a considerable influence upon its motion,
as in the same manner the corresponding attractive power of the earth
hath a considerable influence upon every one of their motions also.
The second supposition is this, that all bodies whatsoever that are
put into a direct and simple motion will so continue to move forward
in a straight line, till they are, by some other effectual powers,
deflected, and sent into a motion describing a circle, ellipsis, or
some other more compounded curve line. The third supposition is, that
those attractive powers are so much the more powerful in operating by
how much the nearer the body wrought upon is to their own centres.
_Now, what these several degrees are I have not yet experimentally
verified_; but it is a notion which, if fully prosecuted, as it ought
to be, will mightily assist the astronomers to reduce all the celestial
motions to a certain rule, which I doubt will never be done without it.
He that understands the nature of the circular pendulum and circular
motion will easily understand the whole of this principle, and will
know where to find directions in nature for the true stating thereof.
This I only hint at present to such as have ability and opportunity of
prosecuting this inquiry, and are not wanting of industry for observing
and calculating, wishing heartily such may be found, having myself
many other things in hand, which I would first complete, and therefore
cannot so well attend it. But this I do not promise the undertaker,
that he will find all the great motions of the world to be influenced
by this principle, and that the true understanding thereof will be the
true perfection of astronomy.”

This passage, which has been considered as a remarkable one by the
philosophers of every country, has, we think, been misapprehended by M.
Delambre, when he asserts that every thing which it contains “is to be
found expressly in Kepler.”[40]




CHAPTER XI.

  _The first Idea of Gravity occurs to Newton in 1666—His first
    Speculations upon it—Interrupted by his Optical Experiments—He
    resumes the Subject in consequence of a Discussion with Dr. Hooke—
    He discovers the true Law of Gravity and the Cause of the Planetary
    Motions—Dr. Halley urges him to publish his Principia—His
    Principles of Natural Philosophy—Proceedings of the Royal Society
    on this Subject—The Principia appears in 1687—General Account
    of it, and of the Discoveries it contains—They meet with great
    Opposition, owing to the Prevalence of the Cartesian System—Account
    of the Reception and Progress of the Newtonian Philosophy in foreign
    Countries—Account of its Progress and Establishment in England._


Such is a brief sketch of the labours and lives of those illustrious
men who prepared the science of astronomy for the application of
Newton’s genius. Copernicus had determined the arrangement and general
movements of the planetary bodies: Kepler had proved that they moved
in elliptical orbits; that their _radii vectores_ described arcs
proportional to the times; and that their periodic times were related
to their distances. Galileo had added to the universe a whole system of
secondary planets; and several astronomers had distinctly referred the
motion of the heavenly bodies to the power of attraction.

In the year 1666, when the plague had driven Newton from Cambridge,
he was sitting alone in the garden at Woolsthorpe, and reflecting on
the nature of gravity,—that remarkable power which causes all bodies
to descend towards the centre of the earth. As this power is not found
to suffer any sensible diminution at the greatest distance from the
earth’s centre to which we can reach, being as powerful at the tops
of the highest mountains as at the bottom of the deepest mines, he
conceived it highly probable, that it must extend much farther than was
usually supposed. No sooner had this happy conjecture occurred to his
mind, than he considered what would be the effect of its extending as
far as the moon. That her motion must be influenced by such a power he
did not for a moment doubt; and a little reflection convinced him that
it might be sufficient for retaining that luminary in her orbit round
the earth. Though the force of gravity suffers no sensible diminution
at those small distances from the earth’s centre at which we can place
ourselves, yet he thought it very possible, that, at the distance of
the moon, it might differ much in strength from what it is on the
earth. In order to form some estimate of the degree of its diminution,
he considered that, if the moon be retained in her orbit by the force
of gravity, the primary planets must also be carried round the sun by
the same power; and by comparing the periods of the different planets
with their distances from the sun, he found, that if they were retained
in their orbits by any power like gravity, its force must decrease in
the duplicate proportion,[41] or as the squares of their distances
from the sun. In drawing this conclusion, he supposed the planets to
move in orbits perfectly circular, and having the sun in their centre.
Having thus obtained the law of the force by which the planets were
drawn to the sun, his next object was to ascertain if such a force,
emanating from the earth and directed to the moon, was sufficient, when
diminished in the duplicate ratio of the distance, to retain her in her
orbit. In performing this calculation, it was necessary to compare the
space through which heavy bodies fall in a second at a given distance
from the centre of the earth, viz. at its surface, with the space
through which the moon, as it were, falls to the earth in a second of
time while revolving in a circular orbit. Being at a distance from
books when he made this computation, he adopted the common estimate of
the earth’s diameter then in use among geographers and navigators, and
supposed that each degree of latitude contained sixty English miles. In
this way he found that the force which retains the moon in her orbit,
as deduced from the force which occasions the fall of heavy bodies to
the earth’s surface, was one-sixth greater than that which is actually
observed in her circular orbit. This difference threw a doubt upon all
his speculations; but, unwilling to abandon what seemed to be otherwise
so plausible, he endeavoured to account for the difference of the two
forces, by supposing that some other cause[42] must have been united
with the force of gravity in producing so great a velocity of the moon
in her circular orbit. As this new cause, however, was beyond the reach
of observation, he discontinued all further inquiries into the subject,
and concealed from his friends the speculations in which he had been
employed.

After his return to Cambridge in 1666, his attention was occupied
with those optical discoveries of which we have given an account in
a preceding chapter; but he had no sooner brought them to a close
than his mind reverted to the great subject of the planetary motions.
Upon the death of Oldenburg in August, 1678, Dr. Hooke was appointed
secretary to the Royal Society; and as this learned body had requested
the opinion of Newton about a system of physical astronomy, he
addressed a letter to Dr. Hooke on the 28th November, 1679. In this
letter he proposed a direct experiment for verifying the motion of
the earth, viz. by observing whether or not bodies that fall from a
considerable height descend in a vertical direction, for if the earth
were at rest the body would describe exactly a vertical line, whereas
if it revolved round its axis, the falling body must deviate from the
vertical line towards the east. The Royal Society attached great value
to the idea thus casually suggested; and Dr. Hooke was appointed to put
it to the test of experiment. Being thus led to consider the subject
more attentively, he wrote to Newton, that wherever the direction of
gravity was oblique to the axis on which the earth revolved, that is,
in every part of the earth except the equator, falling bodies should
approach to the equator, and the deviation from the vertical, in place
of being exactly to the east, as Newton maintained, should be to the
south-east of the point from which the body began to move. Newton
acknowledged that this conclusion was correct in theory, and Dr. Hooke
is said to have given an experimental demonstration of it before the
Royal Society in December, 1679.[43] Newton had erroneously concluded
that the path of the falling body would be a spiral; but Dr. Hooke,
on the same occasion on which he made the preceding experiment, read
a paper to the Society, in which he proved that the path of the body
would be an eccentric ellipse in vacuo, and an ellipti-spiral, if the
body moved in a resisting medium.[44]

This correction of Newton’s error, and the discovery that a projectile
would move in an elliptical orbit when under the influence of a force
varying in the inverse ratio of the square of the distance, led Newton,
as he himself informs us in his letter to Halley,[45] to discover
“the theorem by which he afterward examined the ellipsis,” and to
demonstrate the celebrated proposition, that a planet acted upon by an
attractive force varying inversely as the squares of the distances will
describe an elliptical orbit, in one of whose foci the attractive force
resides.

But though Newton had thus discovered the true cause of all the
celestial motions, he did not yet possess any evidence that such a
force actually resided in the sun and planets. The failure of his
former attempt to identify the law of falling bodies at the earth’s
surface with that which guided the moon in her orbit threw a doubt over
all his speculations, and prevented him from giving any account of them
to the public.

An accident, however, of a very interesting nature induced him to
resume his former inquiries, and enabled him to bring them to a close.
In June, 1682, when he was attending a meeting of the Royal Society
of London, the measurement of a degree of the meridian, executed by
M. Picard in 1679, became the subject of conversation. Newton took a
memorandum of the result obtained by the French astronomer, and having
deduced from it the diameter of the earth, he immediately resumed his
calculation of 1665, and began to repeat it with these new data. In
the progress of the calculation he saw that the result which he had
formerly expected was likely to be produced, and he was thrown into
such a state of nervous irritability that he was unable to carry on
the calculation. In this state of mind he intrusted it to one of his
friends, and he had the high satisfaction of finding his former views
amply realized. The force of gravity which regulated the fall of bodies
at the earth’s surface, when diminished as the square of the moon’s
distance from the earth, was found to be almost exactly equal to the
centrifugal force of the moon as deduced from her observed distance and
velocity.

The influence of such a result upon such a mind may be more easily
conceived than described. The whole material universe was spread out
before him;—the sun with all his attending planets;—the planets with
all their satellites;—the comets wheeling in every direction in their
eccentric orbits;—and the systems of the fixed stars stretching to the
remotest limits of space. All the varied and complicated movements of
the heavens, in short, must have been at once presented to his mind, as
the necessary result of that law which he had established in reference
to the earth and the moon.

After extending this law to the other bodies of the system, he composed
a series of propositions on the motion of the primary planets about the
sun, which were sent to London about the end of 1683, and were soon
afterward communicated to the Royal Society.[46]

About this period other philosophers had been occupied with the same
subject. Sir Christopher Wren had many years before endeavoured to
explain the planetary motions “by the composition of a descent towards
the sun, and an impressed motion; but he at length gave it over,
not finding the means of doing it.” In January, 1683–4, Dr. Halley
had concluded, from Kepler’s Law of the Periods and Distances, that
the centripetal force decreased in the reciprocal proportion of the
squares of the distances, and having one day met Sir Christopher Wren
and Dr. Hooke, the latter affirmed that he had demonstrated upon that
principle all the laws of the celestial motions. Dr. Halley confessed
that his attempts were unsuccessful, and Sir Christopher, in order to
encourage the inquiry, offered to present a book of forty shillings’
value to either of the two philosophers who should, in the space of two
months, bring him a convincing demonstration of it. Hooke persisted in
the declaration that he possessed the method, but avowed it to be his
intention to conceal it for some time. He promised, however, to show
it to Sir Christopher; but there is every reason to believe that this
promise was never fulfilled.

In August, 1684, Dr. Halley went to Cambridge for the express purpose
of consulting Newton on this interesting subject. Newton assured him
that he had brought this demonstration to perfection, and promised
him a copy of it. This copy was received in November by the doctor,
who made a second visit to Cambridge, in order to induce its author
to have it inserted in the register book of the society. On the 10th
of December, Dr. Halley announced to the society, that he had seen
at Cambridge Mr. Newton’s treatise _De Motu Corporum_, which he had
promised to send to the society to be entered upon their register;
and Dr. Halley was desired to unite with Mr. Paget, master of the
mathematical school in Christ’s Hospital, in reminding Mr. Newton of
his promise “for securing the invention to himself till such time as
he can be at leisure to publish it.” On the 25th February Mr. Aston,
the secretary, communicated a letter from Mr. Newton, in which he
expressed his willingness “to enter in the register his notions about
motion, and his intentions to fit them suddenly for the press.” The
progress of his work was, however, interrupted by a visit of five or
six weeks which he made in Lincolnshire; but he proceeded with such
diligence on his return, that he was able to transmit the manuscript to
London before the end of April. This manuscript, entitled _Philosophiæ
Naturalis Principia Mathematica_, and dedicated to the society, was
presented by Dr. Vincent on the 28th April, 1686, when Sir John
Hoskins, the vice-president, and the particular friend of Dr. Hooke,
was in the chair. Dr. Vincent passed a just encomium on the novelty
and dignity of the subject; and another member added, that “Mr. Newton
had carried the thing so far, that there was no more to be added.” To
these remarks the vice-president replied, that the method “was so much
the more to be prized as it was both invented and perfected at the
same time.” Dr. Hooke took offence at these remarks, and blamed Sir
John for not having mentioned “what he had discovered to him;” but
the vice-president did not seem to recollect any such communication,
and the consequence of this discussion was, that “these two, who till
then were the most inseparable cronies, have since scarcely seen one
another, and are utterly fallen out.” After the breaking up of the
meeting, the society adjourned to the coffee-house, where Dr. Hooke
stated that he not only had made the same discovery, but had given the
first hint of it to Newton.

An account of these proceedings was communicated to Newton through two
different channels. In a letter dated May 22d, Dr. Halley wrote to him
“that Mr. Hooke has some pretensions upon the invention of the rule
of the decrease of gravity being reciprocally as the squares of the
distances from the centre. He says you had the notion from him, though
he owns the demonstration of the curves generated thereby to be wholly
your own. How much of this is so you know best, as likewise what you
have to do in this matter. Only Mr. Hooke seems to expect you would
make some mention of him in the preface, which it is possible you may
see reason to prefix.”

This communication from Dr. Halley induced our author, on the 20th
June, to address a long letter to him, in which he gives a minute
and able refutation of Hooke’s claims; but before this letter was
despatched, another correspondent, who had received his information
from one of the members that were present, informed Newton “that Hooke
made a great stir, pretending that he had all from him, and desiring
they would see that he had justice done him.” This fresh charge seems
to have ruffled the tranquillity of Newton; and he accordingly added an
angry and satirical postscript, in which he treats Hooke with little
ceremony, and goes so far as to conjecture that Hooke might have
acquired his knowledge of the law from a letter of his own to Huygens,
directed to Oldenburg, and dated January 14th, 1672–3. “My letter to
Hugenius was directed to Mr. Oldenburg, who used to keep the originals.
His papers came into Mr. Hooke’s possession. Mr. Hooke, knowing my
hand, might have the curiosity to look into that letter, and there take
the notion of comparing the forces of the planets arising from their
circular motion; and so what he wrote to me afterward about the rate of
gravity might be nothing but the fruit of my own garden.”

In replying to this letter, Dr. Halley assured him that Hooke’s “manner
of claiming the discovery had been represented to him in worse colours
than it ought, and that he neither made public application to the
society for justice, nor pretended that you had all from him.” The
effect of this assurance was to make Newton regret that he had written
the angry postscript to his letter; and in replying to Halley on the
14th July, 1686, he not only expresses his regret, but recounts the
different new ideas which he had acquired from Hooke’s correspondence,
and suggests it as the best method “of compromising the present
dispute,” to add a scholium, in which Wren, Hooke, and Halley are
acknowledged to have independently deduced the law of gravity from the
second law of Kepler.[47]

At the meeting of the 28th April, at which the manuscript of the
_Principia_ was presented to the Royal Society, it was agreed that the
printing of it should be referred to the council; that a letter of
thanks should be written to its author; and at a meeting of the council
on the 19th May, it was resolved that the MSS. should be printed at
the society’s expense, and that Dr. Halley should superintend it while
going through the press. These resolutions were communicated by Dr.
Halley in a letter dated the 22d May; and in Newton’s reply on the 20th
June already mentioned, he makes the following observations: “The
proof you sent me I like very well. I designed the whole to consist of
three books; the second was finished last summer, being short, and only
wants transcribing, and drawing the cuts fairly. Some new propositions
I have since thought on, which I can as well let alone. The third wants
the theory of comets. In autumn last I spent two months in calculation
to no purpose for want of a good method, which made me afterward return
to the first book, and enlarge it with diverse propositions, some
relating to comets, others to other things found out last winter. The
third I now design to suppress. Philosophy is such an impertinently
litigious lady, that a man had as good be engaged in lawsuits as have
to do with her. I found it so formerly, and now I can no sooner come
near her again but she gives me warning. The first two books without
the third will not so well bear the title of _Philosophiæ Naturalis
Principia Mathematica_; and therefore I had altered it to this, _De
Motu Corporum Libri duo_. But after second thoughts I retain the former
title. It will help the sale of the book, which I ought not to diminish
now ’tis yours.”

In replying to this letter on the 29th June, Dr. Halley regrets that
our author’s tranquillity should have been thus disturbed by envious
rivals; and implores him in the name of the society not to suppress
the third book. “I must again beg you,” says he, “not to let your
resentments run so high as to deprive us of your third book, wherein
your applications of your mathematical doctrine to the theory of
comets, and several curious experiments, which, as I guess by what you
write ought to compose it, will undoubtedly render it acceptable to
those who will call themselves philosophers without mathematics, which
are much the greater number.”

To these solicitations Newton seems to have readily yielded. His second
book was sent to the society, and presented on the 2d March, 1686–7.
The third book was also transmitted, and presented on the 6th April,
and the whole work was completed and published in the month of May,
1687.

Such is a brief account of the publication of a work which is
memorable, not only in the annals of one science or of one country, but
which will form an epoch in the history of the world, and will ever be
regarded as the brightest page in the records of human reason. We shall
endeavour to convey to the reader some idea of its contents, and of the
brilliant discoveries which it disseminated over Europe.

The _Principia_ consists of three books. The first and second, which
occupy three-fourths of the work, are entitled, _On the Motion of
Bodies_; and the third bears the title, _On the System of the World_.
The first two books contain the mathematical principles of philosophy,
namely, the laws and conditions of motions and forces; and they are
illustrated with several philosophical scholia, which treat of some of
the most general and best established points in philosophy, such as the
density and resistance of bodies, spaces void of matter, and the motion
of sound and light. The object of the third book is to deduce from
these principles the constitution of the system of the world; and this
book has been drawn up in as popular a style as possible, in order that
it may be generally read.

The great discovery which characterizes the Principia is that of the
principle of universal gravitation, as deduced from the motion of the
moon, and from the three great facts or laws discovered by Kepler.
This principle is, _that every particle of matter is attracted by, or
gravitates to, every other particle of matter, with a force inversely
proportional to the squares of their distances_. From the first law of
Kepler, namely, the proportionality of the areas to the times of their
description, Newton inferred that the force which kept the planet in
its orbit was always directed to the sun; and from the second law of
Kepler, that every planet moves in an ellipse with the sun in one of
its foci, he drew the still more general inference, that the force
by which the planet moves round that focus varies inversely as the
square of its distance from the focus. As this law was true in the
motion of satellites round their primary planets, Newton deduced the
equality of gravity in all the heavenly bodies towards the sun, upon
the supposition that they are equally distant from its centre; and in
the case of terrestrial bodies, he succeeded in verifying this truth by
numerous and accurate experiments.

By taking a more general view of the subject, Newton demonstrated
that a conic section was the only curve in which a body could move
when acted upon by a force varying inversely as the square of the
distance; and he established the conditions depending on the velocity
and the primitive position of the body, which were requisite to make it
describe a circular, an elliptical, a parabolic, or a hyperbolic orbit.

Notwithstanding the generality and importance of these results, it
still remained to be determined whether the force resided in the
centres of the planets, or belonged to each individual particle
of which they were composed. Newton removed this uncertainty by
demonstrating, that if a spherical body acts upon a distant body with
a force varying as the distance of this body from the centre of the
sphere, the same effect will be produced as if each of its particles
acted upon the distant body according to the same law. And hence it
follows that the spheres, whether they are of uniform density, or
consist of concentric layers, with densities varying according to
any law whatever, will act upon each other in the same manner as if
their force resided in their centres alone. But as the bodies of the
solar system are very nearly spherical, they will all act upon one
another, and upon bodies placed on their surface, as if they were so
many centres of attraction; and therefore we obtain the law of gravity
which subsists between spherical bodies, namely, that one sphere will
act upon another with a force directly proportional to the quantity of
matter, and inversely as the square of the distance between the centres
of the spheres. From the equality of action and reaction, to which no
exception can be found, Newton concluded that the sun gravitated to the
planets, and the planets to their satellites; and the earth itself to
the stone which falls upon its surface; and, consequently, that the two
mutually gravitating bodies approached to one another with velocities
inversely proportional to their quantities of matter.

Having established this universal law, Newton was enabled, not only to
determine the weight which the same body would have at the surface of
the sun and the planets, but even to calculate the quantity of matter
in the sun, and in all the planets that had satellites, and even to
determine the density or specific gravity of the matter of which they
were composed. In this way he found that the weight of the same body
would be twenty-three times greater at the surface of the sun than at
the surface of the earth, and that the density of the earth was four
times greater than that of the sun, the planets increasing in density
as they receded from the centre of the system.

If the peculiar genius of Newton has been displayed in his
investigation of the law of universal gravitation, it shines with no
less lustre in the patience and sagacity with which he traced the
consequences of this fertile principle.

The discovery of the spheroidal form of Jupiter by Cassini had probably
directed the attention of Newton to the determination of its cause, and
consequently to the investigation of the true figure of the earth. The
spherical form of the planets have been ascribed by Copernicus to the
gravity or natural appetency of their parts; but upon considering the
earth as a body revolving upon its axis, Newton quickly saw that the
figure arising from the mutual attraction of its parts must be modified
by another force arising from its rotation. When a body revolves upon
an axis, the velocity of rotation increases from the poles, where it
is nothing, to the equator, where it is a maximum. In consequence of
this velocity the bodies on the earth’s surface have a tendency to
fly off from it, and this tendency increases with the velocity. Hence
arises a centrifugal force which acts in combination with a force of
gravity, and which Newton found to be the 289th part of the force of
gravity at the equator, and decreasing, as the cosine of the latitude,
from the equator to the poles. The great predominance of gravity over
the centrifugal force prevents the latter from carrying off any bodies
from the earth’s surface, but the weight of all bodies is diminished
by the centrifugal force, so that the weight of any body is greater at
the poles than it is at the equator. If we now suppose the waters at
the pole to communicate with those at the equator by means of a canal,
one branch of which goes from the pole to the centre of the earth,
and the other from the centre of the earth to the equator, then the
polar branch of the canal will be heavier than the equatorial branch,
in consequence of its weight not being diminished by the centrifugal
force, and, therefore, in order that the two columns may be in
equilibrio, the equatorial one must be lengthened. Newton found that
the length of the polar must be to that of the equatorial canal as 229
to 230, or that the earth’s polar radius must be seventeen miles less
than its equatorial radius; that is, that the figure of the earth is
an oblate spheroid, formed by the revolution of an ellipse round its
lesser axis. Hence it follows, that the intensity of gravity at any
point of the earth’s surface is in the inverse ratio of the distance of
that point from the centre, and, consequently, that it diminishes from
the equator to the poles,—a result which he confirmed by the fact, that
clocks required to have their pendulums shortened in order to beat true
time when carried from Europe towards the equator.

The next subject to which Newton applied the principle of gravity was
the tides of the ocean. The philosophers of all ages have recognised
the connexion between the phenomena of the tides and the position
of the moon. The College of Jesuits at Coimbra, and subsequently
Antonio de Dominis and Kepler, distinctly referred the tides to the
attraction of the waters of the earth by the moon, but so imperfect was
the explanation which was thus given of the phenomena, that Galileo
ridiculed the idea of lunar attraction, and substituted for it a
fallacious explanation of his own. That the moon is the principal cause
of the tides is obvious from the well-known fact, that it is high water
at any given place about the time when she is in the meridian of that
place; and that the sun performs a secondary part in their production
may be proved from the circumstance, that the highest tides take place
when the sun, the moon, and the earth are in the same straight line,
that is, when the force of the sun conspires with that of the moon,
and that the lowest tides take place when the lines drawn from the
sun and moon to the earth are at right angles to each other, that is,
when the force of the sun acts in opposition to that of the moon. The
most perplexing phenomenon in the tides of the ocean, and one which
is still a stumbling-block to persons slightly acquainted with the
theory of attraction, is the existence of high water on the side of the
earth opposite to the moon, as well as on the side next the moon. To
maintain that the attraction of the moon at the same instant draws the
waters of the ocean towards herself, and also draws them from the earth
in an opposite direction, seems at first sight paradoxical; but the
difficulty vanishes when we consider the earth, or rather the centre of
the earth, and the water on each side of it as three distinct bodies
placed at different distances from the moon, and consequently attracted
with forces inversely proportional to the squares of their distances.
The water nearest the moon will be much more powerfully attracted than
the centre of the earth, and the centre of the earth more powerfully
than the water farthest from the moon. The consequence of this must be,
that the waters nearest the moon will be drawn away from the centre
of the earth, and will consequently rise from their level, while the
centre of the earth will be drawn away from the waters opposite the
moon, which will, as it were, be left behind, and consequently be in
the same situation as if they were raised from the earth in a direction
opposite to that in which they are attracted by the moon. Hence the
effect of the moon’s action upon the earth is to draw its fluid parts
into the form of an oblong spheroid, the axis of which passes through
the moon. As the action of the sun will produce the very same effect,
though in a smaller degree, the tide at any place will depend on the
relative position of these two spheroids, and will be always equal
either to the sum or to the difference of the effects of the two
luminaries. At the time of new and full moon the two spheroids will
have their axes coincident, and the height of the tide, which will then
be a _spring_ one, will be equal to the sum of the elevations produced
in each spheroid considered separately, while at the first and third
quarters the axes of the spheroids will be at right angles to each
other, and the height of the tide, which will then be a _neap_ one,
will be equal to the difference of the elevations produced in each
separate spheroid. By comparing the spring and neap tides, Newton found
that the force with which the sun acted upon the waters of the earth
was to that with which the sun acted upon them as 4.48 to 1;—that the
force of the moon produced a tide of 8.63 feet;—that of the sun one of
1.93 feet;—and both of them combined, one of 10½ French feet,—a result
which in the open sea does not deviate much from observation. Having
thus ascertained the force of the moon on the waters of our globe, he
found that the quantity of matter in the moon was to that in the earth
as 1 to 40, and the density of the moon to that of the earth as 11 to 9.

The motions of the moon, so much within the reach of our own
observation, presented a fine field for the application of the theory
of universal gravitation. The irregularities exhibited in the lunar
motions had been known in the time of Hipparchus and Ptolemy. Tycho
had discovered the great inequality called the _variation_, amounting
to 37′, and depending on the alternate acceleration and retardation of
the moon in every quarter of a revolution, and he had also ascertained
the existence of the annual equation. Of these two inequalities Newton
gave a most satisfactory explanation. The action of the sun upon the
moon may be always resolved into two, one acting in the direction
of the line joining the moon and earth, and consequently tending to
increase or diminish the moon’s gravity to the earth, and the other
in a direction at right angles to this, and consequently tending to
accelerate or retard the motion in her orbit. Now, it was found by
Newton that this last force was reduced to nothing, or vanished at
the syzigies or quadratures, so that at these four points the moon
described areas proportional to the times. The instant, however, that
the moon quits these positions, the force under consideration, which
we may call the tangential force, begins, and it reaches its maximum
in the four octants. The force, therefore, compounded of these two
elements of the solar force, or the diagonal of the parallelogram
which they form, is no longer directed to the earth’s centre, but
deviates from it at a maximum about 30 minutes, and therefore affects
the angular motion of the moon, the motion being accelerated in passing
from the quadratures to the syzigies, and retarded in passing from
the syzigies to the quadratures. Hence the velocity is in its mean
state in the octants, a maximum in the syzigies, and a minimum in the
quadratures.

Upon considering the influence of the solar force in diminishing
or increasing the moon’s gravity to the earth, Newton saw that her
distance and her periodic time must from this cause be subject to
change, and in this way he accounted for the annual equation observed
by Tycho. By the application of similar principles, he explained the
cause of the motion of the apsides, or of the greater axis of the
moon’s orbit, which has an angular progressive motion of 3° 4′ nearly
in the course of one lunation; and he showed that the retrogradation of
the nodes, amounting to 3′ 10″ daily, arose from one of the elements
of the solar force being exerted in the plane of the ecliptic, and not
in the plane of the moon’s orbit, the effect of which was to draw the
moon down to the plane of the ecliptic, and thus cause the line of the
nodes, or the intersection of these two planes, to move in a direction
opposite to that of the moon. The lunar theory thus blocked out by
Newton, required for its completion the labours of another century. The
imperfections of the fluxionary calculus prevented him from explaining
the other inequalities of the moon’s motions, and it was reserved to
Euler, D’Alembert, Clairaut, Mayer, and Laplace to bring the lunar
tables to a high degree of perfection, and to enable the navigator to
determine his longitude at sea with a degree of precision which the
most sanguine astronomer could scarcely have anticipated.

By the consideration of the retrograde motion of the moon’s nodes,
Newton was led to discover the cause of the remarkable phenomenon of
the precession of the equinoctial points, which moved 50″ annually,
and completed the circuit of the heavens in 25,920 years. Kepler had
declared himself incapable of assigning any cause for this motion, and
we do not believe that any other astronomer ever made the attempt.
From the spheroidal form of the earth, it may be regarded as a sphere
with a spheroidal ring surrounding its equator, one-half of the ring
being above the plane of the ecliptic and the other half below it.
Considering this excess of matter as a system of satellites adhering
to the earth’s surface, Newton saw that the combined actions of the
sun and moon upon these satellites tended to produce a retrogradation
in the nodes of the circles which they described in their diurnal
rotation, and that the sum of all the tendencies being communicated to
the whole mass of the planet, ought to produce a slow retrogradation of
the equinoctial points. The effect produced by the motion of the sun he
found to be 40″, and that produced by the action of the moon 10″.

Although there could be little doubt that the comets were retained
in their orbits by the same laws which regulated the motions of the
planets, yet it was difficult to put this opinion to the test of
observation. The visibility of comets only in a small part of their
orbits rendered it difficult to ascertain their distance and periodic
times, and as their periods were probably of great length, it was
impossible to correct approximate results by repeated observation.
Newton, however, removed this difficulty, by showing how to determine
the orbit of a comet, namely, the form and position of the orbit and
the periodic time, by three observations. By applying this method to
the comet of 1680, he calculated the elements of its orbit, and from
the agreement of the computed places with those which were observed,
he justly inferred that the motions of comets were regulated by the
same laws as those of the planetary bodies. This result was one of
great importance; for as the comets enter our system in every possible
direction, and at all angles with the ecliptic, and as a great part
of their orbits extend far beyond the limits of the solar system, it
demonstrated the existence of gravity in spaces far removed beyond the
planet, and proved that the law of the inverse ratio of the squares of
the distance was true in every possible direction, and at very remote
distances from the centre of our system.[48]

Such is a brief view of the leading discoveries which the _Principia_
first announced to the world. The grandeur of the subjects of which
it treats, the beautiful simplicity of the system which it unfolds,
the clear and concise reasoning by which that system is explained, and
the irresistible evidence by which it is supported might have ensured
it the warmest admiration of contemporary mathematicians, and the
most welcome reception in all the schools of philosophy throughout
Europe. This, however, is not the way in which great truths are
generally received. Though the astronomical discoveries of Newton were
not assailed by the class of ignorant pretenders who attacked his
optical writings, yet they were every where resisted by the errors and
prejudices which had taken a deep hold even of the strongest minds. The
philosophy of Descartes was predominant throughout Europe. Appealing
to the imagination, and not to the reason of mankind, it was quickly
received into popular favour, and the same causes which facilitated
its introduction extended its influence, and completed its dominion
over the human mind. In explaining all the movements of the heavenly
bodies by a system of vortices in a fluid medium diffused through the
universe, Descartes had seized upon an analogy of the most alluring
and deceitful kind. Those who had seen heavy bodies revolving in the
eddies of a whirlpool, or in the gyrations of a vessel of water thrown
into a circular motion, had no difficulty in conceiving how the planets
might revolve round the sun by analogous movements. The mind instantly
grasped at an explanation of so palpable a character, and which
required for its development neither the exercise of patient thought
nor the aid of mathematical skill. The talent and perspicuity with
which the Cartesian system was expounded, and the show of experiments
with which it was sustained, contributed powerfully to its adoption,
while it derived a still higher sanction from the excellent character
and the unaffected piety of its author.

Thus intrenched, as the Cartesian system was, in the strongholds of
the human mind, and fortified by its most obstinate prejudices, it
was not to be wondered at that the pure and sublime doctrines of the
Principia were distrustfully received and perseveringly resisted. The
uninstructed mind could not readily admit the idea, that the great
masses of the planets were suspended in empty space, and retained
in their orbits by an invisible influence residing in the sun; and
even those philosophers who had been accustomed to the rigour of true
scientific research, and who possessed sufficient mathematical skill
for the examination of the Newtonian doctrines, viewed them at first
as reviving the occult qualities of the ancient physics, and resisted
their introduction with a pertinacity which it is not easy to explain.
Prejudiced, no doubt, in favour of his own metaphysical views, Leibnitz
himself misapprehended the principles of the Newtonian philosophy,
and endeavoured to demonstrate the truths in the Principia by the
application of different principles. Huygens, who above all other men
was qualified to appreciate the new philosophy, rejected the doctrine
of gravitation as existing between the individual particles of matter,
and received it only as an attribute of the planetary masses. John
Bernouilli, one of the first mathematicians of his age, opposed the
philosophy of Newton. Mairan, in the early part of his life, was a
strenuous defender of the system of vortices. Cassini and Maraldi were
quite ignorant of the Principia, and occupied themselves with the
most absurd methods of calculating the orbits of comets long after
the Newtonian method had been established on the most impregnable
foundation; and even Fontenelle, a man of liberal views and extensive
information, continued, throughout the whole of his life, to maintain
the doctrines of Descartes.

The Chevalier Louville of Paris had adopted the Newtonian philosophy
before 1720. S’Gravesande had introduced it into the Dutch universities
at a somewhat earlier period, and Maupertuis, in consequence of a visit
which he paid to England in 1728, became a zealous defender of it; but
notwithstanding these and some other examples that might be quoted,
we must admit the truth of the remark of Voltaire, that though Newton
survived the publication of the Principia more than forty years, yet
at the time of his death he had not above _twenty_ followers out of
England.

With regard to the progress of the Newtonian philosophy in England,
some difference of opinion has been entertained. Professor Playfair
gives the following account of it. “In the universities of England,
though the Aristotelian physics had made an obstinate resistance, they
had been supplanted by the Cartesian, which became firmly established
about the time when their foundation began to be sapped by the general
progress of science, and particularly by the discoveries of Newton. For
more than thirty years after the publication of these discoveries, the
system of vortices kept its ground; and a translation from the French
into Latin of the _Physics_ of Rohault, a work entirely Cartesian,
continued at Cambridge to be the text for philosophical instruction.
About the year 1718, a new and more elegant translation of the same
book was published by Dr. Samuel Clarke, with the addition of notes, in
which that profound and ingenious writer explained the views of Newton
on the principal objects of discussion, so that the notes contained
virtually a refutation of the text; they did so, however, only
virtually, all appearance of argument and controversy being carefully
avoided. Whether this escaped the notice of the learned doctor or not
is uncertain, but the new translation, from its better Latinity, and
the name of the editor, was readily admitted to all the academical
honours which the old one had enjoyed. Thus the stratagem of Dr. Clarke
completely succeeded; the tutor might prelect from the text, but the
pupil would sometimes look into the notes; and error is never so sure
of being exposed as when the truth is placed close to it, side by side,
without any thing to alarm prejudice, or awaken from its lethargy
the dread of innovation. Thus, therefore, the Newtonian philosophy
first entered the university of Cambridge under the protection of the
Cartesian.” To this passage Professor Playfair adds the following as a
note:—

“The universities of St. Andrew’s and Edinburgh were, I believe, the
first in Britain where the Newtonian philosophy was made the subject
of the academical prelections. For this distinction they are indebted
to James and David Gregory, the first in some respects the rival, but
both the friends of Newton. Whiston bewails, in the anguish of his
heart, the difference, in this respect, between those universities and
his own. David Gregory taught in Edinburgh for several years prior to
1690, when he removed to Oxford; and Whiston says, ‘He had already
caused several of his scholars to keep acts, as we call them, upon
several branches of the Newtonian philosophy, while we at Cambridge,
poor wretches, were ignominiously studying the fictitious hypotheses
of the Cartesians.’[49] I do not, however, mean to say, that from this
date the Cartesian philosophy was expelled from those universities;
the _Physics_ of Rohault were still in use as a text-book,—at least
occasionally, to a much later period than this, and a great deal, no
doubt, depended on the character of the individual. Professor Keill
introduced the Newtonian philosophy in his lectures at Oxford in 1697;
but the instructions of the tutors, which constitute the real and
efficient system of the university, were not cast in that mould till
long afterward.” Adopting the same view of the subject, Mr. Dugald
Stewart has stated, “that the philosophy of Newton was publicly taught
by David Gregory at Edinburgh, and by his brother, James Gregory,
at St. Andrew’s,[50] before it was able to supplant the vortices of
Descartes in that very university of which Newton was a member. It was
in the Scottish universities that the philosophy of Locke, as well as
that of Newton, was first adopted as a branch of academical education.”

Anxious as we should have been to have awarded to Scotland the honour
of having first adopted the Newtonian philosophy, yet a regard for
historical truth compels us to take a different view of the subject.
It is well known that Sir Isaac Newton delivered lectures on his own
philosophy from the Lucasian chair before the publication of the
Principia; and in the very page of Whiston’s life quoted by Professor
Playfair, he informs us that he had heard him read such lectures in the
public schools, though at that time he did not at all understand them.
Newton continued to lecture till 1699, and occasionally, we presume,
till 1703, when Whiston became his successor, having been appointed
his deputy in 1699. In both of these capacities Whiston delivered in
the public schools a course of lectures on astronomy, and a course of
physico-mathematical lectures, in which the mathematical philosophy
of Newton was explained and demonstrated, and both these courses
were published, the one in 1707, and the other in 1710, “for the use
of the young men in the university.” In 1707, the celebrated blind
mathematician Nicholas Saunderson took up his residence in Christ’s
College without being admitted a member of that body. The society
not only allotted to him apartments, but gave him the free use of
their library. With the concurrence of Whiston he delivered a course
of lectures “on the Principia, Optics, and Universal Arithmetic of
Newton,” and the popularity of these lectures was so great, that Sir
Isaac corresponded on the subject of them with their author; and on the
ejection of Whiston from the Lucasian chair in 1711, Saunderson was
appointed his successor. In this important office he continued to teach
the Newtonian philosophy till the time of his death, which took place
in 1739.

