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Home-made Electrical Apparatus 
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       :PG.Title: Home-made Electrical Apparatus 
       :PG.Id: 63878
       :PG.Rights: Public Domain
       :PG.Producer: James Simmons
       :PG.Credits: This file was produced from page images at the Internet Archive.
       :DC.Creator: Alfred Powell Morgan
       :DC.Title: Home-made Electrical Apparatus 
       :DC.Language: en
       :DC.Created: 1918
       :PG.Released: 2020-11-24
       :coverpage: images/CoverImage.jpg

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.. topic:: Transcriber's Note

    This book was transcribed from scans of the original found at the Internet Archive. The page scans were done by Google.
    The original book was done as three volumes, but the edition I have transcribed put all three volumes together as a
    clothbound book. As a result it had three identical prefaces and duplicated ads. I have included one preface, at the 
    beginning, and put the ads at the end of the book. I have rotated a couple of illustrations.
        
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       Arts and Science Series No. 7 

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       Home-made
   
       Electrical Apparatus 

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       A Practical Handbook for Amateur 

       Experimenters 

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       In Three Parts 

       **Volume I**

       *Second Edition*

       **BY**

       **A. M. Powell**

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       PUBLISHED BY

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       COLE & MORGAN, Inc. 

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       Publishers of the Arts and Science Series 

       \P.O. BOX 473 CITY HALL STATION 

       NEW YORK, N. Y. 

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       Printed in U. S. A. 

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    Copyright 1918 

    by 

    COLE & MORGAN, Inc. 

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PREFACE
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The purpose of this book is to aid the young experimenter 
in building and operating his own electrical apparatus and 
instruments. Every boy of now-a-days experiments with 
electricity and the right sort of book which furnishes him with ideas 
gets close to his heart. Of books upon electricity there is no 
end. That is granted. But there are very few *practical* books 
for the young experimenter who wishes to construct 
miscellaneous electrical apparatus for his own amusement and 
instruction which really amounts to something and which is worth his 
pains when the labor has been finished. 

This book is therefore offered as a volume of instruction for 
making all sorts of batteries, rectifiers, motors, etc., which are 
entirely out of the toy class and yet are not so elaborate that 
they cannot be easily constructed *at home* by the average boy 
who is willing to put a little care into his work. The materials 
required are such that they can he procured without any great 
expense. 

It has been planned to present the material in such a manner 
that it will aid the judgment of the young experimenter and 
assist him in developing his own ideas. Without exception, all 
of the apparatus described in the following pages has been 
actually constructed by the author, not only once but many times 
and put to a practical test before being embodied into the book. 
You may therefore be sure that if you follow the instructions 
carefully, that the result will in each case be a substantial piece 
of apparatus which is capable of fulfilling all of your 
expectations. 

The drawings have all been reproduced on a large scale and 
in almost every case the dimensions of even the smallest details 
have been given. Some of the apparatus has been described in 
the pages of the "Boys' Magazine" and since its publication the 
readers of that magazine have written to the author asking 
questions about the apparatus which have enabled him when 
rewriting the material for publication in book form to clear up 
many questions and further explain in a little more detail many 
of the problems which naturally occur to the boy who likes to 
build his own electrical devices. 

THE AUTHOR. 

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CHAPTER I. STATIC ELECTRICAL APPARATUS
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**Static Electricity. How to Build a Wimshurst Machine. 
Experiments with Static Electrical Apparatus.**

**Static Electricity** is an extremely interesting 
subject for the amateur experimenter, in view of the 
many spectacular experiments which may be 
performed with it. The number of such experiments is 
almost unlimited. 

Static electricity was the first evidence of the 
wonderful force which in the present day moves trains, 
lights our homes, etc., to come to the notice of man. 
Long before the days of batteries, dynamos, telegraphs, 
electric lights and before, perhaps, such things were 
even dreamed of, static electricity absorbed the 
attention of scientists, and the names of some of the world's 
greatest men such as for instance, Aristotle, Roger 
Bacon, Gilbert, Boyle, Newton, Franklin, etc., are 
closely linked with its history. It is probably safe to 
say that experiments with static electricity led the 
famous Italian, Galvani, to the discovery of the sort 
of electricity called **galvanic** currents, and to the 
battery. Galvanic current is the sort of electricity 
produced by batteries and has the same properties in 
many ways as that generated by huge dynamos in the 
power houses of to-day. 

The modern boy can duplicate these old experiments 
far more easily and on a larger scale than any of the 
old scientists could, owing to the fact that he is 
supplied with explicit directions and can easily obtain the 
necessary materials at a neighboring hardware or 
electrical store, whereas men like Newton and Franklin 
not only had to **devise** or **invent** their own apparatus 
but make their materials as well. 

How to Build a Wimshurst Machine.
````````````````````````````````` 

Static electricity and lightning are the same thing. 

A boy can produce static electricity in small 
quantities by rubbing a glass rod with a piece of flannel or 
silk. 

.. figure:: images/Image1.jpg
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   :alt: FIG. 1.—A simple Wimshurst Machine

   FIG. 1.—A simple Wimshurst Machine which any boy can easily make. P P, Plates; BR, Neutralizes; C R, Collectors; DR, Discharge Rods; J J, Leyden Jars; H H, Insulating Handles; C, Crank; U, Upright; B, Belt. 

Rub the rod briskly and then hold it over some tiny 
bits of paper or specks of dust and watch them jump 
up to meet the rod, just as if the latter were a magnet 
attracting small tacks or nails. It is static electricity 
which gives the rod this wonderful power. If you rub 
the rod briskly and then hold it close to your cheek, 
you will feel a slight tickling and hear a faint crackling 
sound. If this is done in the dark you may be able to 
see a very faint phosphorescent light or even small 
sparks. 

The quantity of electricity produced in this manner 
by rubbing a glass rod is extremely limited and while 
a number of very interesting and instructive 
experiments may be performed in this manner, the most 
spectacular ones are only possible with the aid of a 
"static-machine". 

.. figure:: images/Image2.jpg
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   :alt: FIG. 2.—The plates for the Static Machine

   FIG. 2.—The plates for the Static Machine are made of hard rubber and are 7 inches in diameter. Each plate carries sixteen tinfoil sectors.

The most practical form of static machine is that 
known as the "Wimshurst". It consists of two 
circular plates made of glass or hard rubber arranged so 
that by turning a crank, they may be revolved in 
opposite directions. On these plates are a number of small 
strips of tinfoil. The static electricity is generated on 
these tinfoil strips and collected by two metal rods 
having small pins arranged along them in a row. 

A simple form of Wimshurst machine which any 
boy can easily make is illustrated in Figure 1. It will 
generate considerable static electricity and will make 
sparks two inches long. 

**The Plates** on these machines are hard rubber. They 
are illustrated in Figure 2. Glass is usually used for 
static machine plates, but has the disadvantage of 
breaking easily. It is also hard for the young 
experimenter to cut out circular glass plates and drill them. 
The author has had very good success with hard 
rubber. 

.. figure:: images/Image3.jpg
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   :alt: FIG. 3.—The details of the Tinfoil Sector.

   FIG. 3.—The details of the Tinfoil Sector. Sixteen are required for each plate. They are stuck to the plates with shellac. 

Two plates are required for the machine. They 
should be in the form of circles seven inches in 
diameter and be perfectly true. They need to be only 
one-sixteenth of an inch thick. The rubber should be 
perfectly flat and not warped at any point. 

**The Sectors**, as the tinfoil strips are called, are wedge 
shaped pieces having rounded ends as shown in Figure 
\3. They should be cut of heavy tinfoil. Thirty-two 
sectors are required, sixteen for each plate. They are 
seven-sixteenths of an inch wide at the top, one inch 
long and five-sixteenth of an inch wide at the bottom. 

The plates should be very carefully cleaned by 
rubbing with a dry cloth and then laid on a flat surface 
all ready to receive the sectors. 

The sectors should be stuck to the plates with thick 
shellac. They should be arranged all on one face, 
symmetrically and at equal distances apart, with the inner 
ends resting on a circle four and one-half inches in 
diameter. Each sector should be carefully pressed 
down on the rubber so that it sticks smoothly without 
any air bubbles or creases. 

Both plates should be treated in the same manner. 

.. figure:: images/Image4.jpg
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   :alt: FIG. 4.—Details of the Grooved Pulley, attached to each plate. The Pulleys are turned out of wood. 

   FIG. 4.—Details of the Grooved Pulley, attached to each plate. The Pulleys are turned out of wood.  

**The Pulley** illustrated in Figure 4 is one inch in 
diameter and eleven-sixteenths of an inch thick. Two 
of these pulleys will be required. The hole through 
the centre should be about three-sixteenths of an inch 
in diameter. One pulley should be attached to each 
of the rubber plates. The large face of the pulley should 
be against the face of the plate upon which the tinfoil 
sectors are mounted. The hole in the centre of the 
pulley should line up perfectly with a hole of the same size 
in the centre of each one of the plates. The plates are 
fastened to the pulleys by three small brass nails 
driven into the wood through small holes in the rubber. 

**The Base** of the machine is a rectangular shaped 
piece of wood six inches long, four inches wide and 
three-quarters of an inch thick. A notch, one inch wide 
and one-half an inch deep is cut in the centre of the 
front and back as shown in Figure 5. The purpose of 
these notches is to receive the uprights. 

**The Uprights** are strips of wood, seven inches long, 
one inch wide and one-half an inch thick. The 
tipper end of each of the uprights is rounded as shown 
in Figure 6. 

.. figure:: images/Image5.jpg
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   :alt: FIG. 5.—The base of the Wimshurst Machine.

   FIG. 5.—The base of the Wimshurst Machine. All woodwork about the machine should be carefully dried and then shellaced so that it cannot absorb any moisture. 
  
Two holes should be bored through each of the 
uprights from front to back. The lower hole is 
three-sixteenths of an inch in diameter and two and one-quarter 
inches from the bottom. The upper hole is six and 
one-half inches from the bottom and is between one-eighth 
and three-sixteenths of an inch in diameter so that a 
three-sixteenth rod driven into it will fit tightly. 

The uprights should be mounted in position in the 
base and fastened with screws. 

The plates are mounted between the upper ends of 
the uprights in the position shown in Figure 1, by 
driving a short piece of 3/16 round brass rod through the 
uprights into the holes in the centre of the pulleys. 
The rod used to mount the back plate should be one 
and one-half inches long and that used for the front 
plate one and five-eighths inches long. The 3/16 hole in 
the pulleys should be large enough so that the latter 
will revolve freely. 

The plates are revolved by two driving pulleys 
provided with a crank for turning. 

**The Driving Pulleys** are shown in Figure 8. They 
are not so easy to make as the small pulleys attached 
to the plates. They are turned out of wood and should 
be both alike. The exact shape and dimensions are 
shown in the illustration. The hole through the centre 
should be a scant three-sixteenths of an inch so that 
the pulleys will force onto a 3/16 rod very tightly. 

**The Crank** is bent out of a piece of brass or steel 
rod about seven inches long. The straight portion, 
forming the shaft upon which the pulleys are mounted, 
is three and seven-eighths inches long. The portion 
at right angles to this, forming what is known as the 
"throw" of the crank, is one inch and seven-eighths. 
The part forming the crank handle is one inch and 
one-quarter long. 

.. figure:: images/Image6.jpg
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   :alt: FIG. 6.—Details of one of the Uprights which support the Plates, Driving Pulleys, etc.

   FIG. 6.—Details of one of the Uprights which support the Plates, Driving Pulleys, etc. These, being made of wood, should also be dried and shellaced so that they cannot absorb moisture. 

The driving pulleys are placed between the two 
standards with the small projecting portions or 
"bosses" nearest the uprights. The straight portion 
of the crank should then be slipped through the hole 
in the front upright and driven tightly into the driving 
pulleys. The driving pulleys should fit so tightly onto 
the shaft that they will not slip. The end of the shaft 
should project through the pulleys far enough so that 
is rests in the hole in the rear standard. 

The holes in the uprights or standards should be 
just large enough so that the shaft will turn freely. 
The driving pulleys should be lined up so that the 
groove in each comes directly under the groove in the 
corresponding pulley attached to the plate above. 

**The Belts** consist simply of heavy cotton cord. The 
rear belt should be crossed so that the rear plate runs 
in the opposite direction from the front plate when the 
crank is turned. 

The electricity is collected from the sectors on the 
plates by two 

**Collectors.** These are illustrated in Figure 10 and 
consists of a piece of 5/32 brass rod, about six inches 
long, bent into the shape shown. Two small tufts of 
"tinsel" are soldered to the U-shaped portion of the 
collector so that when the latter is placed in its proper 
position on the machine, they will brush against the 
tinfoil-sectors as they pass when the plates revolve. 

.. figure:: images/Image7.jpg
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   :alt: FIG. 7.—Showing the Two Uprights in position on the Base. 

   FIG. 7.—Showing the Two Uprights in position on the Base. 

The other end of the rod is threaded to fit into a hole 
in a small brass ball about three-eighths or one-half 
inch in diameter. Many experimenters may have 
difficulty in securing a suitable brass ball for this purpose. 
An ordinary binding post may be used instead. The 
hole in the bottom of a binding post is usually threaded 
to fit an 8-32 screw. The end of the rod is just the 
right size to receive an 8-32 thread and so there should 
be no trouble in getting the parts to fit. The brass ball 
is marked "A" in the illustration. The ball is 
preferable to the binding because it has no sharp corners 
from which the electricity might leak. Static 
electricity leaks from sharp edges or corners and they must 
always be avoided as far as possible in the construction 
of static apparatus. 

The end of the rod where it screws into the ball or 
binding post should be threaded back for a distance of 
about three-quarters of an inch and two brass nuts 
screwed onto the rod. These nuts are marked "C" in 
the illustration. 

.. figure:: images/Image8.jpg
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   :alt: FIG. 8.—The Driving Pulleys.

   FIG. 8.—The Driving Pulleys. These are turned out of wood and mounted on a shaft having a Crank at one end. 

The collectors are held in position by the supporting 
bar illustrated in Figure 13. This bar is made of a 
strip of hard rubber, five and one quarter inches long, 
five-eighths of an inch wide and three-sixteenths of an 
inch thick. 

Three holes, each five-thirty-seconds of an inch in 
diameter, should be bored in the bar. One hole should 
be exactly in the centre and the other holes 
seven-sixteenths of an inch back from the end. 

The centre hole is slipped over the end of the shaft 
which projects through the front standard supporting 
the plate and the bar fastened across the support at 
right angles like a cross by driving in two small brass 
nails or screws through holes made in the rubber for
that purpose. 

The threaded portion of the collector rods should 
be slipped through the holes near the ends of the hard 
rubber bar and clamped firmly in position by placing 
one of the nuts "C" on the back and the other on the 
front and tightening them up. 

The exact position of the collectors is best 
understood from Figure 1. They are lettered C R in the 
illustration. The brass balls B are screwed onto the 
ends of the rods after the nuts have been tightened. 
Each of these balls should have a hole, one-eighth of an 
inch in diameter drilled through it at right angles 
to the collector rod. The hole provided in the binding 
post for the accommodation of the wire may be used 
in case binding posts are employed instead of the rods. 

These holes are to accommodate the Discharge Rods, 
which are two round brass rods, one-eighth of an inch 
in diameter and three and one-half inches long. One 
end of each of the rods is fitted with a small brass ball. 

.. figure:: images/Image9.jpg
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   :alt: FIG. 9.—The Crank is bent out of a piece of 3/16 rod, 7 inches long, into the shape shown.

   FIG. 9.—The Crank is bent out of a piece of 3/16 rod, 7 inches long, into the shape shown.

The other end of each is provided with a small 
insulating handle. A No. 8003 Electrose Knob is just the
thing. These knobs are provided with a threaded 
bushing so that they may be screwed onto the rod. 

The proper position for the discharge rods is shown 
in Figure 1. By sliding the rods back and forth in the 
balls on the ends of the collectors, the distance 
between the balls on the ends of the rods may be varied. 

The spark discharge from the machine, when the latter 
is completed, takes place between these balls. 

The machine still remains to be fitted with the 
"neutralizers" and a set of Leyden jars. 

**The Neutralizers** are illustrated in Figure 14. Two 
are required. They consist of a piece of one-eighth 
inch brass rod, six inches long, having the ends bent 
over at right angles so as to form a shallow U. The 
distance between the ends when bent should be about 
three and five-eights inches. A tuft of tinsel should 
be soldered to the ends of each of the neutralizers. 

.. figure:: images/Image10.jpg
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   :alt: FIG. 10.—The Collector with the Discharge Rods, etc, in position.

   FIG. 10.—The Collector with the Discharge Rods, etc, in position. A is the Brass Ball forming one terminal of the gap across which the sparks jump. B is another Brass Ball screwed onto the end of the Collector Rod and having a hole in it, through which the Discharge Rod slips. CC are two threaded Washers used to clamp the Discharge Rod in place. 

Each neutralizer rod is supported by a hard rubber 
washer three-quarters of an inch in diameter and 
five-sixteenths of an inch thick. In the centre of the washer 
a hole should be drilled, which will fit snugly onto the 
rods upon which the plates are mounted and revolve. 
The neutralizer rod passes through a hole in the upper 
part of the washer as shown in the illustration.

Before the neutralizers can be put into position it 
will be necessary to pull out the rods which support 
the plates so that the plates can be removed. The hard 
rubber washers supporting the neutralizers are then 
slipped over the rods so that one will come between 
each support and plate when the latter is put back into 
position. The rods should be turned so that the tinsel 
tufts touch the sectors. The rubber washers should 
fit snugly on the rods so that the neutralizer will 
stay in any position in which it is placed. The proper 
position for the front neutralizer is a little less than half 
way between vertical and horizontal as shown in 
Figure 1. The neutralizer behind the rear plate should 
be at right angles to that in front. 

.. figure:: images/Image11.jpg
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   :alt: FIG. 11.—Showing how Binding Posts may be substituted for Round Balls on the Collector Rods. 

   FIG. 11.—Showing how Binding Posts may be substituted for Round Balls on the Collector Rods. 

The machine is now all ready for operation. In order 
for it to operate satisfactorily it is necessary for it to 
be warm and dry. It is, therefore, a very good idea to 
thoroughly dry the woodwork and give it a coat of 
varnish or shellac so that it cannot absorb any 
moisture. It may be necessary to start the machine by 
rubbing a glass rod with a piece of flannel or silk and 
then touching the rod to some of the sectors. The 
handle of the machine should be turned from left to 
right, that is, in such a direction that the front plate 
revolves in the same direction as the hands of a clock. 

If the machine is in proper working order a stream 
of small sparks should flow between the spark balls on 
the ends of the discharger rods, provided they are not 
over a half inch apart, when the crank is turned. 

The spark can be intensified and lengthened by 
fitting the machine with two small Leyden jars. 

**The Leyden Jars** are made from small test tubes 
three inches long. The inside of the tube should be 
coated with tinfoil to within about one inch from the 
top. The outside of the tube should be coated in the 
same manner for the same distance. The tinfoil can 
be secured to the glass with shellac. 

The top of the Leyden jars is closed with an 
ordinary cork. A piece of heavy brass wire bent into the 
form of a hook should pass through the cork and make 
connection with the tinfoil on the inside of the tube. 
One Leyden Jar should be hung over each of the 
collector rods by means of the hook. The tinfoil coatings 
on the outside of the jars should be connected together 
by a piece of wire running across from one tube to the 
other. 

.. figure:: images/Image12.jpg
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   :alt: FIG. 12.—Details of the Discharger Rods. 

   FIG. 12.—Details of the Discharger Rods. 

The machine is now complete and ready for 
performing a number of very interesting experiments. 

Experiments with Static Electrical Apparatus. 
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**A Leyden Jar** is a very simple device for 
accumulating and storing static electricity. It consists simply 
of a wide mouthed jar or bottle coated with tinfoil part 
way up on both the outside and the inside in exactly 
the same manner as the small test tubes used on the 
static machine. 

Not all glass jars are suitable for making Leyden 
Jars. The quality of the glass varies considerably and 
some will be found far superior to the rest. 

The glass vessels used by chemists and called 
"beaker glasses" usually make excellent Leyden Jars. 

It is not very difficult to make a good Leyden Jar. 
After you have selected the jar or bottle you wish to 
use, clean and dry it very thoroughly. Then give the 
inside a thorough brushing over with shellac. Cut a 
strip of tinfoil which is long enough to go all the way 
around the inside of the jar and about two-thirds its 
height. Before the shellac is thoroughly dry but is 
still sticky, insert the tinfoil strip carefully into the jar 
and press it smoothly against the glass. 

.. figure:: images/Image13.jpg
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   :alt: FIG. 13.—The Supporting Bar upon which the Collector Rods are mounted. Made of hard rubber so as to be a perfect Insulator. 

   FIG. 13.—The Supporting Bar upon which the Collector Rods are mounted. Made of hard rubber so as to be a perfect Insulator. 

The outside of the jar should also be given a coat of 
shellac and covered with tinfoil in exactly the same 
manner. The tinfoil on the outside of the jar should 
be the same height as that on the inside. The bottom 
of the jar should be coated, both inside and out by 
cutting two circular pieces out of the tinfoil and 
sticking them on with shellac. 

The jar should be provided with a wooden cover 
which will fit snugly into the top. The wood should 
be dried and then given a coat of shellac so that it 
cannot absorb any moisture. 

.. figure:: images/Image14.jpg
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   :alt: FIG. 14.—The Neutralizers.

   FIG. 14.—The Neutralizers. Two are required. They are bent out of Brass Rod and fitted with a Tinsel Tuft at each end. The centre piece  upon which the Rod is mounted should be of Hard Rubber.

It may perhaps be well at this point to emphasize
how highly important it is to always keep all static 
electrical apparatus thoroughly dry and to construct 
it so that it will not collect or absorb any moisture.

A small hole should be bored through the centre of 
the cover so as to permit a brass rod to pass through. 
A piece of spring wire bent into a spiral should be 
attached to the lower end of the rod. When the cover 
is in position, the spring wire should make contact 
with the tinfoil on the inside of the jar. 

It is a very good idea to fit the top of the rod with a 
small brass ball. This will prevent the electricity from 
"leaking" from the sharp corners on the end of the rod. 
Static electricity leaks very easily from sharp corners 
or points, but does not escape so readily from round 
corners or balls. 

.. figure:: images/Image15.jpg
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   :alt: FIG. 15.—Details of the Leyden Jars.

   FIG. 15.—Details of the Leyden Jars. They are simply small Test Tubes, coated inside and outside with tinfoil for about two-thirds their height and fitted with a Brass Rod connected with the inside coating. 

The Leyden jar may be "charged" with electricity 
from the static machine by connecting a wire from one 
of the discharge rods to the outside tinfoil coating on 
the jar. Another wire should be connected from the 
other discharge rod to the rod on the jar which 
connects with the inside tinfoil coating. 

Turning the handle of the machine rapidly for ten or 
fifteen seconds will charge the jar. Disconnect the 
wires as promptly as possible so that the electricity in 
the jar will not have a chance to leak back into the 
machine. Be very careful while doing this, however, 
because if you should happen to touch the tinfoil on 
the outside of the jar and the rod which connects with 
the inside coating at the same time you will get one of 
the surprises of your life. 

.. figure:: images/Image16.jpg
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   :alt: FIG. 16.—A Large Leyden Jar for experimental purposes. 

   FIG. 16.—A Large Leyden Jar for experimental purposes.

The shock won't really hurt you any but it will be 
very uncomfortable and somewhat surprising. 

You can discharge a Leyden jar by bringing a piece 
of wire which is connected to the outside coating, near 
to the knob on the rod. When the wire is close to the 
ball the electricity will jump across the space in the 
shape of a snapping white spark. 

The Leyden jar can be used in connection with a 
number of experiments described later on. 

.. figure:: images/Image17.jpg
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   :alt: FIG. 17.—Showing how to Discharge a Leyden Jar with a curved piece of stiff wire fitted to a Wooden Handle.

   FIG. 17.—Showing how to Discharge a Leyden Jar with a curved piece of stiff wire fitted to a Wooden Handle.

**Bottled Lightning.** A very pretty effect can be 
obtained by passing the spark from a Leyden jar or a 
static machine over a "lightning board." A "lightning 
board" consists of a pane of glass having a number 
of small squares of tinfoil stuck on it so that when the 
electrical discharge is passed over it, sparks take place 
between the little tinfoil squares and produce an effect 
something like miniature lightning. 

A lightning board suitable for the static machine 
just described may be made from a strip of ordinary 
window glass about nine inches long and two inches 
wide. 

Clean the glass thoroughly and then give it a coat of 
shellac on one side. As soon as the shellac becomes 
sticky, lay on a strip of tinfoil the same size as the 
glass and rub it down smoothly. When the shellac has 
thoroughly dried so that the tinfoil is stuck tightly to 
the glass, the board is ready to be cut up into squares. 
This can be best accomplished by means of a sharp 
knife and a ruler. Use care in doing the work so as 
not to tear the tinfoil and be sure that the knife cuts 
all the way through to the glass. Leave two solid 
strips of tinfoil at each end to which to make 
connections. 

.. figure:: images/Image18.jpg
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   :alt: FIG. 18.—The "Lightning Board" is simply a Strip of Glass covered with small Tinfoil Squares.

   FIG. 18.—The "Lightning Board" is simply a Strip of Glass covered with small Tinfoil Squares. It may be insulated by mounting on a Bottle. The two Wires attached to the wide Tinfoil Strips at the ends of the "Board" are for connection to the Static Machine or Leyden Jar. 

The lightning board should be mounted by 
cementing it in a slot in a cork in a bottle so that the glass 
bottle serves as an insulated support. 

If one of the tinfoil strips left solid at the end of the 
board is connected to one of the discharge rods on the 
static machine and the other end is connected likewise 
to the other discharge rod innumerable little sparks 
will zig-zag between the tinfoil squares when the 
machine is set in operation. The effect is quite pretty if 
the experiment is performed in a dark room. 

The Leyden jar can be charged by the static machine 
and discharged through the lightning board. The 
sparks produced by the Leyden jar will be much more 
brilliant than those of the static machine above. 

A very pretty effect can be produced by arranging 
the tinfoil in the form of a pattern or design as for 
example that illustrated in Figure 19. A strip of glass 
about the same size as that used for the lightning board 
may be employed. The glass is coated with shellac 
and as soon as it becomes sticky, small rectangular 
pieces of tinfoil arranged in a zig-zag pattern and 
having small spaces between them, are stuck in position. 
The end pieces are made larger than the other strips 
so as to afford means for connecting the wires. The 
strip should then be insulated and mounted by 
cementing it in a slot in the cork of a glass bottle. 

.. figure:: images/Image19.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 19.—A very pretty effect can be produced by arranging small tinfoil strips on the Glass in a Pattern.

   FIG. 19.—A very pretty effect can be produced by arranging small tinfoil strips on the Glass in a Pattern. Each strip should be separated from the other just far enough for a Spark to pass. 

The apparatus shown in Figure 20 is made 
according to the same plan but the glass in this case is in the 
form of a square instead of a strip. The tinfoil strips 
are arranged in the form of a seven pointed star or any 
other pattern which may be desirable. The two large 
strips A and B are the ones to which the wires should 
be connected. 

**The Electric Parasol** is illustrated in Figure 21. It is 
made by pasting some narrow strips of tissue paper, 
about three-sixteenths of an inch wide and three or 
four inches long, to a small cork which has previously 
been covered with tinfoil. The strips can be made 
most easily by cutting a small sheet of tissue paper 
into strips like the teeth of a comb as shown in the 
upper right hand corner of Figure 21. The tinfoil 
covered cork should be mounted on the upper end of a 
stiff copper or brass wire supported in a bottle. 

If this wire is then connected to one of the discharge 
rods on the static machine and the hand held to the 
other, the paper strips will spread out like a parasol or 
umbrella, as soon as the machine is set in operation. 

.. figure:: images/Image20.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 20.—A very pretty design made by arranging the Strips in the form of a Seven-pointed Star.

   FIG. 20.—A very pretty design made by arranging the Strips in the form of a Seven-pointed Star. Flowers, initials or almost any pattern may be made in the same way. 

A novel experiment somewhat similar in principle 
to the "electric parasol" is that shown in Figure 22. 

Three small paper birds about the size of that shown 
at the right hand side of the illustration should be cut 
out of tissue paper and each one attached to a piece of 
cotton thread about six inches long. The threads are 
then tied to one end of a T-shaped frame bent out of 
copper wire and supported on a bottle. 

If the wire frame is then connected to one of the 
discharge rods and the hand held to the other while the 
machine is set in operation, the birds will rise in the 
air and fly around as far as the threads will let them. 

.. figure:: images/Image21.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 21.—The Electric Parasol.

   FIG. 21.—The Electric Parasol. The upper right-hand corner shows a piece of Tissue Paper cut into Strips. (1) Is the apparatus before the Tissue Paper is fastened to the Cork. (2) Shows the completed "Parasol" and (3), the Parasol when connected to the machine and the latter is set in operation. 

**Electric Acrobats.** The apparatus shown in Figure 
23 consists of a circular metal plate about four inches 
in diameter suspended by a wire from a wire "T" 
stuck in a cork in a bottle. Another circular metal 
plate of the same size is laid on the table below the 
other. The distance between the two plates should be 
about one inch or an inch and one-half. 

Cut three or four little figures, the same size as that 
shown in the upper right hand part of the illustration, 
out of tissue paper and lay them on the bottom plate. 

.. figure:: images/Image22.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 22.—Electric Birds.

   FIG. 22.—Electric Birds. The Birds are made of Tissue Paper and should be about the size and shape shown in the lower right-hand corner of the illustration above. 

The circular metal plates may be made of sheet tin, 
copper, brass or galvanized iron. Even cardboard, 
provided that it is covered with tinfoil, will serve. 

The upper plate should be connected to one 
discharge rod on the static machine and the lower plate to 
the other. Then as soon as the machine is set in 
operation the little paper figures will begin to dance 
up and down, stand on their heads, hang by one foot 
or hand, turn somersaults and perform all sorts of 
stunts. 

**Gunpowder** may be ignited by the spark from a 
Leyden jar. A miniature mortar may be made from a 
piece of broom handle about an inch and one-half in 
diameter with a hole one inch deep in one end as 
shown by C Figure 24. The mortar should be 
fastened to a small wooden base which will support it 
in an inclined position as in the illustration. 

.. figure:: images/Image23.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 23.—Electric Acrobats.

   FIG. 23.—Electric Acrobats. The Acrobats are made of paper. The little figure in the upper right-hand part of the illustration is the proper size. 

Bore two small holes through the wall of the mortar, 
near the bottom and exactly opposite to each other 
Insert two short pieces of coper wire, W, W, in the 
holes and fasten them tightly in position. The ends 
of the wires should be about one-eighth of an inch 
apart. 

A small pinch of gunpowder is then placed in the 
bottom of the mortar. 

Charge the Leyden jar and then discharge it through 
the mortar by connecting it to the two wires W, W. 
As soon as the spark passes, the powder will explode. 
An experiment such as this should be performed 
cautiously and the face and hands should be kept away 
from the powder. Do not put more than a pinch of 
powder in the mortar at a time and by all means keep 
the reserve supply out of the way so that there will 
be no danger of exploding it by accident. 

**An Electric Whirligig** is an interesting piece of 
apparatus which may be built by following the 
suggestions contained in Figure 25. 

.. figure:: images/Image24.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 24.—The Electric Mortar.

   FIG. 24.—The Electric Mortar. C is the Mortar, P the Powder, B a Small Ball and W W the two Wires between which the Spark igniting the powder takes place. 

Mount four pieces of dowel about three inches long 
at the corners of a wooden base about eight inches 
long and two inches wide so that they form four 
vertical posts as shown by A, B, C, D. 

The dowels, as well as the wooden base should be 
carefully dried and shellaced so that they will not 
absorb any moisture. 

Stretch two pieces of straight stiff wire between the 
posts A C and B D, near the top. The wires should be 
perfectly straight and level. 

The whirligig itself is made by passing a sewing 
needle through the axis of a small cork. Four small 
wires having the ends bent over at right angles should 
then be stuck in the cork as shown in the upper left 
hand part of Figure 25. All of the wires should point 
in the same direction. 

.. figure:: images/Image25.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 25.—An Electric Whirligig. 

   FIG. 25.—An Electric Whirligig. 

The four wires should all be the same length so that 
the whirligig is perfectly balanced. The cork is then 
covered with tinfoil so that there will be an electrical 
connection between the four small wires and the needle 
forming the shaft. 

The two wires A C and B D are connected together 
by a wire A B and a piece of flexible wire led to the 
Wimshurst machine. The opposite side of the 
Wimshurst machine is then grounded or touched with the 
hand. If the whirligig is laid on the wires A C and 
B D as shown in the illustration and it is perfectly 
balanced it will commence to revolve and roll along the 
wires just as soon as the Wimshurst machine is set in 
operation. It is the escape of the electricity from the 
points of the four wires on the whirligig which causes 
this. 

Other interesting experiments in static electricity 
may be performed with the aid of a Wimshurst 
machine and the experimenter who is sufficiently 
interested to continue farther is referred to any good book 
on physics or some such volume as "The Boy 
Electrician".

CHAPTER II. CELLS AND BATTERIES.
--------------------------------

Sources of Current. One of the chief difficulties 
of the average young experimenter is to secure a 
satisfactory source of current for operating his 
apparatus. 

There are three means at his disposal and he may 
draw his electricity from 

1. A power or lighting circuit; 

2. A dynamo; 

3. Batteries. 

.. figure:: images/Image26.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 26.—A Voltaic Cell. 

   FIG. 26.—A Voltaic Cell. A Voltaic Cell consists of a Strip of Copper and a Strip of Zinc immersed in a dilute solution of Sulphuric Acid. 

Only those who are so fortunate as to live in a house 
wired for light and power service and supplied from 
the street mains, are likely to be able to utilize the first 
named. Those experimenters who live in towns where 
there are no commercial power wires or whose homes 
are not wired for such service will have to therefore 
depend upon a dynamo or a battery. 

A dynamo is a very satisfactory source of current, 
provided some sort of power, such as a windmill, water 
motor or small engine is available for driving it. A 
hand dynamo is unsatisfactory for some purposes 
because the experimenter is usually unable to drive the 
dynamo and attend to other work at the same time. 

Batteries are the most expensive source of current 
but for many reasons, as explained above, are all that 
is available to the average experimenter. 

There are two classes of batteries, known as 

1. Primary batteries; 

2. Secondary or storage batteries. 

**Primary Batteries** are those which generate their 
own current by the action of some chemical such as, 
for example, an acid upon a metal. 

**Secondary Batteries** derive their current from a 
dynamo or other source of electricity and store it away in 
the form of **Chemical energy** until it is used up. A 
storage battery might be likened to a pail, which can 
be carried to a dynamo and filled full of electricity. 
Those who possess a storage battery can recharge it 
themselves from the 110-volt lighting or power circuit, 
from a dynamo or by taking it to an automobile garage 
where recharging is done. 

Homemade batteries are not as practical as those 
which can be purchased ready made, but the 
knowledge and experience gained in making your own are 
so valuable that every experimenter is urged to start 
in this way. 

Various materials such as zinc, copper, carbon, etc., 
can be used to make some very interesting and 
valuable batteries. 

One of the most common mistakes made in reference 
to cells and batters is in calling a single cell a 
**battery**. One cell is a cell. More than one cell connected 
together is a **battery of cells** or simply a **battery**. 

The Voltaic Cell.
`````````````````

The first practical cell was invented in 1786 by an 
Italian professor named Volta and it is, therefore 
usually called the Voltaic cell. 

A Voltaic cell may be easily made by the 
experimenter, by placing some water, mixed with sulphuric 
acid, in a glass tumbler or a jelly jar and then 
immersing therein a strip of zinc and a strip of copper, each 
about four inches long and one inch wide. The strips 
must be kept separate from one another and should 
be scraped clean and bright before they are placed in 
the solution. A copper wire is fastened to the top of 
each one of the strips. The acid solution should be 
composed of one part of acid, mixed with ten parts of 
water. 

When mixing acid and water, always remember to 
pour the acid into the water and never pour water into 
acid. Otherwise the solution will suddenly become 
very hot and is liable to crack the jar. Acid should 
always be mixed in a glass or earthenware vessel and 
never in any sort of a wooden or metal receptacle, 
because it will attack and dissolve metals and wood.

As soon as the acid has been prepared for the Voltaic 
cell fill a tumbler about three quarters full and then
immerse the zinc and copper strips therein. As soon
as the strips are in the acid, bubbles will commence to 
rise from the zinc. These bubbles are a gas called 
hydrogen and are evidence of a chemical action which 
takes place in a battery. The zinc is being dissolved
by the acid and during the process, sets free hydrogen
gas.

It will probably be noticed that very few bubbles 
arise from the copper plate and that there seems to be 
little chemical action there. 

It will also be noticed that if the two wires connected 
to the strips are brought together the bubbles will 
arise from the zinc much faster than before. That is 
because, when the wires are connected together, a
complete electrical circuit is formed: The zinc is really
being oxidized or slowly burned. If zinc is burned in 
the open air or in a fire it will give out its energy in 
the form of heat but when it is burned in an acid 
solution in the presence of another metal it gives out its 
energy in the form of electricity. 

The zinc strip in a Voltaic battery is known as the 
**negative** pole or cathode, and the copper strip, as the 
positive pole or anode. When the electrical circuit is 
completed by touching the two wires connected to the 
poles together, the current is supposed to flow from the 
positive pole through the wires and back into the 
solution through the negative pole. 

If the two wires, instead of being connected together, 
are connected to an electrical instrument called a 
voltmeter the needle or pointer on the meter will swing 
over and point to about one volt. 

**A Voltmeter** is an instrument for measuring 
electrical pressure or **potential**. The pressure of an electric 
current is measured in **volts** just as the pressure of 
water may be measured in **pounds**. 

If the copper strip is lifted out of the solution and a 
carbon plate or rod also having a wire attached is 
substituted in its place it will be found that the voltage 
or potential has increased to one and one-half volts. 
Zinc and carbon are said to have a greater potential 
difference than zinc and copper and inasmuch as it is 
usually desirable for a battery to have the greatest 
potential difference possible, zinc and carbon are 
employed in the batteries of to-day instead of zinc and 
copper. 

If the wires are then disconnected from the 
voltmeter and connected to an electrical instrument called 
an **ammeter**, the needle or pointer will probably swing 
over until it indicates a current of perhaps ten amperes. 
An **ammeter** is an instrument for measuring the 
volume of an electric current. An **ampere** is a unit of 
current and is used to designate the rate of flow just 
as feet per second are used to denote rate of flow in 
the case of water in a pipe. 

If the meter is allowed to remain connected to the 
cell for a short time it will be noticed that the pointer 
will commence to slowly drop back towards zero. 

The cell is then becoming **polarized**, which is to say 
that small bubbles of hydrogen which are liberated by 
the chemical action, collect on the carbon and cause 
the strength of the battery to fall off. If the battery 
is agitated or the carbon is lifted out and scraped it 
will be found that the current will immediately rise 
again to its first strength. 

It would be a nuisance if it were continually 
necessary to scrape the carbon or shake the battery so as 
to avoid **polarization** and so another means is 
employed to secure the desired result. 

This is accomplished by introducing certain 
chemicals into the solution which will give forth **oxygen**. 
When oxygen and hydrogen meet under proper 
conditions they combine and form ordinary **water**. 

**Bichromate of potash** or as it is also often called 
**potassium bichromate** is the chemical most commonly 
employed for this purpose. 

.. figure:: images/Image27.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 27.—Ordinary Jelly Glasses, Tumblers, Fruit Jars, etc, make good Jars for small cells by cutting off the tops. 

   FIG. 27.—Ordinary Jelly Glasses, Tumblers, Fruit Jars, etc, make good Jars for small cells by cutting off the tops. 

Homemade Batteries.
``````````````````` 

**The materials** required for making batteries, suitable 
as a source of current for the experimenter, will not 
be found expensive in most cases. 

**Carbon rods** and **plates** may be purchased from an 
electrical supply house but they can also be easily and 
cheaply obtained from old dry cells. Dry cells may 
be split open with a cold chisel and a hammer. Care 
should be exercised not to break the carbon in 
removing it. 

The round carbon rods used in arc lamps may be 
used for making batteries provided that if they are 
copper plated, the copper is first removed by immersing 
the rod in a bath of nitric acid. If this precaution is 
not taken there will be a "local action" set up between 
the copper and the carbon and the battery will not be 
as efficient as it will be if the copper is removed. 

Carbon rods and plates are easily drilled with an 
ordinary hand drill. Carbon is quite brittle and breaks 
easily, therefore only very light pressure should be 
used. 

While zinc rods and plates may also be purchased 
they are easily made by the experimenter who 
possesses a little ingenuity. The melting point of zinc is 
quite low. It can be melted in a small iron pot and 
cast into the form of rods or plates in plaster-of-Paris 
moulds. Plates may also be cut out of heavy sheet 
zinc. 

.. figure:: images/Image28.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 28.—A Simple Home-made Cell.

   FIG. 28.—A Simple Home-made Cell.

Ordinary jelly-glasses, tumblers, fruit jars, etc., make 
good jars for small cells. The tops of fruit jars and 
batteries can be cut off so as to make the opening 
larger. 

The cutting can be done with an ordinary glass 
cutter or by filling a scratch completely around the jar or 
bottle, at the place it is desired to cut it off, with a 
three cornered file. If a hot poker or wire is then held 
against the scratch it will commence to crack along 
the line and follow the hot poker as it is drawn around. 

.. figure:: images/Image29.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 29.—A Home-made Battery having two Carbon Plates with a Zinc Rod between. 

   FIG. 29.—A Home-made Battery having two Carbon Plates with a Zinc Rod between. 

Figure 28 shows a simple arrangement consisting 
of a carbon and a zinc plate mounted upon a wooden 
strip. The strip is used to support the plates and rests 
across the top of the jar so that the plates hang below 
in the solution. Most chemicals attack wood and for 
that reason it is well to dip the strip in some hot 
paraffin. The carbon and zinc plates are fastened on 
opposite sides of the wooden strip by means of a round 
headed screw and a washer. A wire lead should be 
placed under the washer on each plate. If the screw 
and washer are then smeared with some hot paraffin or 
vaseline they will be protected from corrosion. 

Care should be used so that the two screws employed 
to fasten the plates to the strip do not touch each other 
in the wood. If they should, the battery will be "short 
circuited" and the current will flow through the screws 
instead of the wires. 

Figure 29 shows an arrangement consisting of two 
carbon plates mounted upon a wooden strip. The zinc 
element consists of a rod set in a whole in the strip 
between the two carbon plates. 

It will be found that two carbon plates will form a 
better cell than one with only one plate or rod. 

The arrangement illustrated in Figure 30 shows two 
carbon rods and one zinc rod clamped between two 
wooden strips. The zinc rod is placed in the center 
and the carbons to either side. 

.. figure:: images/Image30.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 30.—The Elements for a Simple Home-made Cell composed of two Carbon Rods and one Zinc Rod clamped between two Wooden Strips. 

   FIG. 30.—The Elements for a Simple Home-made Cell composed of two Carbon Rods and one Zinc Rod clamped between two Wooden Strips. 

The wooden strips are cut away a bit at the points 
where they clamp the rods so as to form sort of a 
groove into which the rods fit without slipping or 
twisting. The strips are drawn together tightly at the 
ends by two wood screws. 

When more than one carbon rod or plate is used in 
a cell, the carbons should all be connected together 
so as to form a single unit. 

The drawing in Figure 30 shows a wire twisted 
around the carbons so as to connect them together 
but it would be a far better connection if the wire was 
clamped between the carbons and the wood so that it 
is held firmly. 

Four carbon rods may be utilized by following the 
suggestion shown by the drawing in Figure 31. 

This consists of a square piece of wood about 4 x 4 
inches and one-half of an inch thick. 

.. figure:: images/Image31.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 31.—Four Carbon Rods and one Zinc Rod arranged to form the Elements of a Cell. 

   FIG. 31.—Four Carbon Rods and one Zinc Rod arranged to form the Elements of a Cell. 

A zinc rod is set in a hole in the center. Four carbon 
rods are set in a circle around the zinc and held in 
place by screws. All the carbon rods should be 
connected together. The wooden top not only serves to 
support the carbon and zinc rods, but will also act as 
a cover for the cell and prevent the solution from 
evaporating. 

Battery Solutions or Electrolytes.
``````````````````````````````````

It has already been shown how cells become 
"polarized" when the solution consists simply of sulphuric 
acid and water. An ordinary acid solution also has the 
further disadvantage that the zinc element is 
continually consumed by the acid when it is in the 
solution, regardless of whether current is being drawn from 
the cell or not. It is of course consumed more rapidly 
when the circuit is complete and current is flowing 
than when it is not, but the action is still nevertheless 
sufficiently rapid to entirely consume the zinc even in 
the latter case in a very short time. If an ordinary 
acid solution is used therefore as the liquid or 
**electrolyte**, as it is technically termed, it is always necessary 
to lift the elements out of their solutions whenever the 
cells are not in use. They should be lifted out and 
carefully washed so as to remove all traces of acid.

.. figure:: images/Image32.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 32.—A Battery of Three Cells arranged so that they can all be lifted out of the solution at once. 

   FIG. 32.—A Battery of Three Cells arranged so that they can all be lifted out of the solution at once. 

A milder chemical which does not attack the zinc 
so rapidly as an acid is often used wherever a battery 
is to be employed for ringing bells, operating sounders, 
telephoning, etc., and only a small amount is required. 

Sal-ammoniac or chloride of ammonium, as it is also 
called, is a good chemical for this purpose. It is very 
cheap and only requires to be dissolved in water. A 
good strong solution should be made and an element 
consisting of several carbons and one zinc such as those 
shown in Figures 29, 30 and 31 used. 

Such a cell will give about 1.5 volts and 3 or 4 
amperes. If the current is drawn from the battery 
continuously or too rapidly, it will also **polarize** and the 
current will begin to fall off. The advantage of a 
sal-ammoniac cell is that the elements may be left in the 
solution when the cell is not in use, without 
appreciable waste of the zinc. 

A very powerful cell of the non-polarizing type 
capable of delivering a heavy current and having an E. M. 
\F. of two volts can be made by adding some potassium 
bichromate to a sulphuric acid solution.

An electrolyte of this sort may be prepared by 
dissolving four ounces of bichromate of potash in sixteen 
ounces of water. Add to this, four ounces of sulphuric 
acid. The acid should be added slowly and the solution 
stirred at the same time. 

This solution will be found an excellent one to use 
with cells having carbon and zinc elements. The 
current and voltage are much higher than those of an 
ordinary acid solution. 

This type of cell also has the disadvantage that the 
zincs waste away rapidly when in the solution, 
regardless of whether current is being drawn or not. This 
can be partly overcome by **amalgamating** the zincs 
with mercury. In order to amalgamate your battery 
zincs, procure a little **mercuric nitrate** from a druggist 
or chemical house. Dissolve the mercuric nitrate in 
a small amount of water and then rub the zincs with 
a wad of cotton or cloth which has been dipped in the 
mercuric nitrate solution. 

The arrangement shown in Figure 32 is a very 
convenient one to follow in arranging a battery of three 
or more cells. The elements of three cells are all 
mounted upon a strip of paraffined wood and connected 
in series. The three battery jars are placed in a row 
so that each pair of elements will dip into their proper 
jar when the strip is laid across the tops. 

Such an arrangement is not only more compact 
than one having the elements composing each cell 
mounted upon separate strips, but will be found very 
convenient when an electrolyte composed of 
bichromate of potash and acid is used, because all the 
elements may then be raised out of the solutions at the 
same time. 

It is possible to place the jars in a frame and 
arrange a windlass fitted with a crank so that the 
elements may be easily raised or lowered from and to 
the solution. Such an arrangement is called a "plunge 
battery." 

Connecting Cells. 
`````````````````

Cells may be connected either in **series**, in **multiple**, 
or in **series-multiple**, depending upon the number of 
cells to be used and the amperage and voltage desired. 

.. figure:: images/Image33.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 33.—Showing how Cells are arranged when they are connected in Series.

   FIG. 33.—Showing how Cells are arranged when they are connected in Series. The Voltage of Six Dry Cells connected in series as above would be approximately 6 x 1.5 or 9 Volts. 

Cells are in series when they are connected with a 
wire leading from the negative pole of one of the 
positive pole of another, so that the current flows through 
each one in turn. Figure 33 shows six cells connected
in series. Cells are placed in series when voltage is 
the most important factor. The total voltage of the 
battery is then equal to the sum of the voltages of the 
cells. For example, the voltage of the ordinary dry 
cell is about 1.5 and therefore if four dry cells are 
connected in series the total voltage of the battery will 
be six. If six dry cells are connected in series the 
voltage at the terminals will be about nine. 

When a heavy amperage is desired, cells are 
connected in multiple. Figure 34 shows six cells connected 
in multiple. It will be noticed that all the negative 
poles are connected together to form one terminal, 
while all the positive poles form another. The 
amperage of the average dry cell is about 20. The 
amperage of a battery of cells connected in multiple is equal 
to the sum of the amperages of the separate cells. The 
amperage of four cells connected in multiple will be 
about 80 and about 120 in the case of six cells. 

.. figure:: images/Image34.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 34.—Showing Six Dry Cells connected in Multiple.

   FIG. 34.—Showing Six Dry Cells connected in Multiple. The Voltage of such an arrangement would only be 1.5, but the Amperage available would be six times that possible from Cells connected as in Figure 33. 

The life of the average dry cell is about twenty 
ampere hours under normal conditions. If however the 
cell is discharged at a high rate, say for instance, five 
amperes, it will be found that the life is less than 
twenty ampere hours. On the other hand, if the 
discharge rate is very low, as for example, one-quarter of 
an ampere, the capacity of the cell will be greater. In 
order to get the most economical service from a 
battery it is therefore advisable to lighten the load as far 
as possible, and cells are consequently often connected 
in **series-multiple** with that result in view. In a case, 
for illustration, where it might be desirable to secure 
a current 4 1/2 volts and five amperes from dry cells, 
the series-multiple arrangement could be 
recommended. Three dry cells connected in series will 
furnish 4 1/2 volts and five amperes, but by using two sets 
as in Figure 35, the load is divided between them and 
each set will only have to furnish amperes to the 
circuit. **Two sets of cells used in series-multiple will 
therefore last more than twice as long as either set 
would alone.**

The series-multiple arrangement is recommended 
where cells are to be used for operating toy trains, 
induction coils, motors, etc., as being the most 
economical. 

Always be sure to use large wire in connecting cells. 
Fine wire offers considerable resistance to the 
electrical current and the full benefit of the batteries 
cannot be secured when it is used. 

.. figure:: images/Image35.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 35.—Showing how to connect a Battery of Cells in Series-Multiple. 

   FIG. 35.—Showing how to connect a Battery of Cells in Series-Multiple. 

Use care to scrape all connections so that they are 
clean and bright. Tighten the binding posts with a 
pair of pliers so that there is no chance of their 
becoming loose. 

Another wise precaution is to always arrange 
batteries so that there is a small space between two cells 
and no likelihood of any of the wires or binding posts 
coming into contact with one another so as to form a 
short circuit. 

After the connections have been carefully made a 
little vaseline smeared over them will prevent 
corrosion. 

.. figure:: images/Image36.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 36.—Battery Connectors like that shown above can be obtained for 1 1/2 cents each and will be found to be very handy. 

   FIG. 36.—Battery Connectors like that shown above can be obtained for 1 1/2 cents each and will be found to be very handy. 

Storage or Secondary Cells.
```````````````````````````

Storage or secondary cells (also sometimes called 
accumulators), differs from primary cells in that they 
will not give forth an electric current until they have 
been **charged** by passing an electric current through 
them. 