But while the Newtonian philosophy was thus regularly taught in
Cambridge, after the publication of the Principia, there were not
wanting other exertions for accelerating its progress. About 1694, the
celebrated Dr. Samuel Clarke, while an under-graduate, defended, in the
public schools, a question taken from the Newtonian philosophy; and
his translation of Rohault’s Physics, which contains references in the
notes to the Principia, and which was published in 1697 (and not in
1718, as stated by Professor Playfair), shows how early the Cartesian
system was attacked by the disciples of Newton. The author of the Life
of Saunderson informs us, that public exercises or acts founded on
every part of the Newtonian system were very common about 1707, and so
general were such studies in the university, that the Principia rose to
four times its original price.[51] One of the most ardent votaries of
the Newtonian philosophy was Dr. Laughton, who had been tutor in Clare
Hall from 1694, and it is probable that during the whole, or at least
a greater part, of his tutorship he had inculcated the same doctrines.
In 1709–10, when he was proctor of that college, instead of appointing
a moderator, he discharged the office himself, and devoted his most
active exertions to the promotion of mathematical knowledge. Previous
to this, he had even published a paper of questions on the Newtonian
philosophy, which appear to have been used as theses for disputations;
and such was his ardour and learning that they powerfully contributed
to the popularity of his college. Between 1706 and 1716, the year
of his death, the celebrated Roger Cotes, the friend and disciple
of Newton, filled the Plumian chair of astronomy and experimental
philosophy at Cambridge. During this period he edited the second
edition of the Principia, which he enriched with an admirable preface,
and thus contributed, by his writings as well as by his lectures, to
advance the philosophy of his master. About the same time, the learned
Dr. Bentley, who first made known the philosophy of his friend to
the readers of general literature, filled the high office of master
of Trinity College, and could not fail to have exerted his utmost
influence in propagating doctrines which he so greatly admired. Had any
opposition been offered to the introduction of the true system of the
universe, the talents and influence of these individuals would have
immediately suppressed it; but no such opposition seems to have been
made; and though there may have been individuals at Cambridge ignorant
of mathematical science, who adhered to the system of Descartes, and
patronised the study of the Physics of Rohault, yet it is probable
that similar persons existed in the universities of Edinburgh and St.
Andrew’s; and we cannot regard their adherence to error as disproving
the general fact, that the philosophy of Newton was quickly introduced
into all the universities of Great Britain.

But while the mathematical principles of the Newtonian system were ably
expounded in our seats of learning, its physical truths were generally
studied, and were explained and communicated to the public by various
lecturers on experimental philosophy. The celebrated Locke, who was
incapable of understanding the Principia from his want of mathematical
knowledge, inquired of Huygens if all the mathematical propositions
in that work were true. When he was assured that he might depend upon
their certainty, he took them for granted, and carefully examined
the reasonings and corollaries deduced from them. In this manner he
acquired a knowledge of the physical truths in the Principia, and
became a firm believer in the discoveries which it contained. In the
same manner he studied the treatise on Optics, and made himself master
of every part of it which was not mathematical.[52] From a manuscript
of Sir Isaac Newton’s, entitled “A demonstration that the planets, by
their gravity towards the sun, may move in ellipses,[53] found among
the papers of Mr. Locke, and published by Lord King,” it would appear
that he himself had been at considerable trouble in explaining to his
friend that interesting doctrine. This manuscript is endorsed, “Mr.
Newton, March, 1689.” It begins with three hypotheses (the first
two being the two laws of motion, and the third the parallelogram
of motion), which introduce the proposition of the proportionality
of the areas to the times in motions round an immoveable centre of
attraction.[54] Three lemmas, containing properties of the ellipse,
then prepare the reader for the celebrated proposition, that when a
body moves in an ellipse,[55] the attraction is reciprocally as the
square of the distance of the body from the focus to which it is
attracted. These propositions are demonstrated in a more popular manner
than in the Principia, but there can be no doubt that, even in their
present modified form, they were beyond the capacity of Mr. Locke.

Dr. John Keill was the first person who publicly taught natural
philosophy by experiments. Desaguliers informs us that this author
“laid down very simple propositions, which he proved by experiments,
and from these he deduced others more compound, which he still
confirmed by experiments, till he had instructed his auditors in the
laws of motion, the principles of hydrostatics and optics, and some
of the chief propositions of Sir Isaac Newton concerning light and
colours. He began these courses in Oxford about the year 1704 or 1705,
and in that way introduced the love of the Newtonian philosophy.” When
Dr. Keill left the university, Desaguliers began to teach the Newtonian
philosophy by experiments. He commenced his lectures at Harthall in
Oxford, in 1710, and delivered more than a hundred and twenty courses;
and when he went to settle in London in 1713, he informs us that he
found “the Newtonian philosophy generally received among persons of
all ranks and professions, and even among the ladies by the help of
experiments.” Such were the steps by which the Newtonian philosophy
was established in Great Britain. From the time of the publication
of the Principia, its mathematical doctrines formed a regular part of
academical education; and before twenty years had elapsed, its physical
truths were communicated to the public in popular lectures illustrated
by experiments, and accommodated to the capacities of those who were
not versed in mathematical knowledge. The Cartesian system, though it
may have lingered for a while in the recesses of our universities, was
soon overturned; and long before his death, Newton enjoyed the high
satisfaction of seeing his philosophy triumphant in his native land.




CHAPTER XII.

  _Doctrine of Infinite Quantities—Labours of Pappus—Kepler—Cavaleri—
    Roberval—Fermat—Wallis—Newton discovers the Binomial Theorem—and
    the Doctrine of Fluxions in 1666—His Manuscript Work containing
    this Doctrine communicated to his Friends—His Treatise on Fluxions—
    His Mathematical Tracts—His Universal Arithmetic—His Methodus
    Differentialis—His Geometria Analytica—His Solution of the Problems
    proposed by Bernouilli and Leibnitz—Account of the celebrated
    Dispute respecting the Invention of Fluxions—Commercium Epistolicum—
    Report of the Royal Society—General View of the Controversy._


Previous to the time of Newton, the doctrine of infinite quantities had
been the subject of profound study. The ancients made the first step in
this curious inquiry by a rude though ingenious attempt to determine
the area of curves. The method of exhaustions which was used for this
purpose consisted in finding a given rectilineal area to which the
inscribed and circumscribed polygonal figures continually approached
by increasing the number of their sides. This area was obviously the
area of the curve, and in the case of the parabola it was found by
Archimedes to be two-thirds of the area formed by multiplying the
ordinate by the abscissa. Although the synthetical demonstration of the
results was perfectly conclusive, yet the method itself was limited and
imperfect.

The celebrated Pappus of Alexandria followed Archimedes in the same
inquiries; and in his demonstration of the property of the centre of
gravity of a plane figure, by which we may determine the solid formed
by its revolution, he has shadowed forth the discoveries of later times.

In his curious tract on Stereometry, published in 1615, Kepler made
some advances in the doctrine of infinitesimals. Prompted to the task
by a dispute with the seller of some casks of wine, he studied the
measurement of solids formed by the revolution of a curve round any
line whatever. In solving some of the simplest of these problems, he
conceived a circle to be formed of an infinite number of triangles
having all their vertices in the centre, and their infinitely small
bases in the circumference of the circle, and by thus rendering
familiar the idea of quantities infinitely great and infinitely small,
he gave an impulse to this branch of mathematics. The failure of
Kepler, too, in solving some of the more difficult of the problems
which he himself proposed roused the attention of geometers, and seems
particularly to have attracted the notice of Cavaleri.

This ingenious mathematician was born at Milan in 1598, and was
Professor of Geometry at Bologna. In his method of Indivisibles, which
was published in 1635, he considered a line as composed of an infinite
number of points, a surface of an infinite number of lines, and a solid
of an infinite number of surfaces; and he lays it down as an axiom
that the infinite sums of such lines and surfaces have the same ratio
when compared with the linear or superficial unit, as the surfaces and
solids which are to be determined. As it is not true that an infinite
number of infinitely small points can make a line, or an infinite
number of infinitely small lines a surface, Pascal removed this verbal
difficulty by considering a line as composed of an infinite number of
infinitely short lines, a surface as composed of an infinite number of
infinitely narrow parallelograms, and a solid of an infinite number
of infinitely thin solids. But, independent of this correction, the
conclusions deduced by Cavaleri are rigorously true, and his method of
ascertaining the ratios of areas and solids to one another, and the
theorems which he deduced from it may be considered as forming an era
in mathematics.

By the application of this method, Roberval and Toricelli showed that
the area of the cycloid is three times that of its generating circle,
and the former extended the method of Cavaleri to the case where the
powers of the terms of the arithmetical progression to be summed were
fractional.

In applying the doctrine of infinitely small quantities to determine
the tangents of curves, and the maxima and minima of their ordinates,
both Roberval and Fermat made a near approach to the invention of
fluxions—so near indeed that both Lagrange and Laplace[56] have
pronounced the latter to be the true inventer of the differential
calculus. Roberval supposed the point which describes a curve to be
actuated by two motions, by the composition of which it moves in the
direction of a tangent; and had he possessed the method of fluxions, he
could, in every case, have determined the relative velocities of these
motions, which depend on the nature of the curve, and consequently the
direction of the tangent which he assumed to be in the diagonal of a
parallelogram whose sides had the same ratio as the velocities. But as
he was able to determine these velocities only in the conic sections,
&c. his ingenious method had but few applications.

The labours of Peter Fermat, a counsellor of the parliament of
Toulouse, approached still nearer to the fluxionary calculus. In his
method of determining the maxima and minima of the ordinates of curves,
he substitutes _x_ + _e_ for the independent variable _x_ in the
function which is to become a maximum, and as these two expressions
should be equal when _e_ becomes infinitely small or 0, he frees this
equation from surds and radicals, and after dividing the whole by _e_,
_e_ is made = 0, and the equation for the maximum is thus obtained.
Upon a similar principle he founded his method of drawing tangents to
curves. But though the methods thus used by Fermat are in principle
the same with those which connect the theory of tangents and of maxima
and minima with the analytical method of exhibiting the differential
calculus, yet it is a singular example of national partiality to
consider the inventer of these methods as the inventer of the method of
fluxions.

“One might be led,” says Mr. Herschel, “to suppose by Laplace’s
expression that the calculus of finite differences had then already
assumed a systematic form, and that Fermat had actually observed
the relation between the two calculi, and derived the one from the
other. The latter conclusion would scarcely be less correct than the
former. No method can justly be regarded as bearing any analogy to the
differential calculus which does not lay down a system of rules (no
matter on what considerations founded, by what names called, or by
what extraneous matter enveloped) by means of which the second term of
the development of any function of _x_ + _e_ in powers of _e_, can be
correctly calculated, ‘quæ extendet se,’ to use Newton’s expression,
‘_citra_ ullum molestum calculum in terminis surdis æque ac in integris
procedens.’ It would be strange to suppose Fermat or any other in
possession of such a method before any single surd quantity had ever
been developed in a series. But, in point of fact, his writings present
no trace of the kind; and this, though fatal to his claim, is allowed
by both the geometers cited. Hear Lagrange’s candid avowal. ‘Il fait
disparaitre dans cette equation,’ that of the maximum between _x_
and _e_, ‘les radicaux et les fractions s’il y en à.’ Laplace, too,
declares that ‘il savoit etendre son calcul aux fonctions irrationelles
en se debarrassant des irrationalités par l’elevation des radicaux
aux puissances.’ This is at once giving up the point in question. It
is allowing unequivocally that Fermat in these processes only took a
circuitous route to avoid a difficulty which it is one of the most
express objects of the differential calculus to face and surmount.
The whole claim of the French geometer arises from a confusion (too
often made) of the calculus and its applications, the means and the
end, under the sweeping head of ‘nouveaux calculs’ on the one hand,
and an assertion somewhat too unqualified, advanced in the warmth and
generality of a preface, on the other.”[57]

The discoveries of Fermat were improved and simplified by Hudde,
Huygens, and Barrow; and by the publication of the _Arithmetic of
Infinites_ by Dr. Wallis, Savilian professor of geometry at Oxford,
mathematicians were conducted to the very entrance of a new and
untrodden field of discovery. This distinguished author had effected
the quadrature of all curves whose ordinates can be expressed by any
direct integral powers; and though he had extended his conclusions
to the cases where the ordinates are expressed by the inverse or
fractional powers, yet he failed in its application. Nicolas Mercator
(Kauffman) surmounted the difficulty by which Wallis had been baffled,
by the continued division of the numerator by the denominator to
infinity, and then applying Wallis’s method to the resulting positive
powers. In this way he obtained, in 1667, the first general quadrature
of the hyperbola, and, at the same time, gave the regular development
of a function in series.

In order to obtain the quadrature of the circle, Dr. Wallis considered
that if the equations of the curves of which he had given the
quadrature were arranged in a series, beginning with the most simple,
these areas would form another series. He saw also that the equation of
the circle was intermediate between the first and second terms of the
first series, or between the equation of a straight line and that of a
parabola, and hence he concluded, that by interpolating a term between
the first and second term of the second series, he would obtain the
area of the circle. In pursuing this singularly beautiful thought, Dr.
Wallis did not succeed in obtaining the indefinite quadrature of the
circle, because he did not employ general exponents; but he was led to
express the entire area of the circle by a fraction, the numerator and
denominator of which are each obtained by the continued multiplication
of a certain series of numbers.

Such was the state of this branch of mathematical science, when
Newton, at an early age, directed to it the vigour of his mind. At
the very beginning of his mathematical studies, when the works of
Dr. Wallis fell into his hands, he was led to consider how he could
interpolate the general values of the areas in the second series of
that mathematician. With this view he investigated the arithmetical
law of the coefficients of the series, and obtained a general method
of interpolating, not only the series above referred to, but also
other series. These were the first steps taken by Newton, and, as he
himself informs us, they would have entirely escaped from his memory
if he had not, a few weeks before,[58] found the notes which he made
upon the subject. When he had obtained this method, it occurred to him
that the very same process was applicable to the ordinates, and, by
following out this idea, he discovered the general method of reducing
radical quantities composed of several terms into infinite series, and
was thus led to the discovery of the celebrated _Binomial Theorem_. He
now neglected entirely his methods of interpolation, and employed that
theorem alone as the easiest and most direct method for the quadratures
of curves, and in the solution of many questions which had not even
been attempted by the most skilful mathematicians.

After having applied the Binomial theorem to the rectification of
curves, and to the determination of the surfaces and contents of
solids, and the position of their centres of gravity, he discovered the
general principle of deducing the areas of curves from the ordinate,
by considering the area as a nascent quantity, increasing by continual
fluxion in the proportion of the length of the ordinate, and supposing
the abscissa to increase uniformly in proportion to the time. In
imitation of Cavalerius, he called the momentary increment of a line a
point, though it is not a geometrical point, but an infinitely short
line; and the momentary increment of an area or surface he called a
line, though it is not a geometrical line, but an infinitely narrow
surface. By thus regarding lines as generated by the motion of points,
surfaces by the motions of lines, and solids by the motion of surfaces,
and by considering that the ordinates, abscissæ, &c. of curves thus
formed, vary according to a regular law depending on the equation of
the curve, he deduces from this equation the velocities with which
these quantities are generated; and by the rules of infinite series he
obtains the ultimate value of the quantity required. To the velocities
with which every line or quantity is generated, Newton gave the name
of _Fluxions_, and to the lines or quantities themselves that of
_Fluents_. This method constitutes the doctrine of fluxions which
Newton had invented previous to 1666, when the breaking out of the
plague at Cambridge drove him from that city, and turned his attention
to other subjects.

But though Newton had not communicated this great invention to any
of his friends, he composed his treatise, entitled _Analysis per
equationes numero terminorum infinitas_, in which the principle of
fluxions and its numerous applications are clearly pointed out. In
the month of June, 1669, he communicated this work to Dr. Barrow, who
mentions it in a letter to Mr. Collins, dated the 20th June, 1669, as
the production of a friend of his residing at Cambridge, who possesses
a fine genius for such inquiries. On the 31st July, he transmitted the
work to Collins; and having received his approbation of it, he informs
him that the name of the author of it was Newton, a fellow of his
own college, and a young man who had only two years before taken his
degree of M.A. Collins took a copy of this treatise, and returned the
original to Dr. Barrow; and this copy having been found among Collins’s
papers by his friend Mr. William Jones, and compared with the original
manuscript borrowed from Newton, it was published with the consent of
Newton in 1711, nearly fifty years after it was written.

Though the discoveries contained in this treatise were not at
first given to the world, yet they were made generally known to
mathematicians by the correspondence of Collins, who communicated them
to James Gregory; to MM. Bertet and Vernon in France; to Slusius in
Holland; to Borelli in Italy; and to Strode, Townsend, and Oldenburg,
in letters dated between 1669 and 1672.

Hitherto the method of fluxions was known only to the friends of
Newton and their correspondents; but, in the first edition of the
Principia, which appeared in 1687, he published, for the first time,
the fundamental principle of the fluxionary calculus, in the second
lemma of the second book. No information, however, is here given
respecting the algorithm or notation of the calculus; and it was not
till 1693–5[?] that it was communicated to the mathematical world in
the second volume of Dr. Wallis’s works, which were published in that
year. This information was extracted from two letters of Newton written
in 1692.

About the year 1672, Newton had undertaken to publish an edition of
Kinckhuysen’s Algebra, with notes and additions. He therefore drew up
a treatise, entitled, _A Method of Fluxions_, which he proposed as an
introduction to that work; but the fear of being involved in disputes
about this new discovery, or perhaps the wish to render it more
complete, or to have the sole advantage of employing it in his physical
researches, induced him to abandon this design. At a later period of
his life he again resolved to give it to the world; but it did not
appear till after his death, when it was translated into English, and
published in 1736, with a commentary by Mr. John Colson, Professor of
Mathematics in Cambridge.[59]

To the first edition of Newton’s Optics, which appeared in 1704, there
were added two mathematical treatises, entitled, _Tractatus duo de
speciebus et magnitudine figurarum curvilinearum_, the one bearing the
title of _Tractatus de Quadratura Curvarum_, and the other _Enumeratio
linearum tertii ordinis_. The first contains an explanation of the
doctrine of fluxions, and of its application to the quadrature of
curves; and the second a classification of seventy-two curves of the
third order, with an account of their properties. The reason for
publishing these two tracts in his Optics (in the subsequent editions
of which they are omitted) is thus stated in the advertisement:—“In
a letter written to M. Leibnitz in the year 1679, and published by
Dr. Wallis, I mentioned a method by which I had found some general
theorems about squaring curvilinear figures on comparing them with the
conic sections, or other the simplest figures with which they might be
compared. And some years ago I lent out a manuscript containing such
theorems; and having since met with some things copied out of it, I
have on this occasion made it public, prefixing to it an introduction,
and joining a scholium concerning that method. And I have joined with
it another small tract concerning the curvilineal figures of the second
kind, which was also written many years ago, and made known to some
friends, who have solicited the making it public.”

In the year 1707, Mr. Whiston published the algebraical lectures
which Newton had, during nine years, delivered at Cambridge, under
the title of _Arithmetica Universalis, sive de Compositione et
Resolutione Arithmetica Liber_. We are not accurately informed how
Mr. Whiston obtained possession of this work; but it is stated by one
of the editors of the English edition, that “Mr. Whiston thinking it
a pity that so noble and useful a work should be doomed to a college
confinement, obtained leave to make it public.” It was soon afterward
translated into English by Mr. Ralphson; and a second edition of it,
with improvements by the author, was published at London in 1712,
by Dr. Machin, secretary to the Royal Society. With the view of
stimulating mathematicians to write annotations on this admirable work,
the celebrated S’Gravesande published a tract, entitled, _Specimen
Commentarii in Arithmeticam Universalem_; and Maclaurin’s Algebra seems
to have been drawn up in consequence of this appeal.

Among the mathematical works of Newton we must not omit to enumerate a
small tract entitled, _Methodus Differentialis_, which was published
with his consent in 1711. It consists of six propositions, which
contain a method of drawing a parabolic curve through any given
number of points, and which are useful for constructing tables by the
interpolation of series, and for solving problems depending on the
quadrature of curves.

Another mathematical treatise of Newton’s was published for the
first time in 1779, in Dr. Horsley’s edition of his works.[60] It is
entitled, _Artis Analyticæ Specimina, vel Geometria Analytica_. In
editing this work, which occupies about 130 quarto pages, Dr. Horsley
used three manuscripts, one of which was in the handwriting of the
author; another, written in an unknown hand, was given by Mr. William
Jones to the Honourable Charles Cavendish; and a third, copied from
this by Mr. James Wilson, the editor of Robins’s works, was given to
Dr. Horsley by Mr. John Nourse, bookseller to the king. Dr. Horsley
has divided it into twelve chapters, which treat of infinite series;
of the reduction of affected equations; of the specious resolution
of equations; of the doctrine of fluxions; of maxima and minima;
of drawing tangents to curves; of the radius of curvature; of the
quadrature of curves; of the area of curves which are comparable with
the conic sections; of the construction of mechanical problems, and on
finding the lengths of curves.

In enumerating the mathematical works of our author, we must not
overlook his solutions of the celebrated problems proposed by
Bernouilli and Leibnitz. On the Kalends of January, 1697, John
Bernouilli addressed a letter to the most distinguished mathematicians
in Europe,[61] challenging them to solve the two following problems:

1. To determine the curve line connecting two given points which are
at different distances from the horizon, and not in the same vertical
line, along which a body passing by its own gravity, and beginning
to move at the upper point, shall descend to the lower point in the
shortest time possible.

2. To find a curve line of this property that the two segments of a
right line drawn from a given point through the curve, being raised to
any given power, and taken together, may make every where the same sum.

On the day after he received these problems, Newton addressed to Mr.
Charles Montague, the President of the Royal Society, a solution of
them both. He announced that the curve required in the first problem
must be a cycloid, and he gave a method of determining it. He solved
also the second problem, and he showed that by the same method other
curves might be found which shall cut off three or more segments having
the like properties. Leibnitz, who was struck with the beauty of the
problem, requested Bernouilli, who had allowed six months for its
solution, to extend the period to twelve months. This delay was readily
granted, solutions were obtained from Newton, Leibnitz, and the Marquis
de L’Hopital; and although that of Newton was anonymous, yet Bernouilli
recognised in it his powerful mind, “_tanquam_,” says he, “_ex ungue
leonem_,” as the lion is known by his claw.

The last mathematical effort of our author was made with his usual
success, in solving a problem which Leibnitz proposed in 1716, in a
letter to the Abbé Conti, “for the purpose, as he expressed it, of
feeling the pulse of the English analysts.” The object of this problem
was to determine the curve which should cut at right angles an infinity
of curves of a given nature, but expressible by the same equation.
Newton received this problem about five o’clock in the afternoon, as
he was returning from the Mint; and though the problem was extremely
difficult, and he himself much fatigued with business, yet he finished
the solution of it before he went to bed.

Such is a brief account of the mathematical writings of Sir Isaac
Newton, not one of which were voluntarily communicated to the world by
himself. The publication of his Universal Arithmetic is said to have
been a breach of confidence on the part of Whiston; and, however this
may be, it was an unfinished work, never designed for the public. The
publication of his Quadrature of Curves, and of his Enumeration of
Curve Lines, was rendered necessary, in consequence of plagiarisms from
the manuscripts of them which he had lent to his friends, and the rest
of his analytical writings did not appear till after his death. It is
not easy to penetrate into the motives by which this great man was on
these occasions actuated. If his object was to keep possession of his
discoveries till he had brought them to a higher degree of perfection,
we may approve of the propriety, though we cannot admire the prudence
of such a step. If he wished to retain to himself his own methods, in
order that he alone might have the advantage of them in prosecuting
his physical inquiries, we cannot reconcile so selfish a measure with
that openness and generosity of character which marked the whole of his
life. If he withheld his labours from the world in order to avoid the
disputes and contentions to which they might give rise, he adopted
the very worst method of securing his tranquillity. That this was the
leading motive under which he acted, there is little reason to doubt.
The early delay in the publication of his method of fluxions, after the
breaking out of the plague at Cambridge, was probably owing to his not
having completed the algorithm of that calculus; but no apology can be
made for the imprudence of withholding it any longer from the public.
Had he published this noble discovery even previous to 1673, when his
great rival had not even entered upon those studies which led him to
the same method, he would have secured to himself the undivided honour
of the invention, and Leibnitz could have aspired to no other fame but
that of an improver of the doctrine of fluxions. But he unfortunately
acted otherwise. He announced to his friends that he possessed a method
of great generality and power; he communicated to them a general
account of its principles and applications; and the information which
was thus conveyed directed the attention of mathematicians to subjects
to which they might not have otherwise applied their powers. In this
way the discoveries which he had previously made were made subsequently
by others; and Leibnitz, in place of appearing in the theatre of
science as the disciple and the follower of Newton, stood forth with
all the dignity of a rival; and, by the early publication of his
discoveries had nearly placed himself on the throne which Newton was
destined to ascend.

It would be inconsistent with the popular nature of a work like this,
to enter into a detailed history of the dispute between Newton and
Leibnitz respecting the invention of fluxions. A brief and general
account of it, however, is indispensable.

In the beginning of 1673, Leibnitz came to London in the suite of
the Duke of Hanover, and he became acquainted with the great men who
then adorned the capital of England. Among these was Oldenburg, a
countryman of his own, who was then secretary to the Royal Society.
About the beginning of March, in the same year, Leibnitz went to
Paris, where, with the assistance of Huygens, he devoted himself to
the study of the higher geometry. In the month of July he renewed his
correspondence with Oldenburg, and he communicated to him some of
the discoveries which he had made relative to series, particularly
the series for a circular arc in terms of the tangent. Oldenburg
informed him in return of the discoveries on series which had been
made by Newton and Gregory; and in 1676 Newton communicated to him,
through Oldenburg, a letter of fifteen closely printed quarto pages,
containing many of his analytical discoveries, and stating that he
possessed a general method of drawing tangents, which he thought it
necessary to conceal in two sentences of transposed characters. In this
letter neither the method of fluxions nor any of its principles are
communicated; but the superiority of the method over all others is so
fully described, that Leibnitz could scarcely fail to discover that
Newton possessed that secret of which geometers had so long been in
quest.

Had Leibnitz at the time of receiving this letter been entirely
ignorant of his own differential method, the information thus conveyed
to him by Newton could not fail to stimulate his curiosity, and excite
his mightiest efforts to obtain possession of so great a secret. That
this new method was intimately connected with the subject of series
was clearly indicated by Newton; and as Leibnitz was deeply versed in
this branch of analysis, it is far from improbable that a mind of such
strength and acuteness might attain his object by direct investigation.
That this was the case may be inferred from his letter to Oldenburg (to
be communicated to Newton) of the 21st June, 1677, where he mentions
that he had for some time been in possession of a method of drawing
tangents more general than that of Slusius, namely, by the differences
of ordinates. He then proceeds with the utmost frankness to explain
this method, which was no other than the differential calculus.
He describes the algorithm which he had adopted, the formation of
differential equations, and the application of the calculus to various
geometrical and analytical questions. No answer seems to have been
returned to this letter either by Newton or Oldenburg, and, with the
exception of a short letter from Leibnitz to Oldenburg, dated 12th
July, 1677, no further correspondence seems to have taken place. This,
no doubt, arose from the death of Oldenburg in the month of August,
1677,[62] when the two rival geometers pursued their researches
with all the ardour which the greatness of the subject was so well
calculated to inspire.

In the hands of Leibnitz the differential calculus made rapid progress.
In the _Acta Eruditorum_, which was published at Leipsic in November,
1684, he gave the first account of it, describing its algorithm in the
same manner as he had done in his letter to Oldenburg, and pointing
out its application to the drawing of tangents, and the determination
of maxima and minima. He makes a remote reference to the _similar_
calculus of Newton, but lays no claim to the sole invention of the
differential method. In the same work for June, 1686, he resumes
the subject; and when Newton had not published a single word upon
fluxions, and had not even made known his notation, the differential
calculus was making rapid advances on the Continent, and in the hands
of James and John Bernouilli had proved the means of solving some of
the most important and difficult problems.

The silence of Newton was at last broken, and in the second lemma
of the second book of the Principia, he explained the fundamental
principle of the fluxionary calculus. His explanation, which occupied
only three pages, was terminated with the following scholium:—“In a
correspondence which took place about ten years ago between that very
skilful geometer, G. G. Leibnitz, and myself, I announced to him that
I possessed a method of determining maxima and minima, of drawing
tangents, and of performing similar operations which was equally
applicable to rational and irrational quantities, and concealed the
same in transposed letters involving this sentence, (_data equatione
quotcunque fluentes quantitates involvente, fluxiones invenire et
vice versa_). This illustrious man replied that he also had fallen
on a method of the same kind, and he communicated to me his method
which scarcely differed from mine except in the notation [and in the
idea of the generation of quantities.”][63] This celebrated scholium,
which is so often referred to in the present controversy, has, in
our opinion, been much misapprehended. While M. Biot considers it
as “eternalizing the rights of Leibnitz by recognising them in the
Principia,” Professor Playfair regards it as containing “a highly
favourable opinion on the subject of the discoveries of Leibnitz.”
To us it appears to be nothing more than the simple statement of the
fact, that the method communicated by Leibnitz was nearly the same as
his own; and this much he might have said, whether he believed that
Leibnitz had seen the fluxionary calculus among the papers of Collins,
or was the independent inventor of his own. It is more than probable,
indeed, that when Newton wrote this scholium he regarded Leibnitz as a
second inventor; but when he found that Leibnitz and his friends had
showed a willingness to believe, and had even ventured to throw out the
suspicion, that he himself had borrowed the doctrine of fluxions from
the differential calculus, he seems to have altered the opinion which
he had formed of his rival, and to have been willing in his turn to
retort the charge.

This change of opinion was brought about by a series of circumstances
over which he had no control. M. Nicolas Fatio de Duillier, a Swiss
mathematician, resident in London, communicated to the Royal Society,
in 1699, a paper on the line of quickest descent, which contains
the following observations:—“Compelled by the evidence of facts, I
hold Newton to have been the first inventor of this calculus, and
the earliest by several years; and whether Leibnitz, the _second
inventor_, has borrowed any thing from the other, I would prefer to my
own judgment that of those who have seen the letters and other copies
of the same manuscripts of Newton.” This imprudent remark, which by
no means amounts to a charge of plagiarism, for Leibnitz is actually
designated the _second inventor_, may be considered as showing that
the English mathematicians had been cherishing suspicions unfavourable
to Leibnitz, and there can be no doubt that a feeling had long
prevailed that this mathematician either had, or might have seen, among
the papers of Collins, the “_Analysis per Equationes, &c._,” which
contained the principles of the fluxionary method. Leibnitz replied
to the remark of Duillier with much good feeling. He appealed to the
facts as exhibited in his correspondence with Oldenburg; he referred to
Newton’s scholium as a testimony in his favour; and, without disputing
or acknowledging the priority of Newton’s claim, he asserted his own
right to the invention of the differential calculus. Fatio transmitted
a reply to the Leipsic Acts; but the editor refused to insert it. The
dispute, therefore, terminated, and the feelings of the contending
parties continued for some time in a state of repose, though ready to
break out on the slightest provocation.

When Newton’s Optics appeared in 1704, accompanied by his Treatise on
the Quadrature of Curves, and his enumeration of lines of the third
order, the editor of the Leipsic Acts (whom Newton supposed to be
Leibnitz himself) took occasion to review the first of these tracts.
After giving an imperfect analysis of its contents, he compared the
method of fluxions with the differential calculus, and, in a sentence
of some ambiguity, he states that Newton employed fluxions in place
of the differences of Leibnitz, and made use of them in his Principia
in the same manner as Honoratus Fabri, in his Synopsis of Geometry,
had substituted progressive motion in place of the indivisibles of
Cavaleri.[64] As Fabri, therefore, was not the inventor of the method
which is here referred to, but borrowed it from Cavaleri, and only
changed the mode of its expression, there can be no doubt that the
artful insinuation contained in the above passage was intended to
convey the impression that Newton had _stolen_ his method of fluxions
from Leibnitz. The indirect character of this attack, in place
of mitigating its severity, renders it doubly odious; and we are
persuaded that no candid reader can peruse the passage without a strong
conviction that it justifies, in the fullest manner, the indignant
feelings which it excited among the English philosophers. If Leibnitz
was the author of the review, or if he was in any way a party to it, he
merited the full measure of rebuke which was dealt out to him by the
friends of Newton, and deserved those severe reprisals which doubtless
imbittered the rest of his days. He who dared to accuse a man like
Newton, or indeed any man holding a fair character in society, with
the odious crime of plagiarism, placed himself without the pale of
the ordinary courtesies of life, and deserved to have the same charge
thrown back upon himself. The man who conceives his fellow to be
capable of such intellectual felony, avows the possibility of himself
committing it, and almost substantiates the weakest evidence of the
worst accusers.

Dr. Keill, as the representative of Newton’s friends, could not brook
this base attack upon his countryman. In a letter printed in the
Philosophical Transactions for 1708, he maintained that Newton was
“beyond all doubt” the first inventor of fluxions. He referred for
a direct proof of this to his letters published by Wallis; and he
asserted “that the same calculus was afterward published by Leibnitz,
the name and the mode of notation being changed.” If the reader is
disposed to consider this passage as retorting the charge of plagiarism
upon Leibnitz, he will readily admit that the mode of its expression
is neither so coarse nor so insidious as that which is used by the
writer in the Leipsic Acts. In a letter to Hans Sloane, dated March,
1711, Leibnitz complained to the Royal Society of the treatment he had
received. He expressed his conviction that Keill had erred more from
rashness of judgment than from any improper motive, and that he did not
regard the accusation as a calumny; and he requested that the society
would oblige Mr. Keill to disown publicly the injurious sense which
his words might bear. When this letter was read to the society, Keill
justified himself to Sir Isaac Newton and the other members by showing
them the obnoxious review of the Quadrature of Curves in the Leipsic
Acts. They all agreed in attaching the same injurious meaning to the
passage which we formerly quoted, and authorized Keill to explain and
defend his statement. He accordingly addressed a letter to Sir Hans
Sloane, which was read at the society on the 24th May, 1711, and a copy
of which was ordered to be sent to Leibnitz. In this letter, which is
one of considerable length, he declares that he never meant to state
that Leibnitz knew either the name of Newton’s method or the form of
notation, and that the real meaning of the passage was, “that Newton
was the first inventor of fluxions or of the differential calculus,
and that he had given, in two letters to Oldenburg, and which he had
transmitted to Leibnitz, indications of it sufficiently intelligible to
an acute mind, from which Leibnitz derived, or at least might derive,
the principles of his calculus.”

The charge of plagiarism which Leibnitz thought was implied in the
former letter of his antagonist is here greatly modified, if not
altogether denied. Keill expresses only an _opinion_ that the letter
_seen_ by Leibnitz contained intelligible indications of the fluxionary
calculus. Even if this opinion were correct, it is no proof that
Leibnitz either saw these indications or availed himself of them, or if
he did perceive them, it might have been in consequence of his having
previously been in possession of the differential calculus, or having
enjoyed some distant view of it. Leibnitz should, therefore, have
allowed the dispute to terminate here; for no ingenuity on his part,
and no additional facts, could affect an opinion which any other person
as well as Keill was entitled to maintain.

Leibnitz, however, took a different view of the subject, and wrote a
letter to Sir Hans Sloane, dated December 19, 1711, which excited new
feelings, and involved him in new embarrassments. Insensible to the
mitigation which had been kindly impressed upon the supposed charge
against his honour, he alleges that Keill had attacked his candour and
sincerity more openly than before;—that he acted without any authority
from Sir Isaac Newton, who was the party interested;—and that it was
in vain to justify his proceedings by referring to the provocation
in the Leipsic Acts, because in that journal _no injustice had been
done to any party, but every one had received what was his due_. He
branded Keill with the odious appellation of an upstart, and one little
acquainted with the circumstances of the case;[65] he called upon
the society to silence his vain and unjust clamours,[66] which, he
believed, were disapproved by Newton himself, who was well acquainted
with the facts, and who, he was persuaded, would willingly give his
opinion on the matter.