.. figure:: images/Image37.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 37.—A Simple Experimental Storage Battery consisting of two Lead Plates immersed in Dilute Sulphuric Acid. 

   FIG. 37.—A Simple Experimental Storage Battery consisting of two Lead Plates immersed in Dilute Sulphuric Acid. 

The Storage Cell is therefore a very convenient 
means of taking electric energy at one time or place 
and storing it up for future use. From this it must not 
be implied that electricity is actually stored in such 
a battery. The energy of the electric current is really 
changed into chemical energy and this energy 
produces electricity when the cell is again discharged. 

The superiority of the storage cell over any other 
form of battery is universally recognized. The dry 
cell has an E. M. F. of only 1.5 volts and deteriorates 
rapidly with age. The E. M. F. of a storage cell is 2 
volts, or 33 1/3 per cent higher. Storage cells will 
operate almost any electrical device with increased 
power over any other form of battery. A wireless set 
will send farther, lamps will turn steadier and a motor 
will give more power. 

.. figure:: images/Image38.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 38.—Showing how to charge a Simple Storage Cell composed of two Lead Plates immersed in Sulphuric Acid by connecting it to two Bichromate of Potash Cells. 

   FIG. 38.—Showing how to charge a Simple Storage Cell composed of two Lead Plates immersed in Sulphuric Acid by connecting it to two Bichromate of Potash Cells. 

If properly cared for, a storage cell will last 
indefinitely. It may be recharged an unlimited number of 
times and is exactly as good as new each time. A dry 
cell must be thrown away when discharged. 

Storage cells are rated by their output in 
**Ampere Hours.** An **Ampere Hour** is the amount of current 
represented by one ampere flowing for one hour. A 
10 ampere hour cell will give 2 amperes for five hours, 
1 ampere for 10 hours, 1/2 ampere for 20 hours, etc. 
The ampere hour capacity of a cell divided by the 
amount of current being used will determine how long 
that current can be drawn before recharging is 
necessary. 

Storage cells may be recharged from any source of 
**direct** current, that is, from the lighting circuit, in 
series with a lamp, from a small shunt wound dynamo, 
from dry cells or other primary batteries, or from 
alternating current by using a **Rectifier**. 

An Experimental Storage Cell.
````````````````````````````` 

Storage cells consist of lead plates immersed in an 
electrolyte of dilute sulphuric acid. 

Cut two strips, one inch wide and five inches long, 
out of sheet lead about one-eighth of an inch thick. 

Attach a wire to each one of the plates and then 
immerse them in a jar full of **electrolyte** composed of: 

1. Ten parts of water. 

2. One part of sulphuric acid. 

Connect the wire leading from the plates to a 
voltmeter and you will notice that the pointer will not 
move away from zero. 

Disconnect the wires and mark one plate as the 
**positive**, by means of a little cross; mark the other plate 
**negative**, with a straight line. 

Connect two good bichromate cells in series and lead 
the positive terminal to the lead plate marked with a 
cross. Connect the negative pole of the battery to the 
other lead plate. Bubbles of gas will immediately 
begin to arise from the lead plates. Let the batteries 
remain connected for about five minutes and then 
remove them. If you then connect the two lead plates 
to the voltmeter again you will find that the needle 
now swings nearly to two volts. 

You will also find that your storage cell, for the two 
lead plates are now a storage cell, will also ring a bell 
or run a small motor for a few seconds. 

The two lead plates became **charged** when the 
current from the bichromate cells was passed through 
them. This little experiment illustrates the principle 
of the storage cell very well. 

A storage cell made of lead plates in the manner just 
described would not possess sufficient capacity to make 
it worth while as a practical cell. It has been found 
that if instead of a solid flat plate, a framework or grid 
is used, consisting of a set of bars crossing one another 
at right angles, leaving spaces between, which are 
filled with a paste made of lead oxides, there will be 
a considerable gain in the capacity of the cell. 

A Homemade Storage Cell.
```````````````````````` 

The storage cell illustrated in the accompanying 
illustrations is very simple to make and a battery of 
them capable of delivering six or eight volts will prove 
a very convenient source of current for performing all 
sorts of electrical experiments. 

.. figure:: images/Image39.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 39.—Showing how the Plates for a Storage Cell may be made from Sheet Lead by boring it full of holes and filling with paste.  

   FIG. 39.—Showing how the Plates for a Storage Cell may be made from Sheet Lead by boring it full of holes and filling with paste. 

The plates are cut from sheet lead from one-quarter 
to five-sixteenths of an inch thick. The height and 
width will depend upon the size of the jars used. There 
are several sizes of rectangular glass storage cell jars 
on the market, and if the plates are made about three 
inches wide and three and one-half inches high, they 
will fit the smallest size of jar. A lug about one inch 
and one-half long and three-quarters of an inch wide 
is left projecting at the top. 

Three plates are used in each cell. Each cell will 
have an E. M. F. of two volts when fully charged. In 
order therefore to have a battery capable of delivering 
six volts, three cells will be necessary. Nine plates 
will be required for three cells. 

The body of the plates should then be drilled full of 
holes about one-eighth of an inch in diameter as shown 
by B in Figure 39. 

The plates are now ready for pasting. Select three 
of the plates and mark them with a small cross. These 
are to be **positive** plates when finished. The paste for 
these plates is made by mixing red lead with diluted 
sulphuric acid. The paste should form a good stiff 
mixture. Lay the three plates upon a smooth board 
and press the paste carefully into the holes with a flat 
stick. They are then laid aside to dry and harden. 

.. figure:: images/Image40.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 40.—A set of three Plates composed of One Positive and Three Negatives assembled to form a Cell.  

   FIG. 40.—A set of three Plates composed of One Positive and Three Negatives assembled to form a Cell. 

The six remaining plates are to be **negatives** when 
finished and they are pasted in identically the same 
manner as the positives except that the paste is made 
of a mixture of yellow lead and dilute sulphuric acid 
instead of red lead. 

A pasted plate is shown at the right in Figure 39. 

Cut six rectangular pieces, three by three and 
one-half inches, of heavy blotting paper or thin 
whitewood. The thin wood used in the construction of 
fruit baskets may be used for this purpose. These 
rectangles are to be used as "separators" between the 
plates. 

.. figure:: images/Image41.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 41.—Glass and Rubber Storage Cell Jars which are on the market for the Electrical Experimenter and may be purchased very reasonably.

   FIG. 41.—Glass and Rubber Storage Cell Jars which are on the market for the Electrical Experimenter and may be purchased very reasonably.

The plates should then be assembled in groups of 
three, as shown in Figure 40. The positive plate is 
placed in the centre with a separator on either side. 
Two negative plates are then placed on the outside. 
The lugs on the negative plates should come opposite 
to each other. A square lead block having a hole 
bored through the centre may be placed between the 
two negative lugs. The lugs are then clamped together 
with a binding post and a screw. The plates are held 
in a compact bundle by two heavy rubber bands 
passing around them. 

Each group of plates is then placed in its proper jar 
and the jar filled full of a mixture composed of: 

1. Four parts of water, and 

2. One part of sulphuric acid. 

The plates are now ready for forming. 

The cells are connected in series by leading a wire 
from the negative of one to the positive of another 
and so on. 

The terminals of the battery are then connected to a 
steady source of direct current of at least ten volts. 
The positive pole of the battery should be connected 
to the positive of the current source and the negative 
to the negative. 

The source of current may be (1) the 110 volt D. C. 
supply in series with a lamp bank as described in 
Chapter IV; (2) the 110 volt A. C. supply after it has 
passed through a rectifier; (3) another battery, or (4) 
a shunt wound dynamo. 

.. figure:: images/Image42.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 42.—An empty Storage Cell Grid and also a Pasted Plate both of which are on the market for experimenters who wish to build their own Cells. 

   FIG. 42.—An empty Storage Cell Grid and also a Pasted Plate both of which are on the market for experimenters who wish to build their own Cells. 

The current passed through the storage cells during 
the forming process should be about one ampere for 
cells of the size described above. As soon as the 
positive plates of the storage cells have changed to a dark 
chocolate-brown color and the negatives to a gray-slate, 
disconnect the storage battery from the source of 
current and proceed to use it just as you would any 
ordinary battery. Use it until it is exhausted and then 
connect to the charging current again, taking care to make 
certain that the positive pole of the battery is 
connected to the positive pole of the current source. 

After the cells have been recharged and discharged 
in this manner about ten times they will be completely 
"formed" and ready for permanent service. 

Complete directions for recharging storage cells and 
instructions for their care and maintenance will be 
found further on. 

The only objection to the storage cells just described 
is that the paste is liable to fall out of the plates in 
time. The plates or "grids" as they are called used in 
commercial storage cells are cast in elaborate moulds 
which make it possible to overcome this difficulty. 
Such grids cannot however be made by the 
experimenter. 

Jars, pasted plates and empty grids may be 
purchased from well known firms dealing in apparatus for 
the experimenter, and with their aid it is possible to 
construct a very substantial and durable storage cell 
at home. 

The empty grids or fully formed plates may be 
purchased in the following sizes: 

================================= ==============
Positive or Negative Plate, size  2 7/8 x 2 1/2 
"                                 3 1/8 x 2 7/8 
"                                 3 5/8 x 5 3/4 
"                                 4 3/4 x 2 7/8
"                                 4 3/4 x 5 3/4 
================================= ==============

Glass jars will be found satisfactory for stationary 
batteries. Rubber jars are however advisable for 
portable batteries. Jars of the following sizes may be 
easily obtained: 

================================= =============================
Glass Jar, outside                3 3/4 x 4 x 1 1/2 inches
Glass Jar, outside                3 3/4 x 5 x 1 1/2 inches
Hard Rubber Jar, outside.         6 1/2 x 3 1/2 x 1 1/2 inches 
Hard Rubber Jar, outside.         6 1/2 x 6 1/2 x 1 1/2 inches
================================= =============================

If the empty grids are purchased, they should be 
pasted in the same manner as those plates just 
described. An empty grid of this type is shown in 
Figure 42. A pasted plate is shown along side of it. 

The two negative plates in cells of this type are 
fastened together by "burning" into a lug, The lugs 
for this purpose may also be purchased and will be 
found inexpensive. 

The long lugs on the negative plates are cut off so 
that they will only just project through the rectangular 
holes in the "connecting lug" when the latter is in 
place, as shown by A in Figure 43. 

The plates are "burned" into the connecting lug by 
using a red hot soldering iron to melt the lead until 
they flow together at those points. This is a job 
requiring a little skill and the experimenter had better 
practice burning some odd bits of lead together first 
so as to avoid all possibility of spoiling his plates. 

.. figure:: images/Image43.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 43.—Two Negative Plates "burned" together and the Connecting Lug used.  

   FIG. 43.—Two Negative Plates "burned" together and the Connecting Lug used. 

The positive plate is placed in position, as shown in 
Figure 44. 

Wooden separators of the same size as the plates 
are placed between the plates and the whole strapped 
together with heavy rubber bands near the top and 
bottom. 

The cells are then placed in their jars and the latter 
poured full of electrolyte, providing that the batteries 
are to be of the stationary or open type. 

If it is desirable that they be portable and arranged 
so that the acid will not easily spill, it will be necessary 
to seal them at the top. 

The sealing is accomplished by cutting a "cover" 
strip out of thin wood which will slip down over the 
lugs into the jar so that it comes about one-half an inch 
below the top. A small hole should be bored in the 
centre of the cover strip to receive a short piece of 
hard rubber or lead tubing, which will act as a vent 
and permit the gases formed during charging to escape 
or the electrolyte to be emptied at will. 

.. figure:: images/Image44.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 44.—The Elements of a Storage Cell composed of two Negative Plates and one Positive Plate in their proper position. 

   FIG. 44.—The Elements of a Storage Cell composed of two Negative Plates and one Positive Plate in their proper position. 

The cover strip should fit into the jar tightly so that 
when the sealing mixture is poured in it will not run 
down around the plates or into the jar. 

The top of the battery is then poured full of a molten 
compound of asphaltum and pitch. 

No attempt should be made to seal the batteries 
when they contain acid. The inside of the jar should 
be clean and dry. 

After the cells are sealed and filled with electrolyte 
they are ready for either forming or charging, 
depending upon whether the empty grids were purchased and 
pasted by the experimenter or the plates were bought 
already pasted and formed. 

If they require forming, they must be put through 
the same forming process which has already been 
described. 

The finished cells when sealed will appear like those 
shown in Figure 45, according to the sizes of plates 
and jars used. 

.. figure:: images/Image45.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 45.—Three different sizes of Storage Cells which may be purchased ready made or built by the experimenter out of prepared materials as explained. 

   FIG. 45.—Three different sizes of Storage Cells which may be purchased ready made or built by the experimenter out of prepared materials as explained. 

Recharging and Caring for Storage Cells.
```````````````````````````````````````` 

Storage cells are especially affected by the usage 
given them. If they are mistreated they will quickly 
go to pieces, whereas, on the other hand if well treated 
they will last indefinitely. 

It is important that the electrolyte used in the cells 
should always be of the proper strength. The only 
accurate method of preparing the electrolyte is with 
the aid of a **hydrometer**. A hydrometer is an 
instrument for determining the specific gravity of solutions. 

It is a little device which looks somewhat like a 
thermometer. It is placed in the solution and allowed 
to float. There is a numbered scale along the upper 
part of the hydrometer and the **specific gravity** or 
strength of the solution is indicated on the scale by 
the point which is level with the surface of the solution. 

The normal specific gravity for a storage battery 
solution should be about 1.250. The strength can be 
increased by adding more acid and decreased by 
adding water. 

Ordinary commercial or technical grades of sulphuric 
acid and ordinary water are satisfactory for primary 
batteries, but the acid and water used in making the 
electrolyte for storage cells must be **chemically pure** if 
you wish to obtain good results and desire your 
batteries to hold their charge while standing. 

Storage cells can be recharged with DIRECT 
current only. A dynamo for recharging storage cells must 
be SHUNT wound. The voltage of the charging 
current must be greater than that of the storage cells. 
About three volts of charging current will be required 
for each cell of the storage battery. Cells may be 
connected in multiple when recharging so as to bring the 
voltage of the cells below that of the charging 
current. It will of course, however, take much longer 
to recharge cells connected in multiple than the same 
cells connected in series, provided that the amperage 
of the current is the same. 

Storage cells must not be recharged too rapidly. It 
is better to recharge them slowly rather than too 
rapidly. Two amperes is plenty for small cells of 
10-15 ampere hours capacity. Three amperes is 
sufficient for cells of 15-25 ampere hours capacity. Five to 
six amperes is the right charging rate for a 40 ampere 
hour battery and 8 amperes in the case of a 60 ampere 
hour battery. 

.. figure:: images/Image46.jpg
   :align: center
   :scale: 50 %
   :alt: FIG. 46.—A Hydrometer for preparing and testing the Acid Solution for Storage Batteries. 
   
   FIG. 46.—A Hydrometer for preparing and testing the Acid Solution for Storage Batteries. 

Storage cells should never be allowed to stand 
discharged for any length of time or the plates are liable 
to become hardened and 
"sulphated." They turn white when 
they are sulphated. It will take 
a great deal of charging and 
recharging to get them back in 
shape when once they get in 
that condition. 

Never short circuit a storage 
cell or discharge it too rapidly. 

Whenever any great amount 
of sediment collects in the 
bottom of the jars, pour out the 
acid solution and wash the cell 
out thoroughly with some pure 
water. 

The plates of a storage cell 
should always be raised up off 
the bottom of the jar, so that 
any sediment which collects 
will fall below. 

.. figure:: images/Image47.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 47.—The proper way of Recharging Storage Cells from the 110 Volts D. C. Supply in series with a set of Lamps. 
   
   FIG. 47.—The proper way of Recharging Storage Cells from the 110 Volts D. C. Supply in series with a set of Lamps. 

It is a very good plan to keep the terminals of a 
storage cell or battery smeared with vaseline so that 
they will not become corroded. 

You can tell when a storage cell or battery is fully 
recharged by the color of the plates. The positives 
will in that case be a dark chocolate brown and the 
negatives a light slate gray color. 

A cell which is fully recharged will indicate 2 1/2 
volts on a voltmeter connected across its terminals 
while the charging current is still on. 

CHAPTER III. HOW TO REDUCE THE 110 V. D.C. OR A.C. TO A LOWER VOLTAGE FOR EXPERIMENTAL PURPOSES.
------------------------------------------------------------------------------------------------

It is often desirable to operate experimental 
apparatus and other electrical devices from the 110 volt 
lighting circuit. Such a circuit may be either direct 
or alternating, commonly spoken of as D.C. and A.C.
The easiest method of reducing the voltage of the 
110 volt circuit to a value where it can be used in place 
of an ordinary battery is to use a step-down 
transformer. A transformer will, however, operate only on 
alternating current and it is impossible to use it on a 
direct current circuit. 

.. figure:: images/Image48.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 48.—A Lamp Bank consisting of a Set of 110-Volt Lamps connected Multiple and arranged to be placed in series with any device it is desired to use on the 110-Volt Current.  
   
   FIG. 48.—A Lamp Bank consisting of a Set of 110-Volt Lamps connected Multiple and arranged to be placed in series with any device it is desired to use on the 110-Volt Current. 

It is therefore necessary to secure the desired result 
by placing an adjustable resistance in the circuit and 
the most practical method of accomplishing this is to 
use a "lamp bank." 

**A Lamp Bank** consists of a number of incandescent 
lamps arranged on a board so that any desired number 
may be quickly included in or withdrawn from the 
circuit. 

Figure 48 illustrates such an arrangement. It 
consists of a number of Edison sockets of the type known 
as "flat-base porcelain receptacles", mounted in two 
rows upon a suitable baseboard. Six or ten receptacles 
will usually prove sufficient for the ordinary lamp bank. 

The lamps are connected in "series-multiple." The 
diagram in the upper left hand corner of Figure 48 
shows just how this is done. Four binding posts 
should be mounted upon one end of the board and 
marked A, B, B and C as shown. B and B are 
connected together, or to use an electrical term, are "in 
common."

The 110 volt supply is connected to the posts B and 
\C. If any electrical device is then connected to A and 
B and a lamp placed in each one of the receptacles, 
the lamps will be in series with the apparatus and 
lower the voltage of the 110 volt circuit to a value 
where it may be used for recharging storage cells, 
operating toy motors, electroplating, lighting 
miniature lamps, running toy railways, etc. 

110 volt carbon lamps should be used on a lamp 
bank operated on a 110 volt circuit. Carbon lamps 
consume more current than tungsten lamps and it 
will therefore not be necessary to use as many. Each 
16 c.p. 110 volt lamp used will allow about one-half 
of an ampere to pass through the circuit. Thirty-two 
candle power bulbs of the same voltage will pass 
about one ampere, while an 8 c.p. bulb will only 
permit one-quarter of an ampere to flow. 

It is therefore very easy to regulate the amount of 
current flowing by using lamps of different sizes and 
screwing them in or out of the receptacles. 

A lamp bank such as this may of course be used on 
either the 110 volt A. C. or D. C. circuit. 

CHAPTER IV. HOW AN ALTERNATING CURRENT MAY BE CHANGED INTO DIRECT CURRENT BY MEANS OF AN ELECTROLYTIC RECTIFIER. 
----------------------------------------------------------------------------------------------------------------

Oftentimes the only source of electrical energy 
for experimental work is the 110 volt alternating 
current supply. This may be reduced to a voltage 
suitable for operating small battery motors, trains, 
lamps, etc., by means of a "lamp bank" resistance or a 
step-down transformer. 

Direct current is **necessary** however in order to 
recharge storage batteries and to operate many other 
devices. The electrolytic rectifier is a device for 
changing alternating current into direct current and will be 
found satisfactory for this purpose, provided too much 
is not demanded of it. It is fairly efficient 
if used only to rectify small amounts of 
current. It is not efficient when large 
amounts of currents are passed through 
it and quickly becomes very hot in such 
a case. 

An electrolytic rectifier consists of an 
electrode of iron or lead and one of 
aluminum immersed in a solution of sodium
phosphate.

.. figure:: images/Image49.jpg
   :align: center
   :scale: 50 %
   :alt: FIG. 49.—A Single Cell of Electrolytic Rectifier.
   
   FIG. 49.—A Single Cell of Electrolytic Rectifier.

An ordinary glass battery jar may be 
used to hold the solution, preferably one 
measuring 5 x 7 inches. The electrodes are supported 
by a wooden cover which also serves to prevent the 
solution from evaporating. The cover may be circular 
in form and simply rest on the top of the jar or may 
have a groove turned on the underside so that it fits 
the rim of the jar snugly. 

It is a wise precaution to thoroughly saturate the 
cover with paraffin by immersing it in a molten bath 
of that material. If the cover is allowed to remain in 
the molten paraffin until all bubbles have ceased to 
rise, the paraffin will thoroughly permeate the wood 
and protect it from the action of the Chemical solution 
used in the rectifier. 

.. figure:: images/Image50.jpg
   :align: center
   :scale: 50 %
   :alt: FIG. 50.—An Electrode cut out of Sheet Metal.
   
   FIG. 50.—An Electrode cut out of Sheet Metal. The top is bent over at right angles and drilled so that it can be mounted on the underside of the cover.

As stated above, one electrode may be 
made of iron or lead. The other should 
be aluminum. The electrode may be cut 
out of sheet metal and made in the form 
of a strip about one and one-half inches 
wide and six inches long. The top of each 
electrode is bent over at right angles and 
bored with a small drill and an 8-32 brass 
machine screw is passed through the hole 
and through the cover into the bottom of 
the binding post mounted on the top of 
the cover, thereby serving not only to 
fasten the electrode securely in place to 
the underside of the cover, but also to 
establish connection between the electrode 
and the binding post itself.

Electrodes which are cut out of sheet 
metal possess the disadvantage that they 
are not quite as efficient and will not last 
as long as electrodes which are cast. 

Cast electrodes are much heavier and 
far more efficient in many other ways. 
They cannot be easily made by the young 
experimenter, but may be procured from any one of 
several firms dealing in supplies for experimenters. 

The right hand sketch in Figure 52 shows how the 
electrodes should appear when they are mounted in 
position on the underside of the cover. They are placed 
about two and one-half inches to three inches apart. 

The solution is formed by dissolving 
sodium-phosphate in water until a "saturated solution" is formed, 
that is, until the water will not dissolve any more. 
Sodium-phosphate dissolves rather slowly and it will 
be necessary to stir the solution and crush the lumps 
which form with a stick or glass rod. 

Fill the jars nearly to the top and then place the 
electrodes into position. 

.. figure:: images/Image51.jpg
   :align: center
   :scale: 50 %
   :alt: FIG 51.—A Cast Electrode will last much longer than one cut from Sheet Metal.
   
   FIG 51.—A Cast Electrode will last much longer than one cut from Sheet Metal. Cast Electrodes like that above are on the market and can be purchased very reasonably. 

The action of the electrolytic 
rectifier, in changing alternating current 
into direct current, is interesting and 
peculiar. The rectifier acts much 
like a valve which opens one way 
and closes the other. 

If a battery is connected to the 
electrodes of a rectifier, the positive 
pole of the battery being connected 
to the lead or iron electrode and the 
negative of the battery to the 
aluminum electrode of the rectifier, the 
current from the battery will flow 
through the rectifier and nothing 
unusual will happen. If, however, the 
poles are reversed so that the 
positive pole is connected to the 
aluminum electrode, oxygen gas will form 
on the aluminum. The action of the 
oxygen gas is to combine with the 
aluminum and form a coating of 
**aluminum oxide** all over the 
electrode. Aluminum oxide is an 
insulator and it therefore quickly forms an insulating 
coating which shields the electrode from the solution 
and stops the passage of the current. This action is 
almost instantaneous. 

.. figure:: images/Image52.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 52.—A completed single Cell Rectifier.
   
   FIG. 52.—A completed single Cell Rectifier. The right hand sketch shows how the Electrodes are mounted on the underside of the cover.

If the rectifier is connected to an alternating current 
supply it will act just like a valve permitting the 
current to flow in one direction but stopping it 
whenever the aluminum electrode is **positive**. The 
resulting current is therefore, under proper conditions, an 
intermittent current flowing only in one direction. 

An alternating current may be represented by a 
wavy line drawn above and below a straight line. 
Every time that the wavy line crosses the straight line 
it represents an alternation or a reversal of the 
direction in which the current flows. 

.. figure:: images/Image53.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 53.—A Diagram showing how a Rectifier cuts off one-half of the Alternating Current Wave and changes it into Pulsating Direct Current. 
   
   FIG. 53.—A Diagram showing how a Rectifier cuts off one-half of the Alternating Current Wave and changes it into Pulsating Direct Current. 

The direct current from an electrolytic rectifier 
working under proper conditions is practically 
one-half of the alternating current wave and may be 
represented by the series of waves marked by "C" in the 
lower part of the illustration in Figure 53. 

It will be noticed that these lines do not cross the 
straight line and the current therefore does not 
reverse but flows in one direction only. 

When a single cell of rectifier is used on the 110 volt 
current supply, it should be placed in series with a 
lamp bank or a step-down transformer so that the 
current is reduced to lower voltage.

Figure 54 shows how to connect a storage cell in 
series with a single cell of rectifier and a lamp bank 
so that the storage cell may be recharged from the 
alternating current. A step-down transformer will be 
found more efficient and not quite so wasteful of 
current as a lamp bank. The rectifier and the storage cell 
are simply connected in series with the secondary of 
the step-down transformer in order to secure this 
result. 

.. figure:: images/Image54.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 54.—Circuit showing how a Single Cell of Rectifier should be connected in series with a Lamp Bank to Recharge a Storage Cell.
   
   FIG. 54.—Circuit showing how a Single Cell of Rectifier should be connected in series with a Lamp Bank to Recharge a Storage Cell. A is the Aluminum Plate and L the Lead or Iron Plate.

.. figure:: images/Image55.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 55.—Diagram showing the Difference in Current after it has been passed through a Single Cell or Rectifier and after passing through a Four-Cell Rectifier. 
   
   FIG. 55.—Diagram showing the Difference in Current after it has been passed through a Single Cell or Rectifier and after passing through a Four-Cell Rectifier. 

The negative pole of the storage cell must always 
be connected to the aluminum electrode of the rectifier.

The series of little curved lines at the bottom of 
Figure 53 which represent the alternating current after 
it has been changed into direct current by the action of 
the rectifier, have a space between each two, showing 
that there are periods during which no current flows 
but that the current is intermittent and made up of a 
number of short impulses. One-half of the alternating 
current is therefore really wasted. 

It is possible, by means of four cells of rectifier, to 
so connect them that "both halves of the alternating 
current wave are utilized" and the spaces are filled 
up as shown in the lower part of Figure 55. 

.. figure:: images/Image56.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 56.—Diagram showing how a Four-Cell Rectifier is connected.
   
   FIG. 56.—Diagram showing how a Four-Cell Rectifier is connected. The Alternating Current Source is connected to C and D. The Direct Current is taken off at A and B. The Electrodes marked A, A, A, A are the Aluminum Electrodes. L, L, L, L may be Lead or Iron. 

The current which would normally be in a reverse 
direction, and therefore below the straight line, has 
been completely reversed so that it flows in the same 
direction as that above the line. 

Figure 56 shows how to connect four cells of 
rectifier in order to secure this result. 

An electrolytic rectifier composed of cells 
approximately 5 x 7 inches, as described, will not efficiently 
handle a current of over two to two and one-half 
amperes. A four cell rectifier will operate to the best 
advantage on a voltage over 50, and for that reason 
it is always best to use a lamp bank or step-down 
transformer in connection with it. 

When the solution in a rectifier becomes hot it will 
not operate as efficiently as when cold. The solution 
becomes exhausted after a certain amount of usage 
and requires renewal. This condition will be indicated 
by the failure of the rectifier to operate properly. The 
old solution should then be thrown away and the jars 
and electrodes washed and cleaned thoroughly before 
the new solution is poured in. 

.. figure:: images/Image57.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 57—A Complete Four-Cell Rectifier connected together and Mounted in a Tray. 
   
   FIG. 57—A Complete Four-Cell Rectifier connected together and Mounted in a Tray. 

CHAPTER V. HOW TO BUILD A STEP-DOWN TRANSFORMER FOR REDUCING THE 110 VOLT A. C. FOR EXPERIMENTAL PURPOSES. 
----------------------------------------------------------------------------------------------------------

A Step-Down Transformer will reduce the 
110 volt alternating current to a low voltage. 
These low voltage currents are still alternating but 
will operate almost all sorts of direct current 
apparatus with the exception of permanent magnet type 
motors which are now practically obsolete. 

A suitable step-down transformer may be used to 
operate electrical toys, such as small fans, motors and 
miniature electric railway trains, ring bells, light small 
lamps, operate spark coils, etc., in fact the different 
uses are practically unlimited, depending only upon 
the ingenuity of the experimenter. 

.. figure:: images/Image58.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 58.—Details of the two different Pieces of Sheet Iron used in building up the Core.
   
   FIG. 58.—Details of the two different Pieces of Sheet Iron used in building up the Core. Sufficient of each piece are required to form a pile of each three-quarters of an inch thick. 

A step-down transformer cannot be used to recharge 
storage cells or for electro-plating unless the current 
is first passed through a rectifier. 

A transformer is both in principle and construction 
really very simple. 

It consists simply of two coils of wire wound 
around an iron core. One coil consists of many turns 
of fine wire and is connected to the 110 volt 
alternating current. This coil is called the **primary**. The 
other coil consists of a smaller number of turns of 
larger wire and is called the **secondary**. The lower 
voltage currents are obtained from the secondary. 

The first step to take in making a transformer is 
to procure some sheet iron of the sort used for making 
stove pipes. It is called stove pipe iron. 

This iron will have to be cut into a number of pieces 
like A and B in Figure 58. 

The exact shape and dimensions are most easily 
understood from the illustration. A somewhat 
resembles a three-pronged fork, while B is simply a strip 
2 5/8 inches long and 1/2 inch wide. 

.. figure:: images/Image59.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 59.—The Method used in piling up the Strips to Assemble the Core. 
   
   FIG. 59.—The Method used in piling up the Strips to Assemble the Core.  

A sufficient quantity of each piece will be required 
to make a pile three-quarters of an inch thick when 
tightly compressed. 

The best method of procedure is to lay out one piece 
like "A" very accurately and then cut it out. Hammer 
it out perfectly flat and use it as a pattern to lay out 
the other pieces with. The cutting can be done with 
a pair of ordinary tin snips. The pieces should all be 
cut very accurately and truly so that they will match 
when piled up. The rough edges of the iron can be 
smoothed up with a file. 

Figure 60 shows how the core should look when it 
is assembled. It should form a rectangle three and 
three-quarters inches long and two and five-eighths 
inches wide.

The method of piling up the **laminations**, as the 
pieces forming the core are called, is illustrated in 
Figure 59. One of the strips B is placed against the 
open end of A. The next set of strips is arranged in 
the same manner except that the position is reversed 
so that the strip B is at the opposite end of the pile. 
This method is continued, reversing each alternate 
set of strips until the pile is complete as shown in 
Figure 60. After the core has been assembled, 
examine it carefully and make certain that none of the 
strips are of the wrong size so that some protrude 
farther than others. 

The next step in the work is to make the windings, 
The windings are each made on a cardboard tube 
having an inside diameter of about 1 1/16 inches. The 
tubes may be made by rolling a strip of wrapping 
paper around a piece of broom handle or some other 
round object of the proper size. The edges of the 
tube should be glued so that it cannot unroll. 

.. figure:: images/Image60.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 60.—Assembly of the Core. 
   
   FIG. 60.—Assembly of the Core. 

The **secondary winding** is an inch and 
nine-sixteenths long and one and thirteen-sixteenths of an 
inch in diameter. 

It is composed of 120 turns of No. 17 B. S. gauge 
single cotton covered wire wound in six layers. 

A tap is led out at the end of the second layer. 

The **primary** is one and nine-sixteenths inches in 
diameter and one and one-sixteenth long. It is 
composed of 1040 turns of wire wound in 13 layers. 

.. figure:: images/Image61.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 61.—Details of the Primary and Secondary Windings. 
   
   FIG. 61.—Details of the Primary and Secondary Windings. 

.. figure:: images/Image62.jpg
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   :scale: 85 %
   :alt: FIG. 62.—Showing the Core completely assembled with the Primary and Secondary in position.
   
   FIG. 62.—Showing the Core completely assembled with the Primary and Secondary in position. P, P are the Primary Terminals. 1, 2 and 3 are the Secondary Terminals. 

The windings must be carefully made and every 
care taken to see that they are properly insulated. It 
is a very good plan to insert a layer of paper between 
each two layers of wire. 

After the windings are finished they are ready to 
assemble on the core. In order to put them in place, 
the core must be taken apart first. The primary and 
secondary go along side of each other on the centre 
tongue of the A strips. 

The core is put together again with the windings in 
position by slipping each alternate "A" strip through 
from the opposite direction so that when it is all 
assembled the result is like that shown in Figure 62. 

The transformer is now ready for mounting. The 
usual method of mounting a step-down transformer 
is to place it in an iron box or case. This is of course 
the best way because the windings and core are then 
protected. The experimenter who wishes to go to the 
trouble of building an iron box for his transformer 
will find it worth the time. 

For the benefit of those however who may wish 
to mount the transformer on a switchboard or as part 
of some apparatus, the scheme shown in Figure 63 
is suggested. The base consists simply of a 
rectangular piece of hardwood which has been given a coat 
of shellac. 

.. figure:: images/Image63.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 63.—The Step-down Transformer mounted on a Wooden Base. 
   
   FIG. 63.—The Step-down Transformer mounted on a Wooden Base. 

The transformer core rests on two wooden strips 
marked "S" and "S" in the illustration. It is clamped 
to the base by two strips, "T" and "T," held in position 
by round head wood screws at each end. 

The terminals of the primary winding are led to the 
two binding posts, marked "P" "P." The secondary 
terminals are connected to three binding posts, marked 
1, 2 and 3. 

The 110 volt A. C is connected to the primary posts 
P P by means of a flexible wire and plug which can be 
screwed into the nearest lamp socket. 

The low voltage is secured from the binding posts 
1, 2 and 3. 

* Binding Posts 1 and 2 will give 2 volts 

* Binding Posts 2 and 3 will give 8 volts 

* Binding Posts 1 and 3 will give 12 volts 

.. figure:: images/Image64.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 64.—A detailed Drawing showing how the Sides of the Case are formed by bending a long strip of Sheet Iron at four points. 
   
   FIG. 64.—A detailed Drawing showing how the Sides of the Case are formed by bending a long strip of Sheet Iron at four points. 

The drawings in Figures 64, 65 and 66 will be of 
assistance to those who wish to enclose the 
transformer in an iron case instead of mounting it on a 
board. 

The case is made of sheet iron. The sides are 
composed of a strip of sheet iron fifteen and seven-eighths 
inches long and two and three-quarters inches wide. 
The strip should be bent at four points so as to form 
a rectangular box, the sides of which are four and 
three-sixteenth inches long and the front and back, 
three and nine-sixteenths. 

The ends of the strip should overlap about 
three-eighths of an inch and be riveted or soldered. 

The bottom may be fastened to the sides with a 
couple of rivets or by soldering at one or two points. 

The bottom and top of the case should both be the 
same. They are made from a rectangular shaped piece 
of sheet iron four and seven-eighths inches long and 
four and one-quarter inches wide. 

A notch five-sixteenths of an inch square is cut out 
of each corner and the sides and ends then folded 
down along the dotted lines as indicated in Figure 65. 

.. figure:: images/Image65.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 65.—Details of the Top and Bottom of the Case. 
   
   FIG. 65.—Details of the Top and Bottom of the Case. 

The transformer is laid in the case with a small 
block of wood under the core at either side so as to 
raise the windings up off the bottom. The secondary 
terminals are connected to binding posts marked 1, 2 
and 3 in Figure 66. These binding posts are mounted 
on insulating bushings which pass through the holes 
marked No. 1, No. 2 and No. 3 in Figure 64. The 
insulating bushings consist simply of fibre washers so 
that the binding posts will not short circuit on the 
metal case. 

One end of a piece of double conductor lamp cord 
is led through a hole in the back of the case and 
soldered to the two primary coil terminals. The other 
end of the lamp cord is connected to an attachment 
plug which may be screwed into a lamp socket. 

.. figure:: images/Image66.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 66.—The completed Transformer.
   
   FIG. 66.—The completed Transformer.

The transformer case is then poured full of molten 
coil wax so that the space around the transformer is 
entirely filled. After the wax has cooled, fasten the 
cover on and it is complete. 

.. figure:: images/CoverImage2.jpg
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   :alt: Book Cover Image 

.. clearpage::

.. container:: titlepage 

   .. container:: center large

       Arts and Science Series No. 8 

   .. container:: center xx-large

       Home-made
   
       Electrical Apparatus 

   .. container:: center large

       A Practical Handbook for Amateur 

       Experimenters 

   .. container:: center medium

       In Three Parts 

       **Volume II**

       *Second Edition*

       **BY**

       **A. M. Powell**

       .. vfill::
    
       PUBLISHED BY

   .. container:: center xx-large

       COLE & MORGAN, Inc. 

   .. container:: center large

       Publishers of the Arts and Science Series 

       \P.O. BOX 473 CITY HALL STATION 

       NEW YORK, N. Y. 

   .. container:: center medium

       Printed in U. S. A. 

.. clearpage::

.. container:: center medium

    Copyright 1918 

    by 

    COLE & MORGAN, Inc. 

.. clearpage::

CHAPTER VI. ELECTRIC MEASURING INSTRUMENTS
------------------------------------------

Galvanometers, Ammeters, Voltmeters. How to Make a Galvanometer.
```````````````````````````````````````````````````````````````` 