This unfortunate letter was doubtless the cause of all the rancour and
controversy which so speedily followed, and it placed his antagonist
in a new and a more favourable position. It may be correct, though
few will admit it, that Keill’s second letter was more injurious than
the first; but it was not true that Keill acted without the authority
of Newton, because Keill’s letter was approved of and transmitted by
the Royal Society, of which Newton was the president, and therefore
became the act of that body. The obnoxious part, however, of Leibnitz’s
letter consisted in his appropriating to himself the opinions of the
reviewer in the Leipsic Acts, by declaring that, in a review which
charged Newton with plagiarism, every person had got what was his due.
The whole character of the controversy was now changed: Leibnitz places
himself in the position of the party who had first disturbed the
tranquillity of science by maligning its most distinguished ornament;
and the Royal Society was imperiously called upon to throw all the
light they could upon a transaction which had exposed their venerable
president to so false a charge. The society, too, had become a party to
the question, by their approbation and transmission of Keill’s second
letter, and were on that account alone bound to vindicate the step
which they had taken.

When the letter of Leibnitz, therefore, was read, Keill appealed to the
registers of the society for the proofs of what he had advanced; Sir
Isaac also expressed his displeasure at the obnoxious passage in the
Leipsic Review, and at the defence of it by Leibnitz, and he left it to
the society to act as they thought proper. A committee was therefore
appointed on the 11th March, consisting of Dr. Arbuthnot, Mr. Hill,
Dr. Halley, Mr. Jones, Mr. Machin, and Mr. Burnet, who were instructed
to examine the ancient registers of the society, to inquire into the
dispute, and to produce such documents as they should find, together
with their own opinions on the subject. On the 24th April the committee
produced the following report:—

“We have consulted the letters and letter-books in the custody of the
Royal Society, and those found among the papers of Mr. John Collins,
dated between the years 1669 and 1677, inclusive; and showed them to
such as knew and avouched the hands of Mr. Barrow, Mr. Collins, Mr.
Oldenburg, and Mr. Leibnitz; and compared those of Mr. Gregory with
one another, and with copies of some of them taken in the hand of
Mr. Collins; and have extracted from them what relates to the matter
referred to us; all which extracts herewith delivered to you we believe
to be genuine and authentic. And by these letters and papers we find,—

“I. Mr. Leibnitz was in London in the beginning of the year 1673;
and went thence, in or about March, to Paris, where he kept a
correspondence with Mr. Collins by means of Mr. Oldenburg, till
about September, 1676, and then returned by London and Amsterdam to
Hanover: and that Mr. Collins was very free in communicating to able
mathematicians what he had received from Mr. Newton and Mr. Gregory.

“II. That when Mr. Leibnitz was the first time in London, he contended
for the invention of another differential method properly so called;
and, notwithstanding that he was shown by Dr. Pell that it was Newton’s
method, persisted in maintaining it to be his own invention, by reason
that he had found it by himself without knowing what Newton had done
before, and had much improved it. And we find no mention of his having
any other differential method than Newton’s before his letter of the
21st of June, 1677, which was a year after a copy of Mr. Newton’s
letter of the 10th of December, 1672, had been sent to Paris to be
communicated to him; and above four years after, Mr. Collins began
to communicate that letter to his correspondent; in which letter the
method of fluxions was sufficiently described to any intelligent person.

“III. That by Mr. Newton’s letter of the 13th of June, 1676, it appears
that he had the method of fluxions above five years before the writing
of that letter. And by his Analysis per Æquationes numero Terminorum
Infinitas, communicated by Dr. Barrow to Mr. Collins in July, 1669, we
find that he had invented the method before that time.

“IV. That the differential method is one and the same with the method
of fluxions, excepting the name and mode of notation; Mr. Leibnitz
calling those quantities differences which Mr. Newton calls moments or
fluxions; and marking them with the letter _d_—a mark not used by Mr.
Newton.

“And therefore we take the proper question to be not who invented this
or that method, but who was the first inventor of the method. And we
believe that those who have reputed Mr. Leibnitz the first inventor
knew little or nothing of his correspondence with Mr. Collins and Mr.
Oldenburg long before, nor of Mr. Newton’s having that method above
fifteen years before Mr. Leibnitz began to publish it in the Acta
Eruditorum of Leipsic.

“For which reason we reckon Mr. Newton the first inventor; and are
of opinion that Mr. Keill, in asserting the same, has been no ways
injurious to Mr. Leibnitz. And we submit to the judgment of the society
whether the extract and papers now presented to you, together with what
is extant to the same purpose in Dr. Wallis’s third volume, may not
deserve to be made public.”

This report being read, the society unanimously ordered the collection
of letters and manuscripts to be printed, and appointed Dr. Halley,
Mr. Jones, and Mr. Machin to superintend the press. Complete copies of
it, under the title of _Commercium Epistolicum D. Johannis Collins et
aliorum de analysi promota_, were laid before the society on the 8th
January, 1713, and Sir Isaac Newton, as president, ordered a copy to be
delivered to each person of the committee appointed for that purpose,
to examine it before its publication.

Leibnitz received information of the appearance of the Commercium
Epistolicum when he was at Vienna; and “being satisfied,” as he
expresses it, “that it must contain _malicious falsehoods_, I did not
think proper to send for it by post, but wrote to M. Bernouilli to give
me his sentiments. M. Bernouilli wrote me a letter dated at Basle,
June 7th, 1713, in which he said _that it appeared probable that Sir
Isaac Newton had formed his calculus after having seen mine_.”[67] This
letter was published by a friend of Leibnitz, with reflections, in a
loose sheet entitled _Charta Volans_, and dated July 29, 1713. It was
widely circulated without either the name of the author, printer, or
place of publication, and was communicated to the _Journal Literaire_
by another friend of Leibnitz, who added remarks of his own, and
stated, that when Newton published the Principia in 1687, _he did not
understand the true differential method; and that he took his fluxions
from Leibnitz_.

In this state of the controversy, Mr. Chamberlayne conceived the design
of reconciling the two distinguished philosophers; and in a letter
dated April 28, 1714,[68] he addressed himself to Leibnitz, who was
still at Vienna. In replying to this letter, Leibnitz declared that he
had given no occasion for the dispute; “that Newton procured a book to
be published, which was written purposely to discredit him, and sent
it to Germany, &c. as in the name of the society;” and he stated _that
there was room to doubt whether Newton knew his invention before he
had it of him_. Mr. Chamberlayne communicated this letter to Sir Isaac
Newton, who replied that Leibnitz had attacked his reputation in 1705,
by intimating that he had borrowed from him the method of fluxions;
that if Mr. C. could point out to him any thing in which he had injured
Mr. Leibnitz, he would give him satisfaction; that he would not retract
things which he knew to be true; and that he believed that the Royal
Society had done no injustice by the publication of the Commercium
Epistolicum.

The Royal Society, having learned that Leibnitz complained of their
having condemned him unheard, inserted a declaration in their journals
on the 20th May, 1714, that they did not pretend that the report
of their committee should pass for a decision of the society. Mr.
Chamberlayne sent a copy of this to Leibnitz, along with Sir Isaac’s
letter, and Dr. Keill’s answer to the papers inserted in the Journal
Literaire. After perusing these documents, M. Leibnitz replied, “that
Sir Isaac’s letter was written with very little civility; that he was
not in a humour to put himself in a passion against such people; that
there were other letters among those of Oldenburg and Collins which
should have been published; and that on his return to Hanover, he would
be able to publish a Commercium Epistolicum which would be of service
to the history of learning.” When this letter was read to the Royal
Society, Sir Isaac remarked, that the last part of it injuriously
accused the society of having made a partial selection of papers for
the Commercium Epistolicum; that he did not interfere in any way in
the publication of that work, and had even withheld from the committee
two letters, one from Leibnitz in 1693, and another from Wallis in
1695, which were highly favourable to his cause. He stated that he
did not think it right for M. Leibnitz himself, but that, if he had
letters to produce in his favour, that they might be published in the
Philosophical Transactions, or in Germany.

About this time the Abbé Conti, a noble Venetian, came to England. He
was a correspondent of Leibnitz, and in a letter which he had received
soon after his arrival,[69] he enters upon his dispute with Newton.
He charges the English “with wishing to pass for almost the only
inventors.” He declares “that Bernouilli had judged rightly in saying
that Newton did not possess before him the infinitesimal characteristic
and algorithm.” He remarks that Newton preceded him only in series; and
he confesses that during his second visit to England, “Collins showed
him part of his correspondence,” or, as he afterward expresses it, he
saw “some of the letters of Newton at Mr. Collins’s.” He then attacks
Sir Isaac’s philosophy, particularly his opinions about gravity and
vacuum, the intervention of God for the preservation of his creatures;
and he accuses him of reviving the occult qualities of the schools. But
the most remarkable passage in this letter is the following: “I am a
great friend of experimental philosophy, but Newton deviates much from
it _when he pretends that all matter is heavy_, or that each particle
of matter attracts every other particle.”

The above letter to the Abbé Conti was generally shown in London,
and came to be much talked of at court, in consequence of Leibnitz
having been privy counsellor to the Elector of Hanover when that
prince ascended the throne of England. Many persons of distinction,
and particularly the Abbé Conti, urged Newton to reply to Leibnitz’s
letter, but he resisted all their solicitations. One day, however, King
George I. inquired when Sir Isaac Newton’s answer to Leibnitz would
appear; and when Sir Isaac heard this, he addressed a long reply to the
Abbé Conti, dated February 26th, O. S. 1715–16. This letter, written
with dignified severity, is a triumphant refutation of the allegations
of his adversary; and the following passage deserves to be quoted, as
connected with that branch of the dispute which relates to Leibnitz’s
having seen part of Newton’s letters to Mr. Collins. “He complains of
the committee of the Royal Society, as if they had acted partially in
omitting what made against me; but he fails in proving the accusation.
For he instances in a paragraph concerning my ignorance, pretending
that they omitted it, and yet you will find it in the Commercium
Epistolicum, p. 547, lines 2, 3, and I am not ashamed of it. He saith
that he saw this paragraph in the hands of Mr. Collins when he was in
London the second time, that is in October, 1676. It is in my letter
of the 24th of October, 1676, and therefore he then saw that letter.
And in that and some other letters writ before that time, I described
my method of fluxions; and in the same letter I described also two
general methods of series, one of which is now claimed from me by Mr.
Leibnitz.” The letter concludes with the following paragraph: “But as
he has lately attacked me with an accusation which amounts to plagiary;
if he goes on to accuse me, it lies upon him by the laws of all
nations to prove his accusations, on pain of being accounted guilty of
calumny. He hath hitherto written letters to his correspondents full of
affirmations, complaints, and reflections, without proving any thing.
But he is the aggressor, and it lies upon him to prove the charge.”

In transmitting this letter to Leibnitz, the Abbé Conti informed him
that he himself had read with great attention, and without the least
prejudice, the Commercium Epistolicum, and the little piece[70] that
contains the extract; that he had also seen at the Royal Society the
original papers of the Commercium Epistolicum, and some other original
pieces relating to it. “From all this,” says he, “I infer, that, if
all the digressions are cut off, the only point is, whether Sir Isaac
Newton had the method of fluxions or infinitesimals before you, or
whether you had it before him. You published it first, it is true, but
you have owned also that Sir Isaac Newton had given many hints of it in
his letters to Mr. Oldenburg and others. This is proved very largely in
the Commercium, and in the extract of it. What answer do you give? This
is still wanting to the public, in order to form an exact judgment of
the affair.” The Abbé adds, that Mr. Leibnitz’s own friends waited for
his answer with great impatience, and that they thought he could not
dispense with answering, if not Dr. Keill, at least Sir Isaac Newton
himself, who had given him a defiance in express terms.

Leibnitz was not long in complying with this request. He addressed a
letter to the Abbé Conti, dated April 9th, 1716, but he sent it through
M. Ramond at Paris, to communicate it to others. When it was received
by the Abbé Conti, Newton wrote observations upon it, which were
communicated only to some of his friends, and which, while they placed
his defence on the most impregnable basis, at the same time threw much
light on the early history of his mathematical discoveries.

The death of Leibnitz on the 14th November, 1716, put an end to
this controversy, and Newton some time afterward published the
correspondence with the Abbé Conti, which had hitherto been only
privately circulated among the friends of the disputants.[71]

In 1722, a new edition of the Commercium Epistolicum was published,
and there was prefixed to it a general review of its contents, which
has been falsely ascribed to Newton.[72] When the third edition of
the Principia was published in 1725, the celebrated scholium which we
have already quoted, and in which Leibnitz’s differential calculus was
mentioned, was struck out either by Newton or by the editor. This step
was perhaps rash and ill-advised; but as the scholium had been adduced
by Leibnitz and others as a proof that Newton acknowledged him to be
an independent inventor of the calculus,—an interpretation which it
does not bear, and which Newton expressly states he never intended it
to bear,—he was justified in withdrawing a passage which had been so
erroneously interpreted, and so greatly misapplied.

In viewing this controversy, at the distance of more than a century,
when the passions of the individual combatants have been allayed,
and national jealousies extinguished, it is not difficult to form a
correct estimate of the conduct and claims of the two rival analysts.
By the unanimous verdict of all nations, it has been decided that
Newton invented fluxions at least ten years before Leibnitz. Some of
the letters of Newton which bore reference to this great discovery
were perused by the German mathematician; but there is no evidence
whatever that he borrowed his differential calculus from these letters.
Newton was therefore the _first_ inventor, and Leibnitz the _second_.
It was impossible that the former could have been a plagiarist; but it
was possible for the latter. Had the letters of Newton contained even
stronger indications than they do of the new calculus, no evidence
short of proof could have justified any allegation against Leibnitz’s
honour. The talents which he displayed in the improvement of the
calculus showed that he was capable of inventing it; and his character
stood sufficiently high to repel every suspicion of his integrity. But
if it would have been criminal to charge Leibnitz with plagiarism, what
must we think of those who dared to accuse Newton of borrowing his
fluxions from Leibnitz? This odious accusation was made by Leibnitz
himself, and by Bernouilli; and we have seen that the former repeated
it again and again, as if his own good name rested on the destruction
of that of his rival. It was this charge against Newton that gave
rise to the attack of Keill, and the publication of the Commercium
Epistolicum; and, notwithstanding this high provocation, the committee
of the Royal Society contented themselves with asserting Newton’s
priority, without retorting the charge of plagiarism upon his rival.

Although an attempt has been recently made to place the conduct of
Leibnitz on the same level with that of Newton, yet the circumstances
of the case will by no means justify such a comparison. The conduct
of Newton was at all times dignified and just. He knew his rights,
and he boldly claimed them. Conscious of his integrity, he spurned
with indignation the charge of plagiarism with which an ungenerous
rival had so insidiously loaded him; and if there was one step in his
frank and unhesitating procedure which posterity can blame it is his
omission, in the third edition of the Principia, of the references
to the differential calculus of Leibnitz. This omission, however,
was perfectly just. The scholium which he had left out was a mere
historical statement of the fact, that the German mathematician had
sent him a method which was the same as his own; and when he found
that this simple assertion had been held by Leibnitz and others as a
recognition of his independent claim to the invention, he was bound
either to omit it altogether, or to enter into explanations which might
have involved him in a new controversy.

The conduct of Leibnitz was not marked with the same noble lineaments.
That he was the aggressor is universally allowed. That he first dared
to breathe the charge of plagiarism against Newton, and that he often
referred to it, has been sufficiently apparent; and when arguments
failed him he had recourse to threats—declaring that he would publish
another Commercium Epistolicum, though he had no appropriate letters
to produce. All this is now matter of history; and we may find some
apology for it in his excited feelings, and in the insinuations which
were occasionally thrown out against the originality of his discovery;
but for other parts of his conduct we seek in vain for an excuse.
When he assailed the philosophy of Newton in his letters to the Abbé
Conti, he exhibited perhaps only the petty feelings of a rival; but
when he dared to calumniate that great man in his correspondence with
the Princess of Wales, by whom he was respected and beloved; when he
ventured to represent the Newtonian philosophy as physically false,
and as dangerous to religion; and when he founded these accusations on
passages in the Principia and the Optics glowing with all the fervour
of genuine piety, he cast a blot upon his name, which all his talents
as a philosopher, and all his virtues as a man, will never be able to
efface.




CHAPTER XIII.

  _James II. attacks the Privileges of the University of Cambridge—
    Newton chosen one of the Delegates to resist this Encroachment—He
    is elected a Member of the Convention Parliament—Burning of his
    Manuscripts—His supposed Derangement of Mind—View taken of this by
    foreign Philosophers—His Correspondence with Mr. Pepys and Mr. Locke
    at the time of his Illness—Mr. Millington’s Letter to Mr. Pepys on
    the subject of Newton’s Illness—Refutation of the Statement that he
    laboured under Mental Derangement._


From the year 1669, when Newton was installed in the Lucasian chair,
till 1695, when he ceased to reside in Cambridge, he seems to have been
seldom absent from his college more than three or four weeks in the
year. In 1675, he received a dispensation from Charles II. to continue
in his fellowship of Trinity College without taking orders, and we have
already seen in the preceding chapter how his time was occupied till
the publication of the Principia in 1687.

An event now occurred which drew Newton from the seclusion of his
studies, and placed him upon the theatre of public life. Desirous of
re-establishing the Catholic faith in its former supremacy, King James
II. had begun to assail the rights and privileges of his Protestant
subjects. Among other illegal acts, he sent his letter of mandamus
to the University of Cambridge to order Father Francis, an ignorant
monk of the Benedictine order, to be received as master of arts, and
to enjoy all the privileges of this degree, without taking the oaths
of allegiance and supremacy. The university speedily perceived the
consequences which might arise from such a measure. Independent of
the infringement of their rights which such an order involved, it was
obvious that the highest interests of the university were endangered,
and that Roman Catholics might soon become a majority in the
convocation. They therefore unanimously refused to listen to the royal
order, and they did this with a firmness of purpose which irritated
the despotic court. The king reiterated his commands, and accompanied
them with the severest threatenings in case of disobedience. The
Catholics were not idle in supporting the views of the sovereign. The
honorary degree of M.A. which conveys no civil rights to its possessor,
having been formerly given to the secretary of the ambassador from
Morocco, it was triumphantly urged that the University of Cambridge
had a greater regard for a Mahometan than for a Roman Catholic, and
was more obsequious to the ambassador from Morocco than to their own
lawful sovereign. Though this reasoning might impose upon the ignorant,
it produced little effect upon the members of the university. A few
weak-minded individuals, however, were disposed to yield a reluctant
consent to the royal wishes. They proposed to confer the degree,
and at the same time to resolve that it should not in future be
regarded as a precedent. To this it was replied, that the very act of
submission in one case would be a stronger argument for continuing the
practice than any such resolution would be against its repetition. The
university accordingly remained firm in their original decision. The
vice-chancellor was summoned before the ecclesiastical commission to
answer for this act of contempt. Newton was among the number of those
who resisted the wishes of the court, and he was consequently chosen
one of the nine delegates who were appointed to defend the independence
of the university. These delegates appeared before the High Court. They
maintained that not a single precedent could be found to justify so
extraordinary a measure; and they showed that Charles II. had, under
similar circumstances, been pleased to withdraw his mandamus. This
representation had its full weight, and the king was induced to abandon
his design.[73]

The part which Newton had taken in this affair, and the high character
which he now held in the scientific world, induced his friends to
propose him as member of parliament for the university. He was
accordingly elected in 1688, though by a very narrow majority,[74] and
he sat in the Convention Parliament till its dissolution. In the year
1688 and 1689, Newton was absent from Cambridge during the greater part
of the year, owing, we presume, to his attendance in parliament; but
it appears from the books of the University that from 1690 to 1695 he
was seldom absent, and must therefore have renounced his parliamentary
duties.

During his stay in London he had no doubt experienced the
unsuitableness of his income to the new circumstances in which he was
placed, and it is probable that this was the cause of the limitation of
his residence to Cambridge. His income was certainly very confined, and
but little suited to the generosity of his disposition. Demands were
doubtless made upon it by some of his less wealthy relatives; and there
is reason to think that he himself, as well as his influential friends,
had been looking forward to some act of liberality on the part of the
government.

An event however occurred which will ever form an epoch in his history;
and it is a singular circumstance, that this incident has been for more
than a century unknown to his own countrymen, and has been accidentally
brought to light by the examination of the manuscripts of Huygens. This
event has been magnified into a temporary aberration of mind, which is
said to have arisen from a cause scarcely adequate to its production.

While he was attending divine service in a winter morning, he had left
in his study a favourite little dog called Diamond. Upon returning from
chapel he found that it had overturned a lighted taper on his desk,
which set fire to several papers on which he had recorded the results
of some optical experiments. These papers are said to have contained
the labours of many years, and it has been stated that when Mr. Newton
perceived the magnitude of his loss, he exclaimed, “Oh, Diamond,
Diamond, little do you know the mischief you have done me!” It is a
curious circumstance that Newton never refers to the experiments which
he is said to have lost on this occasion, and his nephew, Mr. Conduit,
makes no allusion to the event itself. The distress, however which it
occasioned is said to have been so deep as to affect even the powers of
his understanding.

This extraordinary effect was first communicated to the world in the
Life of Newton by M. Biot, who received the following account of it
from the celebrated M. Van Swinden.

“There is among the manuscripts of the celebrated Huygens a small
journal in folio, in which he used to note down different occurrences.
It is side ζ, No. 8, p. 112, in the catalogue of the library of
Leyden. The following extract is written by Huygens himself, with
whose handwriting I am well acquainted, having had occasion to peruse
several of his manuscripts and autograph letters. ‘_On the 29th May,
1694, M. Colin,[75] a Scotsman, informed me that eighteen months ago
the illustrious geometer, Isaac Newton, had become insane, either in
consequence of his too intense application to his studies, or from
excessive grief at having lost, by fire, his chymical laboratory and
several manuscripts. When he came to the Archbishop of Cambridge, he
made some observations which indicated an alienation of mind. He was
immediately taken care of by his friends, who confined him to his house
and applied remedies, by means of which he had now so far recovered his
health that he began to understand the Principia._’” Huygens mentioned
this circumstance to Leibnitz, in a letter dated 8th June, 1694, to
which Leibnitz replies in a letter dated the 23d, “I am very glad that
I received information of the cure of Mr. Newton, at the same time
that I first heard of his illness, which doubtless must have been
very alarming. ‘It is to men like you and him, sir, that I wish a long
life.’”

The first publication of the preceding statement produced a strong
sensation among the friends and admirers of Newton. They could not
easily believe in the prostration of that intellectual strength which
had unbarred the strongholds of the universe. The unbroken equanimity
of Newton’s mind, the purity of his moral character, his temperate and
abstemious life, his ardent and unaffected piety, and the weakness of
his imaginative powers, all indicated a mind which was not likely to
be overset by any affliction to which it could be exposed. The loss of
a few experimental records could never have disturbed the equilibrium
of a mind like his. If they were the records of discoveries, the
discoveries themselves indestructible would have been afterward given
to the world. If they were merely the details of experimental results,
a little time could have easily reproduced them. Had these records
contained the first fruits of early genius—of obscure talent, on which
fame had not yet shed its rays, we might have supposed that the first
blight of such early ambition would have unsettled the stability of
an untried mind. But Newton was satiated with fame. His mightiest
discoveries were completed and diffused over all Europe, and he must
have felt himself placed on the loftiest pinnacle of earthly ambition.
The incredulity which such views could not fail to encourage was
increased by the novelty of the information. No English biographer
had ever alluded to such an event. History and tradition were equally
silent, and it was not easy to believe that the Lucasian Professor of
Mathematics at Cambridge, a member of the English parliament, and the
first philosopher in Europe could have lost his reason without the
dreadful fact being known to his own countrymen.

But if the friends of Newton were surprised by the nature of the
intelligence, they were distressed at the view which was taken of it
by foreign philosophers. While one maintained that the intellectual
exertions of Newton had terminated with the publication of the
Principia, and that the derangement of his mind was the cause of his
abandoning the sciences, others indirectly questioned the sincerity of
his religious views, and ascribed to the aberration of his mind those
theological pursuits which gilded his declining age. “But the fact,”
says M. Biot, “of the derangement of his intellect, whatever may have
been the cause of it, will explain why, after the publication of the
Principia in 1687, Newton, though only forty-five years old, never
more published a new work on any branch of science, but contented
himself with giving to the world those which he had composed long
before that epoch, confining himself to the completion of those
parts which might require development. We may also remark, that even
these developments appear always to be derived from experiments and
observations formerly made, such as the additions to the second edition
of the Principia, published in 1713, the experiments on thick plates,
those on diffraction, and the chymical queries placed at the end of the
Optics in 1704; for in giving an account of these experiments Newton
distinctly says that they were taken from ancient manuscripts which he
had formerly composed; and he adds, that though he felt the necessity
of extending them, or rendering them more perfect, he was not able to
resolve to do this, these matters being no longer in his way. Thus
it appears that though he had recovered his health sufficiently to
understand all his researches, and even in some cases to make additions
to them, and useful alterations, as appears from the second edition
of the Principia, for which he kept up a very active mathematical
correspondence with Mr. Cotes, yet he did not wish to undertake new
labours in those departments of science where he had done so much,
and where he so distinctly saw what remained to be done.” Under the
influence of the same opinion, M. Biot finds “it extremely probable
that his dissertation on the scale of heat was written before the fire
in his laboratory;” he describes Newton’s conduct about the longitude
bill as “almost puerile on so solemn an occasion, and one which might
lead to the strangest conclusions, particularly if we refer it to the
fatal accident which Newton had suffered in 1695.”

The celebrated Marquis de la Place viewed the illness of Newton in
a light still more painful to his friends. He maintained that he
never recovered the vigour of his intellect, and he was persuaded
that Newton’s theological inquiries did not commence till after that
afflicting epoch of his life. He even commissioned Professor Gautier of
Geneva to make inquiries on this subject during his visit to England,
as if it concerned the interests of truth and justice to show that
Newton became a Christian and a theological writer only after the decay
of his strength and the eclipse of his reason.

Such having been the consequences of the disclosure of Newton’s illness
by the manuscript of Huygens, I felt it to be a sacred duty to the
memory of that great man, to the feelings of his countrymen, and to
the interests of Christianity itself, to inquire into the nature
and history of that indisposition which seems to have been so much
misrepresented and misapplied. From the ignorance of so extraordinary
an event which has prevailed for such a long period in England, it
might have been urged with some plausibility that Huygens had mistaken
the real import of the information that was conveyed to him; or that
the Scotchman from whom he received it had propagated an idle and a
groundless rumour. But we are, fortunately, not confined to this very
reasonable mode of defence. There exists at Cambridge a manuscript
journal written by Mr. Abraham de la Pryme, who was a student in the
university while Newton was a fellow of Trinity. This manuscript is
entitled “_Ephemeris Vitæ_, or Diary of my own Life, containing an
account likewise of the most observable and remarkable things that I
have taken notice of from my youth up hitherto.” Mr. de la Pryme was
born in 1671, and begins the diary in 1685. This manuscript is in the
possession of his collateral descendant, George Pryme, Esq., Professor
of Political Economy at Cambridge, to whom I have been indebted for the
following extract.

“_1692, February 3d._—What I heard to-day I must relate. There is one
Mr. Newton (whom I have very oft seen), Fellow of Trinity College,
that is mighty famous for his learning, being a most excellent
mathematician, philosopher, divine, &c. He has been Fellow of the
Royal Society these many years; and among other very learned books
and tracts, he’s written one upon the mathematical principles of
philosophy, which has got him a mighty name, he having received,
especially from Scotland, abundance of congratulatory letters for
the same; but of all the books that he ever wrote, there was one of
colours and light, established upon thousands of experiments which he
had been twenty years of making, and which had cost him many hundred
of pounds. This book, which he valued so much, and which was so much
talked of, had the ill luck to perish and be utterly lost just when the
learned author was almost at putting a conclusion at the same, after
this manner: In a winter’s morning, leaving it among his other papers
on his study table while he went to chapel, the candle, which he had
unfortunately left burning there too, catched hold by some means of
other papers, and they fired the aforesaid book, and utterly consumed
it and several other valuable writings; and, which is most wonderful,
did no further mischief. But when Mr. Newton came from chapel, and had
seen what was done, every one thought he would have run mad, he was
so troubled thereat that he was not himself for a month after. A long
account of this his system of light and colours you may find in the
Transactions of the Royal Society, which he had sent up to them long
before this sad mischance happened unto him.”

From this extract we are enabled to fix the approximate date of the
accident by which Newton lost his papers. It must have been previous to
the 3d January, 1692, a month before the date of the extract; but if we
fix it by the dates in Huygens’s manuscript, we should place it about
the 29th November, 1692, eighteen months previous to the conversation
between Collins and Huygens. The manner in which Mr. Pryme refers to
Newton’s state of mind is that which is used every day when we speak
of the loss of tranquillity which arises from the ordinary afflictions
of life; and the meaning of the passage amounts to nothing more than
that Newton was very much troubled by the destruction of his papers,
and did not recover his serenity, and return to his usual occupations,
for a month. The very phrase that “every person thought he would have
run mad” is in itself a proof that no such effect was produced; and,
whatever degree of indisposition may be implied in the phrase “he was
not himself for a month after,” we are entitled to infer that one month
was the period of its duration, and that previous to the 3d February,
1692, the date of Mr. Pryme’s memorandum, “Newton was himself again.”

These facts and dates cannot be reconciled with those in Huygens’s
manuscript. It appears from that document, that, so late as May, 1694,
Newton had only so far recovered his health as _to begin to again
understand the Principia_. His supposed malady, therefore, was in force
from the 3d of January, 1692, till the month of May, 1694,—a period
of more than two years. Now, it is a most important circumstance,
which M. Biot ought to have known, that in _the very middle of this
period_, Newton wrote his four celebrated letters to Dr. Bentley on
the Existence of a Deity,—letters which evince a power of thought and
a serenity of mind absolutely incompatible even with the slightest
obscuration of his faculties. No man can peruse these letters without
the conviction that their author then possessed the full vigour of
his reason, and was capable of understanding the most profound parts
of his writings. The first of these letters was written on the 10th
December, 1692, the second on the 17th January, 1693, the third on
the 25th February, and the 4th on the 11th[76] February, 1693. His
mind was, therefore, strong and vigorous on these four occasions; and
as the letters were written at the express request of Dr. Bentley,
who had been appointed to deliver the lecture founded by Mr. Boyle
for vindicating the fundamental principles of natural and revealed
religion, we must consider such a request as showing his opinion of the
strength and freshness of his friend’s mental powers.

In 1692, Newton, at the request of Dr. Wallis, transmitted to him the
first proposition of his book on quadratures, with examples of it in
first, second, and third fluxions.[77] These examples were written in
consequence of an application from his friend; and the author of the
review of the Commercium Epistolicum, in which this fact is quoted,
draws the conclusion, that he had not at that time forgotten his method
of second fluxions. It appears, also, from the second book of the
Optics,[78] that in the month of June, 1692, he had been occupied with
the subject of haloes, and had made accurate observations both on the
colours and the diameters of the rings in a halo which he had then seen
around the sun.

But though these facts stand in direct contradiction to the statement
recorded by Huygens, the reader will be naturally anxious to know the
real nature and extent of the indisposition to which it refers. The
following letters,[79] written by Newton himself, Mr. Pepys, Secretary
to the Admiralty, and Mr. Millington of Magdalene College, Cambridge,
will throw much light upon the subject.

Newton, as will be presently seen, had fallen into a bad state of
health some time in 1692, in consequence of which both his sleep and
his appetite were greatly affected. About the middle of September,
1693, he had been kept awake for five nights by this nervous disorder,
and in this condition he wrote the following letter to Mr. Pepys:

            _Sept. 13, 1693._

    “SIR,

  “Some time after Mr. Millington had delivered your message, he
  pressed me to see you the next time I went to London. I was averse;
  but upon his pressing consented, before I considered what I did,
  for I am extremely troubled at the embroilment I am in, and have
  neither ate nor slept well this twelvemonth, nor have my former
  consistency of mind. I never designed to get any thing by your
  interest, nor by King James’s favour, but am now sensible that I
  must withdraw from your acquaintance, and see neither you nor the
  rest of my friends any more, if I may but leave them quietly. I beg
  your pardon for saying I would see you again, and rest your most
  humble and most obedient servant,

            “IS. NEWTON.”

From this letter we learn, on his own authority, that his complaint had
lasted for a twelvemonth, and that during that twelvemonth he neither
ate nor slept well, nor enjoyed his former _consistency of mind_. It
is not easy to understand exactly what is meant by not enjoying his
former consistency of mind; but whatever be its import, it is obvious
that he must have been in a state of mind so sound as to enable him to
compose the four letters to Bentley, all of which were written during
the twelvemonth here referred to.

On the receipt of this letter, his friend Mr. Pepys seems to have
written to Mr. Millington of Magdalene College to inquire after Mr.
Newton’s health; but the inquiry having been made in a vague manner,
an answer equally vague was returned. Mr. Pepys, however, who seems to
have been deeply anxious about Newton’s health, addressed the following
more explicit letter to his friend Mr. Millington:—

            _Septemb. 26, 1693._

    “SIR,

  “After acknowledging your many old favours, give me leave to do it
  a little more particularly upon occasion of the new one conveyed
  to me by my nephew Jackson. Though, at the same time, I must
  acknowledge myself not at the ease I would be glad to be at in
  reference to the excellent Mr. Newton; concerning whom (methinks)
  your answer labours under the same kind of restraint which (to tell
  you the truth) my asking did. For I was loth at first dash to tell
  you that I had lately received a letter from him so surprising to
  me for the inconsistency of every part of it, as to be put into
  great disorder by it, from the concernment I have for him, lest it
  should arise from that which of all mankind I should least dread
  from him and most lament for,—I mean a discomposure in head, or
  mind, or both. Let me therefore beg you, sir, having now told you
  the true ground of the trouble I lately gave you, to let me know
  the very truth of the matter, as far at least as comes within your
  knowledge. For I own too great an esteem for Mr. Newton, as for
  a public good, to be able to let any doubt in me of this kind
  concerning him lie a moment uncleared, where I can have any hopes
  of helping it. I am, with great truth and respect, dear sir, your
  most humble, and most affectionate servant,

            “S. PEPYS.”

To this letter Mr. Millington made the following reply:—

          _Coll. Magd. Camb._
            _Sept. the 30, 1693._

    “HONOR’D SIR,

  “Coming home from a journey on the 28th instant at night, I met
  with your letter which you were pleased to honour me with of the
  26th. I am much troubled I was not at home in time for the post,
  that I might as soon as possible put you out of your generous payne
  that you are in for the worthy Mr. Newton. I was, I must confess,
  very much surprised at the inquiry you were pleased to make by your
  nephew about the message that Mr. Newton made the ground of his
  letter to you, for I was very sure I never either received from
  you or delivered to him any such, and therefore I went immediately
  to wayt upon him, with a design to discourse him about the matter,
  but, he was out of town, and since I have not seen him, till upon
  the 28th I met him at Huntingdon, where, upon his own accord, and
  before I had time to ask him any question, he told me that he had
  writt to you a very odd letter, at which he was much concerned;
  added, that it was in a distemper that much seized his head, and
  that kept him awake for above five nights together, which upon
  occasion he desired I would represent to you, and beg your pardon,
  he being very much ashamed, he should be so rude to a person for
  whom he hath so great an honour. He is now very well, and, though I
  fear he is under some small degree of melancholy, yet I think there
  is no reason to suspect it hath at all touched his understanding,
  and I hope never will; and so I am sure all ought to wish that
  love learning or the honour of our nation, _which it is a sign how
  much it is looked after, when such a person as Mr. Newton lyes so
  neglected by those in power_. And thus, honoured sir, I have made
  you acquainted with all I know of the cause of such inconsistencys
  in the letter of so excellent a person; and I hope it will
  remove the doubts and fears you are, with so much compassion and
  publickness of spirit, pleased to entertain about Mr. Newton; but
  if I should have been wanting in any thing tending to the more full
  satisfaction, I shall, upon the least notice, endeavour to amend it
  with all gratitude and truth. Honored sir, your most faithfull and
  most obedient servant,

            “JOH. MILLINGTON.”

Mr. Pepys was perfectly satisfied with this answer, as appears from the
following letter:—

            _October 3d, 1693._

    “SIR,

  “You have delivered me from a fear that indeed gave me much
  trouble, and from my very heart I thank you for it; an evil to Mr.
  Newton being what every good man must feel for his own sake as well
  as his. God grant it may stopp here. And for the kind reflection
  hee has since made upon his letter to mee, I dare not take upon mee
  to judge what answer I should make him to it, or whether any or no;
  and therefore pray that you will bee pleased either to bestow on
  mee what directions you see fitt for my own guidance towards him in
  it, or to say to him in my name, but your own pleasure, whatever
  you think may be most welcome to him upon it, and most expressive
  of my regard and affectionate esteem of him, and concernment for
  him.    *    *    *

            Dear sir, your most humble and most faithful servant,

            “S. PEPYS.”

It does not appear from the memoirs of Mr. Pepys whether he ever
returned any answer to the letter of Mr. Newton which occasioned this
correspondence; but we find that in less than two months after the
date of the preceding letter, an opportunity occurred of introducing
to him a Mr. Smith, who wished to have his opinion on some problem in
the doctrine of chances. This letter from Pepys is dated November 22d,
1693. Sir Isaac replied to it on the 26th November, and wrote to Pepys
again on the 16th December, 1693; and in both these letters he enters
fully into the discussion of the mathematical question which had been
submitted to his judgment.[80]

It is obvious, from Newton’s letter to Mr. Pepys, that the subject of
his receiving some favour from the government had been a matter of
anxiety with himself, and of discussion among his friends.[81] Mr.
Millington was no doubt referring to this anxiety, when he represents
Newton as an honour to the nation, and expresses his surprise “that
such a person should _lye so neglected by those in power_.” And we find
the same subject distinctly referred to in two letters written to Mr.
Locke during the preceding year. In one of these, dated January 26th,
1691–2, he says, “Being fully convinced that Mr. Montague, upon an
old grudge which I thought had been worn out, is false to me, I have
done with him, and intend to sit still, unless my Lord Monmouth be
still my friend.” Mr. Locke seems to have assured him of the continued
friendship of this nobleman, and Mr. Newton, still referring to the
same topic, in a letter dated February 16th, 1691–2, remarks, “I am
very glad Lord Monmouth is still my friend, but intend not to give
his lordship and you any farther trouble. My inclinations are to sit
still.” In a later letter to Mr. Locke, dated September, 1693, and
given below, he asks his pardon for saying or thinking that there was
a design to sell him an office. In these letters Mr. Newton no doubt
referred to some appointment in London which he was solicitous to
obtain, and which Mr. Montague and his other friends may have failed
in procuring. This opinion is confirmed by the letter of Mr. Montague
announcing to him his appointment to the wardenship of the mint, in
which he says that he is very glad he can _at last_ give him good proof
of his friendship.

In the same month in which Newton wrote to Mr. Pepys, we find him in
correspondence with Mr. Locke. Displeased with his opinions respecting
innate ideas, he had rashly stated that they struck at the root of
all morality; and that he regarded the author of such doctrines as a
Hobbist. Upon reconsidering these opinions, he addressed the following
remarkable letter to Locke, written three days after his letter to Mr.
Pepys, and consequently during the illness under which he then laboured.

    “SIR,

  “Being of opinion that you endeavoured to embroil me with women,
  and by other means, I was so much affected with it, as that when
  one told me you were sickly and would not live, I answered,
  ’twere better if you were dead. I desire you to forgive me this
  uncharitableness; for I am now satisfied that what you have done is
  just, and I beg your pardon for my having hard thoughts of you for
  it, and for representing that you struck at the root of morality,
  in a principle you laid in your book of ideas, and designed to
  pursue in another book, and that I took you for a Hobbist.[82] I
  beg your pardon also for saying or thinking that there was a design
  to sell me an office, or to embroil me.—I am your most humble and
  unfortunate servant,

            “IS. NEWTON.

    “_At the Bull, in Shoreditch, London,
        Sept. 16th, 1693._”

To this letter Locke returned the following answer, so nobly
distinguished by philosophical magnanimity and Christian charity:—

            _Oates, Oct. 5th, 1693_.

    “SIR,

  “I have been, ever since I first knew you, so entirely and
  sincerely your friend, and thought you so much mine, that I could
  not have believed what you tell me of yourself had I had it from
  anybody else. And, though I cannot but be mightily troubled that
  you should have had so many wrong and unjust thoughts of me,
  yet next to the return of good offices, such as from a sincere
  good-will I have ever done you, I receive your acknowledgment
  of the contrary as the kindest thing you have done me, since it
  gives me hopes I have not lost a friend I so much valued. After
  what your letter expresses, I shall not need to say any thing to
  justify myself to you. I shall always think your own reflection
  on my carriage, both to you and all mankind, will sufficiently do
  that. Instead of that, give me leave to assure you that I am more
  ready to forgive you than you can be to desire it; and I do it so
  freely and fully, that I wish for nothing more than the opportunity
  to convince you that I truly love and esteem you, and that I have
  the same good-will for you as if nothing of this had happened. To
  confirm this to you more fully, I should be glad to meet you any
  where, and the rather, because the conclusion of your letter makes
  me apprehend it would not be wholly useless to you. But whether you
  think it fit or not, I leave wholly to you. I shall always be ready
  to serve you to my utmost, in any way you shall like, and shall
  only need your commands or permission to do it.

  “My book is going to press for a second edition; and, though I can
  answer for the design with which I write it, yet, since you have so
  opportunely given me notice of what you have said of it, I should
  take it as a favour if you would point out to me the places that
  gave occasion to that censure, that, by explaining myself better,
  I may avoid being mistaken by others, or unawares doing the least
  prejudice to truth or virtue. I am sure you are so much a friend to
  them both, that, were you none to me, I could expect this from you.
  But I cannot doubt but you would do a great deal more than this for
  my sake, who, after all, have all the concern of a friend for you,
  wish you extremely well, and am, without compliment, &c.”[83]

To this letter Newton made the following reply:—

    “SIR,

  “The last winter, by sleeping too often by my fire, I got an ill
  habit of sleeping; and a distemper, which this summer has been
  epidemical, put me farther out of order, so that when I wrote to
  you, I had not slept an hour a night for a fortnight together, and
  for five days together not a wink. I remember I wrote to you, but
  what I said of your book I remember not. If you please to send me a
  transcript of that passage, I will give you an account of it if I
  can.—I am your most humble servant,

            “IS. NEWTON.

    “_Cambridge, Oct. 5th, 1693._”

Although the first of these letters evinces the existence of a nervous
irritability which could not fail to arise from want of appetite and
of rest, yet it is obvious that its author was in the full possession
of his mental powers. The answer of Mr. Locke, indeed, is written upon
that supposition; and it deserves to be remarked, that Mr. Dugald
Stewart, who first published a portion of these letters, never imagines
for a moment that Newton was labouring under any mental alienation.

The opinion entertained by Laplace, that Newton devoted his attention
to theology only in the latter part of his life, may be considered as
deriving some countenance from the fact, that the celebrated general
scholium at the end of the second edition of the Principia, published
in 1713, did not appear in the first edition of that work. This
argument has been ably controverted by Dr. J. C. Gregory of Edinburgh,
on the authority of a manuscript of Newton, which seems to have been
transmitted to his ancestor, Dr. David Gregory, between the years 1687
and 1698. This manuscript, which consists of twelve folio pages in
Newton’s handwriting, contains, in the form of additions and scholia to
some propositions in the third book of the Principia, an account of the
opinions of the ancient philosophers on gravitation and motion, and on
natural theology, with various quotations from their works. Attached to
this manuscript are three very curious paragraphs. The first two appear
to have been the original draught of the general scholium already
referred to; and the third relates to the subject of an ethereal
medium, respecting which he maintains an opinion diametrically opposite
to that which he afterward published at the end of his Optics.[84]
The first paragraph expresses nearly the same ideas as some sentences
in the scholium beginning “Deus summus est ens æternum, infinitum,
absolute perfectum;”[85] and it is remarkable that the second paragraph
is found only in the third edition of the Principia, which appeared in
1726, the year before Newton’s death.

In the middle of the year 1694, about the time when our author is said
to be beginning to understand the Principia, we find him occupied with
the difficult and profound subject of the lunar theory. In order to
procure observations for verifying the equations which he had deduced
from the theory of gravity, he paid a visit to Flamstead, at the Royal
Observatory of Greenwich, on the 1st September, 1694, when he received
from him a series of lunar observations. On the 7th of October he
wrote to Flamstead that he had compared the observations with his
theory, and had satisfied himself that by both together “the moon’s
theory may be reduced to a good degree of exactness, perhaps to the
exactness of two or three minutes.” He wrote him again on the 24th
October, and the correspondence was continued till 1698, Newton making
constant application for observations to compare with his theory of
the planetary motions; while Flamstead, not sufficiently aware of
the importance of the inquiry, received his requests as if they were
idle intrusions in which the interests of science were but slightly
concerned.[86]

In reviewing the details which we have now given respecting the health
and occupations of Newton from the beginning of 1692 till 1695, it is
impossible to draw any other conclusion than that he possessed a sound
mind, and was perfectly capable of carrying on his mathematical, his
metaphysical, and his astronomical inquiries. His friend and admirer,
Mr. Pepys, residing within fifty miles of Cambridge, had never heard of
his being attacked with any illness till he inferred it from the letter
to himself written in September, 1693. Mr. Millington, who lived in the
same university, had been equally unacquainted with any such attack,
and, after a personal interview with Newton, for the express purpose of
ascertaining the state of his health, he assures Mr. Pepys “that he is
very well,—that he fears he is under some small degree of melancholy,
but that there is no reason to suspect that it hath at all touched his
understanding.”

During this period of bodily indisposition, his mind, though in a state
of nervous irritability, and disturbed by want of rest, was capable of
putting forth its highest powers. At the request of Dr. Wallis he drew
up an example of one of his propositions on the quadrature of curves
in second fluxions. He composed, at the desire of Dr. Bentley, his
profound and beautiful letters on the existence of the Deity. He was
requested by Locke to reconsider his opinions on the subject of innate
ideas; and we find him grappling with the difficulties of the lunar
theory.

But with all these proofs of a vigorous mind, a diminution of his
mental powers has been rashly inferred from the cessation of his
great discoveries, and from his unwillingness to enter upon new
investigations. The facts, however, here assumed are as incorrect as
the inference which is drawn from them. The ambition of fame is a
youthful passion, which is softened, if not subdued, by age. Success
diminishes its ardour, and early pre-eminence often extinguishes
it. Before the middle period of life Newton was invested with all
the insignia of immortality; but endowed with a native humility of
mind, and animated with those hopes which teach us to form an humble
estimate of human greatness, he was satisfied with the laurels which
he had won, and he sought only to perfect and complete his labours.
His mind was principally bent on the improvement of the Principia; but
he occasionally diverged into new fields of scientific research,—he
solved problems of great difficulty which had been proposed to try his
strength,—and he devoted much of his time to profound inquiries in
chronology and in theological literature.

The powers of his mind were therefore in full requisition; and, when
we consider that he was called to the discharge of high official
functions which forced him into public life, and compelled him to
direct his genius into new channels, we can scarcely be surprised that
he ceased to produce any original works on abstract science. In the
direction of the affairs of the mint, and of the Royal Society, to
which we shall now follow him, he found ample occupation for his time;
while the leisure of his declining years was devoted to those exalted
studies in which philosophy yields to the supremacy of faith, and hope
administers to the aspirations of genius.




CHAPTER XIV.

  _No Mark of National Gratitude conferred upon Newton—Friendship
    between him and Charles Montague, afterward Earl of Halifax—Mr.
    Montague appointed Chancellor of the Exchequer in 1694—He resolves
    upon a Recoinage—Nominates Mr. Newton Warden of the Mint in 1695—
    Mr. Newton appointed Master of the Mint in 1699—Notice of the Earl
    of Halifax—Mr. Newton elected Associate of the Academy of Sciences
    in 1699—Member for Cambridge in 1701—and President of the Royal
    Society in 1703—Queen Anne confers upon him the Honour of Knighthood
    in 1705—Second Edition of the Principia, edited by Cotes—His
    Conduct respecting Mr. Ditton’s Method of finding the Longitude._


Hitherto we have viewed Newton chiefly as a philosopher leading a life
of seclusion within the walls of a college, and either engaged in the
duties of his professorship, or ardently occupied in mathematical
and scientific inquiries. He had now reached the fifty-third year of
his age, and while those of his own standing at the university had
been receiving high appointments in the church, or lucrative offices
in the state, he still remained without any mark of the respect or
gratitude of his country. All Europe indeed had been offering incense
to his name, and Englishmen themselves boasted of him as the pride
of their country and the ornament of their species, but he was left
in comparative poverty,[87] with no other income than the salary of
his professorship, eked out with the small rental of his paternal
inheritance. Such disregard of the highest genius, dignified by the
highest virtue, could have taken place only in England, and we should
have ascribed it to the turbulence of the age in which he lived, had
we not seen, in the history of another century, that the successive
governments which preside over the destinies of our country have never
been able either to feel or to recognise the true nobility of genius.

Among his friends at Cambridge Newton had the honour of numbering
Charles Montague, grandson of Henry Earl of Manchester, a young man of
high promise, and every way worthy of his friendship. Though devoted to
literary pursuits, and twenty years younger than Newton, he cherished
for the philosopher all the veneration of a disciple, and his affection
for him gathered new strength as he rose to the highest honours and
offices of the state. In the year 1684 we find him co-operating with
Newton in the establishment of a philosophical society at Cambridge;
but though both of them had made personal application to different
individuals to become members, yet the plan failed, from the want, as
Newton expresses it, of persons willing to try experiments.

Mr. Montague sat along with Newton in the convention parliament, and
such were the powers which he displayed in that assembly as a public
speaker, that he was appointed a commissioner of the treasury, and
soon afterward a privy counsellor. In these situations his talents
and knowledge of business were highly conspicuous, and in 1694 he was
appointed chancellor of the exchequer. The current coin of the nation
having been adulterated and debased, one of his earliest designs was to
recoin it and restore it to its intrinsic value. This scheme, however,
met with great opposition. It was characterized as a wild project,
unsuitable to a period of war, as highly injurious to the interests
of commerce, and as likely to sap the foundation of the government.
But he had weighed the subject too deeply, and had intrenched himself
behind opinions too impartial and too well-founded, to be driven from a
measure which the best interests of his country seemed to require.

The persons whom Mr. Montague had consulted about the recoinage were
Newton, Locke, and Halley, and in consequence of Mr. Overton, the
warden of the mint, having been appointed a commissioner of customs, he
embraced the opportunity which was thus offered of serving his friend
and his country by recommending Newton to that important office. The
notice of this appointment was conveyed in the following letter to
Newton.

            _London, 19th March, 1695._

    “SIR,

  “I am very glad that, at last, I can give you a good proof of
  my friendship, and the esteem the king has of your merits. Mr.
  Overton, the warden of the mint, is made one of the commissioners
  of the customs, and the king has promised me to make Mr. Newton
  warden of the mint. The office is the most proper for you. ’Tis the
  chief office in the mint, ’tis worth five or six hundred pounds per
  annum, and has not too much business to require more attendance
  than you can spare. I desire that you will come up as soon as you
  can, and I will take care of your warrant in the mean time. Let me
  see you as soon as you come to town, that I may carry you to kiss
  the king’s hand. I believe you may have a lodging near me.—I am, &c.

            CHARLES MONTAGUE.”

In this new situation the mathematical and chymical knowledge of our
author was of great service to the nation, and he became eminently
useful in carrying on the recoinage, which was completed in the short
space of two years. In the year 1699, he was promoted to the mastership
of the mint,—an office which was worth twelve or fifteen hundred pounds
per annum, and which he held during the remainder of his life. In this
situation he wrote an official report on the Coinage, which has been
published; and he drew up a table of Assays of Foreign Coins, which is
printed at the end of Dr. Arbuthnot’s Tables of Ancient Coins, Weights,
and Measures, which appeared in 1727.

While our author filled the inferior office of warden of the mint,
he retained his professorship at Cambridge; but upon his promotion
in 1699, he appointed Mr. Whiston to be his deputy, with all the
emoluments of the office; and when he resigned the chair in 1703, he
succeeded in getting him nominated his successor.

The appointment of Newton to the mastership of the mint must have been
peculiarly gratifying to the Royal Society, and it was probably from
a feeling of gratitude to Mr. Montague, as much as from a regard for
his talents, that this able statesman was elected president of that
learned body on the 30th November, 1695. This office he held for three
years, and on the 30th January, 1697, Newton had the satisfaction of
addressing to him his solution of the celebrated problems proposed by
John Bernouilli.

This accomplished nobleman was created Earl of Halifax in 1700, and
after the death of his first wife he conceived a strong attachment for
Mrs. Catharine Barton, the widow of Colonel Barton, and the niece of
Newton. This lady was young, gay, and beautiful, and though she did
not escape the censures of her contemporaries, she was regarded by
those who knew her as a woman of strict honour and virtue. We are not
acquainted with the causes which prevented her union with the Earl of
Halifax, but so great was the esteem and affection which he bore her,
that in the will in which he left 100_l._ to Mr. Newton, he bequeathed
to his niece a very large portion of his fortune. This distinguished
statesman died in 1715, in the fifty-fourth year of his age. Himself a
poet and an elegant writer, he was the liberal patron of genius, and he
numbered among his intimate friends Congreve, Halley, Prior, Tickell,
Steele, and Pope. His conduct to Newton will be for ever remembered
in the annals of science. The sages of every nation and of every age
will pronounce with affection the name of Charles Montague, and the
persecuted science of England will continue to deplore that he was
the first and the last English minister who honoured genius by his
friendship and rewarded it by his patronage.

The elevation of Mr. Newton to the highest offices in the mint was
followed by other marks of honour. The Royal Academy of Sciences at
Paris having been empowered by a new charter granted in 1699, to admit
a very small number of foreign associates, Newton was elected a member
of that distinguished body. In the year 1701, on the assembling of a
new parliament, he was re-elected one of the members for the University
of Cambridge.[88] In 1703 he was chosen President of the Royal Society
of London, and he was annually re-elected to this office during the
remaining twenty-five years of his life. On the 16th of April, 1705,
when Queen Anne was living at the royal residence of Newmarket, she
went with Prince George of Denmark and the rest of the court to visit
the University of Cambridge. After the meeting of the Regia Consilia,
her majesty held a court at Trinity Lodge, the residence of Dr.
Bentley, then master of Trinity; where the honour of knighthood was
conferred upon Mr. Newton, Mr. John Ellis, the vice-chancellor, and Mr.
James Montague, the university counsel.[89]

On the dissolution of the parliament, which took place in 1705, Sir
Isaac was again a candidate for the representation of the University,
but notwithstanding the recent expression of the royal favour, he
lost his election by a very great majority.[90] This singular result
was perhaps owing to the loss of that personal influence which his
residence in the university could not fail to command, though it is
more probable that the ministry preferred the candidates of a more
obsequious character, and that the electors looked for advantages which
Sir Isaac Newton was not able to obtain for them.

Although the first edition of the Principia had been for some time
sold off, and copies of it had become extremely rare, yet Sir Isaac’s
attention was so much occupied with his professional avocations that
he could not find leisure for preparing a new edition. Dr. Bentley,
who had repeatedly urged him to this task, at last succeeded, by
engaging Roger Cotes, Plumian Professor of Astronomy at Cambridge, to
superintend its publication at the university press. In June, 1709,
Sir Isaac committed this important trust to his young friend; and
about the middle of July he promised to send him in the course of a
fortnight his own revised copy of the work. Business, however, seems to
have intervened, and Mr. Cotes was obliged to remind Sir Isaac of his
promise, which he did in the following letter:—

            _Cambridge, Aug. 18th, 1709._

    “SIR,

  “The earnest desire I have to see a new edition of your _Principia_
  makes me somewhat impatient till we receive your copy of it, which
  you were pleased to promise me about the middle of last month
  you would send down in about a fortnight’s time. I hope you will
  pardon me for this uneasiness, from which I cannot free myself,
  and for giving you this trouble to let you know it. I have been so
  much obliged by yourself and by your book, that (I desire you to
  believe me) I think myself bound in gratitude to take all the care
  I possibly can that it shall be correct.—Your obliged servant,

            “ROGER COTES.

    “_For Sir Isaac Newton, at his house in
        Jermyn-street, near St. James’s
            Church, Westminster._”

This was the first letter of that celebrated correspondence, consisting
of nearly three hundred letters, in which Sir Isaac and Mr. Cotes
discussed the various improvements which were thought necessary in a
new edition of the Principia. This valuable collection of letters is
preserved in the library of Trinity College; and we cannot refrain
from repeating the wish expressed by Dr. Monk, “that one of the many
accomplished Newtonians who are resident in that society would favour
the world by publishing the whole collection.”

When the work was at last printed, Mr. Cotes expressed a wish that Dr.
Bentley should write the preface to it, but it was the opinion both of
Sir Isaac and Dr. Bentley that the preface should come from the pen of
Mr. Cotes himself. This he accordingly undertook; but previous to its
execution he addressed the following letter to Dr. Bentley, in order
to learn from Sir Isaac the particular view with which it should be
written.

            _March 10th, 1712–13._

    “SIR,

  “I received what you wrote to me in Sir Isaac’s letter. I will set
  about the index in a day or two. As for the preface, I should be
  glad to know from Sir Isaac with what view he thinks proper to have
  it written. You know the book has been received abroad with some
  disadvantage, and the cause of it may be easily guessed at. The
  _Commercium Epistolicum_, lately published by order of the Royal
  Society, gives such indubitable proofs of Mr. Leibnitz’s want of
  candour, that I shall not scruple in the least to speak out the
  full truth of the matter, if it be thought convenient. There are
  some pieces of his looking this way which deserve a censure, as
  his _Tentamen de motuum cælestium causis_. If Sir Isaac is willing
  that something of this nature may be done, I should be glad if,
  while I am making the index, he would consider of it, and put down
  a few notes of what he thinks most material to be insisted on.
  This I say upon supposition that I write the preface myself. But I
  think it will be much more advisable that you, or he, or both of
  you should write it while you are in town. You may depend upon it I
  will own it, and defend it as well as I can, if hereafter there be
  occasion.—I am sir, &c.”

We are not acquainted with the instructions which were given to Mr.
Cotes in consequence of this application; but it appears from the
preface itself, which contains a long and able summary of the Newtonian
philosophy, that Sir Isaac had prohibited any personal reference to the
conduct of Leibnitz.

The general preface is dated 12th May, 1713, and in a subsidiary
preface of only a few lines, dated March 28th, 1713, Sir Isaac mentions
the leading alterations which had been made in this edition. The
determination of the forces by which bodies may revolve in given orbits
was simplified and enlarged. The theory of the resistance of fluids
was more accurately investigated, and confirmed by new experiments.
The theory of the moon and the precession of the equinoxes were more
fully deduced from their principles; and the theory of comets was
confirmed by several examples of their orbits more accurately computed.

In the year 1714, several captains and owners of merchant vessels
petitioned the House of Commons to consider the propriety of bringing
in a bill to reward inventions for promoting the discovery of the
longitude at sea. A committee was appointed to investigate the subject,
and Mr. Ditton and Mr. Whiston, having thought of a new method of
finding the longitude, submitted it to the committee. Four members of
the Royal Society, viz. Sir Isaac Newton, Dr. Halley, Mr. Cotes, and
Dr. Clarke, were examined on the subject, along with Mr. Ditton and Mr.
Whiston. The last three of these philosophers stated their opinions
verbally. Mr. Cotes considered the proposed scheme as correct in theory
and on shore, and both he and Dr. Halley were of opinion that expensive
experiments would be requisite. Newton, when called upon for his
opinion, read the following memorandum, which deserves to be recorded.

“For determining the longitude at sea there have been several projects,
true in theory, but difficult to execute.

“1. One is by a watch to keep time exactly; but by reason of the motion
of the ship, the variation of heat and cold, wet or dry, and the
difference of gravity in different latitudes, such a watch hath not yet
been made.

“2. Another is by the eclipses of Jupiter’s satellites; but by reason
of the length of telescopes requisite to observe them, and the motion
of a ship at sea, those eclipses cannot yet be there observed.

“3. A third is by the place of the moon; but her theory is not yet
exact enough for that purpose; it is exact enough to determine the
longitude within two or three degrees, but not within a degree.

“4. A fourth is Mr. Ditton’s project, and this is rather for keeping an
account of the longitude at sea than for finding it, if at any time it
should be lost, as it may easily be in cloudy weather. How far this is
practicable, and with what charge, they that are skilled in sea affairs
are best able to judge. In sailing by this method, whenever they are to
pass over very deep seas, they must sail due east or west; they must
first sail into the latitude of the next place to which they are going
beyond it, and then keep due east or west till they come at that place.
In the first three ways there must be a watch regulated by a spring,
and rectified every visible sunrise and sunset, to tell the hour of
the day or night. In the fourth way such a watch is not necessary.
In the first way there must be two watches, this and the other above
mentioned. In any of the first three ways, it may be of some service to
find the longitude within a degree, and of much more service to find it
within forty minutes, or half a degree if it may, and the success may
deserve rewards accordingly. In the fourth way, it is easier to enable
seamen to know their distance and bearing from the shore 40, 60, or 80
miles off, than to cross the seas; and some part of the reward may be
given when the first is performed on the coast of Great Britain for the
safety of ships coming home; and the rest when seamen shall be enabled
to sail to an assigned remote harbour without losing their longitude if
it may be.”

The committee brought up their report on the 11th June, and recommended
that a bill should be introduced into parliament for the purpose of
rewarding inventions or discoveries connected with the determination of
the longitude. The bill passed the House of Commons on the 3d July, and
was agreed to by the Lords on the 8th of the same month.[91]

In giving an account of this transaction,[92] Mr. Whiston states,
that nobody understood Sir Isaac’s paper, and that after sitting down
he obstinately kept silence, though he was much pressed to explain
himself more distinctly. At last, seeing that the scheme was likely to
be rejected, Whiston ventured to say that Sir Isaac did not wish to
explain more through fear of compromising himself, but that he really
approved of the plan. Sir Isaac, he goes on to say, repeated word for
word what Whiston had said. This is the part of Mr. Newton’s conduct
which M. Biot has described as puerile, and “tending to confirm the
fact of the aberration of his intellect in 1693.” Before we can admit
such a censure we must be satisfied with the correctness of Whiston’s
statement. Newton’s paper is perfectly intelligible, and we may easily
understand how he might have approved of Mr. Ditton’s plan as ingenious
and practicable under particular circumstances, though he did not think
it of that paramount importance which would have authorized the House
of Commons to distinguish it by a parliamentary reward. The conflict
between public duty and a disposition to promote the interests of Mr.
Whiston and Mr. Ditton was no doubt the cause of that embarrassment of
manner which the former of these mathematicians has so unkindly brought
before the public.




CHAPTER XV.

  _Respect in which Newton was held at the Court of George I.—The
    Princess of Wales delighted with his Conversation—Leibnitz
    endeavours to prejudice the Princess against Sir Isaac and Locke—
    Controversy occasioned by his Conduct—The Princess obtains a
    Manuscript Abstract of his System of Chronology—The Abbé Conti
    is, at her request, allowed to take a Copy of it on the promise of
    Secresy—He prints it surreptitiously in French, accompanied with a
    Refutation by M. Freret—Sir Isaac’s Defence of his System—Father
    Souciet attacks it—and is answered by Dr. Halley—Sir Isaac’s larger
    Work on Chronology published after his Death—Opinions respecting it—
    Sir Isaac’s Paper on the Form of the most ancient Year._


On the accession of George I. to the British throne in 1714, Sir Isaac
Newton became an object of interest at court. His high situation under
government, his splendid reputation, his spotless character, and, above
all, his unaffected piety attracted the attention of the Princess of
Wales, afterward queen-consort to George II. This lady, who possessed a
highly cultivated mind, derived the greatest pleasure from conversing
with Newton and corresponding with Leibnitz. In all her difficulties,
she received from Sir Isaac that information and assistance which
she had elsewhere sought in vain, and she was often heard to declare
in public that she thought herself fortunate in living at a time
which enabled her to enjoy the conversation of so great a genius. But
while Newton was thus esteemed by the house of Hanover, Leibnitz, his
great rival, endeavoured to weaken and undermine his influence. In
his correspondence with the princess, he represented the Newtonian
philosophy, not only as physically false, but as injurious to the
interests of religion. He asserted that natural religion was rapidly
declining in England, and he supported this position by referring
to the works of Locke, and to the beautiful and pious sentiments
contained in the 28th query at the end of the Optics. He represented
the principles of these great men as precisely the same with those of
the materialists, and thus endeavoured to degrade the character of
English philosophers.

These attacks of Leibnitz became subjects of conversation at court,
and when they reached the ear of the king, his majesty expressed his
expectation that Sir Isaac Newton would draw up a reply. He accordingly
entered the lists on the mathematical part of the controversy, and left
the philosophical part of it to Dr. Clarke, who was a full match for
the German philosopher. The correspondence which thus took place was
carefully perused by the princess, and from the estimation in which Sir
Isaac continued to be held, we may infer that the views of the English
philosopher were not very remote from her own.

When Sir Isaac was one day conversing with her royal highness on
some points of ancient history, he was led to mention to her, and
to explain, a new system of chronology which he composed during his
residence at Cambridge, where he was in the habit, as he himself
expresses it, “of refreshing himself with history and chronology when
he was weary with other studies.” The princess was so much pleased with
his ingenious system, that she subsequently, in the year 1718, sent a
message by the Abbé Conti to Sir Isaac, requesting him to speak with
her, and she, on this occasion, requested a copy of the interesting
work which contained his system of chronology. Sir Isaac informed her
that it existed merely in separate papers, which were not only in a
state of confusion, but which contained a very imperfect view of the
subject, and he promised, in a few days, to draw up an abstract of
it for her own private use, and on the condition that it should not
be communicated to any other person. Some time after the princess
received the manuscript, she requested that the Abbé Conti might be
allowed to have a copy of it. Sir Isaac granted this request, and the
Abbé was informed that he received a copy of the manuscript with Sir
Isaac’s leave, and at the princess’s request, and that it was to be
kept secret.[93] The manuscript which was thus rashly put into the
hands of a foreigner was entitled “A Short Chronicle from the First
Memory of Things in Europe to the Conquest of Persia by Alexander the
Great.” It consists of about twenty-four quarto printed pages,[94] with
an introduction of four pages, in which Sir Isaac states that he “does
not pretend to be exact to a year, that there may be errors of five or
ten years, and sometimes twenty, but not much above.”

The Abbé Conti kept his promise of secrecy during his residence in
England, but he no sooner reached Paris than he communicated it to M.
Freret, a learned antiquarian, who not only translated it, but drew up
observations upon it for the purpose of refuting some of its principal
results. Sir Isaac was unacquainted with this transaction till he was
informed of it by the French bookseller, M. Cavalier, who requested
his leave to publish it, and charged one of his friends in London to
procure Sir Isaac’s answer, which was as follows:—

  “I remember that I wrote a Chronological index for a particular
  friend, on condition that it should not be communicated. As I have
  not seen the manuscript which you have under my name, I know not
  whether it be the same. That which I wrote was not at all done
  with design to publish it. I intend not to meddle with that which
  hath been given you under my name, nor to give any consent to the
  publishing of it.—I am your very humble servant,

            “ISAAC NEWTON.

  “_London, May 27th, 1725_, O. S.”

Before this letter was written, viz. on the 21st May, the bookseller
had received the royal privilege for printing the work; and when it was
completed, he sent a copy in a present to Sir Isaac, who received it on
the 11th November, 1725. It was entitled, _Abregé de Chronologie de M.
Le Chevalier Newton, fait par lui-meme, et traduit sur le manuscript
Anglais_, and was accompanied with observations by M. Freret,[95] the
object of which was to refute the leading points of the system.[96]
An advertisement was prefixed to it, in which the bookseller defends
himself for printing it without the author’s leave, on the ground
that he had written three letters to obtain permission, and had
declared that he would take Sir Isaac’s silence for consent. When Sir
Isaac received this work, he drew up a paper entitled, _Remarks on
the Observations made on a Chronological Index of Sir Isaac Newton,
translated into French by the Observator, and published at Paris_,
which was printed in the _Philosophical Transactions for 1725_.[97]
In this paper Sir Isaac gives a history of the transaction,—charges
the Abbé Conti with a breach of promise, and blames the publisher for
having asked his leave to print the translation without sending him
a copy for his perusal, without acquainting him with the name of the
translator, and without announcing his intention of printing along
with it a refutation of the original. The observations made by the
translator against the conclusions deduced by the author were founded
on an imperfect knowledge of Sir Isaac’s system; and they are so
specious, that Halley himself confesses that he was at first prejudiced
in favour of the observations, taking the calculations for granted, and
not having seen Sir Isaac’s work.

To all the observations of M. Freret Sir Isaac returned a triumphant
answer. This presumptuous antiquary had ventured to state at the end
of his observations, “that he believed he had stated enough concerning
the epochs of the Argonauts, and the length of generations, to make
people cautious about the rest; for these are the two foundations of
all this new system of chronology.” He founds his arguments against the
epochs of the Argonauts, as fixed by our author, on the supposition
that Sir Isaac places the vernal equinox at the time of the Argonautic
expedition _in the middle of the sign of Aries_, whereas Sir Isaac
places it _in the middle of the constellation_,—a point corresponding
with the middle of the back of Aries, or 8° from the first star of
Aries. This position of the colure is assigned on the authority of
Eudoxus, as given by Hipparchus, who says that the colure passed over
the back of Aries. Setting out with this mistake, M. Freret concludes
that the Argonautic expedition took place 532 years earlier than Sir
Isaac made it. His second objection to the new system relates to the
length of generations, which he says is made only 18 or 20 years.
Sir Isaac, on the contrary, reckons a generation at 33 years, or 3
generations at 100; and it was the lengths of the reigns of kings that
he made 18 or 20 years. This deduction he founds on the reigns of 64
French kings. Now, the ancient Greeks and Egyptians reckoned the length
of a reign equal to that of a generation; and it was by correcting this
mistake, and adopting a measure founded on fact, that Sir Isaac placed
the Argonautic expedition forty-four years after the death of Solomon,
and fixed some of the other points of his system.

This answer of Sir Isaac’s to the objections of Freret called into
the field a fresh antagonist, Father Souciet, who published five
dissertations on the new chronology. These dissertations were written
in a tone highly reprehensible; and the friends of Sir Isaac, being
apprehensive that the manner in which his system was attacked would
affect him more than the arguments themselves, prevailed upon a friend
to draw up an abstract of Souciet’s objections, stripped of the
“extraordinary ornaments with which they were clothed.” The perusal of
these objections had no other effect upon him than to convince him of
the ignorance of their author; and he was induced to read the entire
work, which produced no change in his opinion.

In consequence of these discussions, Sir Isaac was prevailed upon to
prepare his larger work for the press. He had nearly completed it at
the time of his death, and it was published in 1728, under the title
of _The Chronology of Ancient Kingdoms amended, to which is prefixed
a short Chronicle_, from the first memory of Things in Europe _to
the Conquest of Persia by Alexander the Great_. It was dedicated to
the queen by Mr. Conduit, and consists of six chapters: 1. On the
Chronology of the Greeks;[98] 2. Of the Empire of Egypt; 3. Of the
Assyrian Empire; 4. Of the two contemporary Empires of the Babylonians
and Medes; 5. A Description of the Temple of Solomon; 6. Of the Empire
of the Persians. The sixth chapter was not copied out with the other
five, which makes it doubtful whether or not it was intended for
publication; but as it was found among his papers, and appeared to be a
continuation of the same work, it was thought right to add it to the
other five chapters.[99]

After the death of Newton, Dr. Halley, who had not yet seen the larger
work, felt himself called upon, both as astronomer-royal and as the
friend of the author, to reply to the first and last dissertations of
Father Souciet, which were chiefly astronomical; and in two papers
printed in the Philosophical Transactions for 1727,[100] he has done
this in a most convincing and learned argument.

Among the supporters of the views of Newton, we may enumerate Dr. Reid,
Nauze, and some other writers; and among its opponents, M. Freret, who
left behind him a posthumous work on the subject, M. Fourmond, Mr.
A. Bedford, Dr. Shuckford, Dr. Middleton, Whiston, and the late M.
Delambre. The object of M. Fourmond is to show the uncertainty of the
astronomical argument, arising on the one hand from the vague account
of the ancient sphere as given by Hipparchus; and, on the other, from
the extreme rudeness of ancient astronomical observations. Delambre
has taken a similar view of the subject: he regards the observations
of ancient astronomers as too incorrect to form the basis of a system
of chronology; and he maintains, that if we admit the accuracy of the
details in the sphere of Eudoxus, and suppose them all to belong to the
same epoch, all the stars which it contains ought at that epoch to be
found in the place where they are marked, and we might thence verify
the accuracy, and ascertain the state of the observations. It follows,
however, from such an examination, that the sphere would indicate
almost as many different epochs as it contains stars. Some of them
even had not, in the time of Eudoxus, arrived at the position which
had been for a long time attributed to them, and will not even reach
it for three hundred years to come, and on this account he considers
it impossible to deduce any chronological conclusions from such a rude
mass of errors.

But however well-founded these observations may be, we agree in opinion
with M. Daunou,[101] “that they are not sufficient to establish a new
system, and we must regard the system of Newton as a great fact in the
history of chronological science, and as confirming the observation
of Varro, that the stage of history does not commence till the first
Olympiad.”

Among the chronological writings of Sir Isaac Newton we must enumerate
his _letter to a person of distinction who had desired his opinion of
the learned Bishop Lloyd’s hypothesis concerning the form of the most
ancient year_. This hypothesis was sent by the Bishop of Worcester to
Dr. Prideaux. Sir Isaac remarks, that it is filled with many excellent
observations on the ancient year; but he does not “find it proved that
any ancient nations used a year of twelve months and 360 days without
correcting it from time to time by the luminaries, to make the months
keep to the course of the moon, and the year to the course of the sun,
and returns of the seasons and fruits of the earth.” After examining
the years of all the nations of antiquity, he concludes, “that no other
years are to be met with among the ancients but such as were either
luni-solar, or solar or lunar, or the calendars of these years.” A
practical year, he adds, of 360 days is none of these. The beginning of
such a year would have run round the four seasons in seventy years,
and such a notable revolution would have been mentioned in history, and
is not to be asserted without proving it.[102]




CHAPTER XVI.