If several turns of wire are wrapped about a 
compass, and a current of electricity sent through the 
coil, the compass needle will be deflected. Such an 
instrument is called a **galvanometer** and may be used for 
detecting very feeble currents. 

Figure 67 shows a very simple form of galvanometer 
which may be made by winding about fifty turns of 
No. 36 B. & S. Gauge single silk covered wire around 
an ordinary pocket compass. The compass is set on 
a block of wood and the wire wound around both the 
compass and the block. The terminals of the wire are 
connected to two binding posts. 

.. figure:: images/Image67.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 67.—A Simple Galvanometer.
   
   FIG. 67.—A Simple Galvanometer.

A galvanoscope of this sort may also be used for a 
polarity indicator to distinguish between positive and 
negative poles. Connect an ordinary dry cell to the 
galvanometer and the needle will immediately swing 
to one side or the other, depending upon which way 
the current flows. The carbon of the dry cell is 
**positive** and the zinc is **negative**. Note which way the 
needle swings, whether toward the binding post 
connected to the positive pole or the one connected to the 
negative pole. It will swing towards the 
corresponding pole when any other source of current is connected 
to it and by knowing whether it points towards 
positive or negative it is very easy to determine the 
polarity. 

The Construction of Ammeters and Voltmeters. 
````````````````````````````````````````````

The experimenter will find a voltmeter and an 
ammeter to be very useful instruments about the 
workshop and laboratory. A **voltmeter** is an instrument 
designed to measure electro-motive force or electrical 
pressure. An instrument designed to measure rate of 
flow of current is called an **ammeter**. 

Ammeters and voltmeters are really, in principle, 
galvanometers, the scales of which have been 
calibrated to read in amperes or volts, as the case may be. 

The little meters described below are very simple 
but quite sensitive. 

.. figure:: images/Image68.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 68.—Details of the Bobbin. 
   
   FIG. 68.—Details of the Bobbin. 

The wooden bobbin which holds the wire is shown 
in Figure 68. The exact dimensions are best understood 
from the illustration. The wood can be easily secured 
from an old cigar box. In laying out the work, 
scratch the lines on the wood with the point of a 
darning needle. Pencil lines are too thick to permit of 
accuracy in small work. The bobbin should be perfectly 
square and true when finished. Finish by rubbing 
with fine sandpaper and then give it a coat of shellac. 
Two bobbins will be required, one for the voltmeter 
and one for the ammeter. Do not use any nails in 
putting the bobbins together. Use strong glue only. 

The bobbin for the ammeter should be wound full 
of No. 14 B. & S. Gauge double cotton covered magnet 
wire. The voltmeter requires much smaller wire. No. 
37 B. & S. Gauge single silk covered wire will serve 
the purpose satisfactorily, but a finer size such as No. 
38 or 40, is better. Such fine sizes will probably, 
however, prove more difficult for the experimenter to 
obtain. Sufficient wire should be used to fill the bobbin 
up. The wire should be wound on carefully in smooth 
even layers. 

A small hole should be bored in one of the flanges, 
through which to pass the end of the wire when 
starting the first layer. About six inches of wire should be 
left at both ends of the coils to make connection to 
the terminals with. The whole winding should be 
given a coat of shellac when finished.

.. figure:: images/Image69.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 69.—Details of the Armature, Bearings and Pointer. 
   
   FIG. 69.—Details of the Armature, Bearings and Pointer. 

The armature is a piece of soft steel, one and 
one-eighth inches long, and one-quarter of an inch thick. A 
one-sixteenth inch hole is bored, slightly above the 
centre of the armature, to receive the shaft. The 
centre of gravity is thus thrown below the centre of mass 
and the pointer attached to the armature will always 
return to zero if the instrument is level. The shaft 
is a piece of one-sixteenth inch bessemer steel rod, 
three-eighths of an inch long. The ends are filed to a 
sharp point as shown in the upper pert of Fig. 69. A 
small hole is bored in the top of the armature almost 
directly over the shaft as shown in Fig, 69 to receive 
the lower end of the pointer, which is a piece of No. 
16 aluminum wire, three and one-quarter inches long. 
The other end of the pointer should be flattened 
slightly by tapping with a hammer and then filed into a 
shape resembling a spear head. 

.. figure:: images/Image70.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 70.—A complete Voltmeter having the Scale at the top. 
   
   FIG. 70.—A complete Voltmeter having the Scale at the top. 

After all the holes have been bored and before the 
shaft and the pointer are in place, the armature must 
be tempered so that it will retain its magnetism. In 
order to temper the armature, heat it to a bright red 
and drop it immediately into a basin of strong salt 
water. It may then be magnetized by rubbing one end 
against the pole of a strong magnet. 

The bearings are formed by two 6-32 brass screws, 
one-half an inch long and having a small hole in the 
end to accommodate the end of the shaft. These 
screws pass through the upper flange of the bobbin 
from the opposite sides. The holes in the flanges 
should be slightly smaller than the outside of the 
screw so that the latter will fit snugly and "take hold" 
as if the wood were threaded. 

Figures 70 and 71 show two different methods of 
assembling and completing the instruments. In one, 
the bobbin is mounted on the base and the scale is at 
the top. In the other, this relation is just turned 
abound and the bobbin is at the top and the scale at 
the bottom. In the latter case the pointer must be 
attached to the bottom of the armature instead of the 
top. 

.. figure:: images/Image71.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 71—An Ammeter so constructed that the Scale is at the bottom. 
   
   FIG. 71—An Ammeter so constructed that the Scale is at the bottom. 

Figure 73 shows the shapes and dimensions of the 
wooden parts which compose the case. 

A glass front slides in two shallow grooves cut in 
the wooden sides, one-eighth of an inch from the front. 
Glue and brass screws should be used in putting the 
case together. Do not use iron or iron screws. 

.. figure:: images/Image72.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 72.—Showing how the Armature, Shaft and Pointer are assembled for a Meter having the Scale at the bottom. 
   
   FIG. 72.—Showing how the Armature, Shaft and Pointer are assembled for a Meter having the Scale at the bottom. 

The two binding posts connected to the terminals 
of the wire on the bobbin should be mounted on the 
base. A small, round-headed brass screw, long enough 
to pass all the way through the base will serve to 
level the instrument and bring the pointer exactly at 
zero. If a little brass strip is placed in the slot in 
the screw head and soldered there so as to form what 
is known as a "winged screw", the adjustment may 
be made with the fingers and without the aid of a 
screw driver. 

The scale is formed on a piece of stiff white 
cardboard directly under the pointer. The scale is 
supported by gluing it to two small wooden blocks. The 
various values are marked on the scale with a pen 
and ink. The glass front should therefore not be put 
in place until the instrument has been calibrated. 

To properly calibrate the meters, they must be 
compared with a suitable standard. 

The zero value on the meters is normally in the 
centre of the scale. When a current is passed through 
the bobbins, the armature tends to swing around at 
right angles. But since the armature is pivoted above 
its centre of mass, the centre of gravity is displaced 
when it swings and exerts a pull in opposition to 
that of the bobbin. The amount of swing will be 
greater as the current is correspondingly stronger. 
The pointer will swing either to the right or to the 
left, depending upon the direction in which the 
current passes through the coil of wire on the bobbin. 

.. figure:: images/Image73.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 73.—Details of the Wooden Parts which form the Case. 
   
   FIG. 73.—Details of the Wooden Parts which form the Case. 

The zero point on the two instruments shown in 
the accompanying illustration is at the extreme left 
of the scales. The pointers are bent to the left so 
that the current may be passed through the meters 
in only one direction and the scales will have a greater 
range of values. 

In order to calibrate the ammeter, place it in series 
with a standard ammeter having a calibrated scale 
which is known to be correct. A set of strong 
batteries and a rheostat should be included in the circuit. 
The arrangement is illustrated in Figure 74. The 
rheostat is adjusted so that various current readings 
are obtained. The positions of the pointer on the 
standard meter are carefully noted and corresponding 
graduations made on the scale of the other meter for 
each value. 

.. figure:: images/Image74.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 74.—Showing how the Apparatus is arranged and connected for calibrating the Ammeter. 
   
   FIG. 74.—Showing how the Apparatus is arranged and connected for calibrating the Ammeter. 

.. figure:: images/Image75.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 75.—Showing how the Apparatus is arranged and connected for calibrating the Voltmeter.
   
   FIG. 75.—Showing how the Apparatus is arranged and connected for calibrating the Voltmeter.

In order to calibrate the voltmeter it must be 
compared to a standard voltmeter. The voltmeters must 
be placed in parallel or shunt with each other as shown 
in Figure 75. 

A switch is connected to the battery so that the 
voltage of a varying number of cells may be passed 
through the meters. In order to secure a close 
adjustment of the voltage, a rheostat is placed across the 
battery and switch so that it shunts the cells which 
are in circuit. By adjusting both the rheostat and the 
switch, any voltage within the maximum range of the 
battery may be secured. 

After the meters have been calibrated and 
assembled, they are ready for service and will form a 
very useful and valuable part of the experimenter's 
laboratory. 

When using the meters remember that it is always 
necessary that the ammeter shall be in series and 
the voltmeter in parallel or shunt with the circuit. 

CHAPTER VII. CURRENT CONTROL DEVICES. 
-------------------------------------

How to Make a Pole Changing Switch or Current Reverses How to Reverse a Small Motor. 
````````````````````````````````````````````````````````````````````````````````````

The switch shown in Figure 76 is a very simple 
device which will be found very handy for many 
purposes. It consists of two brass levers mounted 
alongside of each other and connected together with an 
insulating strip or yoke bearing a handle so that they 
can both be moved together. The levers are pivoted 
at their back ends and provided with binding posts 
marked B. P. and B. P. in the illustration. The front 
ends of the levers swing over three switch contact 
points properly spaced so that the levers touch the 
adjoining contacts at the same time. The contacts are 
marked 1, 2, and 3. 

.. figure:: images/Image76.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 76.—A Pole changing Switch for reversing Small Motors or the direction of an Electric Current. 
   
   FIG. 76.—A Pole changing Switch for reversing Small Motors or the direction of an Electric Current. 

We will suppose that the experimenter has some 
device operated by a battery and desires to arrange 
the apparatus so that he can quickly reverse the 
terminals of the battery so as to send the current through 
the device in either direction quickly and at will. The 
apparatus to be operated should be connected to the 
two binding posts mounted on the switch levers and 
marked B. P. and B. P. Connect the negative pole 
of the battery to the contact marked 2 (the center 
one), and the positive pole to both 1 and 3 (the 
outside ones). When the switch is thrown to the right 
so that the levers rest on the contacts 2 and 3, the 
right hand lever will be positive and the left hand one 
negative. When the switch is thrown to the left so 
that the levers rest on 1 and 2, the left hand lever 
will be positive and the right hand one negative. The 
current has been reversed. 

.. figure:: images/Image77.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 77.—Top view of a small Battery Rheostat.
   
   FIG. 77.—Top view of a small Battery Rheostat 

A switch such as this makes it possible to quickly 
reverse the running direction of small motors. In 
order to accomplish this, connect the two brushes on 
the motor to the two switch levers. Connect the 
contracts 1 and 3 (the two outside ones) together and 
lead the wire to one terminal of the battery used for 
operating the motor. In case the motor is operated 
by a generator or from the 110 volt current, connect 
the wire to one terminal of the power source. The 
middle contact on the switch (marked 2) should be 
connected to one end of the field winding on the 
motor. The other end of the field winding should 
be connected to the remaining battery terminal or 
power source.

Moving the switch back and forth will send the 
current through the commutator in opposite directions 
and cause the motor to run in either direction as 
desired. 