  _Theological Studies of Sir Isaac—Their Importance to Christianity—
    Motives to which they have been ascribed—Opinions of Biot and
    Laplace considered—His Theological Researches begun before his
    supposed Mental Illness—The Date of these Works fixed—Letters
    to Locke—Account of his Observations on Prophecy—His Historical
    Account of two notable Corruptions of Scripture—His Lexicon
    Propheticum—His Four Letters to Dr. Bentley—Origin of Newton’s
    Theological Studies—Analogy between the Book of Nature and that of
    Revelation._


The history of the theological studies of Sir Isaac Newton will ever
be regarded as one of the most interesting portions of his life. That
he who among all the individuals of his species possessed the highest
intellectual powers was not only a learned and profound divine, but
a firm believer in the great doctrines of religion, is one of the
proudest triumphs of the Christian faith. Had he distinguished himself
only by an external respect for the offices and duties of religion; and
had he left merely in his last words an acknowledgment of his faith,
his piety would have been regarded as a prudent submission to popular
feeling, and his last aspirations would have been ascribed to the decay
or to the extinction of his transcendent powers. But he had been a
Christian from his youth, and though never intended for the church,
yet he interchanged the study of the Scriptures with that of the laws
of the material universe; and from the examination of the works of the
Supreme Creator he found it to be no abrupt transition to investigate
the revelation of his will, and to contemplate the immortal destinies
of mankind.

But when the religious habits of Sir Isaac Newton could not be ascribed
to an ambition of popularity, to the influence of weak health, or to
the force of professional impulse, it became necessary for the apostles
of infidelity to refer it to some extraordinary cause. His supposed
insanity was therefore eagerly seized upon by some as affording
a plausible origin for his religious principles; while others,
without any view of supporting the cause of skepticism, ascribed his
theological researches to the habits of the age in which he lived,
and to a desire of promoting political liberty, by turning against
the abetters of despotism those powerful weapons which the Scriptures
supplied. The anxiety evinced by M. de Laplace to refer his religious
writings to a late period of his life seems to have been felt also by
M. Biot, who has gone so far as to fix the very date of one of his most
important works, and thus to establish the suspicions of his colleague.

“From the nature of the subject,”[103] says he, “and from certain
indications which Newton seems to give at the beginning of his
dissertation, we may conjecture with probability that he composed it
at the time when the errors of Whiston, and a work of Dr. Clarke on
the same subject, drew upon them the attacks of all the theologians of
England, which would place the date between the years 1712 and 1719. It
would then be truly a prodigy to remark, that a man of from seventy-two
to seventy-five years of age was able to compose, _rapidly_, as he
leads us to believe, so extensive a piece of sacred criticism, of
literary history, and even of bibliography, where an erudition the
most vast, the most varied, and the most ready always supports an
argument well arranged and powerfully combined. * * * At this epoch
of the life of Newton the reading of religious books had become one
of his most habitual occupations, and after he had performed the
duties of his office, they formed, along with the conversation of his
friends, his principal amusement. He had then almost ceased to care
for the sciences, and, as we have already remarked, since the fatal
epoch of 1693, he gave to the world only three really new scientific
productions.”

Notwithstanding the prodigy which it involves, M. Biot has adopted
1712–1719 as the date of this critical dissertation;—it is regarded as
the composition of a man of seventy-two or seventy-five;—the reading
of religious works is stated to have _become_ one of his most habitual
occupations, and such reading is said to have been one of his principal
amusements; and all this is associated with “the fatal epoch of 1693,”
as if his illness at that time had been the cause of his abandoning
science and betaking himself to theology. Carrying on the same views,
M. Biot asks, in reference to Sir Isaac’s work on Prophecy, “How a mind
of the character and force of Newton’s, so habituated to the severity
of mathematical considerations, so exercised in the observation of real
phenomena, and so well aware of the conditions by which truth is to be
discovered, could put together such a number of conjectures without
noticing the extreme improbability of his interpretations from the
infinite number of arbitrary postulates on which he has founded them?”
We would apply the same question to the reasoning by which M. Biot
fixes the date of the critical dissertation; and we would ask how so
eminent a philosopher could hazard such frivolous conjectures upon a
subject on which he had not a single fact to guide his inquiries. The
obvious tendency, though not the design, of the conclusion at which
he arrives is injurious to the memory of Newton, as well as to the
interests of religion; and these considerations might have checked
the temerity of speculation, even if it had been founded on better
data. The Newtonian interpretation of the Prophecies, and especially
that part which M. Biot characterizes as unhappily stamped with the
spirit of prejudice, has been adopted by men of the soundest and
most unprejudiced minds; and in addition to the moral and historical
evidence by which it is supported, it may yet be exhibited in all the
fulness of demonstration. But the speculation of Biot respecting the
date of Newton’s theological works was never maintained by any other
person than himself, and is capable of being disproved by the most
incontrovertible evidence.

We have already seen, in the extract from Mr. Pryme’s manuscript, that
previous to 1692, when a shade is supposed to have passed over his
gifted mind, Newton was well known by the appellation of an “excellent
divine,”—a character which could not have been acquired without the
devotion of many years to theological researches; but, important as
this argument would have been, we are fortunately not left to so
general a defence. The correspondence of Newton with Locke, recently
published by Lord King, places it beyond a doubt that he had begun his
researches respecting the Prophecies before the year 1691,—before the
forty-ninth year of his age, and before the “fatal epoch of 1693.” The
following letter shows that he had previously discussed this subject
with his friend:—

            _Cambridge, Feb. 7, 1690–1._

    “SIR,

  “I am sorry your journey proved to so little purpose, though it
  delivered you from the trouble of the company the day after. You
  have obliged me by mentioning me to my friends at London, and I
  must thank both you and my Lady Masham for your civilities at
  Oates, and for not thinking that I made a long stay there. I hope
  we shall meet again in due time, and then I should be glad to have
  your judgment upon some of my mystical fancies. The Son of Man,
  Dan. vii. I take to be the same with the Word of God upon the White
  Horse in Heaven, Apoc. xii., for both are to rule the nations with
  a rod of iron; but whence are you certain that the Ancient of
  Days is Christ? Does Christ anywhere sit upon the throne? If Sir
  Francis Masham be at Oates, present, I pray, my service to him,
  with his lady, Mrs. Cudworth, and Mrs. Masham. Dr. Covel is not in
  Cambridge.—I am your affectionate and humble servant,

            “IS. NEWTON.

  “Know you the meaning of Dan. x. 21. There is none that holdeth
  with me in these things but Mich. the prince.”

Having thus determined the date of those investigations which
constitute his _observations on the prophecies of holy writ_,
particularly the prophecies of Daniel and the Apocalypse, we shall
proceed to fix the latest date of his _historical account of two
notable corruptions of the Scripture, in a letter to a friend_.

This work seems to have been a _very early_ production of our author.
It was written in the form of a letter to Mr. Locke, and at that time
Sir Isaac seems to have been anxious for its publication. Afraid,
however, of being again led into a controversy, and dreading the
intolerance to which he might be exposed, he requested Mr. Locke, who
was at that time meditating a voyage to Holland, to get it translated
into French, and published on the Continent. Having abandoned his
design of visiting Holland, Locke transmitted the manuscript, without
Newton’s name, to his learned friend M. Le Clerc, in Holland; and
it appears, from a letter of Le Clerc’s to Locke, that he must have
received it before the 11th April, 1691. M. Le Clerc delayed for a
long time to take any steps regarding its publication; but in a letter
dated January 20th, 1692, he announced to Locke his intention of
publishing the tract in Latin. When this plan was communicated to Sir
Isaac, he became alarmed at the risk of detection, and resolved to stop
the publication of his manuscript. This resolution was intimated to Mr.
Locke in the following letter:

            _Cambridge, Feb. 16th, 1691–2._

    “SIR,

  “Your former letters came not to my hand, but this I have. I was
  of opinion my papers had lain still, and am sorry to hear there is
  news about them. Let me entreat you to stop their translation and
  impression so soon as you can; for I design to suppress them. If
  your friend hath been at any pains and charge, I will repay it, and
  gratify him. I am very glad my Lord Monmouth is till my friend, but
  intend not to give his lordship and you any farther trouble. My
  inclinations are to sit still. I am to beg his lordship’s pardon
  for pressing into his company the last time I saw him. I had not
  done it, but that Mr. Paulin pressed me into the room. Miracles, of
  good credit, continued in the church for about two or three hundred
  years. Gregorius Thaumaturgus had his name from thence, and was one
  of the latest who was eminent for that gift; but of their number
  and frequency I am not able to give you a just account. The history
  of those ages is very imperfect. Mr. Paulin told me you had writ
  for some of Mr. Boyle’s red earth, and by that I knew you had the
  receipt.—Your most affectionate and humble servant,

            “IS. NEWTON.”

Hence we see that this celebrated treatise, which Biot alleges to have
been written between 1712 and 1719, was actually in the hands of Le
Clerc in Holland previous to the 11th April, 1691, and consequently
previous to the time of the supposed insanity of its author. Mr. Locke
lost no time in obeying the request of his friend. Le Clerc instantly
stopped the publication of the letter, and, as he had never learned
the name of the author, he deposited the manuscript, which was in the
handwriting of Mr. Locke, in the library of the Remonstrants, where it
was afterward found, and was published at London in 1754, under the
title of _Two letters from Sir Isaac Newton to M. Le Clerc_,—a form
which had never been given to it by its author. The copy thus published
was a very imperfect one, wanting both the beginning[104] and the end,
and erroneous in many places; but Dr. Horsley has published a genuine
edition, which has the form of a single letter to a friend, and was
copied from a manuscript in Sir Isaac Newton’s handwriting, in the
possession of the Rev. Dr. Ekins, Dean of Carlisle.

Having thus determined as accurately as possible the dates of the
principal theological writings of Sir Isaac, we shall now proceed to
give some account of their contents.

_The Observations on the Prophecies of Daniel and the Apocalypse of St.
John_ were published in London in 1733, in one volume 4to. The work is
divided into two parts, the first of which treats of the Prophecies of
Daniel, and the second of the Apocalypse of St. John. It begins with
an account of the different books which compose the Old Testament; and
as the author considers Daniel to be the most distinct in the order of
time, and the easiest to be understood, he makes him the key to all
the prophetic books in those matters which relate to the “last time.”
He next considers the figurative language of the prophets, which he
regards as taken “from the analogy between the world natural and an
empire or kingdom considered as a world politic;” the heavens and the
things therein representing thrones and dynasties; the earth, with
the things therein, the inferior people; and the lowest parts of the
earth the most miserable of the people. The sun is put for the whole
race of kings, the moon for the body of the common people, and the
stars for subordinate princes and rulers. In the earth, the dry land
and the waters are put for the people of several nations. Animals
and vegetables are also put for the people of several regions. When
a beast or man is put for a kingdom, his parts and qualities are put
for the analogous parts and qualities of the kingdom; and when a man
is taken in a mystical sense, his qualities are often signified by his
actions, and by the circumstances and things about him. In applying
these principles he begins with the vision of the image composed of
four different metals. This image he considers as representing a body
of four great nations which should reign in succession over the earth,
viz. the people of Babylonia, the Persians, the Greeks, and the Romans;
while the stone cut out without hands is a new kingdom which should
arise after the four, conquer all those nations, become very great, and
endure to the end of time.

The vision of the four beasts is the prophecy of the four empires
repeated, with several new additions. The lion with eagles’ wings was
the kingdom of Babylon and Media, which overthrew the Assyrian power.
The beast like a bear was the Persian empire, and its three ribs were
the kingdoms of Sardis, Babylon, and Egypt. The third beast, like a
leopard, was the Greek empire, and its four heads and four wings were
the kingdoms of Cassander, Lysimachus, Ptolemy, and Seleucus. The
fourth beast, with its great iron teeth, was the Roman empire, and its
ten horns were the ten kingdoms into which it was broken in the reign
of Theodosius the Great.

In the fifth chapter Sir Isaac treats of the kingdoms represented by
the feet of the image composed of iron and clay which did not stick
to one another, and which were of different strength. These were the
Gothic tribes called Ostrogoths, Visigoths, Vandals, Gepidæ, Lombards,
Burgundians, Alans, &c.; all of whom had the same manners and customs,
and spoke the same language, and who, about the year 416 A. C. were
all quietly settled in several kingdoms within the empire, not only by
conquest, but by grants of emperor.

In the sixth chapter he treats of the _ten_ kingdoms represented by the
ten horns of the fourth beast, into which the western empire became
divided about the time when Rome was besieged and taken by the Goths.
These kingdoms were,

     1. The kingdom of the Vandals and Alans in Spain and Africa.
     2. The kingdom of Suevians in Spain.
     3. The kingdom of the Visigoths.
     4. The kingdom of the Alans in Gaul.
     5. The kingdom of the Burgundians.
     6. The kingdom of the Franks.
     7. The kingdom of the Britains.
     8. The kingdom of the Huns.
     9. The kingdom of the Lombards.
    10. The kingdom of Ravenna.

Some of these kingdoms at length fell, and new ones sprung up; but
whatever was their subsequent number, they still retain the name of the
ten kings from their first number.

The eleventh horn of Daniel’s fourth beast is shown in chapter vii. to
be the Church of Rome in its triple character of a seer, a prophet, and
a king; and its power to change times and laws is copiously illustrated
in chapter viii.

In the ninth chapter our author treats of the kingdom represented in
Daniel by the ram and he-goat, the ram indicating the kingdom of the
Medes and Persians from the beginning of the four empires, and the
he-goat the kingdom of the Greeks to the end of them.

The prophecy of the seventy weeks, which had hitherto been restricted
to the first coming of our Saviour, is shown to be a prediction of
all the main periods relating to the coming of the Messiah, the times
of his birth and death, the time of his rejection by the Jews, the
duration of the Jewish war by which he caused the city and sanctuary to
be destroyed, and the time of his second coming.

In the eleventh chapter Sir Isaac treats with great sagacity and
acuteness of the time of our Saviour’s birth and passion,—a subject
which had perplexed all preceding commentators.

After explaining in the twelfth chapter the last prophecy of Daniel,
namely, that of the scripture of truth, which he considers as a
commentary on the vision of the ram and he-goat, he proceeds in the
thirteenth chapter to the prophecy of the king who did according to his
will, and magnified himself above every god, and honoured Mahuzzims,
and regarded not the desire of women. He shows that the Greek empire,
after the division of the Roman empire into the Greek and Latin
empires, became the king who in matters of religion did according to
his will, and in legislation exalted and magnified himself above every
god.

In the second part of his work on the Apocalypse of St. John, Sir Isaac
treats, _1st_, Of the time when the prophecy was written, which he
conceives to have been during John’s exile in Patmos, and before the
epistle to the Hebrews and the epistles of Peter were written, which in
his opinion have a reference to the Apocalypse; _2dly_, Of the scene of
the vision, and the relation which the Apocalypse has to the book of
the law of Moses, and to the worship of God in the temple; and, _3dly_,
Of the relation which the Apocalypse has to the prophecies of Daniel,
and of the subject of the prophecy itself.

Sir Isaac regards the prophecies of the Old and New Testaments, not
as given to gratify men’s curiosities, by enabling them to foreknow
things, but that after they were fulfilled, they might be interpreted
by the event, and afford convincing arguments that the world is
governed by Providence, he considers that there is so much of this
prophecy already fulfilled as to afford to the diligent student
sufficient instances of God’s providence; and he adds, that “among the
interpreters of the last age, there is scarce one of note who hath not
made some discovery worth knowing, and thence it seems one may gather
that God is about opening these mysteries. The success of others,” he
continues, “put me upon considering it, and if I have done any thing
which may be useful to following writers, I have my design.”

Such is a brief abstract of this ingenious work, which is characterized
by great learning, and marked with the sagacity of its distinguished
author. The same qualities of his mind are equally conspicuous in his
_Historical Account of Two Notable Corruptions of Scripture_.

This celebrated treatise relates to two texts in the Epistles of St.
John and St. Paul. The first of these is in 1 John v. 7. “For there
are three that bear record in heaven, the Father, the Son, and the
Holy Ghost, and these three are one.” This text he considers as a
gross corruption of Scripture, which had its origin among the Latins,
who interpreted the Spirit, Water, and Blood to be the Father, Son,
and Holy Ghost, in order to prove them one. With the same view Jerome
inserted the Trinity in express words in his version. The Latins marked
his variations in the margins of their books; and in the twelfth
and following centuries, when the disputations of the schoolmen
were at their height, the variation began to creep into the text in
transcribing. After the invention of printing, it crept out of the
Latin into the printed Greek, contrary to the authority of all the
Greek manuscripts and ancient versions; and from the Venetian press it
went soon after into Greece. After proving these positions Sir Isaac
gives the following paraphrase of this remarkable passage, which is
given in italics.

“_Who is he that overcometh the world, but he that believeth that
Jesus is the Son of God_, that Son spoken of in the Psalms, where
he saith, ‘thou art my Son; this day have I begotten thee.’ _This
is he that_, after the Jews had long expected him, came, first in a
mortal body, _by_ baptism of _water_, and then in an immortal one, by
shedding his _blood_ upon the cross and rising again from the dead;
_not by water only, but by water and blood_; being the Son of God,
as well by his resurrection from the dead (Acts xiii. 33), as by his
supernatural birth of the virgin (Luke i. 35). _And it is the Spirit_
also _that_, together with the water and blood, _beareth witness_ of
the truth of his coming; _because the Spirit is truth_; and so a fit
and unexceptionable witness. _For there are three that bear record_
of his coming; _the Spirit_, which he promised to send, and which was
since shed forth upon us in the form of cloven tongues, and in various
gifts; _the_ baptism of _water_, wherein God testified ‘this is my
beloved Son;’ _and the_ shedding of his _blood_, accompanied with his
resurrection, whereby he became the most faithful martyr, or witness,
of this truth. _And these three_, the spirit, the baptism, and passion
of Christ, _agree in_ witnessing _one_ and the same thing (namely, that
the Son of God is come); and, therefore, their evidence is strong:
for the law requires but two consenting witnesses, and here we have
three: _and if we receive the witness of men, the_ threefold _witness
of God_, which he bare of his Son, by declaring at his baptism ‘this is
my beloved Son,’ by raising him from the dead, and by pouring out his
Spirit on us, _is greater_; and, therefore, ought to be more readily
received.”

While the Latin Church was corrupting the preceding text, the Greek
Church was doing the same to St. Paul’s 1st Epistle to Timothy iii.
16. _Great is the mystery of godliness, God manifest in the flesh._
According to Sir Isaac, this reading was effected by changing σ into
ΘΣ, the abbreviation of Θεος, and after proving this by a learned and
ingenious examination of ancient manuscripts, he concludes that the
reading should be _Great is the mystery of Godliness who_ (viz. our
Saviour) _was manifest in the flesh_.

As this learned dissertation had the effect of depriving the defenders
of the doctrine of the Trinity of the aid of two leading texts, Sir
Isaac Newton has been regarded as an Antitrinitarian; but such a
conclusion is not warranted by any thing which he has published;[105]
and he distinctly warns us, that his object was solely to “purge the
truth of things spurious.” We are disposed, on the contrary, to think
that he declares his belief in the doctrine of the Trinity when he
says, “In the eastern nations, and for a long time in the western,
the _faith_ subsisted without this text; and it is rather a danger to
religion than an advantage, to make _it now_ lean upon a bruised reed.
There cannot be better service done to the truth than to purge it of
things spurious; and therefore, knowing your prudence and calmness
of temper, I am confident I shall not offend you by telling you my
mind plainly; especially since it is no article of faith, no point of
discipline, nothing but a criticism concerning a text of Scripture
which I am going to write about.” The word faith in the preceding
passage cannot mean faith in the Scriptures in general, but faith in
the particular doctrine of the Trinity; for it is this article of
faith only to which the author refers when he deprecates _its_ leaning
on a bruised reed. But, whatever be the meaning of this passage, we
know that Sir Isaac was greatly offended at Mr. Whiston for having
represented him as an Arian; and so much did he resent the conduct of
his friend in ascribing to him heretical opinions, that he would not
permit him to be elected a Fellow of the Royal Society while he was
President.[106]

The only other religious works which were composed by Sir Isaac Newton
were his _Lexicon Propheticum_, to which was added a Dissertation
on the sacred cubit of the Jews, and _Four Letters addressed to Dr.
Bentley, containing some arguments in proof of a Deity_.

The _Lexicon Propheticum_ was left incomplete, and has not been
published; but the Latin Dissertation which was appended to it, in
which he shows that the cubit was about 26½ Roman unciæ, was published
in 1737 among the Miscellaneous Works of Mr. John Greaves.

Upon the death of the Honourable Robert Boyle, on the 30th of December,
1691, it was found, by a codicil to his will, that he had left a
revenue of 50_l._ per annum to establish a lectureship, in which eight
discourses were to be preached annually in one of the churches of the
metropolis, in illustration of the evidences of Christianity, and in
opposition to the principles of infidelity. Dr. Bentley, though a very
young man, was appointed to preach the first course of sermons, and
the manner in which he discharged this important duty gave the highest
satisfaction, not only to the trustees of the lectureship, but to
the public in general. In the first six lectures Bentley exposed the
folly of atheism even in reference to the present life, and derived
powerful arguments for the existence of a Deity from the faculties of
the soul, and the structure and functions of the human frame. In order
to complete his plan, he proposed to devote his seventh and eighth
lectures to the demonstration of a Divine Providence from the physical
constitution of the universe, as established in the Principia. In
order to qualify himself for this task, he received from Sir Isaac
written directions respecting a list of books necessary to be perused
previous to the study of that work;[107] and having made himself master
of the system which it contained, he applied it with irresistible force
of argument to establish the existence of an overruling mind. Previous
to the publication of these lectures, Bentley encountered a difficulty
which he was not able to solve, and he prudently transmitted to Sir
Isaac during 1692 a series of queries on the subject. This difficulty
occurred in an argument urged by Lucretius, to prove the eternity of
the world from an hypothesis of deriving the frame of it by mechanical
principles from matter endowed with an innate power of gravity, and
evenly scattered throughout the heavens. Sir Isaac willingly entered
upon the consideration of the subject, and transmitted his sentiments
to Dr. Bentley in the four letters which have been noticed in a
preceding chapter.

In the first[108] of these letters Sir Isaac mentions that when he
wrote his treatise about our system, viz. the Third Book of the
Principia, “he had an eye upon such principles as might work, with
considering men, for the belief of a Deity, and he expresses his
happiness that it has been found useful for that purpose. In answering
the first query of Dr. Bentley, the exact import of which we do not
know, he states, that, if matter were evenly diffused through a finite
space, and endowed with innate gravity, it would fall down into the
middle of the space, and form one great spherical mass; but if it were
diffused through an infinite space, some of it would collect into
one mass, and some into another, so as to form an infinite number
of great masses. In this manner the sun and stars might be formed if
the matter were of a lucid nature. But he thinks it inexplicable by
natural causes, and to be ascribed to the counsel and contrivance
of a voluntary Agent, that the matter should divide itself into two
sorts, part of it composing a shining body like the sun, and part an
opaque body like the planets. Had a natural and blind cause, without
contrivance and design, placed the earth in the centre of the moon’s
orbit, and Jupiter in the centre of his system of satellites, and the
sun in the centre of the planetary system, the sun would have been a
body like Jupiter and the earth, that is, without light and heat, and
consequently he knows no reason why there is only one body qualified
to give light and heat to all the rest, but because the Author of the
system thought it convenient, and because one was sufficient to warm
and enlighten all the rest.

To the second query of Dr. Bentley, he replies that the motions which
the planets now have could not spring from any natural cause alone, but
were impressed by an intelligent Agent. “To make such a system with all
its motions required a cause which understood and compared together the
quantities of matter in the several bodies of the sun and planets, and
the gravitating powers resulting from thence; the several distances
of the primary planets from the sun, and of the secondary ones from
Saturn, Jupiter, and the earth, and the velocities with which those
planets could revolve about those quantities of matter in the central
bodies; and to compare and adjust all these things together in so great
a variety of bodies, argues that cause to be not blind and fortuitous,
but very well skilled in mechanics and geometry.”

In the second[109] letter, he admits that the spherical mass formed by
the aggregation of particles would affect the figure of the space in
which the matter was diffused, provided the matter descends directly
downwards to that body, and the body has no diurnal rotation; but he
states, that by earthquakes loosening the parts of this solid, the
protuberance might sink a little by their weight, and the mass by
degrees approach a spherical figure. He then proceeds to correct an
error of Dr. Bentley’s in supposing that all infinites are equal. He
admits that gravity might put the planets in motion, but he maintains
that, without the Divine power, it could never give them such a
circulating motion as they have about the sun, because a proper
quantity of a transverse motion is necessary for this purpose; and he
concludes that he is compelled to ascribe the frame of this system to
an intelligent Agent.

The third letter contains opinions confirming or correcting several
positions which Dr. Bentley had laid down, and he concludes it with a
curious examination of the opinion of Plato, that the motion of the
planets is such as if they had been all created by God in some region
very remote from our system, and let fall from thence towards the
sun, their falling motion being turned aside into a transverse one
whenever they arrived at their several orbits. Sir Isaac shows that
there is no common place such as that conjectured by Plato, provided
the gravitating power of the sun remains constant; but that Plato’s
affirmation is true if we suppose the gravitating power of the sun to
be doubled at that moment of time when they all arrive at their several
orbits. “If we suppose,” says he, “the gravity of all the planets
towards the sun to be of such a quantity as it really is, and that the
motions of the planets are turned upwards, every planet will ascend
to twice its height from the sun. Saturn will ascend till he be twice
as high from the sun as he is at present, and no higher; Jupiter will
ascend as high again as at present, that is, a little above the orb of
Saturn; Mercury will ascend to twice his present height, that is, to
the orb of Venus; and so of the rest; and then, by falling down again
from the places to which they ascended, they will arise again at their
several orbs with the same velocities they had at first, and with which
they now revolve.

“But if so soon as their motions by which they revolve are turned
upwards, the gravitating power of the sun, by which their ascent is
perpetually retarded, be diminished by one-half, they will now ascend
perpetually, and all of them, at all equal distances from the sun,
will be equally swift. Mercury, when he arrives at the orb of Venus,
will be as swift as Venus; and he and Venus, when they arrive at the
orb of the earth, will be as swift as the earth; and so of the rest.
If they begin all of them to ascend at once, and ascend in the same
line, they will constantly, in ascending, become nearer and nearer
together, and their motions will constantly approach to an equality,
and become at length slower than any motion assignable. Suppose,
therefore, that they ascended till they were almost contiguous, and
their motions inconsiderably little, and that all their motions were
at the same moment of time turned back again, or, which comes almost
to the same thing, that they were only deprived of their motions, and
let fall at that time, they would all at once arrive at their several
orbs, each with the velocity it had at first; and if their motions were
then turned sideways, and at the same time the gravitating power of the
sun doubled, that it might be strong enough to retain them in their
orbs, they would revolve in them as before their ascent. But if the
gravitating power of the sun was not doubled, they would go away from
their orbs into the highest heavens in parabolical lines.”[110]

In the fourth letter[111] he states, that the hypothesis that
matter is at first evenly diffused through the universe is in his
opinion inconsistent with the hypothesis of innate gravity without a
supernatural power to reconcile them, and therefore it infers a Deity.
“For if there be innate gravity, it is impossible now for the matter of
the earth and all the planets and stars to fly up from them, and become
evenly spread throughout all the heavens without a supernatural power;
and certainly that which can never be hereafter without a supernatural
power, could never be heretofore without the same power.”

These letters, of which we have endeavoured to give a brief summary,
will well repay the most attentive perusal by the philosopher as well
as the divine. They are written with much perspicuity of language and
great power of thought, and they contain results which incontestably
prove that their author was fully master of his noblest faculties, and
comprehended the profoundest parts of his own writings.[112]

The logical acuteness, the varied erudition, and the absolute freedom
from all prejudice which shine throughout the theological writings
of Newton, might have protected them from the charge of having been
written in his old age, and at a time when a failure of mind was
supposed to have unfitted him for his mathematical investigations. But
it is fortunate for his reputation, as well as for the interests of
Christianity, that we have been able to prove the incorrectness of such
insinuations, and to exhibit the most irrefragable evidence that _all
the theological writings_ of Newton were composed in the vigour of his
life, and before the crisis of that bodily disorder which is supposed
to have affected his reason. The able letters to Dr. Bentley were even
written in the middle of that period when want of sleep and appetite
had disturbed the serenity of his mind, and enable us to prove that
this disturbance, whatever was its amount, never affected the higher
functions of his understanding.

When a philosopher of distinguished eminence, and we believe not
inimical to the Christian faith, has found it necessary to make a
laboured apology for a man like Newton writing on theological subjects,
and has been led to render that apology more complete by referring this
class of his labours to a mind debilitated by age and weakened by its
previous aberrations, it may be expected from an English biographer,
and one who acknowledges the importance of revealed truth, and the
paramount interest of such subjects above all secular studies, to
suggest the true origin of Newton’s theological inquiries.

When a mind of great and acknowledged power first directs its energies
to the study of the material universe, no indications of order attract
his notice, and no proofs of design call forth his admiration. In the
starry firmament he sees no bodies of stupendous magnitude, and no
distances of immeasurable span. The two great luminaries appear vastly
inferior in magnitude to many objects around him, and the greatest
distances in the heavens seem even inferior to those which his own eye
can embrace on the surface of the earth. The planets, when observed
with care, are seen to have a motion among the fixed stars, and to vary
in their magnitude and distances, but these changes appear to follow no
law. Sometimes they move to the east, sometimes to the west, sometimes
towards the north, and sometimes towards the south, and at other
times they are absolutely stationary. No system, in short, appears,
and no general law seems to direct their motions. By the observations
and inquiries of astronomers, however, during successive ages, a
regular system has been recognised in this chaos of moving bodies,
and the magnitudes, distances, and revolutions of every planet which
composes it has been determined with the most extraordinary accuracy.
Minds fitted and prepared for this species of inquiry are capable of
understanding the great variety of evidence by which the truth of the
planetary system is established; but thousands of individuals who are
even distinguished in other branches of knowledge are incapable of such
researches, and view with a skeptical eye the great and irrefragable
truths of astronomy.

That the sun is stationary in the centre of our system,—that the
earth moves round the sun, and round its own axis,—that the earth is
8000 miles in diameter, and the sun _one hundred and ten_ times as
large,—that the earth’s orbit is 190 millions of miles in breadth,—and
that if this immense space were filled with light, it would appear
only like a luminous point at the nearest fixed star,—are positions
absolutely unintelligible and incredible to all who have not carefully
studied the subject. To millions of our species, then, the great book
of nature is absolutely sealed, though it is in the power of all to
unfold its pages, and to peruse those glowing passages which proclaim
the power and wisdom of its mighty Author.

The book of revelation exhibits to us the same peculiarities as that
of nature. To the ordinary eye it presents no immediate indications
of its Divine origin. Events apparently insignificant—supernatural
interferences seemingly unnecessary—doctrines almost contradictory—and
prophecies nearly unintelligible occupy its pages. The history of
the fall of man—of the introduction of moral and physical evil—the
prediction of a Messiah—the actual advent of our Saviour—his
instructions—his miracles—his death—his resurrection—and the subsequent
propagation of his religion by the unlettered fishermen of Galilee,
are each a stumbling block to the wisdom of this world. The youthful
and vigorous mind, when first summoned to peruse the Scriptures, turns
from them with disappointment. It recognises in them no profound
science—no secular wisdom—no Divine eloquence—no disclosures of
nature’s secrets—no direct impress of an Almighty hand. But, though
the system of revealed truth which this book contains is, like that of
the universe, concealed from common observation, yet the labours of
centuries have established its Divine origin, and developed in all its
order and beauty the great plan of human restoration. In the chaos of
its incidents we discover the whole history of our species, whether it
is delineated in events that are past or shadowed forth in those which
are to come,—from the creation of man and the origin of evil, to the
extinction of his earthly dynasty and the commencement of his immortal
career.

The antiquity and authenticity of the books which compose the sacred
canon,—the fulfilment of its prophecies,—the miraculous works of its
founder,—his death and resurrection, have been demonstrated to all who
are capable of appreciating the force of historical evidence; and in
the poetical and prose compositions of the inspired authors we discover
a system of doctrine and a code of morality traced in characters as
distinct and legible as the most unerring truths in the material world.
False systems of religion have indeed been deduced from the sacred
record,—as false systems of the universe have sprung from the study of
the book of nature,—but the very prevalence of a false system proves
the existence of one that is true; and though the two classes of facts
necessarily depend on different kinds of evidence, yet we scruple
not to say that the Copernican system is not more demonstrably true
than the system of theological truth contained in the Bible. If men of
high powers, then, are still found, who are insensible to the evidence
which sustains the system of the universe, need we wonder that there
are others whose minds are shut against the effulgent evidence which
intrenches the strongholds of our faith.

If such, then, is the character of the Christian faith, we need not
be surprised that it was embraced and expounded by such a genius
as Sir Isaac Newton. Cherishing its doctrines, and leaning on its
promises, he felt it his duty, as it was his pleasure, to apply to
it that intellectual strength which had successfully surmounted the
difficulties of the material universe. The fame which that success
procured him he could not but feel to be the breath of popular
applause, which administered only to his personal feelings; but the
investigation of the sacred mysteries, while it prepared his own
mind for its final destiny, was calculated to promote the spiritual
interests of thousands. This noble impulse he did not hesitate to obey,
and by thus uniting philosophy with religion, he dissolved the league
which genius had formed with skepticism, and added to the cloud of
witnesses the brightest name of ancient or of modern times.




CHAPTER XVII.

  _The minor Discoveries and Inventions of Newton—His Researches on
    Heat—On Fire and Flame—On Elective Attraction—On the Structure of
    Bodies—His supposed Attachment to Alchymy—His Hypothesis respecting
    Ether as the Cause of Light and Gravity—On the Excitation of
    Electricity in Glass—His Reflecting Sextant invented before 1700—
    His Reflecting Microscope—His Prismatic Reflector as a Substitute
    for the small Speculum of Reflecting Telescopes—His Method of
    varying the Magnifying Power of Newtonian Telescopes—His Experiments
    on Impressions on the Retina._


In the preceding chapters we have given an account of the principal
labours of Sir Isaac Newton; but there still remain to be noticed
several of his minor discoveries and inventions, which could not
properly be introduced under any general head.

The most important of these, perhaps, are his chymical researches,
which he seems to have pursued with more or less diligence from the
time when he first witnessed the practical operations of chymistry
during his residence at the apothecary’s at Grantham. His first
chymical experiments were probably made on the alloys of metals, for
the purpose of obtaining a good metallic composition for the specula
of reflecting telescopes. In his paper on thin plates he treats of the
combinations of solids and fluids; but he enters more largely on these
and other subjects in the queries published at the end of his Optics.

One of his most important chymical papers is his _Tabula quantitatum
et graduum caloris_, which was published in the Philosophical
Transactions. This short paper contains a comparative scale of
temperature from that of melting ice to that of a small kitchen
coal-fire. The following are the principal points of the scale, the
intermediate degrees of heat having been determined with great care.

    Degrees   Equal Parts
    of Heat.    of Heat.
       0           0      Freezing point of water.
       1          12      Blood-heat.
       2          24      Heat of melting wax.
       3          48      Melting point of equal parts of tin and
                              bismuth.
       4          96      Melting point of lead.
       5         192      Heat of a small coal-fire.

The first column of this table contains the degrees of heat
in arithmetical progression, and the second in geometrical
progression,—the second degree being twice as great as the first, and
so on. It is obvious from this table, that the heat at which equal
parts of tin and bismuth melt is _four_ times greater than that of
blood-heat, the heat of melting lead _eight_ times greater, and the
heat of a small coal-fire _sixteen_ times greater.

This table was constructed by the help of a thermometer, and of red-hot
iron. By the former he measured all heats as far as that of melting
tin; and by the latter he measured all the higher heats. For the heat
which heated iron loses in a given time is as the total heat of the
iron; and therefore, if the times of cooling are taken equal, the heats
will be in a geometrical progression, and may therefore be easily found
by a table of logarithms.

He found by a thermometer constructed with linseed oil, that if the
oil, when the thermometer was placed in melting snow, occupied a space
of 1000 parts, the same oil, rarefied with _one_ degree of heat, or
that of the human body, occupied a space of 10256; in the heat of water
beginning to boil, a space of 10705; in the heat of water boiling
violently, 10725; in the heat of melted tin beginning to cool, and
putting on the consistency of an amalgam, 11516, and when the tin had
become solid, 11496. Hence the oil was rarefied in the ratio of 40 to
39 by the heat of the human body; of 15 to 14 by the heat of boiling
water; of 15 to 13 in the heat of melting tin beginning to solidify;
and of 23 to 20 in the same tin when solid. The rarefaction of air
was, with the same heat, _ten_ times greater than that of oil, and
the rarefaction of oil _fifteen_ times greater than that of spirit of
wine. By making the heats of oil proportional to its rarefaction, and
by calling the heat of the human body 12 parts, we obtain the heat of
water beginning to boil, 33; of water boiling violently, 34; of melted
tin beginning to solidify, 72; and of the same become solid, 70.