How to Make a Small Battery Rheostat for Regulating the Speed of Small Motors, Etc. 
```````````````````````````````````````````````````````````````````````````````````

**A Rheostat** is a variable resistance for regulating 
the amount of current flowing in a circuit. It is a 
very useful device about the experimental laboratory. 
It may be used, for regulating the speed of small 
motors, the amount of current flowing into a storage 
battery when recharging, the brilliancy of a lamp, etc. 

.. figure:: images/Image78.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 78.—Details of the Rheostat Base. The lower part of the illustration is a cross section. 
   
   FIG. 78.—Details of the Rheostat Base. The lower part of the illustration is a cross section. 

Figure 77 shows a form of small rheostat which 
may be easily built by the experimenter. It consists 
of a coil of German silver resistance wire wound 
around a fibre form and set in a groove in a wooden 
base. A brass lever slides over the edge of the 
resistance coil so that the portion included in the circuit 
may be increased or decreased easily at will. 

The dimensions shown in the several drawings which 
follow are for a rheostat having a resistance of 
approximately ten ohms and suitable for general 
experimental work. It is possible to use the same plans 
and by doubling the dimensions, make a rheostat 
which is much larger and may be used to carry 
heavier currents or which possesses more resistance. 

.. figure:: images/Image79.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 79.—Looking at the Base from the bottom showing the grooves in which the Wires are laid. 
   
   FIG. 79.—Looking at the Base from the bottom showing the grooves in which the Wires are laid. 

The details of the wooden base are given in 
Figures 78 and 79. The outside diameter of the base 
is four inches. It is five-eighths of an inch thick. The 
lower 7 part of Figure 78 shows a cross section of the 
base. The groove is three and one-eighth inches in 
diameter inside, five-sixteenths of an inch thick and
five thirty-seconds of an inch wide. The hole in the 
centre of the base is to accommodate the shaft of the 
switch lever, Two holes, seven-eighths of an inch 
apart are drilled at the back of the base to 
accommodate the binding posts. The binding posts' holes 
and also the hole in the centre of the base for the 
shaft are countersunk at the bottom as shown in 
Figure 79. 

The fibre strip which supports the German silver 
resistance wire is shown in Figure 80. It is eight 
inches long, three-eighths of an inch wide and 
one-eighth of an inch thick. 

If the experimenter has access to a lathe it is 
possible to wind the wire on the fibre strip under tension 
with the aid of the screw feed so that the wire will 
go on very tightly and with a small air space between 
the turns. When a lathe is not available it will be 
necessary to groove the top and bottom of the fibre 
strip with the aid of a three-cornered file. The grooves 
should be evenly spaced and as close together as 
possible. They serve to prevent the wire from 
slipping and the adjacent turns becoming short circuited. 

The wire used to wind the strip should be No. 24 
\B. & S. Gauge German Silver wire and should be bare. 
Wind the wire tightly into the grooves in the strip 
and fasten both ends by looping through a small hole 
bored in the ends of the fibre for that purpose. 

The fibre strip can be bent so that it will fill in the 
groove in the wooden base by heating it in the flame 
of a bunsen burner. It should not, of course, be 
heated too hot or the fibre will burn. Warm it 
thoroughly and bend into a circle of the same diameter 
as the groove in the base. Then force the strip into 
the groove with the two ends opposite the two 
binding post holes. The strip should fit into the groove 
tightly so that there is no danger of it shifting or 
slipping out. 

.. figure:: images/Image80.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 80.—The German-silver Resistance Wire is wound around a Fibre Strip. 
   
   FIG. 80.—The German-silver Resistance Wire is wound around a Fibre Strip. 

The details of the switch lever, knob and binding 
posts, are shown in Figure 81. The lever is made of 
sheet brass cut into the shape shown and is one and 
three-quarter inches long. The knob is similar to 
those used on typewriters for turning the paper roller.
It is fitted with a threaded stem moulded into the 
head. These knobs may be obtained at almost any 
supply house carrying goods for experimenters. The 
lever is slipped over the stem and clamped tightly 
against the knob by a nut on the under side. The 
end of the stem or shaft fits into the hole in the centre 
of the wooden base. Slip a washer over the end and 
then thread on a brass washer. Tighten the nut up 
until the end of the lever makes firm contact with the 
resistance wire but is not so tight that it binds and 
cannot be easily moved by turning the knob. When 
the right position for the nut is found, solder it to 
the stem so that it cannot change its adjustment. 

.. figure:: images/Image81.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 81.—The Lever, Knob, Binding Posts, etc. 
   
   FIG. 81.—The Lever, Knob, Binding Posts, etc. 

The completed rheostat is shown in Figure 82. The 
right hand terminal of the German Silver wire is 
connected to the right hand binding post. The other 
binding post is connected to the washer around the 
lever shaft on the under side of the base. The wires 
should be laid in grooves cut in the bottom of the 
base for that purpose. 

Drive a brass headed upholsterer's nail into the base 
near the left hand terminal of the resistance so that 
when the lever is swung around in that direction as 
far as it will go, the tack will raise the lever up off
the resistance wire and break the circuit completely. 
Two small nails should be driven into the base in such 
a position that they will limit the swing of the lever 
and prevent it from moving so far that it passes over 
the ends of the resistance unit. 

The rheostat may be connected in a circuit by 
attaching two wires to the binding posts. It should be 
placed in series with any device which it is desired to 
regulate. The carrying capacity is limited to two 
amperes owing to the fact that a heavier current than
this will cause the wire to overheat. Turning the knob 
so that the lever moves towards the upholsterer's nail, 
which raises it up off the wire, increases the amount 
of resistance in the circuit and cuts down the current, 
until the lever slides up on the nail when the circuit 
is broken entirely. Moving the knob in the other 
direction decreases the resistance and increases the 
current until the lever has moved as far as it may, 
when the current will be at a maximum. 

.. figure:: images/Image82.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 82.—The completed Rheostat. 
   
   FIG. 82.—The completed Rheostat. 

CHAPTER VIII. HOW TO MAKE A TELEGRAPH KEY AND SOUNDER AND INSTALL A TELEGRAPH LINE. 
-----------------------------------------------------------------------------------

The modern telegraph consists essentially of four 
things: 

1. A battery which produces the electric current. 

2. A wire to conduct the current from one point to another. 

3. A key or switch for turning the current off and on. 

4. An electro-magnetic receiving apparatus, which changes the pulsations of the electric current into sounds. 

.. figure:: images/Image83.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 83.—Key Frame.
   
   FIG. 83.—Key Frame.

Its operation is not, as many suppose, complicated 
and difficult to understand, but is quite simple. 

The key is really a form of switch and is simply a 
contrivance for controlling the electric current. It 
consists of a steel lever, pivoted in the centre, and 
provided with a rubber knob, which the operator grasps 
lightly with the thumb and forefinger. When the 
lever is pressed downwards, a platinum point on the 
under side is brought into contact with another 
similar point set into a rubber bushing in the base of the 
key, so that there is no electrical connection between 
the two points unless the key is pressed down or 
"closed" as it is usually termed. 

The receiving device, or "sounder," consists of two 
electro-magnets mounted on a base under a flat strip 
or iron, called the armature, which is attracted by the 
magnetism of the electro-magnets when a current 
flows through them, and is withdrawn by a spring 
when no magnetism is produced by the windings. 

.. figure:: images/Image84.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 84.—Sounder Frame.
   
   FIG. 84.—Sounder Frame.

The armature is usually mounted on a strip of brass 
or aluminum called the "lever". The lever strikes 
against an anvil and produces the clicks which form 
the dots and dashes of the telegraph alphabet. 

Every time the key is pressed, an electric current 
goes through the line, causing the magnets to draw the 
armature downward and produce a click. When the 
key lever is released, the current is shut off and the 
lever flies up and clicks against the top of the anvil. 

The time between the first and second clicks may 
be easily varied at will, by changing the length of time 
that the key lever is held down. Two clicks very close 
together, made by pressing the key and immediately 
releasing it, are called a "dot". A "dash" is made by 
pressing the key down and holding it down for a 
fraction of a second so that the interval between the first 
and second clicks is about three times as long as that 
between the clicks of a dot. 

.. figure:: images/Image85.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 85.—The Electro Magnets.
   
   FIG. 85.—The Electro Magnets.

Any boy can make a simple telegraph set quite 
easily. The only drawback of such an apparatus, 
however, is that it is usually not practical for long lines 
but may only be used for ticking messages from one 
room to another. 

It is equally possible for the young experimenter to 
make a perfectly practical telegraph outfit which will 
operate over a line a mile long, if he is willing to give 
the time and labor necessary to the work. 

The telegraph set-described below is one which, 
because of its simplicity, particularly lends itself to 
construction by the young experimenter whose tools are 
rather limited. 

In order to make a really practical telegraph outfit, 
it is almost essential that the key and sounder frame 
be made out of cast iron so as to give the instruments 
the requisite stiffness. It is easier to use castings than 
to attempt to bend the parts out of metal. 

In order to secure the proper castings it will be 
necessary to first make a set of "patterns". This is 
not very difficult. 

The key frame is shown in Figure 83 and the 
Sounder frame in Figure 84. The patterns should be 
cut out of wood according to the exact shape and 
dimensions shown in the illustrations. Omit all the 
holes, however, because no holes should appear in the 
patterns but only in the finished castings. 

.. figure:: images/Image86.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 86—The Sounder Armature. 
   
   FIG. 86—The Sounder Armature. 

The patterns should be made perfectly smooth and 
be a good, clean job throughout. After they are 
finished, give them each a coat of shellac and they are 
ready for the foundry. Almost any iron foundry will 
make up the castings if supplied with the patterns. 
If a number of experimenters "chip in" and make up 
a set of patterns from which several sets of castings 
are ordered at the same time, the cost will be very 
slight. 

After the castings are secured, they should be 
cleaned up with a file and drilled according to the 
illustration in Figures 83 and 84. Several of the holes 
should be tapped to receive an 8-30 machine screw. 
Such holes are marked in the illustrations. 

The holes not marked "Tap" should be just large 
enough to allow an 8-32 screw to slip through. 

.. figure:: images/Image87.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 87.—Sounder Frame with Lever in Position. 
   
   FIG. 87.—Sounder Frame with Lever in Position. 

**The Electro-magnets** are illustrated in Figure 85. 
The magnet core is made of a piece of 5-16 inch round 
iron rod an inch and a quarter long. A fibre washer, 
three-quarters of an inch in diameter is fitted over 
each end of the core. One end of the core is drilled 
and tapped to receive an 8-32 screw. 

The magnet bobbin, before winding is shown at the 
left of the illustration and a finished magnet at the 
right. Two magnets are required. They should both 
be wound in the same direction with No. 25 single 
cotton covered wire. The wire should be wound in 
smooth, even layers and the terminals led out through 
two small holes in the fibre heads. 

**The Sounder Armature** is a piece of steel or iron 
rod, five-sixteenths of an inch square and three and 
three-eighths inches long. It serves both as the 
armature and the sounder lever. The exact location of the 
holes is shown in Figure 86. The holes "h" and "i" 
should be tapped to receive an 8-32 screw. The hole 
"j" should pass a screw of the same size. This screw 
serves as the pivot for the armature. Figure 87 
shows how the sounder frame should appear when the 
lever is in position. The screw A controls the 
distance which the armature moves on its upward stroke. 
The screw B strikes the "anvil" on the downward 
stroke and controls the distance between the 
armature and the electro-magnets. 

.. figure:: images/Image88.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 88.—Top View of Completed Instrument 
   
   FIG. 88.—Top View of Completed Instrument 

The armature is pushed upwards and held away 
from the magnets against the screw A by a small 
spiral spring. The lower end of the spring sets in the 
hole "C" in the sounder frame and the upper end 
rests against the end of the screw C so that the 
tension of the spring can be regulated by moving the 
screw up and down. The armature should be free to 
move up and down on the pivot screw but should not 
move sideways. 

**The Base** of the instrument is a rectangular piece of 
hardwood, four and one-half inches long, three and 
three-quarter inches wide and one-half inch thick. The 
sounder is mounted on the base in the position shown 
in Figure 88, which is a top view of the complete 
instrument. Two long 8-32 machine screws pass 
upwards through the wooden base, through the holes "e" 
and "f" in the sounder frame and into the bottom of 
the magnets, thus serving not only to hold the magnets 
in position but also the sounder frame to the base. 

.. figure:: images/Image89.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 89.—Side View of Key. 
   
   FIG. 89.—Side View of Key. 

Figure 89 is a side view of the completed key. The 
key lever and the circuit closing lever are illustrated 
in Figure 90. The lever is four and three-eighths 
inches long and five-sixteenths of an inch wide. It 
should be made from spring brass. The circuit closing 
lever is a strip of brass of the same width. All the 
holes in both levers, with the exception of the centre 
hole in the key lever should be large enough to pass 
an 8-32 screw. The centre hole should be tapped to 
receive an 8-32 screw. 

The key lever is fastened to the frame by means of 
a round headed 8-32 machine screw. The screw 
should be tightened so that the lever cannot move 
from side to side. The circuit closing lever is pivoted 
to the back end so that it can swing. The key lever 
should be fitted with a regular key knob and the 
circuit closing lever with a small knob such as is 
generally used for the purpose. Both of these styles of 
knobs can be purchased from almost any electrical 
supply house. 

The contact points are best made of silver. Silver 
makes a better contact metal than almost anything 
else, with the exception of platinum. If silver cannot 
be obtained a piece of large german-silver wire may 
be used. 

.. figure:: images/Image90.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 90.—Key and Circuit Closing Levers. 
   
   FIG. 90.—Key and Circuit Closing Levers. 

One contact is soldered to the under side of the key 
lever. The other contact should be mounted on the 
head of a screw and pass through a hole in the iron 
key frame and through the wooden base underneath. 
This lower contact should be directly underneath the 
upper contact and be thoroughly insulated from the 
base. Several thicknesses of well shellaced paper will 
form a first class insulating medium. The length of 
the contacts should be such that there is a distance of 
about 3-32 of an inch between them when the lever is 
horizontal. 

The circuit closing lever should make contact with 
a small strip of spring brass under the lower contact 
point so that the contact is connected to the frame of 
the key through the circuit closing lever when the 
latter is "closed". 

The adjustment screw on the key frame is used to 
regulate the upward stroke of the key lever. 

The adjustment screw on the key lever is used to 
regulate the spring tension of the lever. The lower 
end rests against the top of a small spiral spring made 
of brass wire. 

.. figure:: images/Image91.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 91.—American Morse Code.
   
   FIG. 91.—American Morse Code.

Connecting the outfit is a very simple mater. The 
two inside terminals of the sounder magnets should 
be connected together. One of the outside terminals 
is led to a binding post mounted on the back of the 
base. The other terminal is connected to the lower 
key contact. The frame of the key is connected to a 
second binding post at the back of the base. The 
connecting wires should pass through small holes and 
along the under side of the base. 

The Morse Telegraph Code is shown in Figure 91. 

A single dry cell will provide sufficient current for 
practising the Code. The cell should be connected to 
the two binding posts and the circuit closing lever 
should be kept open at all times or the battery will 
become exhausted. 

.. figure:: images/Image92.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 92.—Circuit for Two Instruments. 
   
   FIG. 92.—Circuit for Two Instruments. 

The number of batteries required on a long line will 
depend upon the resistance of the line and cannot 
easily be pre-determined. 

Figure 92 shows a circuit for connecting two 
instruments on a line. When the double contact switch 
is on point A the batteries are out of circuit. 
Throwing the switch on B puts the batteries into circuit. 
They should be kept out of circuit when the stations 
are not in use. The circuit closer at Station 1 must 
be kept closed when Station 2 is telegraphing and 
vice versa. 

CHAPTER IX. HOW TO MAKE AND INSTALL A TELEPHONE. 
------------------------------------------------

Not many years ago, the telephone was the wonder 
of the times just as the aeroplane and the 
wireless are to-day. The original telephone apparatus was 
an exceedingly crude and simple arrangement which 
has gradually developed into a wonderful and complex 
system which makes it possible to carry on a 
conversation with almost any other point in the United 
States as easily as it is face to face. 

.. figure:: images/Image93.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 93.—The Wooden Back for the Telephone. 
   
   FIG. 93.—The Wooden Back for the Telephone. 

Many of my young readers have undoubtedly 
already constructed a set of telegraph instruments and 
rigged up a line with some nearby chum. Like the 
telegraph, the principle of the telephone is that of a 
current of electricity flowing over a line wire into a 
pair of electro-magnets, and it is not any more 
difficult to install a short telephone line than a telegraph. 
Of course there are many important differences 
between a telephone and a telegraph but they are not 
intricate or complex. 

The telephone is exceedingly sensitive when 
compared to the telegraph. An ordinary telegraph relay 
requires about one hundredth of an ampere to operate 
it, whereas a telephone receiver will produce an 
audible sound on a current of less than one millionth of 
an ampere. 

.. figure:: images/Image94.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 94.—The Complete Telephone. 
   
   FIG. 94.—The Complete Telephone. 

The telephone may be defined as an apparatus for 
transmitting speech to a distance by means of 
electricity. The part of the apparatus which takes up the 
sounds and changes them into electric currents is the 
transmitter. Where words are spoken into the 
mouth-piece of the transmitter, they strike a thin metal 
diaphragm, to the back of which is fastened a small 
cup-shaped piece of carbon. A second cup is mounted in a 
rigid position directly back of the first and the space 
between is filled with small polished granules of 
carbon. When the granules are undisturbed and are 
lying loosely together their resistance to an electric 
current is so great that they allow almost none to flow. 

When the vibrations of the voice strike the 
diaphragm they move it back and forth and cause the 
carbon cup mounted on its back to move and exert a 
varying pressure on the granules. When the granules 
are compressed their resistance is greatly lowered and 
they permit current to pass. 

That part of the apparatus which transforms the 
pulsating current back into sound waves is called the 
receiver. It consists of a thin iron disk, placed very 
near but not quite touching the end of a small 
permanent magnet about which is wound a coil of fine 
insulated wire. 

.. figure:: images/Image95.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 95.—Details of the Receiver Hook.
   
   FIG. 95.—Details of the Receiver Hook.

If the transmitter and receiver are connected 
together in series with a battery and words are spoken 
into the transmitter, the little carbon granules are 
immediately thrown into motion, and being alternately 
compressed and released cause corresponding changes 
in the current flowing through the receiver from the 
battery. 

The strength of the magnetic pull exerted by the 
combined permanent magnet and coil of wire varies 
with each change in the electric current and thus by 
alternately attracting and repelling the diaphragm 
causes it to vibrate and emit sounds. 

This is the general principle of the telephone. The 
telephones in actual service to-day are complicated 
with bells, induction coils, condensers and relays, 
which render them more efficient, but the general 
principle of the transmission of the speech is the same. 

I would not advise the young experimenter to 
attempt to build his own transmitter and receiver except 
for the knowledge and experience gained thereby. 
Homemade instruments of this sort are not likely to 
prove sensitive enough for practical purposes over a 
long line. 

A first class telephone receiver can be purchased for 
90 cents and an equally good transmitter for $2.25 
These, together with an ordinary electric bell can be 
built into a first class telephone instrument which will 
give excellent service over a long line. 

.. figure:: images/Image96.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 96.—Showing how the Push Button is arranged. 
   
   FIG. 96.—Showing how the Push Button is arranged. 

Any boys can easily build and install such an 
arrangement. When completed it will prove invaluable 
as a source of communication from one part of the 
house to another, from the house to the barn or 
between two chums living in the same neighborhood. 
Figure 93 shows the wooden back of the instrument. 
It is made from a piece of board 12 inches long and 7 
inches wide, by cutting into the shape shown. This 
back serves to mount the transmitter, receiver, bell, 
etc. 

**The Bell** is for the purpose of giving an audible 
signal so that the person hearing it will know that some 
one at the other end of the line wishes, to talk. 

Figure 94 is a front view of the completed 
instrument. The bell is mounted on the upper part of the 
back as shown in the illustration. 

**The Receiver Hook** is shown in detail in Figure 95. 
It should be cut out of heavy sheet brass and finished 
in the shape shown. 

The receiver hook is mounted directly under the 
bell as shown in Figure 94. The hook should project 
out to the left beyond the edge of the back. The hook 
is mounted by a round headed brass screw passing 
through the hole in the right hand end. 

.. figure:: images/Image97.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 97.—Circuit showing how to connect two Telephone Stations to the Line. 
   
   FIG. 97.—Circuit showing how to connect two Telephone Stations to the Line. 

The hook should move freely up and down between 
two contacts (marked 1 and 2 in Figure 94). These 
contacts are simply two small brass strips bent at 
right angles and fastened about an inch apart along 
the left hand edge of the wooden back by means of 
two small round headed brass wood screws. The 
position of the contacts should be such that the hook is in 
a horizontal position when it is half way between the 
two. A small spring is arranged so as to pull the hook 
up against the upper contact (No. 1) when the 
receiver is lifted off. When the receiver is hung on the 
hook, it should overcome the lift of the spring and 
pull the hook down against the lower contact (No. 2). 

**The Receiver** may be purchased at almost any 
reliable electrical supply house. It should be provided 
with a ring so that it can be hung onto the hook.

**The Transmitter** is preferably of the "solid back" 
long distance type. It also can be purchased ready 
made from almost any electrical supply house. 

The transmitter is mounted on the wooden back 
directly under the hook. It is marked T in Figure 94. 

**A Push Button**, made out of two round headed brass 
wood screws and a strip of spring brass as shown in 
Figure 96, is mounted to the right of the transmitter. 

One end of the spring is fastened down firmly with 
a screw, the other end is bent so that it is directly over 
but does not touch the second screw mounted about 
seven-eighths of an inch away. 

Four binding posts should be arranged along the 
bottom of the wooden back and two more just to the 
left of the transmitter. 

The set is now ready to "wire" or connect. The 
connections can be understood best by following the 
diagrams in Figures 94 and 97. 

Starting with the four binding posts along the 
bottom of the back, mark the left hand one B1, mark the 
next one B2, the third E and the fourth L. 

Connect a wire from binding post B1 to the post P1 
directly above it. Run the wire from P1 to the brass 
strip on the push button. Connect binding posts B2 
and E together and from E run a wire to the right 
hand binding post on the bell. Connect a wire from 
the left hand post on the bell to the lower contact 2. 
The hook should be connected to binding post L. The 
upper contact 1 is connected to one terminal of the 
transmitter. The other terminal of the transmitter 
goes to binding post P2. The telephone receiver 
should be connected to the posts P1 and P2 by means, 
of flexible wire. The contact on the push button 
should be connected to the upper hook contact 1. 

The set is now complete, ready to connect to a 
similar outfit. 

The battery is connected to the binding posts 
marked B1 and B2. E and L are the line posts to 
which the wires connecting the two sets are led. 

The wire connecting the two outfits should not be 
smaller than No. 18 B. & S. gauge. No. 14 will prove 
better if the line is a long one. 

The wire should be very carefully insulated. 
Ordinary porcelain knobs will serve as suitable insulators. 

If desirable, only one wire need be used, the circuit 
being completed by connecting the post E on each 
instrument to the ground or earth. The gas or water 
pipes will form the most suitable ground connection. 

The number of batteries required will depend upon 
the length of the line. The actual number necessary 
to ring the bell properly can be best ascertained by 
experiment. It should be noticed that the battery 
connections at each station are reversed so that the 
batteries will be series. The negative of the battery at 
one station is connected to E and the positive pole 
of the other battery at the other station to the similar 
post. 

When the stations are not in use the receivers 
should be left hanging on the hooks. In order to call 
the other station, lift the receiver off the hook. This 
throws the transmitter, receiver and battery into the 
circuit. The resistance of the receiver and transmitter, 
however, are so great that they will prevent enough 
current from flowing to ring the bell at the other 
station. Pressing the push button will short circuit 
the transmitter and receiver and allow enough current 
to flow to ring the bell at the other station. The other 
person has merely to lift up his receiver in order that 
the two parties may talk back and forth. 

When the receivers are on the hooks both bells are 
in circuit ready for either party to call up. 

CHAPTER X. MEDICAL COILS AND SHOCKING COILS. 
--------------------------------------------

Medical coils and "shocking coils" are the same. 
The term "shocking coil" is usually applied to 
the low priced medical coils which most boys are 
familiar with for giving "shocks". 

.. figure:: images/Image98.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 98.—Bobbin for Medical Coil. 
   
   FIG. 98.—Bobbin for Medical Coil.
   
A medical coil is nothing more or less than a small 
induction coil for raising the voltage of a battery high 
enough to produce a shock. The human body 
possesses so much resistance that the voltage of one or 
two cells of ordinary battery is not sufficient to pass 
enough current through to be felt except under 
exceptional conditions, as for instance when contact is 
made directly with a nerve through an open cut or a 
metal filling in a tooth. 

A small lathe will be of much assistance in making 
some of the parts and fittings for the medical coil, 
although it is not absolutely essential and the ingenious 
young experimenter can undoubtedly find some 
method of doing without it. It is not necessary to 
follow the dimensions given here exactly, and a very 
good coil can be built by adapting spools, binding 
posts, etc., which may already be on hand, although, 
of course, they should be used with some sense of 
proportion in mind so that nothing is carried to an 
extreme. 

The first part which will be required is the bobbin. 
This is shown in Fig. 98 and consists of a wooden
spool, two and seven-sixteenth inches long and one 
inch in diameter. It has a three-eighths inch hole 
running all the way through the center. The 
dimensions of the flanges, etc., can probably be best 
understood by referring directly to the illustration. The 
flanges are flattened slightly on one side so that when
the bobbin is mounted the flat portion will rest on the 
base and give a better support.

.. figure:: images/Image99.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 99.—Bobbin with Winding. 
   
   FIG. 99.—Bobbin with Winding. 
   
**The Primary Winding** consists of two layers of No. 
24 B. & S. Gauge single cotton covered wire. The 
terminals of the winding should be led out through 
two small holes in the right hand head of the bobbin. 
Cover the winding with two or three layers of thin 
shellaced paper and then wind on the secondary. The 
secondary is composed of ten layers of No. 36 B. & S. 
Gauge single cotton covered wire. The inside end of 
the secondary should be connected to the outside end 
of the primary. The outside terminal is led out 
through a small hole in the head at the opposite end 
from the primary leads. 

The wire on both the primary and secondary should 
be wound on in smooth even layers. The illustration 
in Figure 99 shows the bobbin after the windings are 
finished. 

**The Core** is made out of thin sheet iron rolled up 
into a cylinder two and three-sixteenths inches long 
and nine-thirty-seconds inches in diameter. The core 
should be rolled up just as tightly as possibly, because 
the more iron there is in the core, within of course 
reasonable limit, the better the coil will work. Thin 
tin plated iron cut from a cracker box may be used 
for the core. The thinner it is the better. A core of 
this sort, rolled up out of sheet iron will give much 
better results than a core composed of a solid bar 
of iron. 

.. figure:: images/Image100.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 100.—Construction of the Core. 
   
   FIG. 100.—Construction of the Core. 
   
The end of the core is slipped into an iron "core" 
cap. This is shown in Figure 101. It consists of a 
small cylinder, seven-sixteenths of an inch in length, 
cut from a piece of iron rod, three-eighths of an inch 
in diameter. A hole nine-thirty-seconds of an inch in 
diameter and five-sixteenths of an inch deep should 
be drilled in one end. This cap is slipped over one 
end of the core. It should fit very tightly so that it 
will not pull out. 

The core is then slipped into the bobbin with the 
outside end of the core cap projecting about 
one-sixteenth of an inch out of the end at which the 
primary terminals lead out. The cap should fit into 
the bobbin very snugly so that the core is held firmly 
in place. 

Since the hole through the bobbin is three-eighths 
of an inch in diameter and the core is only 
nine-thirty-seconds of an inch in diameter there should be a space 
all around the core, except at the end where the cap 
is, so that a thin brass "regulator" tube can be slipped 
in and out over the tube. 

.. figure:: images/Image101.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 101.—Vibrator Parts and Core Cap. 
   
   FIG. 101.—Vibrator Parts and Core Cap. 
   
**The Regulator Tube** should be two and 
seven-sixteenths inches long and have an inside diameter of 
five-sixteenths of an inch. In case the experimenter 
has any difficulty in securing a tube of this size he can 
easily make one by rolling a piece of sheet brass 
around a suitable sized rod and soldering the edges. 

When the tube is slipped over the core and moved 
in and out of the bobbin, after the coil has been 
finished and set in operation, it will regulate the strength 
of the secondary or "shocking" current. When the 
tube is completely out of the bobbin, the current will 
be the strongest. 

If a paper scale, divided into sixteenths of an inch 
and bearing numbers, is pasted around the tube it will 
act as an indicator of the current strength.

The base is wood and measures four and 
five-eighths inches long, two and three-quarters inches 
wide and is one-half an inch thick. The proper 
location of the various holes can be found by referring 
to the illustration in Figure 103. The corners of the 
base should be slightly rounded so as to improve the 
appearance. 

Figure 104 is a top view of the coil after it has 
been assembled. The bobbin is mounted a little back 
of the centre of the base so that the core cap will be 
opposite the armature of the vibrator. 

.. figure:: images/Image102.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 102.—Regulator Tube. 
   
   FIG. 102.—Regulator Tube. 
   
**The Vibrator Parts** are illustrated in Figures 101 
and 106. 

The vibrator spring is a piece of thin steel or 
phosphor bronze, one-quarter of an inch wide and 
one and three-sixteenths inches long. A soft iron 
armature, five-sixteenths of an inch in diameter and 
one-eighth of an inch thick is fastened to one end of 
the spring. A five-thirty-seconds inch hole is drilled 
in the other end and it is then mounted in the 
"vibrator posts". This consists of a small brass pillar, 
one-quarter of an inch in diameter and five-eighths 
of an inch long. The lower end is drilled, and tapped 
to receive a 4-36 screw which fastens it to the base. 
A saw slot one-quarter of an inch deep is made in 
the top to receive the vibrator spring. 

The post which holds the adjustment screw is 
identical with that which supports the vibrator spring, 
except that a threaded hole is drilled through the 
saw slot, fifteen-thirty-seconds of an inch from the 
bottom, through which the screw passes. The end of 
the adjustment screw, which may be an ordinary 
knurled thumbscrew from a binding post, should be 
fitted with a "contact" point. The best contact point 
is a piece of platinum, but a small piece of silver can 
be made to serve the purpose very well. 

.. figure:: images/Image103.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 103.—The Base with Location of Holes. 
   
   FIG. 103.—The Base with Location of Holes. 
   
.. figure:: images/Image104.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 104.—Top View of Finished Coil. 

   FIG. 104.—Top View of Finished Coil. 

The vibrator spring should also be fitted with a 
similar contact point. 

.. figure:: images/Image105.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 105.—Side View of Completed Coil. 

   FIG. 105.—Side View of Completed Coil.

The medical coil is very easy to connect. Run the 
inside primary terminal to the binding post on the 
rear left hand corner of the base. Connect the other 
terminal to the vibrator post. A wire should be led 
from the adjustment screw post to the binding post 
mounted on the forward left hand corner of the base. 

.. figure:: images/Image106.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 106.—Vibrator Parts. 

   FIG. 106.—Vibrator Parts. 

One or two cells of battery should be sufficient to 
operate the coil. Connect the battery to the two 
binding posts. Adjust the thumbscrew until the contact 
on the end just touches the contact point on the 
vibrator spring. The current will then flow through the 
primary winding and magnetize the core. The 
magnetism of the core will draw the armature towards 
it, thus pulling the contacts apart and interrupting 
the current. The process will repeat itself very rapidly 
at a speed depending upon the adjustment of the 
thumbscrew and as long as the battery remains 
connected. 

.. figure:: images/Image107.jpg
   :align: center
   :scale: 85 %
   :alt: FIGS. 107 and 108.—Two Types of Handles. 

   FIGS. 107 and 108.—Two Types of Handles. 

The handles for the coil are very easily made out 
of a piece of brass tubing about two and one-half 
inches long and five-eighths of an inch in diameter. 
They can also be made by rolling a piece of sheet 
brass or tin into a tube and soldering the edges 
together. The illustration shows two methods of 
making the handles and attaching the cords. The handle 
in the upper part of the illustration is made from a 
piece of tubing. A wooden plug or cork is fitted into 
one end. The wire passes through a hole in the centre 
of the plug and is turned back over the edge so that 
when the plug is forced into the tube, the wire will 
make contact with it. The handle in the lower part 
of the illustration is made from one of the brass 
cylinders in which the indelible ink for rubber stamps 
is supplied. A hole is bored in the bottom through 
which the wire passes. The end of the wire is soldered 
to a piece of stiff brass wire bent into the shape of a 
hairpin. The ends of the wire are spread apart so 
that they will spring against the inside of the tube. 
The connector is then pulled up inside of the handle. 

The flexible wires or "cords" as they are sometimes 
called, attached to the handles, should be about 
eighteen inches long. The opposite ends to the handles 
should be led through two holes in the base, in front 
of the bobbin. The left hand cord should be connected 
to the vibrator post and the right hand cord to the 
outside secondary terminal. 

The coil is now complete, ready for operation. 
Connect the battery to the binding posts. Start the 
interrupter and grasp one of the handles in each hand. 
Draw the regulator tube out of the bobbin gradually 
and the current will gradually grow stronger and 
stronger until it is impossible to hold the handles. 
When the regulator tube is all the way in the bobbin 
it is practically impossible to feel the current. Of 
course any intermediate strength between the two 
extremes can easily be secured. The shock from the 
coil is harmless. When the regulator is all the way 
out, the shock is very strong. The only result, 
however, is to make the person receiving it drop the 
handles. The current from medical coils is often 
prescribed by physicians for rheumatism and nervous 
disorders, but it must be properly applied in order to
be of benefit. 

CHAPTER XI. THE CONSTRUCTION OF SPARK COILS. 
--------------------------------------------

A Spark Coil is one of the most interesting pieces 
of apparatus that an experimenter can possess. 
Not only can it be used to transmit wireless messages, 
but numerous and various experiments may be 
performed with its aid. 

The purpose of a spark coil is to generate 
enormously high voltages which are able to send sparks 
across an air space which ordinary battery currents 
of low voltage could not possibly pierce. 

.. figure:: images/Image109.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 109.—Induction or Spark Coil. 

   FIG. 109.—Induction or Spark Coil. 

It consists of an iron core surrounded by a coil of 
heavy wire known as the "primary" and a second 
outside winding of finer wire known as the 
"secondary." The primary is connected to a few cells of 
dry battery in series with an "interrupter." 

Every time that the interrupter shuts off the 
battery current in the primary, currents are induced in 
the secondary which are of sufficiently high voltage 
or pressure to leap across a space in the shape of 
sparks. 

A spark coil is not very hard to construct, but it 
requires careful workmanship and patience. It is not 
usually a job which can be finished in a day, but will 
take quite a little time, especially in winding the 
secondary. 

In describing the construction of a spark coil in this 
chapter, directions and dimensions have been given 
for a one-quarter inch coil. The general method of 
procedure is the same for all sizes of coils, the 
dimensions only, are different. The experimenter may 
therefore easily build a larger coil than the 
one-quarter inch by consulting the tables of dimensions. 

Parts for spark coils are for sale by many electrical 
houses and it is possible to purchase the complete 
parts for less than the separate materials would cost. 

Such parts are made by special machinery and 
therefore are produced quite cheaply. 

The Core is made of soft iron "core wire" about 
No. 20 or 22 B. & S. Gauge. Each piece should be 
four and three-quarters inches long. Iron wire may 
be bought already cut to length from various houses 
dealing in experimenter's supplies. Considering the 
amount of labor that is required to cut each piece to 
length arid then straighten it out, it is cheaper to 
purchase the wire already cut. 

.. figure:: images/Image110.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 110.—The Primary and Core. 

   FIG. 110.—The Primary and Core. 

============== ================= ================== =============
Size of Coil.  O Length of Core  P Diameter of Core Primary Wire 
============== ================= ================== =============
1/4 inch       4 3/4 inches      1/2 inch           18 B. & S.
1/2 inch       5 inches          5/8 inch           18 B. & S. 
1 inch         7 inches          5/8 inch           18 B. & S.
============== ================= ================== =============

"Core wire" is a special grade of wire which is 
very soft and has been annealed. 

If ordinary iron wire is used in making a core, it 
must first be annealed. This is accomplished by 
tying the wire in a compact bundle and placing it in a 
wood fire until it is red hot. After the wire is hot, 
cover it with ashes and allow the fire to die away. 

When the fire has gone out and the wire has 
cooled the annealing process is complete. Enough 
wires each four and three-quarters inches long to 
form a compact bundle one-half inch in diameter will 
be required. 

.. figure:: images/Image111.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 111.—The Secondary Winding. 

   FIG. 111.—The Secondary Winding. 

================ ======================= ================== =============== ======================== =========
L Size of Coil   L Length of Secondary   M No. of Sections  M Size of Hole  No. of Turns per Section  Wire
================ ======================= ================== =============== ======================== =========
1/4 in.          2 3/8 in.               1                  1 1/18 in.      5,000                    37 en.
1/2 in.          2 3/8 in.               1                  1 1/8 in.       10,000                   37 en.
1 in. [#]_       2 2/8 in.               1                  1 1/8 in.       10,000                   37 en.
================ ======================= ================== =============== ======================== =========

.. [#] There are two sections of secondary used on the 1-inch coils. 

Cut a piece of tough wrapping paper about six 
inches long and four and one-half inches wide. Roll 
it up in the form of a tube so that it is six inches long 
and one-half inch in diameter inside. 

Glue the inside and outside edges of the paper so 
that the tube cannot unroll and then slip the core 
wires into it until the tube is packed tightly and no 
more can be slipped in.

The core is now ready for the primary, which 
consists of two layers of No. 18 B. & S. Gauge cotton 
covered wire wound over the core for a distance of 
three and three-quarters inches. The winding should 
start five-eighths of an inch from one end of the core. 
The wire must be wound very smoothly and 
carefully. The inside end of the wire can be fastened so 
that it will not become loose by placing a short piece 
of tape lengthwise of the core and winding two or 
three turns over it. Then double the end back and 
complete the winding over it. The end of the wire 
can be fastened by imbedding a piece of tape under 
the winding with a small loop projecting and then 
passing the wire through the loop. 

Figure 110 shows the complete core with primary 
winding in position. 

**The Secondary** is a much more tedious job than 
the primary and must be very carefully made. 
Whenever it is possible for the experimenter to purchase a 
secondary already wound he is advised to do so. 

The secondary consists of 5,000-6,000 turns of No. 
37 B. & S. Gauge, enameled wire wound in smooth, 
even layers, with two layers of paper between every 
two layers of wire. 

The primary winding is wrapped with six layers of 
"empire cloth or paper." Empire cloths and papers 
are a yellow insulating material made by treating 
linen or paper with linseed oil. 

Roll up a paper tube of five or six layers of paper 
so that the finished tube is two and one-half inches 
long and of proper inside diameter to just slip over 
the primary winding when the empire cloth or paper 
is in position. 

The secondary is wound over this paper tube. It 
will be necessary to mount the tube on a round 
wooden mandrel fitted with a small crank or handle 
so that the tube may be revolved. A "winder" may be 
very easily made by mounting a round wooden stick of 
the same diameter as the inside of the paper tube in a 
pair of wooden supports. Bore a hole in one end of 
the stick and bend a piece of stiff wire in it so as to 
form a crank. 

.. figure:: images/Image112.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 112.—The Fixed Condenser. 

   FIG. 112.—The Fixed Condenser. 

============== ================ ================ =================== ================== ===================== ======================
Size of Coil   Length of Paper  Width of Paper   Length of Tinfoil   Width of Tinfoil   No. of Paper Sheets   No. of Tinfoil Sheets 
============== ================ ================ =================== ================== ===================== ======================
1/4 in.        30 in.           4 3/8 in.        30 in.              4 in.              5                     4
1/2 in.        30 in.           4 3/8 in.        30 in.              4 in.              5                     4
1 in.          30 in.           4 3/8 in.        30 in.              4 in.              7                     6
============== ================ ================ =================== ================== ===================== ======================

The paper placed between each two layers of the 
secondary winding should be the special waxed paper 
which is made for that purpose. 

Start and end each layer of wire one-half inch from 
the edges of the paper. Wind the wire in smooth, 
even layers, permitting each turn to touch the other, 
but none to lap over. Wind on two layers of waxed 
paper between each layer of wire and the next. The 
paper must be put on smoothly and evenly so as to 
afford a firm foundation for the next layer of wire. 

The wire should never come nearer to the edges of 
the paper than one-half inch or the insulation of the 
secondary will be weak and the coil not liable to give 
a long spark. 

The utmost care should be used not to break the 
wire. If it should break, the ends must be very 
carefully connected. The number of turns that each layer 
averages should be carefully noted so that by keeping 
a record of the number of layers it is possible to tell 
how many turns have been wound on. When five to 
six thousand turns have been wound on the secondary 
it is sufficiently large, and the outside end of the wire 
should be fastened and prevented from unwinding by 
securing it with a drop of sealing wax. 

When winding a secondary remember that if at any 
point in the work, you allow the winding to become 
irregular or uneven, the irregularity will be much 
exaggerated on the succeeding layers. For this reason 
do not allow any irregularities to occur and if the wire 
tends to go unevenly, wind on two or three extra 
layers of the waxed paper to smooth it out. 

.. figure:: images/Image113.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 113.—Details of the Wooden Coil Heads.

   FIG. 113.—Details of the Wooden Coil Heads.
   
================== ========= ========= ==========
Size of Coil       D         K         J
================== ========= ========= ==========
1/4 in.            3 in.     2 1/2 in. 1/2 in.
1/2 in.            3 in.     2 1/2 in. 5/8 in.
1 in.              3 1/2 in. 3 in.     5/8 in.
================== ========= ========= ==========

**The Condenser** consists of alternate layers of tinfoil 
and paraffined paper piled on top of each other and 
then rolled up. 

Four sheets of tinfoil, thirty-six inches by two and 
three-quarters inches wide will be required. Eight 
strips of waxed condenser paper, three and 
one-quarter inches wide and thirty-six inches long are 
necessary. 

Lay one sheet of paper out flat on a table or board 
and place a sheet of tinfoil over it. The tinfoil should 
be along the centre of the paper strip so that there 
is a one-quarter inch paper margin along the sides. 
One end of the tinfoil should project over the end of 
the paper about two inches. Lay two sheets of waxed 
paper over the tinfoil making them line up with the 
first paper sheet all around. Then place another strip 
of tinfoil on the paper. It should be directly above 
the first sheet of tinfoil, but the end of the tinfoil 
must overlap the paper by two inches at the opposite 
end from the first sheet. Place two more sheets of 
paper over the tinfoil and on top of that a third strip 
of foil. The third strip of foil should line up exactly 
with the first strip. Then lay two more sheets of 
waxed paper over the third sheet of foil and place the 
fourth sheet of tinfoil in position making it exactly 
line up with the second sheet. Place a single sheet 
of paper on top.

The result should consist of four sheets of tinfoil 
insulated from each other with two strips of paper 
between each two strips of foil.

Connect the first and third sheets together with a 
wire and the second and fourth sheets likewise. 

Cut out a piece of cardboard, one and one-quarter 
inches wide and three and one-quarter inches long. 
Lay the cardboard on one end of the condenser and 
roll the condenser up around it very tightly. Tie it 
with a piece of string to keep it from unrolling, and 
dip it in some melted paraffine. Then place it 
between two boards with a weight on top so as to press 
it out flat. 

**The Coil Heads** are made from two hardwood 
blocks three inches square and one-half an inch thick. 
A circular groove, two and one-half inches in diameter 
and one-quarter of an inch deep is turned in each 
block to receive a cardboard tube of the same diameter. 
The two upper corners of each of the blocks are 
rounded slightly to improve their appearance. One 
of the heads has a round hole one-half inch in diameter
bored through the centre so that one end of the core 
may be passed through. The core should project 
through about one-eighth of an inch. The other head 
is bored with a hole of the same diameter but the 
hole should not pass all the way through, and serves 
merely to receive and support the other end of the 
core. 

.. figure:: images/Image114.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 114.—Details of the Wooden Base. 

   FIG. 114.—Details of the Wooden Base. 
   
============== ========== ========== ==========
Size of Coil   A          B          C 
============== ========== ========== ==========
1/4 in.        8 in.      4 in.      1 1/8 in. 
1/2 in.        8 1/4 in.  4 1/2 in.  1 1/8 in. 
1 in.          10 1/4 in. 4 1/2 in.  1 1/4 in.
============== ========== ========== ==========

**The Base** of the coil is a box eight inches long, 
four inches wide and one and one-eighth inches deep. 
It is made in the form of a hollow box. Give the base 
a coat of stain, preferably some dark color, such as 
mahogany, and then a coat of shellac or varnish. 

The wooden heads should be stained black. 

The parts of the interrupter are shown in Figure 
\115. They cannot be made by every experimenter on 
account of the tools required, but can be purchased 
very cheaply from concerns dealing in material for 
experimenters. 

**The Standard** is a piece of hexagonal brass rod one 
and three-sixteenths inches long and three-eighths of 
an inch in diameter. The lower end of the standard is 
tapped to receive an 8-32 machine screw. A hole is 
bored at right angles to the axis of the standard, one 
inch from the lower end and tapped to receive an 8-32 
thumbscrew. 

.. figure:: images/Image115.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 115.—Details of the Interrupter. The Spring and Standard for the One inch coil should be made one-quarter of an inch longer. 

   FIG. 115.—Details of the Interrupter. The Spring and Standard for the One inch coil should be made one-quarter of an inch longer. 
   
The Thumbscrew should be about seven-eighths of 
an inch long and be provided with a lock nut so that 
it can be fastened in position. The end of the 
thumb-screw is drilled with a small hole and a contact point 
driven in tightly. The contact point is usually a 
piece of platinum wire, but in the case of a small coil 
may be a piece of the special contact wire which is 
sold for just this purpose. 

.. figure:: images/Image116.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 116.—The tube. 

   FIG. 116.—The tube. 
   
=================== ==================== ==================
Size of Coil        Length of Tube       Diameter of Tube 
=================== ==================== ==================
1/4 inch            4 1/4 inch           2 1/2 inch
1/2 inch            4 1/2 inch           2 1/2 inch
1 inch              6 1/2 inch           3 inch 
=================== ==================== ==================

**The Spring** is a piece of thin steel, three-eighths of 
an inch wide and two and one-eighth inches long. 
Several holes are drilled in it. The illustration shows 
the exact location of these holes. The holes A and C 
should be just large enough to allow an 8-32 machine 
screw to slip through. The hole B is just large enough 
to receive a piece of contact wire. 

**The Contact** wire should be about 
three-thirty-seconds of an inch long and be slipped in the hole and 
riveted in place. 

**The Armature** is a piece of soft iron cut out of a 
rod one-half an inch in diameter. It should be about 
one-quarter of an inch thick, but should have a small 
stud left on one face so that the stud may be slipped 
into the hole marked C in the steel spring and the 
armature then riveted firmly to the spring by 
flattening out the stud. 

.. figure:: images/Image117.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 117.—The Bridge. 

   FIG. 117.—The Bridge. 
   
============== ============ =============
Size of Coil   E Length     I Width 
============== ============ =============
1/4 inch       4 7/8 inch   3/4 inch 
1/2 inch       5 1/8 inch   3/4 inch 
1 inch         7 1/8 inch   3/4 inch 
============== ============ =============

The spring is bent at right angles about one-half 
inch from the end as shown by the dotted line in 
Figure 115. 

**A Cardboard Tube**, two and one-half inches in 
diameter and four and one-quarter inches long, is used 
to inclose the primary and secondary windings when 
they are in position. The tube may be given a very 
fine appearance by gluing a single layer of black 
bookbinders' cloth over it.

**The Bridge** shown in Figure 117 is a strip of wood 
about one-eighth of an inch thick, four and 
seven-eighths inches long and three-quarters of an inch wide. 
It is stained to match the base and is then given a 
coat of shellac or varnish. Two holes are bored in, 
the bridge, one inch from each end. 

The coil is now ready for assembling. Figure 118. 
shows a cross-section of the complete coil. 

Slip the secondary over the insulating cloth or 
paper wrapped around the primary. Pass one end of 
the core through the hole in the coil head making 
sure that the groove is on the side towards the 
secondary. The secondary should be exactly in the centre 
of the primary. 

.. figure:: images/Image118.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 118.—Section of the Spark Coil showing the arrangement of the Parts. 

   FIG. 118.—Section of the Spark Coil showing the arrangement of the Parts. 

Slide the cardboard tube over the primary and 
secondary into the groove. Lead the secondary 
terminals out through small holes in the cardboard tube at 
opposite ends so that the wires are separated as far 
as possible. Slip the other coil head over the end of 
the core and the tube and then mount the coil on the 
top of the base. The coil should be in the centre of 
the base when considered from front to back. It 
should be to the left of centre, however, when viewed 
from side to side. 

The two primary heads should be four inches apart 
When the coil is assembled.

The primary wires are led down close to the wooden
head and through the base under the coil. They 
should be kept as far away from the secondary as is 
possible. 

The coil is fastened to the base by a wood screw 
passing through the base into each of the wooden 
heads. 

Figure 122 will show best how the interrupter is 
arranged. The brass spring carrying the armature at 
its upper end is mounted in front of the core end 
projecting through the wooden head. The standard 
carrying the thumbscrew and the lock nut are 
mounted directly behind the spring in such a position 
that the contacts touch each other and line up 
perfectly. 

.. figure:: images/Image119.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 119.—End View of the Complete Coil. 

   FIG. 119.—End View of the Complete Coil. 

================ ================== ================= 
Size of Coil     B Width of Base    D Width of Head 
================ ================== ================= 
1/4 inch         4 inch             3 inch 
1/2 inch         4 inch             3 inch 
1 inch           4 1/2 inch         3 1/2 inch
================ ================== ================= 

A small brass washer is placed between the standard 
and the base so that it will not "bite" into the wood 
when the screw is tightened. The standard and the 
spring are both mounted by 8-32 brass machine screws 
passing through the base. 

Two binding posts are mounted on the corners of 
the base near the interrupter. 

.. figure:: images/Image120.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 120.—Side View of the Completed Coil. 

   FIG. 120.—Side View of the Completed Coil. 

=============== ========== ========= ========= ========= ======== ========== ======== =========
Size of Coil    A          C         D         E         F        G          H        Q 
=============== ========== ========= ========= ========= ======== ========== ======== =========
1/4 in.         8 in.      1 1/8 in. 3 in.     4 7/8 in. 3 in.    1 7/16 in. 5/8 in.  4 1/4 in. 
1/2 in.         8 1/4 in.  1 1/8 in. 3 in.     5 1/8 in. 3 in.    1 7/16 in. 5/8 in.  4 1/2 in. 
1 in.           10 1/4 in. 1 1/4 in. 3 1/2 in. 7 1/8 in. 4 in.    1 7/16 in. 5/8 in.  6 1/2 in. 
=============== ========== ========= ========= ========= ======== ========== ======== =========

The condenser is fastened to the under side of the 
base by means of a wooden strip passing across it and 
secured to the base by means of two small wood 
screws. 

One of the binding posts is connected to one of the 
primary wires. The other primary wire is connected 
to the spring. The other binding post is connected to 
the standard. 

The condenser is connected directly "across" the 
interrupter, that is, one wire is connected to the spring 
and the other wire to the standard. 

Two binding posts are mounted on the wooden 
bridge and then the bridge is fastened across the top 
of the coil by means of two brass nails. The 
secondary terminals are connected to these binding posts. 

The Coil is now ready for operation. Connect two 
pieces of wire to the secondary binding posts and 
bring them toward each other until they almost touch. 
The space between should be about one-quarter of an 
inch long. 

.. figure:: images/Image121.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 121.—Diagram of Connections. 

   FIG. 121.—Diagram of Connections. 

Connect three or four good dry cells to the 
primary posts and turn the thumbscrew until the contact 
point on the end touches the contact on the spring. 
The interrupter should immediately commence to 
"buzz" and if the coil has been properly constructed 
and connected, a stream of sparks will jump between 
the wires connected to the secondary. 

It may be possible that the action of the interrupter 
and consequently the strength of the sparks at the 
secondary can be improved by bending the spring' 
either away or towards the core. A little 
experimenting will soon show just how much tension the spring 
should have. When the proper position of the 
thumb-screw is found, tighten the lock nut so that it cannot 
change its adjustment. 

.. figure:: images/Image122.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 122.—Perspective view of Coil showing names of the various parts. 

   FIG. 122.—Perspective view of Coil showing names of the various parts. 

Details and instructions for building and 
experimenting with larger spark coils are given in our books 
"Experimental Wireless Construction" and "Induction 
Coils." 

.. container:: center large

   EXPERIMENTS WITH SPARK COILS.

Experiment 1—An Imitation Gassiot's Cascade.
````````````````````````````````````````````

Wrap a piece of copper wire around a small glass 
jar and connect it to one of the secondary 
terminals of the coil. Fill the jar up with water and dip 
a wire connected to the other secondary terminal into 
the water. If the coil is then set into operation, the 
entire outside of the jar will be covered with sparks 
starting from the wires and rushing upwards into the 
neck of the jar. If the coil used for this experiment 
is a very small one, the glass jar should also be very 
small, as for example, a small medicine vial. This 
experiment shows off the best when performed in the 
dark. 

Experiment 2—A Ghostly Light
````````````````````````````

Grasp the bulb of an old incandescent electric light 
bulb in one hand and touch the base of the lamp to 
one of the secondary terminals of the coil. Set the 
coil in operation and the bulb will glow with a weird 
greenish light. This experiment will work best in the 
dark. 

Experiment 3—Lighting Geissler Tubes.
`````````````````````````````````````

The most beautiful and wonderful effects may be 
obtained from Geissler tubes operated from a spark 
coil in a dark room. These tubes come in an almost 
endless variety of styles and shapes. They are 
exhausted of air and fitted with metallic wires, sealed 
into the ends, a portion of the wire projecting outside 
in the form of small rings, so that the connections 
are easily established. 

Some of the tubes are of ordinary glass, while others 
are made of glass having in its composition certain 
metallic oxides. Some of the tubes are filled with 
various gases in a highly rarified state. Others have 
a double wall with the outside filled with a fluorescent 
liquid, such as an aqueous solution of sulphate of 
quinine or an alcoholic solution of strammonium, and 
other compounds. 