Sir Isaac then heated a sufficiently thick piece of iron till it was
red-hot; and having fixed it in a cold place, where the wind blew
uniformly, he put upon it small pieces of different metals and other
fusible bodies, and noted the times of cooling, till all the particles,
having lost their fluidity, grew cold, and the heat of the iron was
equal to that of the human body. Then, by assuming that the excesses of
the heats of the iron and of the solidified particles of metal above
the heat of the atmosphere, were in geometrical progression when the
times were in arithmetical progression, all the heats were obtained.
The iron was placed in a current of air, in order that the air heated
by the iron might always be carried away by the wind, and that cold air
might replace it with a uniform motion; for thus equal parts of the
air were heated in equal times, and received a heat proportional to
that of the iron. But the heats thus found had the same ratio to one
another with the heats found by the thermometer; and hence he was right
in assuming that the rarefactions of the oil were proportional to its
heats.

Another short chymical paper by Sir Isaac Newton has been published by
Dr. Horsley. It is entitled _De Natura Acidorum_, but is principally
occupied with a number of brief opinions on chymical subjects. This
paper was written later than 1687, as it bears a reference to the
Principia; and the most important facts which it contains seem to have
been more distinctly reproduced in the queries at the end of the Optics.

The most important of these queries relate to fire, flame, and electric
attractions, and as they were revised in the year 1716 and 1717, they
may be regarded as containing the most matured opinions of their
author. Fire he regards as a body heated so hot as to emit light
copiously, and flame as a vapour, fume, or exhalation heated so hot
as to shine. In his long query on elective attractions, he considers
the small particles of bodies as acting upon one another at distances
so minute as to escape observation. When salt of tartar deliquesces,
he supposes that this arises from an attraction between the saline
particles and the aqueous particles held in solution in the atmosphere,
and to the same attraction he ascribes it that the water will not
distil from the salt of tartar without great heat. For the same reason
sulphuric acid attracts water powerfully, and parts with it with great
difficulty. When this attractive force becomes very powerful, as in the
union between sulphuric acid and water, so as to make the particles
“coalesce with violence,” and rush towards one another with an
accelerated motion, heat is produced by the mixture of the two fluids.
In like manner, he explains the production of flame from the mixture
of cold fluids,—the action of fulminating powders,—the combination of
iron filings with sulphur,—and all the other chymical phenomena of
precipitation, combination, solution, and crystallization, and the
mechanical phenomena of cohesion and capillary attraction. He ascribes
hot springs, volcanoes, fire-damps, mineral coruscations, earthquakes,
hot suffocating exhalations, hurricanes, lightning, thunder, fiery
meteors, subterraneous explosions, land-slips, ebullitions of the sea,
and waterspouts, to sulphureous steams abounding in the bowels of the
earth, and fermenting with minerals, or escaping into the atmosphere,
where they ferment with acid vapours fitted to promote fermentation.

In explaining the structure of solid bodies, he is of opinion,
“that the smallest particles of matter may cohere by the strongest
attractions, and compose bigger particles of weaker virtue; and many
of these may cohere and compose bigger particles whose virtue is still
weaker; and so on for divers successions, until the progression end
in the biggest particles, on which the operations in chymistry and
the colours of natural bodies depend, and which, by adhering, compose
bodies of a sensible magnitude. If the body is compact, and bends or
yields inward to pression, without any sliding of its parts, it is
hard and elastic, returning to its figure with a force rising from the
mutual attraction of its parts. If the parts slide upon one another,
the body is malleable or soft. If they slip easily, and are of a fit
size to be agitated by heat, and the heat is big enough to keep them
in agitation, the body is fluid; and if it be apt to stick to things,
it is humid; and the drops of every fluid affect a round figure, by
the mutual attraction of their parts, as the globe of the earth and
sea affects a round figure, by the mutual attraction of its parts, by
gravity.”

Sir Isaac then supposes, that, as the attractive force of bodies can
reach but to a small distance from them, “a repulsive virtue ought
to succeed;” and he considers such a virtue as following from the
reflection of the rays of light, the rays being repelled without the
immediate contact of the reflecting body, and also from the emission of
light, the ray, as soon as it is shaken off from a shining body by the
vibrating motion of the parts of the body, getting beyond the reach of
attraction, and being driven away with exceeding great velocity by the
force of reflection.[113]

Many of the chymical views which Sir Isaac thus published in the form
of queries were in his own lifetime illustrated and confirmed by Dr.
Stephen Hales, in his book on _Vegetable Statics_,—a work of great
originality, which contains the germ of some of the finest discoveries
in modern chymistry.

Although there is no reason to suppose that Sir Isaac Newton was
a believer in the doctrines of alchymy, yet we are informed by
the Reverend Mr. Law that he had been a diligent student of Jacob
Behmen’s writings, and that there were found among his papers copious
abstracts from them in his own handwriting.[114] He states also that
Sir Isaac, together with one Dr. Newton, his relation, had, in the
earlier part of his life, set up furnaces, and were for several months
at work in quest of the philosopher’s tincture. These statements may
receive some confirmation from the fact, that there exist among the
Portsmouth papers many sheets, in Sir Isaac’s own writing, of Flammel’s
Explication of Hieroglyphic Figures, and in another hand, many sheets
of William Yworth’s _Processus Mysterii Magni Philosophicus_, and also
from the manner in which Sir Isaac requests Mr. Aston to inquire after
one Borry in Holland, who always went clothed in green, and who was
said to possess valuable secrets; but Mr. Law has weakened the force of
his own testimony, when he asserts that Newton borrowed the doctrine
of attraction from Behmen’s first three propositions of eternal nature.

On the 7th December, 1675, Sir Isaac Newton communicated to the
Royal Society a paper entitled _An hypothesis explaining properties
of light_, in which he, for the first time, introduces his opinions
respecting ether, and employs them to explain the nature of light, and
the cause of gravity. “He was induced,” he says, “to do this, because
he had observed the heads of some great virtuosos to run much upon
hypotheses, and he therefore gave one which he was inclined to consider
as the most probable, if he were obliged to adopt one.”[115]

This hypothesis seems to have been afterward a subject of discussion
between him and Mr. Boyle, to whom he promised to communicate his
opinion more fully in writing. He accordingly addressed to him a long
letter, dated February 28th, 1678–9, in which he explains his views
respecting ether, and employs them to account for the refraction of
light,—the cohesion of two polished pieces of metal in an exhausted
receiver,—the adhesion of quicksilver to glass tubes,—the cohesion
of the parts of all bodies,—the cause of filtration,—the phenomena
of capillary attraction,—the action of menstrua on bodies,—the
transmutation of gross compact substances into aerial ones,—and the
cause of gravity. From the language used in this paper, we should
be led to suppose that Sir Isaac had entirely forgotten that he had
formerly treated the general subject of ether, and applied it to the
explanation of gravity. “I shall set down,” says he, “one conjecture
more _which came into my mind now as I was writing this letter; it is
about the cause of gravity,_” which he goes on to explain;[116] and
he concludes by saying, that “he has so little fancy to things of this
nature, that, _had not your encouragement moved me to it_, I should
never, I think, thus far have set pen to paper about them.”

These opinions, however, about the existence of ether, Newton seems to
have subsequently renounced; for in the manuscript in the possession
of Dr. J. C. Gregory, which we have already mentioned, and which was
written previous to 1702, he states, that ether is neither obvious
to our senses, nor supported by any arguments, but is a gratuitous
assumption, which, if we are to trust to reason and to our senses, must
be banished from the nature of things; and he goes on to establish,
by various arguments, the validity of this opinion. This renunciation
of his former hypothesis probably arose from his having examined more
carefully some of the phenomena which he endeavoured to explain by it.
Those of capillary attraction, for example, he had ascribed to the
ether “standing rarer in the very sensible cavities of the capillary
tubes than without them,” whereas he afterward discovered their true
cause, and ascribed them to the reciprocal attraction of the tube and
the fluid. But, however this may be, there can be no doubt that he
resumed his early opinions before the publication of his Optics, which
may be considered as containing his views upon this subject.

The queries which contain these opinions are the 18th–24th, all of
which appeared for the first time in the second English edition of the
Optics. If a body is either heated or loses its heat when placed in
vacuo, he ascribes the conveyance of the heat in both cases “to the
vibration of a much subtiler medium than air;” and he considers this
medium as the same with that by which light is refracted and reflected,
and by whose vibrations light communicates heat to bodies, and is put
into fits of easy reflection and transmission.

This ethereal medium, according to our author, is exceedingly more rare
and more elastic than air. It pervades all bodies, and is expanded
through all the heavens. It is much rarer within the dense bodies of
the sun, stars, planets, and comets, than in the celestial spaces
between them, and also more rare within glass, water, &c. than in the
free and open spaces void of air and other grosser bodies. In passing
out of glass, water, &c. and other dense bodies into empty space, it
grows denser and denser by degrees, and this gradual condensation
extends to some distance from the bodies. Owing to its great
elasticity, and, consequently, its efforts to spread in all directions,
it presses against itself, and, consequently, against the solid
particles of bodies, so as to make them continually approach to one
another, the body being impelled from the denser parts of the medium
towards the rarer with all that power which we call gravity.

In employing this medium to explain the nature of light, Newton does
not suppose, with Descartes, Hooke, Huygens, and others, that light is
nothing more than the impression of those undulations on the retina.
He regards light as a peculiar substance, composed of heterogeneous
particles thrown off with great velocity, and in all directions, from
luminous bodies; and he supposes that these particles while passing
through the ether, excite in it vibrations or pulses which accelerate
or retard the particles of light, and thus throw them into their
alternate fits of easy reflection and transmission.

Hence, if a ray of light falls upon a transparent body, in which the
ether consists of strata of variable density, the particles of light
acted upon by the vibrations which they create will be urged with an
accelerated velocity in entering the body, while their velocity will
be retarded in quitting it. In this manner he conceives the phenomena
of refraction to be produced, and he shows how in such a case the
refraction would be regulated by the law of the sines.

In order that the ethereal medium may produce the fits of easy
reflection and transmission, he conceives that its vibrations must be
swifter than light. He computes its elasticity to be 490,000,000,000
times greater than that of air, in proportion to its density, and about
600,000,000 times more rare than water, from which he infers that the
resistance which it would oppose to the motions of the planets would
not be sensible in 10,000 years. He considers that the functions of
vision and hearing may be performed chiefly by the vibrations of this
medium, executed in the bottom of the eye, or in the auditory nerve
by the rays of light, and propagated through the solid, pellucid, and
uniform capillamenta of the optic or auditory nerves into the place of
sensation; and he is of opinion that animal motion may be performed by
the vibrations of the same medium, excited in the brain by the power
of the will, and propagated from thence by the solid, pellucid, and
uniform capillamenta of the nerves into the muscles for contracting and
dilating them.

In the registers of the Royal Society there exist several letters[117]
on the excitation of electricity in glass, which were occasioned
by an experiment of this kind having been mentioned in Sir Isaac’s
hypothesis of light. The society had ordered the experiment to be tried
at their meeting of the 16th December, 1675; but, in order to secure
its success, Mr. Oldenburg wrote to Sir Isaac for a more particular
account of it. Sir Isaac being thus “put upon recollecting himself a
little farther about it,” remembers that he made the experiment with a
glass fixed at the distance of the 1/3d of an inch from one end of a
brass hoop, and only the 1/8th of an inch from the other. Small pieces
of thin paper were then laid upon the table; when the glass was laid
above them and rubbed, the pieces of paper leaped from the one part of
the glass to the other, and twirled about in the air. Notwithstanding
this explicit account of the experiment, it entirely failed at the
Royal Society, and the secretary was desired to request the loan of
Sir Isaac’s apparatus, and to inquire whether or not he had secured
the papers from being moved by the air, which might have somewhere
stole in. In a letter, dated 21st December, Sir Isaac recommended to
the society to rub the glass “with stuff whose threads may rake its
surface, and, if that will not do, to rub it with the fingers’ ends
to and fro, and knock them as often upon the glass.” These directions
enabled the society to succeed with the experiment on the 13th January,
1676, when they used a scrubbing brush of short hog’s bristles, and the
heft of a knife made with whalebone.

Among the minor inventions of Sir Isaac Newton, we must enumerate
his reflecting instrument for observing the moon’s distance from
the fixed stars at sea. The description of this instrument was
communicated to Dr. Halley in the year 1700; but, either from having
mislaid the manuscript, or from attaching no value to the invention,
he never communicated it to the Royal Society, and it remained among
his papers till after his death in 1742, when it was published in
the Philosophical Transactions. The following is Sir Isaac’s own
description of it as communicated to Dr. Halley.

“In the annexed figure PQRS denotes a plate of brass, accurately
divided in the limb DQ, into ½ degrees, ½ minutes, and 1/12 minutes, by
a diagonal scale; and the ½ degrees, and ½ minutes, and 1/12 minutes,
counted for degrees, minutes, and 1/6 minutes. AB is a telescope three
or four feet long, fixed on the edge of that brass plate. G is a
speculum fixed on the brass plate perpendicularly as near as may be
to the object-glass of the telescope, so as to be inclined forty-five
degrees to the axis of the telescope, and intercept half the light
which would otherwise come through the telescope to the eye. CD is a
moveable index turning about the centre C, and, with its fiducial edge,
showing the degrees, minutes, and 1/6 minutes on the limb of the brass
plate PQ; the centre C must be over against the middle of the speculum
G. H is another speculum, parallel to the former, when the fiducial
edge of index falls on 0° 0′ 0″; so that the same star may then appear
through the telescope in one and the same place, both by the direct
rays and by the reflexed ones; but if the index be turned, the star
shall appear in two places, whose distance is showed on the brass limb
by the index.

[Illustration: _Fig. 12._]

“By this instrument the distance of the moon from any fixed star is
thus observed: view the star through the perspicil by the direct
light, and the moon by the reflexed (or on the contrary); and turn the
index till the star touch the limb of the moon, and the index shall
show on the brass limb of the instrument the distance of the star from
the moon’s limb; and though the instrument shake by the motion of the
ship at sea, yet the moon and star will move together as if they did
really touch one another in the heavens; so that an observation may be
made as exactly at sea as at land.

“And by the same instrument may be observed exactly the altitudes of
the moon and stars, by bringing them to the horizon; and thereby the
latitude and times of observation may be determined more exactly than
by the ways now in use.

“In the time of the observation, if the instrument move angularly about
the axis of the telescope, the star will move in a tangent of the
moon’s limb, or of the horizon; but the observation may notwithstanding
be made exactly, by noting when the line described by the star is a
tangent to the moon’s limb, or to the horizon.

“To make the instrument useful, the telescope ought to take in a large
angle; and to make the observation true, let the star touch the moon’s
limb, not on the outside, but on the inside.”

This ingenious contrivance is obviously the very same invention as
that which Mr. Hadley produced in 1731, and which, under the name of
Hadley’s Quadrant, has been of so great service in navigation. The
merit of its first invention must therefore be transferred to Sir Isaac
Newton.

In the year 1672, Sir Isaac communicated to Mr. Oldenburg his design
for a microscope, which he considered to be as capable of improvement
as the telescope, and perhaps more so, because it requires only one
speculum. This microscope is shown in the annexed diagram, where AB is
the object-metal, CD the eye-glass, F their common focus, and O the
other focus of the metal in which the object is placed. This ingenious
idea has been greatly improved in modern times by Professor Amici, who
makes AB a portion of an ellipsoid, whose foci are O and F, and who
places a small plain speculum between O and AB, in order to reflect
the object, which is placed on one side AP, for the purpose of being
illuminated.

[Illustration: _Fig. 13._]

In another letter to Mr. Oldenburg, dated July 11th in the same year,
he suggests another improvement in microscopes, which is to “illuminate
the object in a darkened room with the light of any convenient colour
not too much compounded: for by that means the microscope will, with
distinctness, bear a deeper charge and larger aperture, especially
if its construction be such as I may hereafter describe.”[118]
This happy idea I have some years ago succeeded in realizing, by
illuminating microscopic objects with the light of a monochromatic
lamp, which discharges a copious flame of pure yellow light of definite
refrangibility.[119]

[Illustration: _Fig. 14._]

[Illustration: _Fig. 15._]

In order to remedy the evils arising from the weak reflecting power of
speculum metal, and from its tarnishing by exposure to the air, Sir
Isaac proposed to substitute for the small oval speculum a triangular
prism of glass or crystal ABC. Its side AB _ba_ he supposes to perform
the office of that metal, by reflecting towards the eye-glass the light
which comes from the concave speculum DF, _fig. 13_, whose light he
supposes to enter into this prism at its side CB _bc_, and lest any
colours should be produced by the refraction of these planes, it is
requisite that the angles of the prism at A_a_ and B_b_ be precisely
equal. This may be done most conveniently, by making them half right
angles, and consequently the third angle at C_c_ a right one. The plane
AB _ba_ will reflect all the light incident upon it; but in order to
exclude unnecessary light, it will be proper to cover it all over with
some black substance excepting two circular spaces of the planes A_c_
and B_c_, through which the useful light may pass. The length of the
prism should be such that its sides A_c_ and B_c_ may be square, and
so much of the angles B and _b_ as are superfluous ought to be ground
off, to give passage for as much light as is possible from the object
to the speculum.

[Illustration: _Fig. 16._]

One great advantage of this prism, which cannot be obtained from the
oval metal, is, that without using two glasses the object may be
erected, and the magnifying power of the telescope varied at pleasure,
by merely varying the distances of the speculum, the prism, and the
eye-glass. This will be understood from _fig. 16_, where AI represents
the great concave speculum, EF the eye-glass, and BCD the prism of
glass, whose sides BC and CD are not flat, but spherically convex. The
rays which come from G, the focus of the great speculum AI, will, by
the refraction of the first side BC, be reduced to parallelism, and
after reflection from the base CD, will be made by the refraction of
the next side BD to converge to the focus H of the eye-glass EF. If we
now bring the prism BCD nearer the image at G, the point H will recede
from BD, and the image formed there will be greater than that at G, and
if we remove the prism BCD from G, the point H will approach to BD, and
the image at H will be less than that at G. The prism BCD performs the
same part as a convex lens, G and H being its conjugate foci, and the
relative size of the images formed at these points being proportional
to their distance from the lens. This construction would be a good one
for varying optically the angular distance of a pair of wires placed in
the focus of the eye-glass EF; and by bisecting the lenticular prism
BCD, and giving the halves a slight inclination, we should be able
to separate and to close the two images or disks which would thus be
produced, and thus form a double image micrometer.

Among the minor and detached labours of Sir Isaac, we must not omit his
curious experiments on the action of light upon the retina. Locke seems
to have wished his opinion respecting a fact stated in Boyle’s Book
on Colours, and in a letter from Cambridge, dated June 30th, 1691, he
communicated to his friend the following very remarkable observations
made by himself.

“The observation you mention in Mr. Boyle’s book of colours I once
made upon myself with the hazard of my eyes. The manner was this; I
looked a very little while upon the sun in the looking-glass with my
right eye, and then turned my eyes into a dark corner of my chamber,
and winked, to observe the impression made, and the circles of colours
which encompassed it, and how they decayed by degrees, and at last
vanished. This I repeated a second and a third time. At the third time,
when the phantasm of light and colours about it were almost vanished,
intending my fancy upon them to see their last appearance, I found, to
my amazement, that they began to return, and by little and little to
become as lively and vivid as when I had newly looked upon the sun. But
when I ceased to intend my fancy upon them, they vanished again. After
this, I found, that as often as I went into the dark, and intended my
mind upon them, as when a man looks earnestly to see any thing which
is difficult to be seen, I could make the phantasm return without
looking any more upon the sun; and the oftener I made it return, the
more easily I could make it return again. And at length, by repeating
this without looking any more upon the sun, I made such an impression
on my eye, that, if I looked upon the clouds, or a book, or any bright
object, I saw upon it a round bright spot of light like the sun, and,
which is still stranger, though I looked upon the sun with my right eye
only, and not with my left, yet my fancy began to make an impression
upon my left eye, as well as upon my right. For if I shut my right
eye, or looked upon a book or the clouds with my left eye, I could
see the spectrum of the sun almost as plain as with my right eye, if
I did but intend my fancy a little while upon it; for at first, if I
shut my right eye, and looked with my left, the spectrum of the sun
did not appear till I intended my fancy upon it; but by repeating,
this appeared every time more easily. And now, in a few hours’ time, I
had brought my eyes to such a pass, that I could look upon no bright
object with either eye but I saw the sun before me, so that I durst
neither write nor read; but to recover the use of my eyes, shut myself
up in my chamber made dark, for three days together, and used all means
to divert my imagination from the sun. For if I thought upon him, I
presently saw his picture, though I was in the dark. But by keeping in
the dark, and employing my mind about other things, I began in three or
four days to have some use of my eyes again; and, by forbearing to look
upon bright objects, recovered them pretty well, though not so well but
that, for some months after, the spectrum of the sun began to return
as often as I began to meditate upon the phenomena, even though I lay
in bed at midnight with my curtains drawn. But now I have been very
well for many years, though I am apt to think, if I durst venture my
eyes, I could still make the phantasm return by the power of my fancy.
This story I tell you, to let you understand, that in the observation
related by Mr. Boyle, the man’s fancy probably concurred with the
impression made by the sun’s light to produce that phantasm of the sun
which he constantly saw in bright objects. And so your question about
the cause of this phantasm involves another about the power of fancy,
which I must confess is too hard a knot for me to untie. To place this
effect in a constant motion is hard, because the sun ought then to
appear perpetually. It seems rather to consist in a disposition of the
sensorium to move the imagination strongly, and to be easily moved,
both by the imagination and by the light, as often as bright objects
are looked upon.”

These observations possess in many respects a high degree of interest.
The fact of the transmission of the impression from the retina of the
one eye to that of the other is particularly important; and it deserves
to be remarked, as a singular coincidence, that I had occasion to
observe and to describe the same phenomena above twenty years ago,[120]
and long before the observations of Sir Isaac were communicated to the
scientific world.




CHAPTER XVIII.

  _His Acquaintance with Dr. Pemberton, who edits the Third Edition of
    the Principia—His first Attack of ill Health—His Recovery—He is
    taken ill in consequence of attending the Royal Society—His Death
    on the 20th March, 1727—His Body lies in state—His Funeral—He is
    buried in Westminster Abbey—His Monument described—His Epitaph—A
    Medal struck in honour of him—Roubiliac’s full-length Statue of him
    erected in Cambridge—Division of his Property—His Successors._


About the year 1722, Sir Isaac was desirous of publishing a third
edition of his Principia, and the premature death of Mr. Cotes
having deprived him of his valuable aid, he had the good fortune to
become acquainted with Dr. Henry Pemberton, a young and accomplished
physician, who had cultivated mathematical learning with considerable
success. M. Poleni, an eminent professor in the University of Padua,
having endeavoured, on the authority of a new experiment, to overturn
the common opinion respecting the force of bodies in motion, and to
establish that of Leibnitz in its place, Dr. Pemberton transmitted
to Dr. Mead a demonstration of its inaccuracy. Dr. Mead communicated
this paper to Sir Isaac, who not only highly approved of it, but added
a demonstration of his own, drawn from another consideration of the
subject; and this was printed without his name, as a postscript to
Pemberton’s paper, when it appeared in the Transactions.[121]

In a short time after the commencement of their acquaintance, Sir Isaac
engaged Dr. Pemberton to superintend the new edition of the Principia.
In discharging this duty, Dr. Pemberton had occasion to make many
remarks on this work, which Sir Isaac always received with the utmost
goodness, and the new edition appeared with numerous alterations in
1726. On the occasions upon which he had personal intercourse with Sir
Isaac, and which were necessarily numerous, he endeavoured to learn
his opinions on various mathematical subjects, and to obtain some
historical information respecting his inventions and discoveries. Sir
Isaac entered freely into all these topics and during the conversations
which took place, and while they were reading together Dr. Pemberton’s
popular account of Sir Isaac’s discoveries, he obtained the most
perfect evidence that, though his memory was much decayed, yet he was
fully able to understand his own writings.

During the last twenty years of his life, which he spent in London,
the charge of his domestic concerns devolved upon his beautiful and
accomplished niece, Mrs. Catharine Barton, the wife of Colonel Barton,
for whom, as we have already seen, the Earl of Halifax had conceived
the warmest affection. This lady, who had been educated at her uncle’s
expense, married Mr. Conduit, and continued to reside with her husband
in Sir Isaac’s house till the time of his death.

In the year 1722, when he had reached the eightieth year of his age, he
was seized with an incontinence of urine, which was ascribed to stone
in the bladder, and was considered incurable. By means of a strict
regimen, however, and other precautions, he was enabled to alleviate
his complaint, and to procure long intervals of ease. At this time he
gave up the use of his carriage, and always went out in a chair. He
declined all invitations to dinner, and at his own house he had only
small parties. In his diet he was extremely temperate. Though he took a
little butcher meat, yet the principal articles of his food were broth,
vegetables, and fruit, of which he always ate very heartily. In spite
of all his precautions, however, he experienced a return of his old
complaint, and in August, 1724, he passed a stone the size of a pea,
which came away in two pieces, the one at the distance of two days from
the other. After some months of tolerable good health, he was seized
in January, 1725, with a violent cough and inflammation of the lungs;
and in consequence of this attack, he was prevailed upon, with some
difficulty, to take up his residence at Kensington, where his health
experienced a decided improvement. In February, 1725, he was attacked
in both his feet with a fit of the gout, of which he had received a
slight warning a few years before, and the effect of this new complaint
was to produce a great and beneficial change in his general health. On
Sunday the 7th March, when his head was clearer and his memory stronger
than Mr. Conduit had known it to be for some time, he entered into a
long conversation on various subjects in astronomy. He explained to
Mr. Conduit how comets might be formed out of the light of vapours
discharged from the sun and the fixed stars as the centres of systems.
He conceived that these luminaries were replenished by the same comets
being again returned to them; and upon this principle he explained
the extraordinary lights which were seen among the fixed stars by
Hipparchus, Tycho Brahe, and Kepler’s disciples, and which he supposed
to arise from the additional fuel which they received.[122]

Notwithstanding the improvement which his health had experienced,
his indisposition was still sufficiently severe to unfit him for the
discharge of his duties at the mint; and as his old deputy was confined
with the dropsy, he was desirous in 1725 of resigning his office to
Mr. Conduit. Difficulties probably were experienced in making this
arrangement, but his nephew discharged for him all the duties of his
office; and during the last year of his life he hardly ever went to the
mint.

But though every kind of motion was calculated to aggravate his
complaint, and though he had derived from absolute rest and from
the air at Kensington the highest benefit, yet great difficulty was
experienced in preventing him from occasionally going to town. Feeling
himself able for the journey, he went to London on Tuesday the 28th of
February, 1727, to preside at a meeting of the Royal Society. On the
following day Mr. Conduit considered him better than he had been for
many years, and Sir Isaac was himself so sensible of this improvement
in his health, that he assured his nephew that on the Sunday preceding,
he had slept from eleven o’clock at night till eight o’clock next
morning without waking. He had undergone, however, great fatigue in
attending the meeting of the Royal Society, and in paying and receiving
visits, and the consequence of this was a violent return of his former
complaint. He returned to Kensington on Saturday the 4th March, and was
attended by Dr. Mead and Dr. Cheselden, who pronounced his disease to
be stone, and held out no hopes of his recovery. From the time of his
last journey to London he had experienced violent fits of pain with
very short intermissions; and though the drops of sweat ran down his
face during these severe paroxysms, yet he never uttered a cry or a
complaint, or displayed the least marks of peevishness or impatience;
but during the short intervals of relief which occurred, he smiled and
conversed with his usual gayety and cheerfulness. On Wednesday the 15th
of March he seemed a little better; and slight, though groundless hopes
were entertained of his recovery. On the morning of Saturday the 18th
he read the newspapers, and carried on a pretty long conversation with
Dr. Mead, when all his senses and faculties were strong and vigorous;
but at six o’clock of the same evening he became insensible, and he
continued in that state during the whole of Sunday, and till Monday the
20th, when he expired between one and two o’clock in the morning, in
the eighty-fifth year of his age.

His body was removed from Kensington to London, and on Tuesday the
28th March it lay in state in the Jerusalem Chamber, and was thence
conveyed to Westminster Abbey, where it was buried near the entrance
into the choir on the left-hand. The pall was supported by the Lord
High Chancellor, the Dukes of Roxburghe and Montrose, and the Earls
of Pembroke, Sussex, and Macclesfield, who were Fellows of the Royal
Society. The Hon. Sir Michael Newton, Knight of the Bath, was chief
mourner, and was followed by some other relations, and several
distinguished characters who were intimately acquainted with the
deceased. The funeral service was performed by the Bishop of Rochester,
attended by the prebend and choir.

Sensible of the high honour which they derived from their connexion
with so distinguished a philosopher, the relations of Sir Isaac Newton
who inherited his personal estate,[123] agreed to devote 500_l._ to
the erection of a monument to his memory, and the dean and chapter
of Westminster appropriated for it a place in the most conspicuous
part of the Abbey, which had often been refused to the greatest of
our nobility. This monument was erected in 1731. On the front of a
sarcophagus resting on a pedestal are sculptured in basso-relievo
youths bearing in their hands the emblems of Sir Isaac’s principal
discoveries. One carries a prism, another a reflecting telescope, a
third is weighing the sun and planets with a steelyard, a fourth is
employed about a furnace, and two others are loaded with money newly
coined. On the sarcophagus is placed the figure of Sir Isaac in a
cumbent posture, with his elbow resting on several of his works. Two
youths stand before him with a scroll, on which is drawn a remarkable
diagram relative to the solar system, and above that is a converging
series. Behind the sarcophagus is a pyramid, from the middle of
which rises a globe in mezzo-relievo, upon which several of the
constellations are drawn, in order to show the path of the comet of
1681, whose period Sir Isaac had determined, and also the position of
the solstitial colure mentioned by Hipparchus, and by means of which
Sir Isaac had, in his Chronology, fixed the time of the Argonautic
expedition. A figure of Astronomy as Queen of the Sciences sits
weeping on the Globe with a sceptre in her hand, and a star surmounts
the summit of the pyramid. The following epitaph is inscribed on the
monument.

                             Hic situs est
                     Isaacus Newton, Eques Auratus,
                       Qui Animi Vi prope divina,
                       Planetarum Motus, Figuras,
                  Cometarum Semitas, Oceanique Æstus,
                     Sua Mathesi facem preferente,
                          Primus demonstravit.
                    Radiorum Lucis dissimilitudines,
                Colorumque inde nascentium Proprietates,
          Quas nemo antea vel suspicatus erat, pervestigavit,
                  Naturæ, Antiquitates, S. Scripturæ,
                    Sedulus, sagax, fidus Interpres,
             Dei Opt. Max. Majestatem Philosophia asseruit,
               Evangelii simplicitatem moribus expressit.
          Sibi gratulentur Mortales, tale tantumque extitisse,
                         HUMANI GENERIS DECUS.
              Natus xxv. Decemb. MDCXLII. Obiit. xx. Mar.
                               MDCCXXVII.

Of which the following is a literal translation:

                               Here lies
                         Isaac Newton, Knight,
             Who, by a Vigour of Mind almost supernatural,
                           First demonstrated
                The Motions and Figures of the Planets,
          The Paths of the Comets, and the Tides of the Ocean.
                       He diligently investigated
          The different Refrangibilities of the Rays of Light,
       And the Properties of the Colours to which they give rise.
           An assiduous, sagacious, and faithful Interpreter
             Of Nature, Antiquity, and the Holy Scriptures,
           He asserted in his Philosophy the Majesty of God,
       And exhibited in his conduct the Simplicity of the Gospel.
                          Let Mortals rejoice
                That there has existed such and so great
                      AN ORNAMENT OF HUMAN NATURE.
              Born 25th Dec. 1642, Died 20th March, 1727.

In the beginning of 1731, a medal was struck at the Tower in honour
of Sir Isaac Newton. It had on one side the head of the philosopher,
with the motto, _Felix cognoscere causas_, and on the reverse a figure
representing the mathematics.

On the 4th February, 1755, a magnificent full-length statue of Sir
Isaac Newton in white marble was erected in the antechapel of Trinity
College. He is represented standing on a pedestal in a loose gown,
holding a prism, and looking upwards with an expression of the deepest
thought. On the pedestal is the inscription,

    Qui genus humanum ingenio superavit.
      Who surpassed all men in genius.

This statue, executed by Roubiliac, was erected at the expense of
Dr. Robert Smith, the author of the _Compleat System of Optics_, and
professor of astronomy and experimental philosophy at Cambridge.—It has
been thus described by a modern poet:

    Hark where the organ, full and clear,
    With loud hosannas charms the ear;
    Behold, a prism within his hands,
    Absorbed in thought great Newton stands
    Such was his brow, and looks serene,
    His serious gait and musing mien,
    When taught on eagle wings to fly,
    He traced the wonders of the sky;
    The chambers of the sun explored,
    Where tints of thousand hues were stored.

Dr. Smith likewise bequeathed the sum of 500_l._ for executing a
painting on glass for the window at the south end of Trinity College,
Cambridge. The subject represents the presentation of Sir Isaac Newton
to his majesty George III., who is seated under a canopy with a laurel
chaplet in his hand, and attended by the British Minerva, apparently
advising him to reward merit in the person of the great philosopher.
Below the throne, the Lord Chancellor Bacon is proposing to register
the reward about to be conferred upon Sir Isaac. The original drawing
of this absurd picture was executed by Cypriani, and cost one hundred
guineas.

The personal estate of Sir Isaac Newton, which was worth about
32,000_l._, was divided among his four nephews and four nieces of the
half-blood, the grandchildren of his mother by the Reverend Mr. Smith.
The family estates of Woolsthorpe and Sustern he bequeathed to John
Newton, the heir-at-law, whose great-grandfather was Sir Isaac’s uncle.
This gentleman does not seem to have sufficiently valued the bequest,
for he sold them in 1732, to Edmund Turnor of Stoke Rocheford.[124] A
short time before his death, Sir Isaac gave away an estate in Berkshire
to the sons and daughter of a brother of Mrs. Conduit, who, in
consequence of their father dying before Sir Isaac, had no share in the
personal estate; and he also gave an estate of the same value, which he
bought at Kensington, to Catharine, the only daughter of Mr. Conduit,
who afterward married Mr. Wallop, the eldest son of Lord Lymington.
This lady was afterward Viscountess Lymington, and the estate of
Kensington descended to the late Earl of Portsmouth, by whom it was
sold. Sir Isaac was succeeded as master and warden in the mint by his
nephew, John Conduit, Esq., who wrote a treatise on the gold and silver
coin, and who died in 1737, leaving behind him his wife and daughter,
the former of whom died in 1739, in the 59th year of her age.




CHAPTER XIX.

  _Permanence of Newton’s Reputation—Character of his Genius—His
    Methods of Investigation similar to that used by Galileo—Error in
    ascribing his Discoveries to the Use of the Methods recommended by
    Lord Bacon—The Pretensions of the Baconian Philosophy examined—Sir
    Isaac Newton’s social Character—His great Modesty—The Simplicity of
    his Character—His religious and moral Character—His Hospitality and
    Mode of Life—His Generosity and Charity—His Absence—His personal
    Appearance—Statues and Pictures of him—Memorials and Recollections
    of him._


Such were the last days of Sir Isaac Newton, and such the last laurels
which were shed over his grave. A century of discoveries has since his
day been added to science; but brilliant as these discoveries are,
they have not obliterated the minutest of his labours, and have served
only to brighten the halo which encircles his name. The achievements
of genius, like the source from which they spring, are indestructible.
Acts of legislation and deeds of war may confer a high celebrity, but
the reputation which they bring is only local and transient; and while
they are hailed by the nation which they benefit, they are reprobated
by the people whom they ruin or enslave. The labours of science, on
the contrary, bear along with them no counterpart of evil. They are
the liberal bequests of great minds to every individual of their race,
and wherever they are welcomed and honoured they become the solace of
private life, and the ornament and bulwark of the commonwealth.

The importance of Sir Isaac Newton’s discoveries has been sufficiently
exhibited in the preceding chapters: the peculiar character of his
genius, and the method which he pursued in his inquiries, can be
gathered only from the study of his works, and from the history of
his individual labours. Were we to judge of the qualities of his mind
from the early age at which he made his principal discoveries, and
from the rapidity of their succession, we should be led to ascribe to
him that quickness of penetration, and that exuberance of invention,
which is more characteristic of poetical than of philosophical genius.
But we must recollect that Newton was placed in the most favourable
circumstances for the development of his powers. The flower of his
youth and the vigour of his manhood were entirely devoted to science.
No injudicious guardian controlled his ruling passion, and no ungenial
studies or professional toils interrupted the continuity of his
pursuits. His discoveries were, therefore, the fruit of persevering and
unbroken study; and he himself declared, that whatever service he had
done to the public was not owing to any extraordinary sagacity, but
solely to industry and patient thought.

Initiated early into the abstractions of geometry, he was deeply imbued
with her cautious spirit; and if his acquisitions were not made with
the rapidity of intuition, they were at least firmly secured; and the
grasp which he took of his subject was proportional to the mental
labour which it had exhausted. Overlooking what was trivial, and
separating what was extraneous, he bore down with instinctive sagacity
on the prominences of his subject, and having thus grappled with its
difficulties, he never failed to intrench himself in its strongholds.