The tubes are not very expensive. They can be 
obtained in a great variety of sizes. Most well stocked 
electrical houses carrying goods for the electrical 
experimenter have them on hand. 

Such tubes are of necessity very fragile articles and 
should be handled with extreme care. It is a good 
plan to keep them wrapped in cotton and to put them 
away in a strong wooden box, so as to reduce the 
danger of breakage. 

The very smallest coil, even the one-quarter inch 
size, will serve to light a large tube. . In fact, if too 
large a coil is used, there is danger of spoiling the tube. 

The tubes are connected to the spark coil by running 
a wire from each of the small rings at the ends of the 
tubes to the secondary terminals. Several tubes may 
be connected in series when a or 1-inch coil is 
available. 

To show the best effects, the room should be in 
perfect darkness and the tubes should be placed 
against a background of black velvet. 

Experiment 4—Flickering Light.
``````````````````````````````

Spread your fingers out and move your hand rapidly 
back and forth over a lighted Geissler tube in a 
darkened room. Your hand will appear to have ten or 
twelve fingers instead of five. This is due to the fact 
that the light from a Geissler tube is flickering and 
not at all steady. Each time the interrupter of the 
coil opens, the current is sent through the tube and 
lights it momentarily. The flickering is almost too 
rapid to be perceived by the naked eye until you have 
something like the fingers or a pencil in front of it. 

Experiment 5—Rotating a Geissler Tube.
``````````````````````````````````````

An extremely pretty effect can be secured by 
rotating a Geissler tube at high speed while it is lighted. 
This may be accomplished by means of an electric 
motor of small size. The tube is tied tightly to a 
stick of wood which has a hole drilled exactly in its
center into which the motor shaft fits tightly. Two 
rings of metal are mounted on the motor shaft, and a 
wire is led from each to a terminal of the tube. A 
copper strip rests on each ring, and these two copper 
strips are connected to the secondary of the spark 
coil. 

When the motor is started and the coil set into 
operation, the tube will appear like the spokes of a 
wheel. The intermittent light will make the tube 
visible for a fraction of a second in various positions 
around the circle as it rotates, and this gives the effect 
which is much like that of a pinwheel. 

Experiment 6—Fluorescent Writing.
`````````````````````````````````

Dissolve some sulphate of quinine in water and then 
draw a picture or design or write a sentence on a 
piece of white paper with it, and allow it to dry. The 
writing will be invisible, but if you hold it up to a 
lighted Geissler tube in a dark room, it will appear as 
if written with a beautiful blue ink. 

Experiment 7—An Electric Bomb.
``````````````````````````````

This is a very interesting experiment from which 
there is no danger if it is performed carefully. 

The mortar is nothing more or less than a piece of 
wood which is hard and well seasoned, and has a 
small hole bored in its axis about three-eighths of an 
inch in diameter and an inch deep. 

Two short lengths of stiff copper wire should be 
inserted through the sides near the bottom of the hole 
so as to form a small spark gap between the ends. 

Put a little gunpowder in the mortar and connect 
two wires from the secondary terminals of the spark 
coil to the spark gap. Place a cork loosely in the 
muzzle of the mortar and then, standing well away, 
close the switch in the primary circuit of the coil, so 
that a spark passes through the mortar. The spark 
will ignite the powder and it will explode with a loud 
report. 

**Caution**.—Do not use more than a pinch of powder 
at a time as this is sufficient to cause a sharp explosion. 

Experiment 8—Electrifying the Garbage Can.
``````````````````````````````````````````

If you are ever annoyed by dogs or cats that knock 
the cover off the garbage can in their search for canine 
and feline delicacies, you can give them the surprise 
of their lives with the aid of a spark coil upon the 
occasion of their next visit. 

Set the can upon a thick piece of perfectly dry wood 
and run a wire from the can to one secondary terminal 
of the spark coil. Connect the other secondary 
terminal to the ground or to a water or gas pipe. 

The next time you see a dog with his nose in the 
can, close the switch connected to the primary circuit. 
What happens will not hurt the dog, but he will travel 
for home as fast as four legs can carry him. 

Experiment 9—How to Make an Electric Spark Photograph Itself.
`````````````````````````````````````````````````````````````

This experiment must be conducted in a dark room 
with the aid of a photographer's ruby lamp so that 
the photographic plates used will not become "light 
struck" and spoiled. 

Place an ordinary photographic plate on a piece of 
sheet metal with the coated or sensitive side up. 
Connect the piece of sheet metal to one of the secondary 
terminals of the spark coil by means of a wire. 

Then sift some dry starch powder, flour of sulphur 
or talcum powder through a thin piece of gauze on to 
the plate. Lead a sharp pointed wire from the other 
secondary terminal of the coil. Complete the primary 
circuit of the coil just long enough to make one single 
spark. 

Wipe the powder off the plate thoroughly and 
develop it in the usual manner. The negative will show 
a peculiar electric discharge looking very much like 
sea moss. No two photographs will be alike. The 
test results are obtained when only one or two sparks 
are allowed to pass. 

.. figure:: images/CoverImage3.jpg
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   :alt: Book Cover Image 

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.. container:: titlepage 

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       Arts and Science Series No. 9 

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       Home-made
   
       Electrical Apparatus 

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       A Practical Handbook for Amateur 

       Experimenters 

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       In Three Parts 

       **Volume III**

       *Second Edition*

       **BY**

       **A. M. Powell**

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       PUBLISHED BY

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       COLE & MORGAN, Inc. 

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       Publishers of the Arts and Science Series 

       \P.O. BOX 473 CITY HALL STATION 

       NEW YORK, N. Y. 

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       Printed in U. S. A. 

.. clearpage::

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    Copyright 1918 

    by 

    COLE & MORGAN, Inc. 

.. clearpage::

CHAPTER XII. HOW TO MAKE A DYNAMO-MOTOR
---------------------------------------

It is very difficult to construct a first class dynamo 
without resort to the materials and methods 
employed in the manufacture of commercial machines. 
The necessity for careful workmanship in every detail, 
can hardly be overestimated. Poor workmanship and 
poor materials will always result in an inefficient 
machine. Telegraph instruments, toy motors, etc., may 
be constructed from all sorts of odds and ends of 
materials, and they will work fairly well, but in order to 
make a real dynamo it will be necessary to use certain 
materials for which nothing can be substituted. 

.. figure:: images/Image123.jpg
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   :alt: FIG. 123—Front view of the Field Casting. 

   FIG. 123—Front view of the Field Casting. 

The field casting must be soft gray cast iron and the 
magnet wire should be of good quality. 

Both the field and the armature of the small dynamo 
described in the following pages are cast iron and 
patterns will be necessary in order to form the moulds for 
the castings. It may be possible for several 
experimenters to club together and make the patterns, or 
have them made, for building this dynamo. 

The dynamo described has an output of about ten 
watts. It may also be used as a motor and as such will 
develop considerable power. The castings for this 
machine are already on the market and may be obtained 
from the publishers of this book. 

.. figure:: images/Image124.jpg
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   :alt: FIG. 124.—Side elevation of the Field Casting. 

   FIG. 124.—Side elevation of the Field Casting. 

**The Field** is shown in Figures 123 and 124. The 
details in both illustrations are fully dimensioned and 
probably no comment in that direction will be 
necessary. 

If the experimenter decides to make his own patterns 
he should use every care to make certain that they are 
carefully and accurately made. They should be made 
of wood and finished by rubbing with fine sandpaper 
until perfectly smooth and then given a coat of shellac. 
The parts should also be given a slight "draft" or taper 
toward one side so that the pattern may be easily 
withdrawn from the mould. 

.. figure:: images/Image125.jpg
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   :alt: FIG. 125.—Details of the Armature. 

   FIG. 125.—Details of the Armature. 

The easiest way to bore out the "tunnel" of the field 
is to perform the work on a lathe. If no lathe is 
handy, the work can be accomplished with nothing 
more than the aid of a file and a little patience. It 
should be cleaned out until it is perfectly round and 
measures one and five-sixteenths of an inch in diameter. 

Any rough spots on the casting should be smoothed 
up with a file. 

**The Armature** is illustrated in Figure 125. The 
centre of the armature should be bored out to fit a 
three-sixteenths inch shaft. 

The shaft is a piece of steel rod four inches long. 
The outside of the armature should be turned down 
to a diameter of one and one-quarter inches, making 
it one-sixteenth of an inch smaller in diameter than 
the tunnel in the field. 

**The Commutator** is illustrated in Figure 126. It 
has two sections and consists of a short piece of brass 
tubing fitted on a fibre core and split lengthwise on two 
opposite sides so that each section is insulated from the 
other. 

It is not very difficult to make such a commutator. 
A hole is drilled through the fibre, which fits very 
tightly on the shaft. The shaft is then placed in a 
lathe with the fibre in position and the latter turned 
down until a piece of seven-sixteenths inch brass 
tubing can be driven on. The tube should be five-eighths 
of an inch long. Then mark two lines along the tube 
at points diametrically opposite. Bore two small holes 
to receive two small screws, a short distance away 
from each side of these lines and on each side of them. 
Make certain that the screws do not go into the fibre 
far enough to touch the shaft. The commutator may 
then be split along each side of the lines with a 
hacksaw, continuing the cut right through the brass and 
slightly into the insulating core. The heads of the 
screws should be filed off flush with the surface of the 
commutator and the latter trued up and made perfectly 
smooth. 

.. figure:: images/Image126.jpg
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   :alt: FIG. 126.—The Commutator. 

   FIG. 126.—The Commutator. 

If each section of the commutator is provided with 
a small brass machine screw near the back edge as 
shown in Figure 126, it will greatly facilitate 
connection with the ends of the armature windings. 

The armature, shaft and commutator, as they should 
appear when assembled are shown in Figure 127. 

Those portions of the armature and shaft which will 
come into contact with the armature wire should be 
insulated with shellaced paper. Soak the paper in the 
shellac until it is soft and it can be very easily pressed 
into proper shape to fit the armature. Allow the 
shellac to dry and harden before winding on the wire. 

.. figure:: images/Image127.jpg
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   :alt: FIG. 127.—The Armature and Commutator Assembled on the Shaft ready for winding. 

   FIG. 127.—The Armature and Commutator Assembled on the Shaft ready for winding. 

The armature will not need to be fastened on the 
shaft if it is a tight fit and cannot be twisted. If it is 
loose, it may be fastened by means of a small set screw 
or pin. The commutator should fit the shaft very 
tightly so that it will not slip or twist. 

**The Armature Winding** is No. 20 B. & S. Gauge 
single-cotton covered magnet wire. Sufficient wire 
should be put on to fill up the winding space 
completely. Do not, however, put on too much wire or it 
will interfere with the field magnets and prevent the 
armature from revolving. Test the winding after it is 
finished to see that the wire is not "grounded" or 
connected to the armature at any point. If the insulation 
is perfect, give the winding a good coat of shellac and 
allow it to dry. The ends of the winding are each 
connected to one of the commutator sections as shown 
in Figure 127. 

**The Field Winding** is No. 20 B. & S. Gauge single 
cotton covered wire. The wire should be wound on 
in smooth, even layers, and the winding space between 
the flanges completely filled up. The winding space 
in the field frame should be insulated with shellaced 
paper by covering the core and the flanges. The flanges 
are best insulated with paper disks cut in two halves 
so that they will slip around the core. 

.. figure:: images/Image128.jpg
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   :alt: FIG. 128.—Details of the Wooden Base. 

   FIG. 128.—Details of the Wooden Base. 

The details of the wooden base are shown in Figure 
\128. It is a rectangular shaped piece of wood, five 
inches long, four inches wide and five-eighths of an 
inch thick. The corners are slightly rounded. 

**The Bearings** are small brass castings. They are 
both alike. The details are illustrated in Figure 129. 
It will be necessary to make a wooden pattern and send 
it to a brass foundry for castings. The castings should 
be smoothed up with a file and then drilled. The shaft 
hole should be three-sixteenths of an inch in diameter 
and the screw holes just large enough to pass an 8-32 
screw. The bearings are fastened to the projecting 
arms on the field casting by means of round headed 
8-32 brass machine screws. The armature should 
revolve exactly in the centre of the tunnel in the field 
and should be free in the bearings so that it runs easily 
and without binding. 

**The Brushes** are illustrated in Figure 131. They are 
cut out of spring copper and bent according to the 
shape and dimensions shown. 

The field is fastened to the base by means of two 
large machine screws passing upwards through the 
base into threaded holes in the bottom of the casting. 
The brushes are bent at right angles and mounted on 
the base on either side of the commutator with small 
round headed wood screws. They should bear firmly 
against the commutator. The commutator should be 
in such a position on the shaft, in relation to the 
armature, that the dividing lines between the two sections 
are directly opposite the centre of the iron faces of the 
armature as shown in Figure 127. 

.. figure:: images/Image129.jpg
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   :alt: FIG. 129.—Details of the Bearings. 

   FIG. 129.—Details of the Bearings. 

.. figure:: images/Image130.jpg
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   :alt: FIG. 130.—The Pulley. 

   FIG. 130.—The Pulley. 

.. figure:: images/Image131.jpg
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   :alt: FIG. 131.—The Brushes. 

   FIG. 131.—The Brushes. 

The shaft should be fitted with a small grooved 
pulley to accommodate a small round belt. The completed 
dynamo is shown in Figure 132. The dynamo is 
connected in what is known as "shunt." One terminal of 
the field magnet is connected to one brush and the 
other terminal to the other brush. A wire is then led 
from each one of the brushes to a binding post. 

Before the dynamo will generate current it will be 
necessary to magnetize the field by connecting the 
terminals to several strong batteries and allowing the 
current to flow through for several seconds. A shunt 
wound dynamo will only generate when run in a 
certain direction. In order to make it generate when run 
in the opposite direction, it is necessary to reverse the 
field connections to the brushes. 

.. figure:: images/Image132.jpg
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   :alt: FIG. 132.—The Completed Dynamo. 

   FIG. 132.—The Completed Dynamo. 

The dynamo will be found to operate as a very 
powerful little motor, but on account of having only 
a two pole armature, it must be started when the 
current is turned on by giving the shaft a twist. 

The dynamo may be driven by a small water motor 
or from the driving wheel of a sewing machine. It 
may be used as a generator for lighting lamps, ringing 
bells, electroplating, etc. 

CHAPTER XIII. AN ELECTRIC BATTERY MOTOR. 
----------------------------------------

AN electric motor has two essential parts. These 
are a field magnet for furnishing a strong 
magnetic field and a revolving armature. 

It is an easy matter to make a strong electric motor 
suitable to operate on batteries by the exercise of a 
little careful workmanship. 

The field frame and armature of the motor shown in 
Figure 133 are laminated, that is, built up of separate 
sheets of iron. They may be made out of sheet tin or 
ordinary stove pipe iron. The cheapest and simplest 
method of securing good flat material is to get some 
old scrap from a tinner's or plumbing shop. 

**The Details of the Field** are shown in Figure 134. 
The exact shape and dimensions can be understood by 
reference to the illustration. Lay out one lamination 
very carefully as a pattern. Cut it out and smooth up 
the edges, making certain that it is perfectly true to 
size and shape. Then use it as a template to lay out 
the other laminations by placing it on the metal and 
scribing a line around the edges with a sharp pointed 
needle. Enough laminations should be cut out to make 
a pile five-eighths of an inch high when tightly pressed 
together. 

.. figure:: images/Image133.jpg
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   :alt: FIG. 133.—The completed Electric Motor. 

   FIG. 133.—The completed Electric Motor. 

**The Armature** is made in exactly the same manner 
as the field frame, that is, by cutting out a pattern 
according to the shape and dimensions shown in Figure 
136 and using it as a template to lay out the other 
laminations. Enough should be cut to make a pile 
five-eighths of an inch high when tightly squeezed together. 

.. figure:: images/Image134.jpg
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   :alt: FIG. 134.—Details of the Field Frame. 

   FIG. 134.—Details of the Field Frame. 

.. figure:: images/Image135.jpg
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   :alt: FIG. 135.—The Assembled Field ready for Winding. 

   FIG. 135.—The Assembled Field ready for Winding. 

The armature is one and three-sixteenths inches in 
diameter. The hole in the field frame which 
accommodates the armature is one inch and one-quarter in 
diameter so that there is a space in between for the 
armature to revolve in. 

The hole through the center for the shaft should be 
of such diameter that the laminations will force very 
tightly on a shaft one-eighth of an inch in diameter. 
The laminations should be very carefully flattened and 
then forced over the steel shaft which is two and 
one-eighth inches long. Clean up all the rough edges with 
a file and smooth the outside so that it will revolve 
properly in the field without scraping. 

.. figure:: images/Image136.jpg
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   :alt: FIG. 136.—Details of the Armature Lamination. 

   FIG. 136.—Details of the Armature Lamination. 

.. figure:: images/Image137.jpg
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   :alt: FIG. 137.—The Armature assembled on the Shaft ready to Wind. 

   FIG. 137.—The Armature assembled on the Shaft ready to Wind. 

Figure 137 illustrates the armature assembled on the 
shaft and ready to be wound. 

**The Armature Windings** consist of four layers of 
No. 22 B. & S. Gauge double cotton covered magnet 
wire wound around each leg. The iron should be very 
carefully insulated with shellaced paper before the wire 
is put in position so that there will not be any danger 
of short circuit due to the sharp edges of the metal 
cutting through the insulation. Each leg should 
contain the same number of turns of wire and all should 
be wound in the same direction. 

The Commutator is illustrated in Figure 138. It 
consists of a piece of brass tubing seven-sixteenths of 
an inch long, five-sixteenths inside and three-eighths 
of an inch outside. It should be forced onto a piece of 
fibre five-sixteenths of an inch in diameter and 
seven-sixteenths of an inch long. Split the tube into three 
equal parts by dividing it longitudinally with a 
hack-saw. Make a fibre ring which will force onto the tube 
very tightly when it is in position on the fibre core and 
so hold the three commutator sections firmly in 
position. The sections should be so arranged that there is 
a small space between each two and they are perfectly 
insulated from each other. The fibre core should have 
a one-eighth inch hole through the centre so that it 
may be forced tightly onto the shaft and up against 
the armature after the windings are in position. The 
commutator should be in such a position that the split 
between each two sections come directly opposite the 
centre of each winding. Suppose that the windings 
are lettered A, B, and C, the commutator section 
between A and B is numbered 1, that between A and C 
is No. 2, and the one between C and B is No. 3. Then 
the inside terminal of B is connected to the outside 
terminal of A and soldered to the end of 
commutator section No. 1 close to the winding. The inside 
end of B is connected to the outside terminal of C and 
to commutator section No. 2. The inside end of 
winding C is connected to the outside of B and to 
commutator section No. 3. The connection of the armature 
windings to the commutator are represented by the 
diagram in Figure 139. 

.. figure:: images/Image138.jpg
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   :alt: FIG. 138.—The Commutator. 

   FIG. 138.—The Commutator. 

.. figure:: images/Image139.jpg
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   :alt: FIG. 139.—Diagram showing how the Armature Coils are connected to the Commutator Sections. 

   FIG. 139.—Diagram showing how the Armature Coils are connected to the Commutator Sections. 

.. figure:: images/Image140.jpg
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   :alt: FIG. 140.—The Bearings. 

   FIG. 140.—The Bearings. 

**The Field Winding** consists of five layers of No. 18 
\B. & S. double cotton covered wire. A much neater 
job may be made of this part of the work if two fibre 
heads are cut to slip over the field and support the 
ends of the winding as shown in the illustration in 
Figure 133. 

**The Bearings** are illustrated in Figure 140. They 
are made out of three-eighths inch brass strip 
one-sixteenth of an inch thick by bending and drilling as 
shown in the illustration. The location of the holes is 
best understood from the drawing. The larger bearing 
is assembled on the field at the side towards the 
commutator. 

Assembling the motor is a comparatively easy 
matter if it is done properly and carefully. The bearings 
are mounted on the field frame by screws passing 
through the holes B and B into a nut on the outside of 
the bearing at the opposite side of the field. 

The armature should revolve freely without binding 
and without any danger of scraping against the field. 
Slip some small fibre washers over the ends of the 
shaft between the armature and the bearings so as to 
take up all end play. 

**The Brushes** are made of spring copper according to 
the shape and dimensions shown in Figure 141. They 
can be cut out with a pair of snips. 

Each brush is mounted on a small fibre block 
supported on the large motor bearing. The holes marked 
A and C in the illustration should be threaded with a 
4-36 tap. The hole B should be made one-eighth of an 
inch in diameter and drilled all the way through the 
block. 

The holes A and C are used to fasten the blocks to 
the bearing. The brushes are fastened to the blocks by 
means of a 6-32 screw with a nut on the lower end. 

**The Base** is a rectangular block, three inches wide, 
three and one-half inches long and three-eighths of an 
inch thick. The motor is fastened to the base by four 
small right angled brackets bent out of strip brass and 
secured to the field frame by two machine screws 
passing through the holes H and H into a nut at the 
opposite end. 

.. figure:: images/Image141.jpg
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   :alt: FIG. 141.—The Brushes. 

   FIG. 141.—The Brushes. 

One terminal of the field winding is connected to a 
binding post mounted on the base. The other terminal 
of the field is connected to the right hand brush. The 
end of the wire should be placed under the head of the 
screw which holds the brush to the fibre block. The 
brush should be on the under side of the block so that 
it bears against the under side of the commutator. 

The left hand brush bears against the upper side of 
the commutator and is connected to a second binding 
post on the base of the motor. This makes it a "series" 
motor, that is, the armature and the field are connected 
in series. 

.. figure:: images/Image142.jpg
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   :alt: FIG. 142.—The Fibre Block for supporting each Brush. 

   FIG. 142.—The Fibre Block for supporting each Brush. 

The motor is now ready to run. Put a drop of oil on 
each bearing and make certain that the curved portion 
of the brushes bear firmly against the centre of the 
commutator on opposite sides. The armature having 
three poles, should start without assistance and run at 
high speed as soon as the current is applied. Two cells 
of dry or other battery should be sufficient. The motor 
may be fitted with a small pulley so that its power may 
be utilized for driving small models. 

CHAPTER XIV. HOW TO BUILD AN ELECTRIC ENGINE. 
---------------------------------------------

An Electric engine is really a form of electric motor 
but differs from the most common form of the 
latter in that the armature, instead of revolving, 
oscillates back and forth, like the piston of a steam or 
gasoline engine. Electric engines are not as efficient as 
electric motors from the standpoint of the amount of power 
delivered in proportion to the current used, but they 
make very interesting models and the young 
experimenter will derive fully as much pleasure in 
constructing one as from the construction of an electric motor. 
Various forms of electric engines were made before 
the first practical electric motor was invented. They 
amounted to little more than curiosities, however, and 
could only be used where the expense of electric 
current was not to be regarded. 

.. figure:: images/Image143.jpg
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   :alt: FIG. 143.—Completed Electric Engine. 

   FIG. 143.—Completed Electric Engine. 

The engine illustrated in Figure 143 is of the double 
action type. It is provided with two electromagnets 
arranged so that one pulls the armature forward and 
the other pulls it back. The motion of the armature is 
transmitted to the shaft by means of a connecting rod 
and crank. It is very simple to build and the design 
is such that it will operate equally well whether it is 
made large or small. If you do not happen to have all 
the necessary materials to build an engine according to 
the dimensions shown in the drawings you can make it 
just one-half that size and it will work equally well 
although it will of course not give as much power. 

The complete engine is shown in Figure 143. All the 
various parts have been marked so that you can easily 
identify them in the other drawings. It is well to study 
this illustration carefully first so that you will 
understand just how all the parts are arranged. 

**The Base** is illustrated in Figure 144. It is made 
of a piece of hardwood, seven inches long, three and 
one-half inches wide and one-half an inch thick. 

.. figure:: images/Image144.jpg
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   :alt: FIG. 144.—The Engine Base. 

   FIG. 144.—The Engine Base. 

**The Magnets**. The size of the electromagnets will 
largely determine the dimensions of the rest of the 
engine. The magnets shown in Figure 145 are made of 
three-eighths inch round iron, two and one-half inches 
long, provided with two fibre washers one and 
one-eighth inches in diameter. One end of each of the steel 
cores is drilled and tapped to receive an 8-32 iron screw. 
The experimenter may possibly be able to secure some 
old magnet cores fitted with fibre heads from an old 
telephone bell or "ringer" as they are sometimes called. 
A suitable bolt can be made to serve the purpose by 
cutting it off to the right dimensions with a hack saw. 
If a drill and a tap are not available for drilling and 
tapping the end so that the core can be properly 
mounted in the frame of the engine it is possible by 
the exercise of a little ingenuity to use the threaded 
portion of a bolt to good advantage. The hole in the 
frame should then be made larger so that the end of 
the bolt will slip through instead of an 8-32 screw and 
the core clamped in position by a nut on each side. 

The fibre washers are spaced two and one-sixteenth 
inches apart. The space in between should be wound 
full of No. 18 B. & S. Gauge cotton covered magnet 
wire. Before winding in the wire, cover the core with 
a layer of paper so that the wire does not touch the 
metal. The ends of the wire should be led out through 
small holes in the fibre heads. 

.. figure:: images/Image145.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 145.—Details of the Electromagnet Bobbin. 

   FIG. 145.—Details of the Electromagnet Bobbin. 

It is not absolutely necessary to use No. 18 B. & S. 
Gauge wire in winding the magnets but this is the size 
which will give the best results on the average battery. 

.. figure:: images/Image146.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 146.—Details of the Engine Frame. 

   FIG. 146.—Details of the Engine Frame. 

If you use larger wire, the engine will require more 
current from the battery. If you use finer wire, a 
battery of a higher voltage will be necessary. The current 
consumption will, however, be less. 