To the highest powers of invention Newton added, what so seldom
accompanies them, the talent of simplifying and communicating his
profoundest speculations.[125] In the economy of her distributions,
nature is seldom thus lavish of her intellectual gifts. The inspired
genius which creates is rarely conferred along with the matured
judgment which combines, and yet without the exertion of both the
fabric of human wisdom could never have been reared. Though a ray from
heaven kindled the vestal fire, yet an humble priesthood was required
to keep alive the flame.

The method of investigating truth by observation and experiment, so
successfully pursued in the Principia, has been ascribed by some
modern writers of great celebrity to Lord Bacon; and Sir Isaac Newton
is represented as having owed all his discoveries to the application
of the principles of that distinguished writer. One of the greatest
admirers of Lord Bacon has gone so far as to characterize him as a
man who has had no rival in the times which are past, and as likely
to have none in those which are to come. In a eulogy so overstrained
as this, we feel that the language of panegyric has passed into that
of idolatry; and we are desirous of weighing the force of arguments
which tend to depose Newton from the high-priesthood of nature, and to
unsettle the proud destinies of Copernicus, Galileo, and Kepler.

That Bacon was a man of powerful genius, and endowed with varied
and profound talent,—the most skilful logician,—the most nervous
and eloquent writer of the age which he adorned, are points which
have been established by universal suffrage. The study of ancient
systems had early impressed him with the conviction that experiment
and observation were the only sure guides in physical inquiries; and,
ignorant though he was of the methods, the principles, and the details
of the mathematical sciences, his ambition prompted him to aim at the
construction of an artificial system by which the laws of nature might
be investigated, and which might direct the inquiries of philosophers
in every future age. The necessity of experimental research, and of
advancing gradually from the study of facts to the determination of
their cause, though the groundwork of Bacon’s method, is a doctrine
which was not only inculcated but successfully followed by preceding
philosophers. In a letter from Tycho Brahe to Kepler, this industrious
astronomer urges his pupil “to lay a solid foundation for his views
by actual observation, and then by ascending from these to strive to
reach the causes of things;” and it was no doubt under the influence of
this advice that Kepler submitted his wildest fancies to the test of
observation, and was conducted to his most splendid discoveries. The
reasonings of Copernicus, who preceded Bacon by more than a century,
were all founded upon the most legitimate induction. Dr. Gilbert had
exhibited in his treatise on the magnet[126] the most perfect specimen
of physical research. Leonardo da Vinci had described in the clearest
manner the proper method of philosophical investigation;[127] and
the whole scientific career of Galileo was one continued example of
the most sagacious application of observation and experiment to the
discovery of general laws. The names of Paracelsus, Van Helmont, and
Cardan have been ranged in opposition to this constellation of great
names, and while it is admitted that even they had thrown off the yoke
of the schools, and had succeeded in experimental research, their
credulity and their pretensions have been adduced as a proof that to
the “bulk of philosophers” the method of induction was unknown. The
fault of this argument consists in the conclusion being infinitely
more general than the fact. The errors of these men were not founded
on their ignorance, but on their presumption. They wanted the patience
of philosophy and not her methods. An excess of vanity, a waywardness
of fancy, and an insatiable appetite for that species of passing fame
which is derived from eccentricity of opinion, moulded the reasonings
and disfigured the writings of these ingenious men; and it can scarcely
admit of a doubt, that, had they lived in the present age, their
philosophical character would have received the same impress from the
peculiarity of their tempers and dispositions. This is an experiment,
however, which cannot now be made; but the history of modern science
supplies the defect, and the experience of every man furnishes a proof
that in the present age there are many philosophers of elevated talents
and inventive genius who are as impatient of experimental research as
Paracelsus, as fanciful as Cardan, and as presumptuous as Van Helmont.

Having thus shown that the distinguished philosophers who flourished
before Bacon were perfect masters both of the principles and practice
of inductive research, it becomes interesting to inquire whether or
not the philosophers who succeeded him acknowledged any obligation to
his system, or derived the slightest advantage from his precepts. If
Bacon constructed a method to which modern science owes its existence,
we shall find its cultivators grateful for the gift, and offering the
richest incense at the shrine of a benefactor whose generous labours
conducted them to immortality. No such testimonies, however, are to be
found. Nearly two hundred years have gone by, teeming with the richest
fruits of human genius, and no grateful disciple has appeared to
vindicate the rights of the alleged legislator of science. Even Newton,
who was born and educated after the publication of the Novum Organon,
never mentions the name of Bacon or his system, and the amiable and
indefatigable Boyle treated him with the same disrespectful silence.
When we are told, therefore, that Newton owed all his discoveries to
the method of Bacon, nothing more can be meant than that he proceeded
in that path of observation and experiment which had been so warmly
recommended in the Novum Organon; but it ought to have been added,
that the same method was practised by his predecessors,—that Newton
possessed no secret that was not used by Galileo and Copernicus,—and
that he would have enriched science with the same splendid discoveries
if the name and the writings of Bacon had never been heard of.

From this view of the subject we shall now proceed to examine the
Baconian process itself, and consider if it possesses any merit as an
artificial method of discovery, or if it is at all capable of being
employed, for this purpose, even in the humblest walks of scientific
inquiry.

The process of Lord Bacon was, we believe, never tried by any
philosopher but himself. As the subject of its application, he
selected that of heat. With his usual erudition, he collected all
the facts which science could supply,—he arranged them in tables,—he
cross-questioned them with all the subtlety of a pleader,—he combined
them with all the sagacity of a judge,—and he conjured with them by all
the magic of his exclusive processes. But, after all this display of
physical logic, nature thus interrogated was still silent. The oracle
which he had himself established refused to give its responses, and the
ministering priest was driven with discomfiture from his own shrine.
This example, in short, of the application of his system, will remain
to future ages as a memorable instance of the absurdity of attempting
to fetter discovery by any artificial rules.

Nothing even in mathematical science can be more certain than that a
collection of scientific facts are of themselves incapable of leading
to discovery, or to the determination of general laws, unless they
contain the predominating fact or relation in which the discovery
mainly resides. A vertical column of arch-stones possesses more
strength than the same materials arranged in an arch without the
key-stone. However nicely they are adjusted, and however nobly the arch
may spring, it never can possess either equilibrium or stability. In
this comparison all the facts are supposed to be necessary to the final
result; but, in the inductive method, it is impossible to ascertain the
relative importance of any facts, or even to determine if the facts
have any value at all, till the master-fact which constitutes the
discovery has crowned the zealous efforts of the aspiring philosopher.
The mind then returns to the dark and barren waste over which it has
been hovering; and by the guidance of this single torch it embraces,
under the comprehensive grasp of general principles, the multifarious
and insulated phenomena which had formerly neither value nor
connexion. Hence it must be obvious to the most superficial thinker,
that discovery consists either in the detection of some concealed
relation—some deep-seated affinity which baffles ordinary research,
or in the discovery of some simple fact which is connected by slender
ramifications with the subject to be investigated; but which, when once
detected, carries us back by its divergence to all the phenomena which
it embraces and explains.

In order to give additional support to these views, it would be
interesting to ascertain the general character of the process by
which a mind of acknowledged power actually proceeds in the path of
successful inquiry. The history of science does not furnish us with
much information on this head, and if it is to be found at all, it must
be gleaned from the biographies of eminent men. Whatever this process
may be in its details, if it has any, there cannot be the slightest
doubt that in its generalities at least it is the very reverse of the
method of induction. The impatience of genius spurns the restraints of
mechanical rules, and never will submit to the plodding drudgery of
inductive discipline. The discovery of a new fact unfits even a patient
mind for deliberate inquiry. Conscious of having added to science
what had escaped the sagacity of former ages, the ambitious spirit
invests its new acquisition with an importance which does not belong
to it. He imagines a thousand consequences to flow from his discovery:
he forms innumerable theories to explain it, and he exhausts his
fancy in trying all its possible relations to recognised difficulties
and unexplained facts. The reins, however, thus freely given to his
imagination, are speedily drawn up. His wildest conceptions are all
subjected to the rigid test of experiment, and he has thus been hurried
by the excursions of his own fancy into new and fertile paths, far
removed from ordinary observation. Here the peculiar character of his
own genius displays itself by the invention of methods of trying his
own speculations, and he is thus often led to new discoveries far more
important and general than that by which he began his inquiry. For a
confirmation of these views, we may refer to the History of Kepler’s
Discoveries; and if we do not recognise them to the same extent in the
labours of Newton, it is because he kept back his discoveries till
they were nearly perfected, and therefore withheld the successive steps
of his inquiries.

The social character of Sir Isaac Newton was such as might have been
expected from his intellectual attainments. He was modest, candid,
and affable, and without any of the eccentricities of genius, suiting
himself to every company, and speaking of himself and others in such
a manner that he was never even suspected of vanity. “But this,”
says Dr. Pemberton, “I immediately discovered in him, which at once
both surprised and charmed me. Neither his extreme great age nor his
universal reputation had rendered him stiff in opinion, or in any
degree elated. Of this I had occasion to have almost daily experience.
The remarks I continually sent him by letters on the Principia were
received with the utmost goodness. These were so far from being any
ways displeasing to him, that on the contrary it occasioned him to
speak many kind things of me to my friends, and to honour me with a
public testimony of his good opinion.”

The modesty of Sir Isaac Newton in reference to his great discoveries
was not founded on any indifference to the fame which they conferred,
or upon any erroneous judgment of their importance to science. The
whole of his life proves, that he knew his place as a philosopher,
and was determined to assert and vindicate his rights. His modesty
arose from the depth and extent of his knowledge, which showed him
what a small portion of nature he had been able to examine, and how
much remained to be explored in the same field in which he had himself
laboured. In the magnitude of the comparison he recognised his own
littleness; and a short time before his death he uttered this memorable
sentiment:—“I do not know what I may appear to the world; but to
myself I seem to have been only like a boy playing on the seashore,
and diverting myself in now and then finding a smoother pebble or a
prettier shell than ordinary, while the great ocean of truth lay all
undiscovered before me.” What a lesson to the vanity and presumption
of philosophers,—to those especially who have never even found the
smoother pebble or the prettier shell! What a preparation for the
latest inquiries, and the last views of the decaying spirit,—for those
inspired doctrines which alone can throw a light over the dark ocean of
undiscovered truth!

The native simplicity of Sir Isaac Newton’s mind is finely portrayed
in the affecting letter in which he acknowledges to Locke that he had
thought and spoken of him uncharitably; and the humility and candour in
which he asks forgiveness could have emanated only from a mind as noble
as it was pure.

In the religious and moral character of our author there is much to
admire and to imitate. While he exhibited in his life and writings an
ardent regard for the general interests of religion, he was at the same
time a firm believer in revelation. He was too deeply versed in the
Scriptures, and too much imbued with their spirit, to judge harshly of
other men who took different views of them from himself. He cherished
the great principles of religious toleration, and never scrupled to
express his abhorrence of persecution, even in its mildest form.
Immorality and impiety he never permitted to pass unreproved; and when
Dr. Halley[128] ventured to say any thing disrespectful to religion,
he invariably checked him, and said, “I have studied these things,—you
have not.”[129]

After Sir Isaac Newton took up his residence in London, he lived in
a very handsome style, and kept his carriage, with an establishment
of three male and three female servants. In his own house he was
hospitable and kind, and on proper occasions he gave splendid
entertainments, though without ostentation or vanity. His own diet was
frugal, and his dress was always simple; but on one occasion, when he
opposed the Honourable Mr. Annesley in 1705, as a candidate for the
university, he is said to have put on a suit of laced clothes.

His generosity and charity had no bounds, and he used to remark, that
they who gave away nothing till they died never gave at all. Though his
wealth had become considerable by a prudent economy, yet he had always
a contempt for money, and he spent a considerable part of his income
in relieving the poor, in assisting his relations, and in encouraging
ingenuity and learning. The sums which he gave to his relations at
different times were enormous;[130] and in 1724 he wrote a letter to
the Lord Provost of Edinburgh, offering to contribute 20_l._ per annum
to a provision for Mr. Maclaurin, provided he accepted the situation of
assistant to Mr. James Gregory, who was professor of mathematics in the
university.

The habits of deep meditation which Sir Isaac Newton had acquired,
though they did not show themselves in his intercourse with society,
exercised their full influence over his mind when in the midst of
his own family. Absorbed in thought he would often sit down on his
bedside after he rose, and remain there for hours without dressing
himself, occupied with some interesting investigation which had fixed
his attention. Owing to the same absence of mind, he neglected to take
the requisite quantity of nourishment, and it was therefore often
necessary to remind him of his meals.[131]

Sir Isaac Newton is supposed to have had little knowledge of the world,
and to have been very ignorant of the habits of society. This opinion
has, we think, been rashly deduced from a letter which he wrote in the
twenty-seventh year of his age to his young friend, Francis Aston,
Esq., who was about to set out on his travels. This letter is a highly
interesting production; and while it shows much knowledge of the human
heart, it throws a strong light upon the character and opinions of its
author.

In his personal appearance, Sir Isaac Newton was not above the
middle size, and in the latter part of his life was inclined to be
corpulent. According to Mr. Conduit “he had a very lively and piercing
eye, a comely and gracious aspect, with a fine head of hair as white
as silver, without any baldness, and when his peruke was off was a
venerable sight.” Bishop Atterbury asserts,[132] on the other hand,
that the lively and piercing eye did not belong to Sir Isaac during the
last twenty years of his life. “Indeed,” says he, “in the whole air
of his face and make there was nothing of that penetrating sagacity
which appears in his compositions. He had something rather languid in
his look and manner which did not raise any great expectation in those
who did not know him.” This opinion of Bishop Atterbury is confirmed
by an observation of Mr. Thomas Hearne,[133] who says “that Sir Isaac
was a man of no very promising aspect. He was a short, well-set man.
He was full of thought, and spoke very little in company, so that his
conversation was not agreeable. When he rode in his coach, one arm
would be out of his coach on one side and the other on the other.” Sir
Isaac never wore spectacles, and never “lost more than one tooth to the
day of his death.”

Besides the statue of Sir Isaac Newton executed by Roubiliac, there is
a bust of him by the same artist in the library of Trinity College,
Cambridge. Several good paintings of him are extant. Two of these are
in the hall of the Royal Society of London, and have, we believe, been
often engraved. Another, by Vanderbank, is in the apartments of the
Master’s lodge in Trinity College, and has been engraved by Vertue.
Another, by Valentine Ritts, is in the landing-place near the entrance
to Trinity College library; but the best, from which our engraving is
copied, was painted by Sir Godfrey Kneller, and is in the possession of
Lord Egremont at Petworth. In the university library there is preserved
a cast taken from his face after death.

Every memorial of so great a man as Sir Isaac Newton has been preserved
and cherished with peculiar veneration. His house at Woolsthorpe,
of which we have given an engraving, has been religiously protected
by Mr. Turnor of Stoke Rocheford, the proprietor. Dr. Stukeley, who
visited it in Sir Isaac’s lifetime, on the 13th October, 1721, gives
the following description of it in his letter to Dr. Mead, written in
1727: “’Tis built of stone as is the way of the country hereabouts, and
a reasonable good one. They led me up stairs and showed me Sir Isaac’s
study, where I suppose he studied when in the country in his younger
days, or perhaps when he visited his mother from the university. I
observed the shelves were of his own making, being pieces of deal
boxes which probably he sent his books and clothes down in on those
occasions. There were some years ago two or three hundred books in it
of his father-in-law, Mr. Smith, which Sir Isaac gave to Dr. Newton of
our town.”[134]

When the house was repaired in 1798, a tablet of white marble was
put up by Mr. Turnor in the room where Sir Isaac was born, with the
following inscription:

“Sir Isaac Newton, son of John Newton, Lord of the manor of
Woolsthorpe, was born in this room on the 25th December, 1642.”

    Nature and Nature’s laws lay hid in night,
    God said, “Let Newton be,” and all was light.

The following lines have been written upon the house:

    Here Newton dawned, here lofty wisdom woke,
    And to a wondering world divinely spoke.
    If Tully glowed, when Phædrus’ steps he trode,
    Or fancy formed Philosophy a god;
    If sages still for Homer’s birth contend
    The Sons of Science at this dome must bend.
    All hail the shrine! All hail the natal day,
    Cam boasts his noon,—This _Cot_ his morning ray.

The house is now occupied by a person of the name of John Wollerton. It
still contains the two dials made by Newton, but the styles of both are
wanting. The celebrated apple-tree, the fall of one of the apples of
which is said to have turned the attention of Newton to the subject of
gravity, was destroyed by wind about four years ago; but Mr. Turnor has
preserved it in the form of a chair.[135]

The chambers which Sir Isaac inhabited at Cambridge are known by
tradition. They are the apartments next to the great gate of Trinity
College, and it is believed that they then communicated by a staircase
with the observatory in the Great Tower,—an observatory which was
furnished by the contributions of Newton, Cotes, and others. His
telescope, represented in _fig. 3_, page 41, is preserved in the
library of the Royal Society of London, and his globe, his universal
ring-dial, quadrant, compass, and a reflecting telescope said to have
belonged to him, in the library of Trinity College. There is also in
the same collection a long and curled lock of his silver white hair.
The door of his bookcase is in the Museum of the Royal Society of
Edinburgh.

The manuscripts, letters, and other papers of Newton have been
preserved in different collections. His correspondence with Cotes
relative to the second edition of the Principia, and amounting to
between sixty and a hundred letters, a considerable portion of the
manuscript of that work, and two or three letters to Dr. Keill on
the Leibnitzian controversy, are preserved in the library of Trinity
College, Cambridge. Newton’s letters to Flamstead, about thirty-four
in number, are deposited in the library of Corpus Christi College,
Oxford.[136] Several letters of Newton, and, we believe, the original
specimen which he drew up of the Principia, exist among the papers
of Mr. William Jones (the father of Sir William Jones), which are
preserved at Shirburn Castle, in the library of Lord Macclesfield.
But the great mass of Newton’s papers came into the possession of the
Portsmouth family through his niece, Lady Lymington, and have been
safely preserved by that noble family. There is reason to believe that
they contain nothing which could be peculiarly interesting to science;
but as the correspondence of Newton with contemporary philosophers must
throw considerable light on his personal history, we trust that it will
ere long be given to the public.




APPENDIX.




No. I.

OBSERVATIONS ON THE FAMILY OF SIR ISAAC NEWTON.


In the year 1705, Sir Isaac gave into the Herald’s Office an elaborate
pedigree, stating upon oath _that he had reason to believe_ that John
Newton of Westby, in the county of Lincoln, was his great-grandfather’s
father, and that this was the same John Newton who was buried in
Basingthorpe church, on the 22d December, 1563. This John Newton had
four sons, John, Thomas, Richard, and William Newton of Gunnerly,
the last of whom was great-grandfather to Sir John Newton, Bart., of
Hather. Sir Isaac considered himself as descended from the eldest of
these, _he having, by tradition from his kindred ever since he can
remember, reckoned himself next of kin (among the Newtons) to Sir John
Newton’s family_.

The pedigree, founded upon these and other considerations, was
accompanied by a certificate from Sir John Newton, of Thorpe, Bart.,
who states that he had heard his father speak of Sir Isaac Newton _as
of his relation and kinsman_, and that _he himself believed that Sir
Isaac was descended from John Newton, son to John Newton of Westby, but
knoweth not in what particular manner_.

The pedigree of Sir Isaac, as entered at the Herald’s Office, does not
seem to have been satisfactory either to himself or to his successors,
as it could not be traced with certainty beyond his grandfather; and
it will be seen from the following interesting correspondence, that
upon making further researches, he had found some reason to believe
that he was of Scotch extraction.


  _Extract of a Letter from the Reverend Dr. Reid of Glasgow to Dr.
    Gregory of Edinburgh, dated 14th March, 1784._

  “I send you on the other page an anecdote respecting Sir Isaac
  Newton, which I do not remember whether I ever happened to mention
  to you in conversation. If his descent be not clearly ascertained
  (as I think it is not in the books I have seen), might it not be
  worth while to inquire if evidence can be found to confirm the
  account which he is said to have given of himself. Sheriff Cross
  was very zealous about it when death put a stop to his inquiries.

  “When I lived in old Aberdeen above twenty years ago, I happened
  to be conversing over a pipe of tobacco with a gentleman of that
  country, who had been lately at Edinburgh. He told me that he had
  been often in company with Mr. Hepburn of Keith, with whom I had
  the honour of some acquaintance. He said that, speaking of Sir
  Isaac Newton, Mr. Hepburn mentioned an anecdote, which he had from
  Mr. James Gregory, professor of mathematics at Edinburgh, which was
  to this purpose:

  “Mr. Gregory, being at London for some time after he resigned the
  mathematical chair, was often with Sir Isaac Newton. One day Sir
  Isaac said to him, ‘Gregory, I believe you don’t know that I am
  connected with Scotland.’—‘Pray how, Sir Isaac?’ said Gregory. Sir
  Isaac said he was told that his grandfather was a gentleman of East
  Lothian; that he came to London with King James at his accession to
  the crown of England, and there spent his fortune, as many more
  did at that time, by which his son (Sir Isaac’s father) was reduced
  to mean circumstances. To this Gregory bluntly replied, ‘Newton a
  gentleman of East Lothian, I never heard of a gentleman of East
  Lothian of that name.’ Upon this Sir Isaac said, ‘that being very
  young when his father died, he had it only by tradition, and it
  might be a mistake;’ and immediately turned the conversation to
  another subject.

  “I confess I suspected that the gentleman who was my author had
  given some colouring to this story, and therefore I never mentioned
  it for a good many years.

  “After I removed to Glasgow, I came to be very intimately
  acquainted with Mr. Cross, then sheriff of Lanark, and one day at
  his own house mentioned this story, without naming my author, of
  whom I expressed some diffidence.

  “The sheriff immediately took it up as a matter worth being
  inquired into. He said he was well acquainted with Mr. Hepburn
  of Keith (who was then alive), and that he would write him to
  know whether he ever heard Mr. Gregory say that he had such a
  conversation with Sir Isaac Newton. He said he knew that Mr. Keith,
  the ambassador, was also intimate with Mr. Gregory, and that he
  would write him to the same purpose.

  “Some time after, Mr. Cross told me that he had answers from both
  the gentlemen above mentioned, and that both remembered to have
  heard Mr. Gregory mention the conversation between him and Sir
  Isaac Newton, to the purpose above narrated, and at the same time
  acknowledged that they had made no further inquiry about the matter.

  “Mr. Cross, however, continued the inquiry, and a short time before
  his death told me that all he had learned was, that there is,
  or was lately, a baronet’s family of the name of Newton in West
  Lothian or Mid Lothian (I have forgot which): that there is a
  tradition in that family that Sir Isaac Newton wrote a letter to
  the old knight that then was (I think Sir John Newton of Newton was
  his name), desiring to know what children, and particularly what
  sons he had, their age, and what professions they intended: that
  the old baronet never deigned to return an answer to this letter,
  which his family was sorry for, as they thought Sir Isaac might
  have intended to do something for them.”

Several years after this letter was written, a Mr. Barron, a relation
of Sir Isaac Newton, seems to have been making inquiries respecting the
family of his ancestor, and in consequence of this the late Professor
Robison applied to Dr. Reid, to obtain from him a more particular
account of the remarkable conversation between Sir Isaac and Mr.
James Gregory referred to in the preceding letter. In answer to this
request, Dr. Reid wrote the following letter, for which I was indebted
to John Robison, Esq. Sec. R. S. E., who found it among his father’s
manuscripts.


  _Letter from Dr. Reid to Professor Robison respecting the Family of
    Sir Isaac Newton._

    “DEAR SIR,

  “I am very glad to learn by yours of April 4, that a Mr. Barron, a
  near relation of Sir Isaac Newton, is anxious to inquire into the
  descent of that great man, as the family cannot trace it farther,
  with any certainty, than his grandfather. I therefore, as you
  desire, send you a precise account of all I know; and am glad to
  have this opportunity, before I die, of putting this information in
  hands that will make the proper use of it, if it shall be found of
  any use.

  “Several years before I left Aberdeen (which I did in 1764), Mr.
  Douglas of Feckel, the father of Sylvester Douglas, now a barrister
  at London, told me, that having been lately at Edinburgh, he
  was often in company with Mr. Hepburn of Keith, a gentleman of
  whom I had some acquaintance, by his lodging a night at my house
  at New Machar, when he was in the rebel army in 1745. That Mr.
  Hepburn told him that he had heard Mr. James Gregory, professor
  of mathematics, Edinburgh, say, that being one day in familiar
  conversation with Sir Isaac Newton at London, Sir Isaac said,
  ‘Gregory, I believe you don’t know that I am a Scotchman.’—‘Pray,
  how is that?’ said Gregory. Sir Isaac said he was informed that
  his grandfather (or great-grandfather) was a gentleman of East (or
  West) Lothian: that he went to London with King James the I. at his
  accession to the crown of England: and that he attended the court
  in expectation, as many others did, until he spent his fortune, by
  which means his family was reduced to low circumstances. At the
  time this was told me Mr. Gregory was dead, otherwise I should have
  had his own testimony, for he was my mother’s brother. I likewise
  thought at that time that it had been certainly known that Sir
  Isaac had been descended from an old English family, as I think
  is said in his _eloge_ before the Academy of Sciences at Paris,
  and therefore I never mentioned what I had heard for many years,
  believing that there must be some mistake in it.

  “Some years after I came to Glasgow, I mentioned (I believe for
  the first time) what I had heard to have been said by Mr. Hepburn
  to Mr. Cross, late sheriff of this county, whom you will remember.
  Mr. Cross was moved by this account, and immediately said, ‘I know
  Mr. Hepburn very well, and I know he was intimate with Mr. Gregory:
  I shall write him this same night, to know whether he heard Mr.
  Gregory say so or not.’ After some reflection, he added, ‘I know
  that Mr. Keith, the ambassador, was also an intimate acquaintance
  of Mr. Gregory, and as he is at present in Edinburgh, I shall
  likewise write to him this night.’

  “The next time I waited on Mr. Cross he told me that he had wrote
  both to Mr. Hepburn and Mr. Keith, and had an answer from both, and
  that both of them testified that they had several times heard Mr.
  James Gregory say, that Sir Isaac Newton told him what is above
  expressed, but that neither they nor Mr. Gregory, as far as they
  knew, ever made any further inquiry into the matter. This appeared
  very strange both to Mr. Cross and me, and he said he would
  reproach them for their indifference, and would make inquiry as
  soon as he was able.

  “He lived but a short time after this, and in the last conversation
  I had with him upon the subject, he said, that all he had yet
  learned was, that there was a Sir John Newton of Newton in one of
  the counties of Lothian (but I have forgot which), some of whose
  children were yet alive: that they reported that their father, Sir
  John, had a letter from Sir Isaac Newton, desiring to know the
  state of his family, what children he had, particularly what sons,
  and in what way they were. The old knight never returned an answer
  to this letter, thinking probably that Sir Isaac was some upstart,
  who wanted to claim a relation to his worshipful house. This
  omission the children regretted, conceiving that Sir Isaac might
  have had a view of doing something for their benefit.

  “After this I mentioned occasionally in conversation what I knew,
  hoping that these facts might lead to some more certain discovery,
  but I found more coldness about the matter than I thought it
  deserved. I wrote an account of it to Dr. Gregory, your colleague,
  that he might impart it to any member of the Antiquarian Society
  who he judged might have the curiosity to trace the matter further.

  “In the year 1787, my colleague, Mr. Patrick Wilson, professor
  of astronomy, having been in London, told me on his return that
  he had met accidentally with a James Hutton, Esq. of Pimlico,
  Westminster, a near relation of Sir Isaac Newton,[137] to whom he
  mentioned what he had heard from me with respect to Sir Isaac’s
  descent, and that I wished much to know something more decisive
  on that subject. Mr. Hutton said, if I pleased to write to him
  he would give me all the information he could give. I wrote him
  accordingly, and had a very polite answer, dated at Bath, 25th
  December, 1787, which is now before me. He says, ‘I shall be glad
  when I return to London, if I can find in some old notes of my
  mother any thing that may fix the certainty of Sir Isaac’s descent.
  If he spoke so to Mr. James Gregory, it is most certain he spoke
  truth. But Sir Isaac’s grandfather, not his great-grandfather, must
  be the person who came from Scotland with King James I. If I find
  any thing to the purpose, I will take care it shall reach you.’

  “In consequence of this letter I expected another from Mr. Hutton
  when he should return to London, but have never had any. Mr. Wilson
  told me he was a very old man, and whether he be dead or alive I
  know not.

  “This is all I know of the matter, and for the facts above
  mentioned I pledge my veracity. I am much obliged to you, dear sir,
  for the kind expressions of your affection and esteem, which, I
  assure you, are mutual on my part, and I sincerely sympathize with
  you on your afflicting state of health, which makes you consider
  yourself as out of the world, and despair of seeing me any more.

  “I have been long out of the world by deafness and extreme old age.
  I hope, however, if we should not meet again in this world, that we
  shall meet and renew our acquaintance in another. In the mean time,
  I am with great esteem, dear sir, yours affectionately,

            “THO. REID.

    “_Glasgow College_,
    ”_12th April, 1792_.”

This curious letter I published in the Ed. Phil. Journal for October 1,
1820. It excited the particular attention of the late George Chalmers,
Esq., who sent me an elaborate letter upon the subject; but as I was at
that time in the expectation of obtaining some important information
through other channels, this letter was not published. This hope,
however, has been disappointed. A careful search has been made through
the charter-chest of the Newtons of Newton in East Lothian, by Mr.
Richard Hay Newton, the representative of that family, but no document
whatever has been found that can throw the least light upon the matter.
It deserves to be remarked, however, that Sir Richard Newton, the
alleged correspondent of Sir Isaac, appears to have destroyed his
correspondence; for though the charter-chest contains the letters
of his predecessors for some generations, yet there is not a single
epistolary document either of his own or of his lady’s.

Hitherto the evidence of Sir Isaac’s Scottish descent has been derived
chiefly from his conversation with Mr. James Gregory; but I am enabled,
by the kindness of Mr. Robison, to corroborate this evidence by the
following information, derived, as will be seen, from the family of
the Newtons of Newton. Among various memoranda in the handwriting of
Professor Robison, who at one time proposed to write the life of Sir
Isaac, are the following:—

“1st, Lord Henderland informed me in a letter dated March, 1794,
that he had heard from his infancy that Sir Isaac considered himself
as descended from the family of Newton of Newton. This he heard
from his uncle Richard Newton of Newton (who was third son of Lord
William Hay of Newhall):” “He said that Sir Isaac wrote to Scotland
to learn whether any descendants of that family remained, and this
(it was thought) with the view to leave some of his fortune to the
family possessing the estate with the title of baronet. Mr. Newton,
not having this honour, and being a shy man, did not encourage the
correspondence, because he did not consider _himself_ as of kin to Sir
Isaac, &c.”

“2d, Information communicated to me by Hay Newton, Esq., of that ilk,
18th August, 1800.”

“The late Sir Richard Newton of Newton, Bart., chief of that name,
having no male children, settled the estate and barony of Newton in
East Lothian county upon his relation Richard Hay Newton, Esq., son
of Lord William Hay.”[138]—“It cannot be discovered how long the
family of Newton have been in possession of the barony, there being
no tradition concerning that circumstance further than that they came
originally from England at a very distant period, and settled on these
lands.”—“The celebrated Sir Isaac Newton was a distant relation of the
family, and corresponded with the last baronet, the above-mentioned Sir
Richard Newton.”

The preceding documents furnish the most complete evidence that the
conversation respecting Sir Isaac Newton’s family took place between
him and Mr. Gregory; and the testimony of Lord Henderland proves that
his own uncle, Richard Newton of Newton, the immediate successor of
Sir Richard Newton, with whom Sir Isaac corresponded, was perfectly
confident that such a correspondence took place.

All these circumstances prove that Sir Isaac Newton could not trace
his pedigree with any certainty beyond his grandfather, and that there
were two different traditions in his family,—one which referred his
descent to John Newton of Westby, and the other to a gentleman of East
Lothian who accompanied King James VI. to England. In the first of
these traditions he seems to have placed most confidence in 1705, when
he drew out his traditionary pedigree; but as the conversation with
Professor James Gregory respecting his Scotch extraction took place
_twenty years_ afterward, namely, between 1725 and 1727, it is probable
that he had discovered the incorrectness of his first opinions, or at
least was disposed to attach more importance to the other tradition
respecting his descent from a Scotch family.

In the letter addressed to me by the learned George Chalmers, Esq. I
find the following observations respecting the immediate relations of
Sir Isaac. “The Newtons of Woolsthorpe,” says he, “who were merely
yeomen farmers, were not by any means opulent. The son of Sir Isaac’s
father’s brother was a carpenter called John. He was afterward
appointed gamekeeper to Sir Isaac, as lord of the manor, and died at
the age of sixty in 1725. This John had a son, Robert, (John?) who was
Sir Isaac’s second cousin, and who became possessed of the whole land
estates at and near Woolsthorpe, which belonged to the great Newton, as
his heir-at-law.[139] Robert (John?) became a worthless and dissolute
person, who very soon wasted this ancient patrimony, and falling down
with a tobacco-pipe in his mouth when he was drunk, it broke in his
throat, and put an end to his life at the age of thirty years, in 1737.”




No. II.

  LETTER FROM SIR ISAAC NEWTON TO FRANCIS ASTON, ESQ., A YOUNG FRIEND
    WHO WAS ON THE EVE OF SETTING OUT UPON HIS TRAVELS.


Mr. Aston was elected a Fellow of the Royal Society in 1678. He held
the office of Secretary between 1681 and 1685; and he was the author
of some observations on certain unknown ancient characters, which were
published in the Philosophical Transactions for 1693.

This letter has been referred to in pages 270 and 303, and was written
when Newton was only twenty-six years of age. It is in every respect an
interesting document.

        “_Trinity College, Cambridge,
            May 18, 1669._

    “SIR,

  “Since in your letter you give mee so much liberty of spending
  my judgement about what may be to your advantage in travelling,
  I shall do it more freely than perhaps otherwise would have been
  decent. First, then, I will lay down some general rules, most of
  which, I believe, you have considered already; but if any of them
  be new to you, they may excuse the rest; if none at all, yet is my
  punishment more in writing than yours in reading.

  “When you come into any fresh company, 1. Observe their humours. 2.
  Suit your own carriage thereto, by which insinuation you will make
  their converse more free and open. 3. Let your discours be more in
  querys and doubtings than peremptory assertions or disputings, it
  being the designe of travellers to learne, not to teach. Besides,
  it will persuade your acquaintance that you have the greater
  esteem of them, and soe make them more ready to communicate what
  they know to you; whereas nothing sooner occasions disrespect and
  quarrels than peremtorinesse. You will find little or no advantage
  in seeming wiser or much more ignorant than your company. 4. Seldom
  discommend any thing though never so bad, or doe it but moderately,
  lest you bee unexpectedly forced to an unhansom retraction. It
  is safer to commend any thing more than it deserves, than to
  discommend a thing soe much as it deserves; for commendations meet
  not soe often with oppositions, or, at least, are not usually soe
  ill resented by men that think otherwise, as discommendations;
  and you will insinuate into men’s favour by nothing sooner than
  seeming to approve and commend what they like; but beware of doing
  it by a comparison. 5. If you bee affronted, it is better, in
  a forraine country, to pass it by in silence, and with a jest,
  though with some dishonour, than to endeavour revenge; for, in the
  first case, your credit’s ne’er the worse when you return into
  England, or come into other company that have not heard of the
  quarrell. But, in the second case, you may beare the marks of the
  quarrell while you live, if you outlive it at all. But, if you
  find yourself unavoidably engaged, ’tis best, I think, if you can
  command your passion and language, to keep them pretty evenly at
  some certain moderate pitch, not much hightning them to exasperate
  your adversary, or provoke his friends, nor letting them grow
  overmuch dejected to make him insult. In a word, if you can keep
  reason above passion, that and watchfullnesse will be your best
  defendants. To which purpose you may consider, that, though such
  excuses as this,—He provok’t mee so much I could not forbear,—may
  pass among friends, yet amongst strangers they are insignificant,
  and only argue a traveller’s weaknesse.

  “To these I may add some general heads for inquirys or
  observations, such as at present I can think on. As, 1. To observe
  the policys, wealth, and state-affairs of nations, so far as a
  solitary traveller may conveniently doe. 2. Their impositions upon
  all sorts of people, trades, or commoditys, that are remarkable.
  3. Their laws and customs, how far they differ from ours. 4. Their
  trades and arts wherein they excell or come short of us in England.
  5. Such fortifications as you shall meet with, their fashion,
  strength, and advantages for defence, and other such military
  affairs as are considerable. 6. The power and respect belonging to
  their degrees of nobility or magistracy. 7. It will not be time
  mispent to make a catalogue of the names and excellencys of those
  men that are most wise, learned, or esteemed in any nation. 8.
  Observe the mechanisme and manner of guiding ships. 9. Observe the
  products of nature in several places, especially in mines, with
  the circumstances of mining and of extracting metals or minerals
  out of their oare, and of refining them; and if you meet with any
  transmutations out of their own species into another (as out of
  iron into copper, out of any metall into quicksilver, out of one
  salt into another, or into an insipid body, &c.), those, above all,
  will be worth your noting, being the most luciferous, and many
  times lucriferous experiments too, in philosophy. 10. The prices of
  diet and other things. 11. And the staple commoditys of places.

  “These generals (such as at present I could think of), if they
  will serve for nothing else, yet they may assist you in drawing
  up a modell to regulate your travells by. As for particulars,
  these that follow are all that I can now think of, viz. Whether at
  Schemnitium, in Hungary (where there are mines of gold, copper,
  iron, vitrioll, antimony, &c.), they change iron into copper by
  dissolving it in a vitriolate water, which they find in cavitys of
  rocks in the mines, and then melting the slimy solution in a strong
  fire, which in the cooling proves copper. The like is said to be
  done in other places, which I cannot now remember; perhaps, too, it
  may be done in Italy. For about twenty or thirty years agone there
  was a certain vitrioll came from thence (called Roman vitrioll),
  but of a nobler virtue than that which is now called by that name;
  which vitrioll is not now to be gotten, because, perhaps, they
  make a greater gain by some such trick as turning iron into copper
  with it than by selling it. 2. Whether, in Hungary, Sclavonia,
  Bohemia, near the town Eila, or at the mountains of Bohemia near
  Silesia, there be rivers whose waters are impregnated with gold;
  perhaps, the gold being dissolved by some corrosive waters like
  _aqua regis_, and the solution carried along with the streame, that
  runs through the mines. And whether the practice of laying mercury
  in the rivers, till it be tinged with gold, and then straining the
  mercury through leather, that the gold may stay behind, be a secret
  yet, or openly practised. 3. There is newly contrived, in Holland,
  a mill to grind glasses plane withall, and I think polishing them
  too; perhaps it will be worth the while to see it. 4. There is in
  Holland one —— Borry, who some years since was imprisoned by the
  Pope, to have extorted from him secrets (as I am told) of great
  worth, both as to medicine and profit, but he escaped into Holland,
  where they have granted him a guard. I think he usually goes
  clothed in green. Pray inquire what you can of him, and whether
  his ingenuity be any profit to the Dutch. You may inform yourself
  whether the Dutch have any tricks to keep their ships from being
  all worm-eaten in their voyages to the Indies. Whether pendulum
  clocks do any service in finding out the longitude, &c.

  “I am very weary, and shall not stay to part with a long
  compliment, only I wish you a good journey, and God be with you.

            “IS. NEWTON.

  “Pray let us hear from you in your travells. I have given your two
  books to Dr. Arrowsmith.”




No. III.

  “A REMARKABLE AND CURIOUS CONVERSATION BETWEEN SIR ISAAC NEWTON AND
    MR. CONDUIT.”


  “I was on Sunday night, the 7th of March, 1724–5, at Kensington
  with Sir Isaac Newton, in his lodgings, just after he was come
  out of a fit of the gout, which he had had in both his feet, for
  the first time, in the eighty-third year of his age. He was
  better after it, and his head clearer, and memory stronger than I
  had known them for some time. He then repeated to me, by way of
  discourse, very distinctly, though rather in answer to my queries
  than in one continued narration, what he had often hinted to me
  before, viz. that it was his conjecture (he would affirm nothing)
  that there was a sort of revolution in the heavenly bodies; that
  the vapours and light emitted by the sun, which had their sediment
  as water and other matter, had gathered themselves by degrees into
  a body, and attracted more matter from the planets, and at last
  made a secondary planet (viz. one of those that go round another
  planet) and then by gathering to them, and attracting more matter,
  became a primary planet; and then by increasing still became a
  comet, which after certain revolutions, by coming nearer and nearer
  to the sun, had all its volatile parts condensed, and became a
  matter fit to recruit and replenish the sun (which must waste by
  the constant heat and light it emitted) as a fagot would this
  fire if put into it (we were sitting by a wood fire), and that
  that would probably be the effect of the comet of 1680, sooner or
  later, for, by the observations made upon it, it appeared, before
  it came near the sun, with a tail only two or three degrees long;
  but by the heat it contracted in going so near the sun, it seemed
  to have a tail of thirty or forty degrees when it went from it;
  that he could not say when this comet would drop into the sun;
  it might perhaps have five or six revolutions more first, but
  whenever it did it would so much increase the heat of the sun
  that this earth would be burnt, and no animals in it could live.
  That he took the three phenomena seen by Hipparchus, Tycho Brahe,
  and Kepler’s disciples to have been of this kind, for he could
  not otherwise account for an extraordinary light as those were,
  appearing all at once among the fixed stars (all which he took
  to be suns enlightening other planets as our sun does ours) as
  big as Mercury or Venus seems to us, and gradually diminishing
  for sixteen months, and then sinking into nothing. He seemed to
  doubt whether there were not intelligent beings superior to us
  who superintended these revolutions of the heavenly bodies by the
  direction of the Supreme Being. He appeared also to be very clearly
  of opinion that the inhabitants of this world were of a short
  date, and alleged as one reason for that opinion, that all arts,
  as letters, ships, printing, needle, &c., were discovered within
  the memory of history, which could not have happened if the world
  had been eternal; and that there were visible marks of ruin upon it
  which could not be effected by a flood only. When I asked him how
  this earth could have been repeopled if ever it had undergone the
  same fate it was threatened with hereafter by the comet of 1680, he
  answered, that required the power of a Creator. He said he took all
  the planets to be composed of the same matter with this earth, viz.
  earth, water, stones, &c., but variously concocted. I asked him why
  he would not publish his conjectures as conjectures, and instanced
  that Kepler had communicated his; and though he had not gone near
  so far as Kepler, yet Kepler’s guesses were so just and happy that
  they had been proved and demonstrated by him. His answer was, ‘I
  do not deal in conjectures.’ But upon my talking to him about the
  four observations that had been made of the comet of 1680, at 574
  years’ distance, and asking him the particular times, he opened
  his _Principia_, which laid on the table, and showed me there the
  particular periods, viz. 1st, the Julium Sidus, in the time of
  Justinian, in 1106, in 1680.

  And I, observing that he said there of that comet, ‘incidet in
  corpus solis,’ and in the next paragraph adds, ‘stellæ fixæ refici
  possunt,’ told him I thought he owned there what we had been
  talking about, viz. that the comet would drop into the sun, and
  that fixed stars were recruited and replenished by comets when
  they dropped into them; and, consequently, that the sun would be
  recruited too; and asked him why he would not own as freely what he
  thought of the sun as well as what he thought of the fixed stars.
  He said, ‘that concerned us more;’ and, laughing, added, ‘that he
  had said enough for people to know his meaning.’”

The preceding paper, with the title prefixed to it, was first published
by Mr. Turnor in his _Collections, &c._ p. 172. It was found among the
Portsmouth manuscripts, in the handwriting of Mr. Conduit.


THE END.




FOOTNOTES


[1] The Marquis La Place.—See _Systême du Monde_, p. 336.

[2] Sir Isaac Newton told Mr. Conduit, that he had often heard his
mother say that when he was born he was so little that they might have
put him into a quart mug.

[3] In Leicestershire, and about three miles south-east of Woolsthorpe.

[4] “I remember once,” says Dr. Stukely, “when I was deputy to Dr.
Hailey, secretary at the Royal Society, Sir Isaac talked of these
kind of instruments. That he observed the chief inconvenience in
them was, that the hole through which the water is transmitted being
necessarily very small, was subject to be furred up by impurities in
the water, as those made with sand will wear bigger, which at length
causes an inequality in time.”—Stukely’s Letter to Dr. Mead.—Turnor’s
_Collections_, p. 177.

[5] Mr. Clark informed Dr. Stukely that the walls of the room in which
Sir Isaac lodged were covered with charcoal drawings of birds, beasts,
men, ships, and mathematical figures, all of which were very well
designed.

[6] “One of his uncles,” says M. Biot, “having one day found him under
a hedge with a book in his hand and entirely absorbed in meditation,
took it from him, and found that he was occupied in the solution of a
mathematical problem. Struck with finding so serious and so active a
disposition at so early an age, he urged his mother no longer to thwart
him, and to send him back to Grantham to continue his studies.” I have
omitted this anecdote in the text, as I cannot find it in Turner’s
Collections, from which M. Biot derived his details of Newton’s
infancy, nor in any other work.

[7] Pemberton’s _View of Sir Isaac Newton’s Philosophy_. Pref.

[8] Peregregiæ vir indolis ac insignis peritiæ.—_Epist ad. Lect._

[9] See Newton’s Letter to the Abbé Conti, dated February 26, 1715–16,
in the _Additamenta Comm. Epistolici_.

[10] Newtoni _Opera_, tom. iv. p. 205, Letter to Oldenburg.

[11] M. Biot, in his Life of Newton, has stated that Newton was
preceded in the invention of the reflecting telescope by Gregory, _but
probably without knowing it_. It is quite certain, however, that Newton
was acquainted with Gregory’s invention, as appears from the following
avowal of it. “When I first applied myself to try the effects of
reflection, Mr. Gregory’s _Optica Promota_ (printed in the year 1663)
having fallen into my hands, where there is an instrument described
with a hole in the midst of the object-glass, to transmit the light to
an eye-glass placed behind it, I had thence an occasion of considering
that sort of construction, and found their disadvantages so great, that
I saw it necessary before I attempted any thing in the practice to
alter the design of them, and place the eye-glass at the side of the
tube rather than at the middle.”—_Letter to Oldenburg_, May 4th, 1672.

[12] Letter to Oldenburg, February 10, 1671.

[13] This gentleman was the author of a paper in the Philosophical
Transactions, entitled “Optical Assertions concerning the Rainbow.”
How such a paper could be published by so learned a body seems in the
present day utterly incomprehensible. The dials which Linus erected at
Liege, and which were the originals of those formerly in the Priory
Gardens in London, are noticed in the Philosophical Transactions for
1703. In one of them the hours were distinguished by touch.

[14] Newton speaks with singular positiveness on this subject. “For _I
know_,” says he, “that Mr. Lucas’s observations _cannot hold_ where
the refracting angle of the prism is full 60°, and the day is clear,
and the full length of the colours is measured, and the breadth of the
image answers to the sun’s diameter; and seeing I am well assured of
the truth and exactness of my own observations, I shall be unwilling
to be diverted by any other experiments from having a fair end made of
this in the first place.” On the supposition that his prism was one of
very low dispersive power, Mr. Lucas might, with perfect truth, have
used the very same language towards Newton.

[15] Letter to Oldenburg in 1672, containing his first reply to Huygens.

[16] In an experiment made by Newton, he had occasion to counteract the
refraction of a prism of _glass_ by another prism of _water_; and had
he completed the experiment, and studied the result of it, he could not
have failed to observe a quantity of uncorrected colour, which would
have led him to the discovery of the different dispersive powers of
bodies. But in order to increase the refractive power of the water,
he mixed with it a little sugar of lead, the high dispersive power of
which seems to have rendered the dispersive power of the water equal to
that of the glass, and thus to have corrected the uncompensated colour
of the glass prism.

[17] See the article OPTICS in the _Edinburgh Encyclopædia_, vol xv. p.
479, _note_.

[18] “This result was obtained,” as Newton says, “by an assistant
whose eyes were more critical than mine, and who, by right lines drawn
across the spectrum, noted the confines of the colours. And this
operation being divers times repeated both on the same and on several
papers, I found that the observations agreed well enough with one
another.”—OPTICS, Part II. Book III.

[19] Optics, Book ii. Prop. iv.

[20] In the same paragraph, when speaking of black bodies becoming hot,
and burning sooner than others, he says that their “effect may proceed
partly from the _multitude of refractions_ in a little room and partly
from the easy commotion of so very small corpuscles.”—Optics, Part iii.
Prop. vii. p. 235.

[21] See page 354.

[22] When Newton speaks of bodies losing their reflecting power from
their thinness he means the reflecting power of their second surfaces,
as is evident from the reason he assigns.—See Optics, Part iii. Prop.
xiii. p. 257.

[23] _Edinburgh Journal of Science_, No. 1. p. 108.

[24] See the _Phil. Trans._ 1829, Part I. p. 189.

[25] _Idem._

[26] _Phil. Trans._ 1819, p. 11.

[27] If this view of the matter be just, we should expect that
the specific gravity of the black would exceed that of the yellow
phosphorus.

[28] Since the two preceding chapters were written, I have had occasion
to confirm and extend the views which they contain by many new
experiments.

[29] _Physico-Mathesis de Lumine coloribus et iride aliisque annexis._
Bonon. 1665.

[30] This doctrine is thus announced. 1. That the same rays of light
falling upon the same point of an object will turn into all sorts of
colours by the various inclination of the object. 2. That colours begin
to appear when two pulses of light are blended so well and so near
together that the sense takes them for one.

[31] This effect is so great, that at the distance of _four_ inches
from the point of divergence, the angular inflexion of the _red_ rays
of the first fringe is 12′ 6″, while at the distance of about twenty
feet, it is only 3′ 55″.

[32] See the twenty-ninth query at the end of his Optics, where the
sides of a ray are compared with the poles of a magnet.

[33] The English edition was reprinted at London in 1714, 1721, and
1730, and the Latin one at London in 1706, 1719, 1721, 1728, at
Lausanne in 1740, and at Padua in 1773.

[34] When James I. went to Copenhagen in 1590, to conclude his marriage
with the Princess Anne of Denmark, he spent eight days under the roof
of Tycho at Uraniburg. As a token of his gratitude, he composed a set
of Latin verses in honour of the astronomer, and left him a magnificent
present at his departure. He gave him also his royal license for the
publication of his works in England, and accompanied it with the
following complimentary letter:—

“Nor am I acquainted with these things on the relation of others, or
from a mere perusal of your works, but I have seen them with my own
eyes, and heard them with my own ears, in your residence at Uraniburg,
during the various learned and agreeable conversations which I there
held with you, which even now affect my mind to such a degree, that it
is difficult to decide whether I recollect them with greater pleasure
or admiration.”

[35] The cube, the sphere, the tetrahedron, the octohedron, the
dodecahedron, and the icosahedron.

[36] Simon Marius, mathematician to the Marquis of Brandenburg, assures
us that he discovered the satellites of Jupiter in November, 1609.

[37] It is distinctly stated in the sentence of the Inquisition, that
Galileo’s enemies had charged him with having abjured his opinions in
1616, and affirmed that he had been punished by the Inquisition. In
order to refute these calumnies, Galileo applied to Cardinal Bellarmine
for a certificate to prove that he neither abjured his opinions nor
suffered any punishment for them; but that the doctrine of the motion
of the earth and the stability of the sun was only denounced to him
as contrary to Scripture, and as one which could not be defended or
maintained. Cardinal Bellarmine drew up such a certificate in his own
handwriting.

[38] _Theoricæ Medicearum planetarum ex causis physicis deductæ._ Flor.
1666, 4to.

[39] M. Delambre maintains that these views of Borelli are only those
of Kepler slightly modified. Newton and Huygens have attached to them
a greater value. The last of these philosophers remarks, “Refert
Plutarchus, fuisse jam olim qui putaret ideo manere lunam in orbe suo,
quod vis recedendi a terra, ob motum circularem, inhiberetur pari vi
gravitatis, qua ad terram accedere conaretur. Idemque ævo nostro, non
de luna tantum sed et planetis ceteris statuit Alphonsus Borellus,
ut nempe primariis eorum gravitas esset solem versus; lunis vero ad
terram, Jovem ac Saturnum quos comitantur.”—Huygen, _Cosmotheor_, lib.
ii.; _Opera_, t. ii. p. 720.

[40] _Hist. de l’Astronomie aux Dix-huitieme Siècle_, p. 9.

[41] “But for the duplicate proportion, I gathered it from Kepler’s
theorem about twenty years ago.”—Newton’s _Letter to Halley_, July 14,
1686.

[42] Whiston asserts that this cause was supposed by Newton to be
something analogous to the vortices of Descartes.—See Whiston’s
_Memoirs of himself_, p. 231.

[43] Waller’s _Life of Hooke_, p. 22.

[44] _Ibid._

[45] July 27, 1686, _Biog. Brit._ p. 2662.

[46] _Commercium Epistolicum_, No. 7.

[47] This Scholium is added to Prop. iv. lib. i. coroll. 6.

[48] In writing to Flamstead, Newton requests from him the long
diameters of the orbits of Jupiter and Saturn, that he “_may see how
the sesquialteral proportion fills the heavens_.”

[49] Whiston’s _Memoirs of his own Life_.

[50] “Dr. Reid states, that James Gregory, Professor of Philosophy
at St. Andrew’s, printed a thesis at Edinburgh in 1690, containing
twenty-five positions, of which twenty-two were a compend of Newton’s
Principia.”

[51] Nichols’s Literary Anecdotes, vol. iii. p. 322. Cotes states in
his preface to the second edition of the Principia, that copies of the
first edition could only be obtained at an immense price.

[52] Preface to Desaguliers’s _Experimental Philosophy_. Dr.
Desaguliers states that he was told this anecdote several times by Sir
Isaac Newton himself.

[53] _The Life of John Locke_, p. 209–215, Lond. 1829.

[54] _Principia_, lib. i. prop. i.

[55] _Ib._ lib. i. prop. xi.

[56] “On peut regarder Fermat,” says Lagrange, “comme le premier
inventeur des nouveaux calculs;” and Laplace observes, “Il paraitque
Fermat le veritable inventeur du calcul differentiel, l’ait envisagé
comme un cas particulier de celui des differences,” &c.

[57] Art. _Mathematics_, in the _Edinburgh Encyclopædia_, volume xiii.
p. 365.

[58] These facts are mentioned in Newton’s letter to Oldenburgh,
October 24, 1676.

[59] Dr. Pemberton informs us that he had prevailed upon Sir Isaac to
publish this treatise during his lifetime, and that he had for this
purpose examined all the calculations and prepared part of the figures.
But as the latter part of the treatise had never been finished, Sir
Isaac was about to let him have other papers to supply what was
wanting, when his death put a stop to the plan.—Preface to Pemberton’s
_View of Sir Isaac Newton’s Philosophy_.

[60] Isaci Newtoni Opera quæ extant omnia, vol. i. p. 388–519.

[61] “Acutissimis qui toto orbe florent Mathematicis.”

[62] Henry Oldenburg, whose name is so intimately associated with the
history of Newton’s discoveries, was born at Bremen, and was consul
from that town to London during the usurpation of Cromwell. Having
lost his office, and being compelled to seek the means of subsistence,
he became tutor to an English nobleman, whom he accompanied to Oxford
in 1656. During his residence in that city he became acquainted with
the philosophers who established the Royal Society, and upon the
death of William Crown, the first secretary, he was appointed in
1663, joint secretary along with Mr. Wilkins. He kept up an extensive
correspondence with the philosophers of all nations, and he was the
author of several papers in the Philosophical Transactions, and of some
works which have not acquired much celebrity. He died at Charlton, near
Greenwich, in August, 1677.

[63] These words in brackets are in the second edition, but not in the
first.

[64] As this passage is of essential importance in this controversy, we
shall give it in the original. “_Pro differentiis igitur Leibnitianis
D. Newtonus adhibet, semperque adhibuit, fluxiones_, quæ sunt quam
proxime ut fluentium augmenta, æqualibus temporis particulis quam
minimis genita; iisque tam in suis Principiis Naturæ Mathematicis, tum
in aliis postea editis, eleganter est usus; _quem admodum et Honoratus
Fabrius in sua Synopsi Geometrica, motuumque progressus Cavallerianæ
methodo substituit_.”

[65] Homine docto, sed novo, et parum perito rerum ante actarum
cognitare.

[66] Vanæ et injustæ vociferationes.

[67] Letter to Count Bothman in Des Maizeaux’s _Recueil de diverses
pieces_, tom. ii. p. 44, 45.

[68] See Des Maizeaux, tom. ii. p. 116.

[69] Written in November or December, 1715.

[70] This is the _Recensio Commercii Epistolici_, or review of it,
which was first published in the _Phil. Trans. 1715_.

[71] M. Biot remarks, that the animosity of Newton was not calmed
by the death of Leibnitz, for he had no sooner heard of it than he
caused to be printed two manuscript letters of Leibnitz, written in
the preceding year, accompanying them with a very bitter refutation
(en les accompagnant d’un refutation tres-amere). Who that reads this
sentence does not believe that the bitter refutation was written after
Leibnitz’s death? The animosity could not be shown by the simple
publication of the letters. It could reside only in the _bitterness_
of the refutation. The implied charge is untrue; the bitter refutation
was written before Leibnitz’s death, and consequently he showed no
animosity over the grave of his rival; and in our opinion none even
before his death.

[72] M. Biot states that Sir Isaac Newton _caused_ this edition of
the Commercium Epistolicum to be printed; that _Sir Isaac placed_ at
the head of it a partial abstract of the collection; and that this
abstract _appeared to have been written by himself_. These groundless
charges may be placed, without any refutation, beside the assertion of
Montucla, that Newton wrote the notes (les notes) on the Commercium
Epistolicum; and the equally incorrect statement of La Croix, that
Newton added to it notes (des notes), with his own hand. We should not
have noticed the charges of M. Biot, had he not adduced them as proofs
of Newton’s animosity to Leibnitz after his death. See Mr. Herschel’s
History of _Mathematics_ in the _Edinburgh Encyclopædia_, vol. xiii. p.
368, _note_.

[73] See Burnet’s _History of his own Times_, vol. i. p. 697. Lond.
1724.

[74] The other candidates were Sir Robert Sawyer and Mr. Finch, and the
votes stood thus.

    Sir Robert Sawyer,    125
    Mr. Newton,           122
    Mr. Finch,            117

[75] This M. Colin was probably a young bachelor of arts whom Newton
seems afterward to have employed in some of his calculations. These
bachelors were distinguished by the title of Dominus, and it was usual
to translate this word and to call them _Sir_. In a letter from Newton
to Flamstead, dated Cambridge, June 29th, 1695, is the following
passage: “I want not your calculations, but your observations only,
for besides myself and my servant, Sir Collins (whom I can employ for
a little money, which I value not) tells me that he can calculate an
eclipse and work truly.”

[76] They are thus dated in Horsley’s edition of Newton’s Works, the
_fourth_ letter having an earlier date than the _third_.

[77] See _Newtoni Opera_, tom. iv. p. 480, and _Wallasii Opera_, 1693,
tom. ii. p. 391–396.

[78] _Optics_, part iv. obs. 13.

[79] For these letters I have been indebted to the kindness of Lord
Braybrooke.

[80] These three letters have been published by Lord Braybrooke in the
Life and Correspondence of Mr. Pepys.

[81] This anxiety will be understood from the fact that, by an order of
council dated January 28th, 1674–5, Mr. Newton was excused from making
the usual payments of one shilling per week, “on account of his low
circumstances, as he represented.”

[82] The system of Hobbes was at this time very prevalent. According to
Dr. Bentley, “the taverns and coffee-houses, nay, Westminster Hall and
the very churches, were full of it;” and he was convinced from personal
observation, that “not one English infidel in a hundred was other than
a Hobbist.”—Monk’s _Life of Bentley_, p. 31.

[83] The draft of this letter is endorsed “J. L. to I. Newton.”

[84] Dr. Gregory concludes his account of this manuscript, which he
has kindly permitted me to read, in the following words:—“I do not
know whether it is true, as stated by Huygens, ‘Newtonum incidisse in
Phrenitim;’ but I think every gentleman who examines this manuscript
will be of opinion that he must have thoroughly recovered from his
phrenitis before he wrote either the Commentary on the Opinions of
the Ancients, or the Sketch of his own Theological and Philosophical
Opinions which it contains.”

[85] This paragraph is as follows:—“Deum esse ens summe perfectum
concedunt omnes. Entis autem summe perfecti Idea est ut sit substantia,
una, simplex, indivisibilis, viva et vivifica, ubique semper necessario
existens, summe intelligens omnia, libere volens bona, voluntate
efficiens possibilia, effectibus nobilioribus similitudinem propriam
quantum fieri potest communicans, omnia in se continens tanquam eorum
principium et locus, omnia per presentiam substantialem cernens et
regens, et cum rebus omnibus, secundum leges accuratas ut naturæ totius
fundamentum et causa constanter co-operans, nisi ubi aliter agere bonum
est.”

[86] The following extract, characteristic of Flamstead’s manner, is
from a letter to Newton dated January 6, 1698–9.

“Upon hearing occasionally that you had sent a letter to Dr. Wallis
about the parallax of the fixed stars to be printed, and that you had
mentioned me therein with respect to the theory of the moon, I was
concerned to be publicly brought upon the state about what, perhaps,
will never be fitted for the public, and thereby the world _put into
an expectation of what perhaps they are never likely to have_. I do
not love to be printed upon every occasion, much less to be dunned
and teased by foreigners about mathematical things, or to be thought
_by your own people to be trifling_ away my time when I should be
about the king’s business.” On the first of the above passages in
italics Flamstead has the following memorandum:—“When Mr. Halley
boasts ’tis done, and given to him as a secret, tells the Society
so and foreigners.” In the second passage in italics, Mr. Flamstead
refers, in a note, to Mr. Colson’s letter to him, in which he seems
to have represented practical astronomy as trifling. Mr. Flamstead
adds, “Was Mr. Newton a trifler when he read mathematics for a salary
at Cambridge: surely, then, astronomy is of some good use, though
his place be more beneficial.” For these extracts from the original
manuscript in the collection of Corpus Christi College, Oxford, I have
been indebted to the kindness of Professor Rigaud of Oxford.

[87] See page 215, note.

[88] The candidates in 1701 were as follows:

    Mr. Henry Boyle, afterward Lord Carleton, 180} Both of Trinity
    Mr. Newton                                161} College.
    Mr. Hammond                                64

[89] The banquet which was on this occasion given in the college
hall to the royal visiter seems to have cost about 1000_l._, and the
university was obliged to borrow 500_l._, to defray the expense of
it.—Monk’s _Life of Bentley_, p. 143, 144.

[90] The candidates in 1705 were as follows:

    The Hon. Arthur Annesley      182
        Hon. Dixie Windsor        170
        Mr. Godolphin             162
        Sir Isaac Newton          117

[91] Journals of the House of Commons, vol. xvii. p. 677, 716.

[92] Whiston’s “Longitude Discovered.” Lond 1738.

[93] This anecdote concerning the Chronological manuscript is not
correctly given in the Biographia Britannica, and in some of the other
lives of Newton. I have followed implicitly Newton’s own account of it
in the _Phil. Trans. 1725_, vol. xxxiii. No. 389, p. 315.

[94] M. Biot has supposed that this abstract was an imperfect edition
of Newton’s work on Chronology.

[95] Father Souciet was supposed by Halley and others to have been the
author of these observations, but there is no doubt that they were
written by M. Freret.

[96] It is stated in the _Biogr. Britannica_, Art. _Newton_, that the
copy of the French translation was not accompanied with the refutation.
Though the reverse of this is not distinctly stated by Sir Isaac
himself, yet it may be inferred from his observations.

[97] Vol. xxxiii. No. 389, p. 315.

[98] According to Whiston, Sir Isaac wrote out eighteen copies
of this chapter with his own hand, differing little from one
another.—_Whiston’s Life_, p. 39.

[99] This work is the first article in the fifth volume of Dr.
Hersley’s edition of Newton’s works. The next article in the volume is
entitled, “A Short Chronicle from a MS., the property of the Reverend
Dr. Ekins, Dean of Carlisle;” which is nothing more than the abstract
of the Chronology already printed in the same volume. We cannot even
conjecture the reasons for publishing it, especially as it is less
perfect than the abstract, two or three dates being wanting.

[100] See vol. xxxiv. p. 205, and vol. xxxv. p. 296.

[101] See an excellent view of this chronological controversy in an
able note by M. Daunou, attached to Biot’s Life of Newton in the _Biog.
Universelle_, tom. xxxi. p. 180.

[102] This letter is published without any date in the _Gentleman’s
Magazine_ for 1755, vol. xxv. p. 3. It bears internal evidence of being
genuine.

[103] His _Historical Account of two notable Corruptions of the
Scriptures_. 50 pp quarto.

[104] The editor supplied the beginning down to the 13th page, where he
mentions in a note that “_thus far is not Sir Isaac’s_.”

[105] M. Biot has well remarked that there is absolutely nothing in
the writings of Newton to justify, or even to authorize, the idea
that he was an Antitrinitarian. This passage is strangely omitted
in the English translation of Biot’s Life of Newton. We do not know
upon what authority Dr. Thomson states, in his History of the Royal
Society, that Newton “did not believe in the Trinity,” and that Dr.
Horsley considered Newton’s papers unfit for publication, because they
contained proofs of his hostility to that doctrine.

[106] Whiston’s _Memoirs of his own Life_, p. 178, 249, 250. Edit. 1753.

[107] Dr. Monk’s _Life of Bentley_, p. 31.

[108] Dated December 10th, 1692. This letter is endorsed, in Bentley’s
hand, “Mr. Newton’s answer to some queries sent by me after I had
preached my two last sermons.”—Monk’s _Life of Bentley_, p. 34, note.

[109] Dated Jan. 17th, 1692–3.

[110] “These things,” says he, “follow from my _Princip. Math._ lib. i.
prop. 33, 34, 35, 36.”

[111] Dated February 11th, 1693.

[112] The originals of these four letters to Bentley “were given by Dr.
Richard Bentley to Cumberland, his nephew, and executor, while a
student at Trinity College, and were printed by him in a separate
pamphlet in 1756. This publication was reviewed by Dr. Samuel Johnson
in the Literary Magazine, vol. i. p. 89. See Johnson’s Works, vol.
ii. p. 328. The original letters are preserved in Trinity College, to
which society they were given by Cumberland a short time before his
death.”—Monk’s _Life of Bentley_, p. 33, note.

[113] Mr. Herschel, in his Treatise on Light, § 553, has maintained
that Newton’s Doctrine of Reflection is accordant with the idea that
the attractive force extends beyond the repulsive or reflecting force.
In the query above referred to, Sir Isaac, in the most distinct
manner, places the sphere of the reflecting force without that of the
attractive one.

[114] In a tract annexed to his _Appeal to all that doubt or disbelieve
the truths of the Gospel_. See _Gent. Mag._ 1782, vol. iii. p. 227, 239.

It is stated in a letter of Mr. Law’s, quoted in this magazine, that
Charles I. was a diligent reader and admirer of Jacob Behmen; that
he sent a well-qualified person from England to Goerlitz, in Upper
Lusatia, to acquire the German language, and to collect every anecdote
he could meet with there relative to this great alchymist.

[115] In a letter to Dr. Halley, dated June 20th, 1686, Sir Isaac
refers to this paper, and observes, that it is only to be looked upon
as one of his guesses that he did not rely upon.

[116] See page 273.

[117] See _Newtoni Opera_, by Horsley, vol. iv. p. 375–382.

[118] Sir Isaac does not seem to have afterward described this
construction.

[119] See _Edinburgh Transactions_, vol. ix. p. 433, and the _Edinburgh
Journal of Science_, July, 1829, No. I. New Series, p. 108.

[120] Art. _Accidental Colours_ in the _Edinburgh Encyclopædia_.

[121] See _Phil. Trans._ 1722, vol. xxxiii. p. 57.

[122] This conversation, originally copied from Mr. Conduit’s
handwriting, is given in the Appendix, No. iii. p. 320.

[123] These were the three children of his half-brother Smith, the
three children of his half-sister Pilkington, and the two daughters of
his half-sister Barton, all of whom survived Sir Isaac. _New Anecdotes
of Sir Isaac Newton, by J. H., a Gentleman of his Mother’s Family._ See
_Annual Register_, 1776, vol. xix. p. 25 of Characters. The author of
this paper was James Hutton, Esq. of Pimlico.

[124] Turnor’s _Collections_, &c. p. 158. See APPENDIX, p. 316.

[125] This valuable faculty characterizes all his writings, whether
theological, chymical, or mathematical; but it is peculiarly displayed
in his treatise on Universal Arithmetic, and in his Optical Lectures.

[126] _De Magnete_, p. 42, 52, 169, and Pref. p. 30.

[127] The following passages from Leonardo da Vinci are very striking:

“Theory is the general, and practice the soldiers.

“Experiment is the interpreter of the artifices of nature. It never
deceives us; it is our judgment itself which sometimes deceives us,
because we expect from it effects which are contrary to experiment.
We must consult experiment by varying the circumstances till we have
deduced from it general laws; for it is it which furnishes true laws.

“In the study of the sciences which depend on mathematics, those who do
not consult nature, but authors, are not the children of nature; they
are only her grandchildren. Nature alone is the master of true genius.

“In treating any particular subject, I would first of all make some
experiments, because my design is first to refer to experiment, and
then to demonstrate why bodies are constrained to act in such a
manner. This is the method which we ought to follow in investigating
the phenomena of nature. It is very true that nature begins by
reasoning and ends with experiment; but it matters not, _we must take
the opposite course_; _as I have said, we must begin by experiment_,
and endeavour by its means to discover general principles.” Thus,
says Venturi, spoke Leonard a century before Bacon, and thus, we
add, did Leonard tell philosophers all that they required for the
proper investigation of general laws. See _Essai sur les œuvrages
physico-mathematiques de Leonard de Vinci_, par J. B. Venturi. Paris,
1799, p. 32, 33, &c. See also Carlo Amoretti’s _Memorie storiche su la
vita gli studi e le Opere de Lionardo da Vinci_. Milano, 1804.

[128] Mr. Hearne, in a memorandum dated April 4th, 1726, states, that
a great quarrel happened between Sir Isaac Newton and Mr. Halley. If
this is true, the difference is likely to have originated in Halley’s
impiety.

[129] Professor Rigaud of Oxford heard this anecdote from Dr. Maskelyne.

[130] “He was very kind to all the Ayscoughs. To one he gave 800_l._,
to another 200_l._, and to a third 100_l._, and many other sums; and
other engagements did he enter into also for them. He was the ready
assistant of all who were any way related to him,—to their children and
grandchildren.”—_Annual Register_, 1776, vol. xix. p. 25. Sir Isaac
gave some donations to the chapel and parish of Colsterworth. Hearne
says “that he promised to become a benefactor to the Royal Society, but
failed.”

[131] The following anecdote of Sir Isaac’s absence has been published,
but I cannot vouch for its authenticity. His intimate friend Dr.
Stukely, who had been deputy to Dr. Halley as secretary to the Royal
Society, was one day shown into Sir Isaac’s dining-room, where his
dinner had been for some time served up. Dr. Stukely waited for a
considerable time, and getting impatient, he removed the cover from a
chicken, which he ate, replacing the bones under the cover. In a short
time Sir Isaac entered the room, and after the usual compliments sat
down to his dinner, but on taking off the cover, and seeing nothing but
bones, he remarked, “How absent we philosophers are. I really thought
that I had not dined.”

[132] _Epistolary Correspondence_, vol. i. p. 180, sec. 77.

[133] MS. Memoranda in the Bodleian Library.

[134] Turnor’s _Collections_, p. 176.

[135] The anecdote of the falling apple is mentioned neither by Dr.
Stukely nor by Mr. Conduit, and as I have not been able to find any
authority for it whatever, I did not feel myself at liberty to use it.

[136] In the Monthly Review for August, 1829, p. 593, it is stated,
that the correspondence between Newton and Flamstead, from 1680 to
1698, exists in the Sloane collection of Manuscripts in the British
Museum. Professor Rigaud, however, has had the kindness to inquire
into the accuracy of this statement, and he has ascertained that these
letters are merely copies, which Dr. Birch had made from the originals
at Oxford.

[137] See page 288, note.

[138] This entail was executed in 1724, a year or two before Sir
Richard’s death.—D. B.

[139] See p. 291.




      *      *      *      *      *      *




Transcriber’s note:

Punctuation, hyphenation, and spelling were made consistent when a
predominant preference was found in this book; otherwise they were not
changed.

Many abbreviations, and some sentences, did not end with periods.
Transcriber added missing periods only at the ends of sentences, and
did not attempt to resolve other inconsistencies.

Simple typographical errors were corrected; occasional unpaired
quotation marks retained.

Ambiguous hyphens at the ends of lines were retained.

In some letters, the salutations and dates were printed on the same
line, and the signatures sometimes were printed on the same lines as
the end of the body. In this eBook, the dates always appear above the
salutations and the signatures are on their own lines.

Superscripts were used only as abbreviations for names and words, not
in mathematical expressions, and have been printed as normal lower-case
letters in the Plain Text version of this eBook.

The Transcriber did not review the spelling of non-English words.

Second page (unnumbered), last line: “with whom they abide.” The word
shown here as “abide” was poorly printed and unclear.

At the bottom of the Title page, the date is “1833”; at the bottom of
the cover, the date is “1835”.

Page 66: “piece of plane glass” was printed that way.

Page 66: Transcriber added the comma in “and LR, LR the extreme red”.

Page 70: Transcriber added italics to “makes _orange_”.

Page 126: “on the 7th January, 1618” should be “1610”.

Page 306 referred to Newton’s telescope being shown in “fig. 1”, but
it actually is in “fig. 3” and is referenced that way in this eBook.

Page 321: The opening parenthesis before “viz. one of those that go
round another” has no matching closing parenthesis. Transcriber added a
closing parenthesis after “round another planet”, but that may not be
where it belongs.