**The Frame.**—The electromagnets are mounted in 
the frame of the engine by means of two screws 
passing through the holes E and D. The details of the 
frame are illustrated in Figure 146. It is made of a 
strip of wrought iron or cold rolled steel, nine and 
one-quarter inches long, an inch or an inch and one-eighth 
wide and one-eighth of an inch thick. The material 
for making this part of the engine and also the 
bearings can probably best be obtained at some blacksmith 
shop or hardware store. Heavy galvanized iron can 
be used but it is not usually thick enough and it may 
be necessary use two thicknesses. The ends of the 
strip are rounded and bent at right angles so as to 
form a U-shaped piece with sides one and 
three-quarters inches high. The holes D and E should be 
large enough to pass an 8-32 screw. The holes A, B 
and C should be about one-eighth of an inch in 
diameter. They are used to pass the screw which hold 
the frame of the engine to the wooden base. 

.. figure:: images/Image147.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 147—The Bearings. 

   FIG. 147—The Bearings. 

**The Bearings** are shown in Figure 147. They are 
U-shaped and are made out of a strip of iron or steel 
in the same manner as the frame of the engine but are 
three-quarters of an inch wide instead of an inch and 
one-eighth. The dimensions will be understood best 
by referring to the drawing. The 3/32 inch holes near 
the top of each side are the bearing holes for each end 
of the shaft. The one-eighth inch holes below are 
used to fasten the brush holder in position. The holes 
in the bottom serve to fasten the bearings to the base. 

.. figure:: images/Image148.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 148.—Details of the Shaft. 

   FIG. 148.—Details of the Shaft. 

**The Shaft** will probably prove the most difficult 
part of the engine to make properly. The details are 
given in Figure 148. It is made of a piece of 
one-eighth inch steel rod bent so that it has a "throw" of 
one-half an inch, that is, is offset one-quarter of an 
inch so that the connecting rod moves back and forth 
a distance of one half an inch. The finished shaft 
should be three inches long. The piece of steel used 
should be longer than this, so that it can be cut off to 
exact dimensions after the shaft is finished. A second 
crank should be bent in one end of the shaft so as to 
form an offset contact for the brushes. This second 
crank will have to be at right angles to the first one 
and should be much smaller. The ends of the shaft are 
turned or filed down to a diameter of three-thirty 
second of an inch for a distance of about the same 
amount so that they will fit in the bearing holes and 
turn freely but not allow the whole shaft to slip 
through. The work of making the shaft will require a 
small vice, a light hammer, files and a couple of pairs 
of pliers. One pair of pliers should be of the round 
nosed type and the other a pair of ordinary square 
jawed side cutters. It may require two or three 
attempts before a perfect shaft is secured. When 
finished it should be perfectly true and turn freely in 
the holes. The bearings can be adjusted slightly 
by bending so that the shaft will fit in the holes and 
be free but yet not be loose enough to slip out. 

**The Armature** is a strip of soft iron, two and 
one-eighth inches long, seven-sixteenths of an inch wide 
and three-sixteenths of an inch thick. A one-sixteenth 
inch slot, three-eighths of an inch long is cut in one 
end. A one-sixteenth inch hole is drilled through from 
one side to the other, one-eighth of an inch from each 
end. The hole which passes through the slot is used 
to pass the pin which pivots the armature to the 
connecting rod. The other hole is used to mount the 
armature in its bearing. The armature bearing is a 
small edition of the one which is used to support the 
engine shaft. The details and the dimensions are 
given in the lower left hand side of Figure 149. The 
armature is shown in the centre of the same 
illustration. The connecting rod is illustrated at the right. 
This is made from a strip of three-sixty-fourths inch 
brass, three-sixteenths of an inch wide and one and 
five-eighths inches long. A one-eighth inch hole 
should be drilled close to one end and a one-sixteenth 
inch hole close to the other. 

.. figure:: images/Image149.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 149.—The Armature, Armature Bearing and Connecting Rod. 

   FIG. 149.—The Armature, Armature Bearing and Connecting Rod. 

**The Brushes** are two strips of thin phosphor 
bronze sheet, two and three-sixteenths inches long and 
nine-thirty-seconds of an inch wide. They are 
illustrated in Figure 150. The block upon which they are 
mounted is hard fibre. It is one and five-eighths inches 
long and three-eighths of an inch square. 

.. figure:: images/Image150.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 150.—The Brushes. 

   FIG. 150.—The Brushes. 

**The Flywheel**. It may be possible to secure a 
flywheel for the engine from some old toy. It should 
be about three and one-half inches in diameter. A 
flywheel can be made out of sheet iron or steel by 
following the suggestion in Figure 151, which shows a wheel 
cut out of one-eighth inch sheet steel. It is given the 
appearance of having spokes by boring six 
three-quarter inch holes through the face as shown. The 
hole in the centre of the wheel should be one-eighth of 
an inch in diameter. The wheel is slipped over the 
shaft and fastened in position by soldering. 

The parts are now all ready to assemble into the 
complete engine. Mount the electromagnets in the 
frame and fasten the frame down to the wooden base 
so that one end of the frame comes practically flush 
with the left hand edge of the base. Fasten the 
bearing across the frame at right angles by a screw 
passing through the centre hole in the bottom of the 
bearing, through the hole A and into the base. The 
bottom of the bearing should be bent slightly so 
as to straddle the frame. The bearings should be 
secured and prevented from turning or twisting by two 
screws passed through the other two holes in the 
bottom. Use round-headed wood screws in mounting the 
bearing and the frame. The armature bearing should 
be mounted on the frame directly between the two 
electromagnets. Then place the armature in position 
by slipping a piece of one-sixteenth inch brass rod 
through the bearing holes and the hole in the lower 
part of the armature. 

.. figure:: images/Image151.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 151.—A Flywheel may be cut from sheet iron.

   FIG. 151.—A Flywheel may be cut from sheet iron.

Solder the flywheel in position on the shaft and snap 
the latter into the bearings. Adjust the bearings so 
that the shaft will turn freely. The connecting rod 
should be slipped over the shaft before it is placed in 
the bearings. Fasten the other end of the connecting 
rod to the armature by means of a piece of 
one-sixteenth inch brass rod which passes through the small 
holes bored for that purpose. When the flywheel is 
spun with the fingers, the armature should move back 
and forth between the two electromagnets and almost 
but not quite touch the two magnet poles. All the 
moving parts should be fitted firmly together but be 
free enough so that there is no unnecessary friction 
and so that the engine will continue to run for a few 
seconds when the flywheel is spun with the fingers. 

The brushes, supported on their fibre block should 
be mounted on the bearing by means of two screws 
passing through the holes in the bearing into the 
block. The position of the brushes should be such that 
the shaft passes between the two upper ends but does 
not touch them unless the small contact crank 
mentioned above is in proper position to do so. The proper 
adjustment of the brushes, so that they make contact 
with the shaft at the proper moment, will largely 
determine the speed and power which the finished engine 
will develop. 

Two binding posts should be mounted on the right 
hand end of the base so that the engine can be easily 
connected to a battery. Connect one terminal of the 
right hand electromagnet to one of the binding posts. 
Run the other terminal of the electromagnet to the 
brush on the opposite side of the shaft. Connect one 
terminal of the left hand electromagnet to the other 
binding post and run the other terminal to the brush 
on the opposite side of the shaft. Save for a few 
minor adjustments, the engine is now ready to run. 
Connect two or three cells of dry battery to the two 
binding posts and turn the flywheel so that it moves 
from right to left across the top. Just as the crank 
passes "dead centre" and the armature starts to move 
back away from the left hand magnet, the small 
contact crank should touch the left hand brush and send 
the current through the right hand magnet. This will 
draw the armature over to the right. Just before the 
armature gets all the way over to the right, the 
contact should break connection with the left hand brush 
and interrupt the current so that the inertia of the 
flywheel will cause it to keep moving and the armature 
to start to move over towards the left hand magnet at 
which point the contact on the shaft should commence 
to bear against the right hand brush, thus throwing the 
left hand magnet into circuit and drawing the armature 
over to that side. If the brushes and the cranks are in 
proper relation to each other the engine will continue 
to repeat this operation and gradually gain speed until 
it is running at a good rate. 

The appearance of the engine can be improved by 
painting the metal parts black and the flywheel red. 
The magnets can be wrapped with a piece of bright 
red cloth to protect the wire against injury and 
brighten the appearance of the engine. 

CHAPTER XV. MINIATURE BATTERY LIGHTING. 
---------------------------------------

The tungsten lamp has opened wonderful 
possibilities in the field of electric lighting by means of 
miniature lamps operated from batteries.

The tungsten lamp uses less than one third the 
amount of current required by the old-fashioned 
carbon filament lamps in producing the same candle 
power. This means that the battery will last three 
times as long. 

Miniature lighting is one of the most practical 
phases of experimental electricity to which the 
experimenter can apply his time. Battery operated lamps 
will be found invaluable in many places for lighting 
dark corners, hallways, barns, garages, camps, 
bungalows, workshops, etc. 

**Tungsten Battery Lamps** are made in a great many 
different styles and sizes. 

The smallest sizes are used for flashlights, 
hand-lanterns, etc. These are not rated according to their 
candlepower, but to the voltage which they should be 
operated on. Flashlight lamps will be found 
satisfactory as a means of illuminating closets, cellars, 
stairways, etc., but do not give sufficient light for reading 
or any purpose of that sort. The light which they 
give varies from one to three candle-power according 
to the size of the lamp. They are made for 1.5, 2.8, 
\3.8 and 5.8 volts or respectively one, two, three and 
four dry cells. Flashlight lamps are provided with 
what is known as a miniature base only. 

A very simple lighting arrangement which will prove 
exceedingly useful for illuminating a dark closet, a coal 
bin or the face of a clock, etc., consists of a 1.5 volt 
lamp, a single cell of dry battery and a suitable switch 
and wire. Such an installation may be made at a cost 
of less than seventy-five cents. 

.. figure:: images/Image152.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 152.—Small Tungsten Battery Lamps. 

   FIG. 152.—Small Tungsten Battery Lamps. 

The lamp is mounted in what is known as a 
miniature porcelain base receptacle. The switch may most 
conveniently be the type termed a "wood base" switch. 
In case the lamp is installed for illuminating a clock, 
a "pear push" and a flexible cord may be substituted 
for turning the light off and on in place of the switch. 
It can then be suitably hung alongside of the clock 
or bed as desired. 

The wire should not be smaller than No. 18 B. & S. 
Gauge or else it will offer too much resistance to the 
electric current and full benefit of the candle-power of 
the lamp will not be secured. Annunciator wire is 
preferable. It has good insulation and at the same time is 
not too large to be easily run through corners, cracks, 
etc. 

The diagram in Figure 153 shows how to connect the 
lamp to the battery and switch. Figure 156 shows two 
dry cells connected in series for use with a 2.8 volt 
lamp. 

.. figure:: images/Image153.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 153.—A Simple Lighting Arrangement. 

   FIG. 153.—A Simple Lighting Arrangement. 

When more illumination is desired than that 
furnished by flashlight lamps greater candle-power will be 
required. The following table shows the voltages and 
candle-powers of those lamps which are most suitable 
in such an instance: 

* G6....4 volts 4 candle-power 

* G6....6 volts 4 candle-power 

* G8 6 volts 6 candle-power 

They may also be operated from dry cells. If they 
are intended to be in use for other than a few minutes 
at a time it will be well to use a battery consisting of 
two sets of cells connected in series multiple. The 
method of connecting cells in series multiple has 
already been illustrated in Figure 35. This will lighten 
the strain on the battery and it will be found that two 
sets of batteries used in series multiple will last 
**more than twice** as long as one set used alone. 

.. figure:: images/Image154.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 154.—Showing the differences between the Candelabra, Single Ediswan and Double Ediswan Types of Lamp Bases. 

   FIG. 154.—Showing the differences between the Candelabra, Single Ediswan and Double Ediswan Types of Lamp Bases. 

Six volt lamps of more than six candle-power are 
best operated on storage batteries because the current 
required is too great for dry cells to give efficient 
service in such a case. 

The tungsten lamps made for automobiles are ideal 
for miniature lighting plants operated by storage 
batteries. The list below shows some of the sizes on a 
current of six to eight volts. 

The bases are made of brass and come in four 
different styles, miniature, candelabra, single Ediswan and 
double Ediswan. The single and double Ediswan are 
used on automobiles because the construction of the 
base and the socket or the receptacle into which it fits 
is such that the lamp cannot jar loose. 

.. figure:: images/Image155.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 155.—Miniature Sockets of the types known as "Flat Base Porcelain," "Pin" and "Weatherproof." 

   FIG. 155.—Miniature Sockets of the types known as "Flat Base Porcelain," "Pin" and "Weatherproof." 

The candelabra base is probably the type best 
adapted to miniature lighting elsewhere than on an 
automobile. 

The letter "G" and the number in the first column 
indicates the size of the glass globe or bulb of the 
lamps. 

You can compute the approximate amount of 
current drawn from a battery by a tungsten lamp, by 
dividing the candle-power by the voltage. The result 
is the current in amperes. For example, a 6 volt, 12 
candle-power lamp will consume 12 divided by 6, or 2 
amperes. 

.. figure:: images/Image156.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 156.—Connections for a 2.8 Volt Lamp. 

   FIG. 156.—Connections for a 2.8 Volt Lamp. 

Storage batteries are rated by their output in **ampere 
hours**. An ampere hour is the amount of current 
represented by one ampere flowing for one hour. A 
forty ampere hour cell will deliver one ampere for 
forty hours, 4 amperes for ten hours or 5 amperes for 
eight hours. The ampere hour capacity of a storage 
cell divided by the amount of current being used will 
determine how long that current can be drawn before 
recharging is necessary. 

The maximum amount of current it is safe to draw 
from a storage cell without impairing its life and 
efficiency is the maximum current which that cell can 
deliver continuously for eight hours. In order to 
determine this current simply divide the manufacturer's 
rating of the battery in ampere hours by eight. The 
answer is the maximum current you should require 
from the battery if you wish to obtain good service 
from it. For example, the maximum safe discharge 
rate of a 40 ampere hour battery is 40 divided by 8 or 
5 amperes. 

.. figure:: images/Image157.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 157.—A Miniature Base Tungsten Filament Battery Lamp for small lighting. 

   FIG. 157.—A Miniature Base Tungsten Filament Battery Lamp for small lighting. 

The method of computing the current required by a 
lamp and the method for determining the maximum 
safe discharge rate of a battery will enable you to 
figure the size of the smallest battery it is desirable 
to use in a lighting plant. 

Suppose that you intend to use three 6 volt 12 
candlepower lamps. Each lamp will require two 
amperes or a total of six when all three lamps are 
burning at the same time. Six amperes multiplied by 
eight ampere hours equals 48 ampere hours. This is 
the smallest size of battery which should be used. If 
it is larger, it will be advantageous, because it will 
supply the lamps a correspondingly longer time 
without recharging. 

Figure 155 shows some of the sockets or receptacles 
which are on the market. The illustration to the left 
is a "flat base receptacle." It will be found most 
useful when the lamp is to be mounted directly on the 
wall or ceiling. The weatherproof type of socket may 
be secured with either a fibre or a porcelain shell. 

.. figure:: images/Image158.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 158.—A Tungsten Automobile Lamp with Ediswan Base. 

   FIG. 158.—A Tungsten Automobile Lamp with Ediswan Base. 

The brass shell socket is the best wherever 
appearance counts. It is patterned after the standard Edison 
sockets and is made so that it will screw onto several 
different sizes and styles of brackets which may be 
mounted on either the ceiling or the wall. This type 
of socket is also made with a small switch built inside 
so that the lamp may be turned on or off directly at 
the socket. 

**The Wire** used to connect the system will depend 
upon where the lamps are located. Annunciator or 
office wire as it is sometimes called will serve in most 
cases where the wires are to be run entirely indoors. 
The largest size made is No. 16 B. & S. Gauge. This 
is the size which should be used. Annunciator wire is 
made in various colors so that it can be more easily 
concealed. 

If the wires are run outdoors, or somewhat exposed 
to the weather, as on a porch or in a barn, it is 
advisable to use weatherproof or rubber covered wire. Lead 
covered twin conductor is recommended for use aboard 
boats or wherever the wire is liable to abrasion. 

.. figure:: images/Image159.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 159.—Lamps Controlled by One Switch. 
   
   FIG. 159.—Lamps Controlled by One Switch. 

If the lamps are larger than eight candle-power, or 
several are to be used on the same line, the wires 
should be larger than No. 16. When a battery is 
connected to a system of wires, the voltage at the end of 
the line is much lower than it is at the battery 
terminals. This is due to the resistance of the wire and is 
called "voltage drop." The lamps at the end of the 
line will not burn as brilliantly as those close to the 
battery. This can be partially overcome by using 
large wire. 

The lamps may be either connected in series or in 
multiple. When a six volt battery is used, it will be 
necessary to connect them in multiple. Figure 159 
shows how several lamps may be connected in multiple 
and controlled by one switch. Figure 160 shows the 
same lamps with three separate switches so that each 
lamp may be turned on or off individually. 

.. figure:: images/Image160.jpg
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   :scale: 85 %
   :alt: FIG. 160.—Lamps Controlled by Separate switches.
   
   FIG. 160.—Lamps Controlled by Separate switches.

It is possible to arrange a lamp and two switches so 
that it can be turned on or off at either switch 
independently of the other. This is a very convenient 
method of installing a light on a stairway or in a hall. 
One switch may be placed at the top of the stairs and 
the other at the bottom. A person going either up 
or down stairs can light the lamps ahead and turn it 
out as he passes the last switch regardless of its 
position at the other end. 

The switches must be of the type called "two point" 
or "double throw single pole" and the levers must 
always rest on one of the contacts and never be left 
in between. 

.. figure:: images/Image161.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 161.—Double Control System. 
   
   FIG. 161.—Double Control System. 

CHAPTER XVI. COHERER OUTFITS FOR WIRELESS TELEGRAPHY. 
-----------------------------------------------------

Making a Coherer. How to Adjust the Instruments. 
````````````````````````````````````````````````

MANY experimenters desire some device by which 
wireless signals may be made clearly audible 
without the necessity of holding a telephone receiver 
to the ear. It is not possible for the amateur to make 
such an arrangement which will receive signals over 
long distances. It is, however, possible to arrange a 
"coherer" so that signals coming from a nearby station 
may be indicated by the ringing of a bell. 

.. figure:: images/Image162.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 162.—The Coherer Details. 
   
   FIG. 162.—The Coherer Details. 

Such a "coherer" outfit will receive messages coming 
within a radius of one mile and may also be used for 
demonstrating the principles of wireless telegraphy 
when both the receiving and transmitting station are 
located in the same room or building. 

In order to secure these results it will be necessary 
to substitute a device called a "coherer" for the 
detector in the receiving apparatus. 

A coherer consists essentially of a few metal filings 
between two metal plugs. The filings are made part 
of a circuit which includes a relay and a battery. 
Under ordinary conditions the filings lie loosely together 
and their resistance to an electric current is so great 
that they will not allow enough energy to flow to 
operate the relay. If, however, the two plugs are connected 
to the aerial and ground so that the currents of the 
incoming wireless signals also pass through the filings, 
they will suddenly "cohere" or stick together and 
permit sufficient current to pass to operate the relay. 

.. figure:: images/Image163.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 163.—The Complete Coherer. 
   
   FIG. 163.—The Complete Coherer. 

A "tapper," or as it is also sometimes called a 
"decoherer," is also arranged in the circuit so as to 
automatically shake the filings up and restore them to 
their loose state as soon as each signal is received. 
The decoherer consists simply of an ordinary bell 
mounted so that the hammer will strike the coherer 
and jar it. 

The first thing required in order to make a coherer 
is a pair of double binding posts. These should be 
mounted on a wooden base six inches long and four 
inches wide as shown in Figure 163. 

A piece of glass tubing about one and one-half inches 
long and one-eighth of an inch in diameter inside 
together with some brass rod which will just slip into the 
tube tightly will be required. 

Cut two pieces of the brass rod one and 
three-quarters inches long and face off the ends perfectly
square and smooth. 

Slip these rods through the upper holes in the 
binding posts and into the glass tube as shown in Figure 
\163. Be sure that everything lines up perfectly and 
then remove one of the plugs. 

Before putting the plug back in place put some nickel 
and silver filings in the tube so that when the rods are 
pushed almost together, with only a distance of 
three-sixty-fourths to one-sixteenth of an inch between, the 
filings will about half fill the space. 

.. figure:: images/Image164.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 164.—Pony Type Relay. 
   
   FIG. 164.—Pony Type Relay. 

The filings are a mixture of silver and nickel and 
must be very carefully prepared. The mixture should 
be nine-tenths nickel and one-tenth silver. The filings 
may be secured by holding a five cent piece over a 
clean sheet of paper and filing it with a coarse file. The 
silver filings are made in the same way by using a ten 
cent piece or a quarter in place of the nickel. 

Do not use the fine dust and powder which is 
formed, but only the coarse filings. 

The success of the coherer will depend upon its 
adjustment and it will probably be necessary for the 
beginner to experiment considerably to find out just the 
right amount of filings to place in the tube and how 
far apart the brass plugs should be placed. 

The decoherer is made by removing the gong from 
an old electric bell and mounting the bell on the base 
in the position shown in Figure 163. The hammer 
should be bent so that it will tap the coherer lightly 
when a battery is connected to the bell binding posts. 

The only thing required to complete the apparatus 
is a relay. 

A relay of the "Pony" type such as that shown in 
Figure 164 will serve for ordinary work. It should be 
wound to at least 150 ohms, for to a certain extent, the 
higher the resistance, the more sensitive it will be. 

When it is desired to secure the maximum possible 
distance with the coherer a "polarized" relay will be 
necessary. A polarized relay is much more sensitive 
than the ordinary sort. The polarized relay should be 
wound to 1000 ohms. 

.. figure:: images/Image165.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 165.—Connections for the Receiving Set. 
   
   FIG. 165.—Connections for the Receiving Set. 

Figure 165 illustrates how the coherer, decoherer and 
relay should be connected. Two wires connected to 
the coherer posts lead to the magnets of the relay in 
series with a single dry cell. The contact posits of the 
relay are connected to the decoherer in series with 
another dry cell. 

When wireless signals pass through the relay they 
will cause the resistance to drop and allow sufficient 
current from the dry cell to pass through the coherer 
to energize the magnets of the relay and draw the 
armature in, thus closing the decoherer circuit. When 
the armature of the relay is drawn in towards the 
magnets the relay contacts are brought together. This 
closes the decoherer circuit and starts the hammer to 
tapping the coherer, thus restoring the filings to their 
former loose state. The decoherer will tap the coherer 
as long as the incoming signals continue. By 
breaking the signals up into dots and dashes of the telegraph 
code a message may be easily transmitted and read 
from the tapping of the decoherer.
 
.. figure:: images/Image166.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 166.—Coherer, Decoherer and Relay Connections. 
   
   FIG. 166.—Coherer, Decoherer and Relay Connections. 

The best results are secured from a coherer outfit if 
it is connected to the aerial and ground by substituting 
it for the detector in a circuit employing a double slide 
tuning coil and a fixed condenser. The two wires that 
would ordinarily be connected to the detector terminals 
are simply connected to the coherer posts. 

When the apparatus is to be used for demonstration 
or experiment and the transmitting and receiving 
stations are both located in the same room or house it will 
not be necessary to use an aerial and ground but 
merely to attach two copper wires about 18 or 24 
inches long to the opposite sides of the coherer as 
shown in Figure 163. 

In such a case the transmitter should be arranged 
as in Figure 167. 

A spark gap made especially for this purpose is 
illustrated in Figure 168. Some of the details of the gap 
are shown in Figure 169. 

.. figure:: images/Image167.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 167.—How the Transmitter is Connected. 
   
   FIG. 167.—How the Transmitter is Connected. 

The ball may be made in the form of a complete 
sphere or else consist simply of half of one as 
illustrated. It should have a radius of about five-eighths 
of an inch and arranged so that it may be mounted 
upon the end of a "catch-wire." 

.. figure:: images/Image168.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 168.—The Complete Spark Gap.
   
   FIG. 168.—The Complete Spark Gap.

The "catch-wires" are mounted in two standards 
similar in construction to a large binding post three 
and one-quarter inches high. The standards should be 
mounted by screwing them on top of the secondary 
terminals of the spark coil. The spark balls should be 
adjusted so that the distance between them is not over 
one-eighth of an inch. 

The coherer apparatus will probably require to be 
very accurately adjusted before it will work properly. 

Patience and a little experience will soon enable one 
to overcome the difficulties and to put the apparatus 
in sensitive condition without much trouble. 

.. figure:: images/Image169.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 169.—Details of Spark Gap. 
   
   FIG. 169.—Details of Spark Gap. 

The coherer will be found to be the most sensitive 
when only a very few filings are used. 

The adjustment desired in the relay is the one in 
which the armature is given the smallest possible 
amount of motion and the spring which pulls the 
armature away from the magnets, the least tension. 

The best method of finding the most sensitive 
adjustment for the apparatus is to place the transmitting 
and receiving stations only a few feet apart from each 
other in the same room. After you learn how to adjust 
the coherer and relay properly you will then find that 
you can move the transmitter quite a distance away 
from the coherer and it will still operate. 

Of course a coherer outfit is not very satisfactory 
and reliable for the regular reception of wireless 
signals even over short distances because of its 
irregular working. It is, however, very useful for sort of a 
calling or signal outfit. It may be connected to the 
tuning coil by means of a double-pole, double-throw 
switch and left in the circuit so as to indicate by the 
working of the tapper when any of the other stations 
in the near neighborhood are sending. The detector 
can then be quickly inserted in the circuit in place of 
the coherer by throwing the switch in the opposite 
direction and the signals read in the telephone receiver. 

CHAPTER XVII. HOW TO BUILD A TESLA HIGH FREQUENCY COIL. 
-------------------------------------------------------

IF the discharge from a Leyden jar or a condenser is 
passed through a coil of wire acting as a primary 
and the primary is provided with a secondary coil of a 
larger number of turns, a peculiar current known as 
high frequency electricity is generated in the 
secondary. Such a device is known as a Tesla Coil or 
Transformer. 

.. figure:: images/Image170.jpg
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   :alt: FIG. 170.—Tesla Coil Circuits. 
   
   FIG. 170.—Tesla Coil Circuits. 

When a Leyden jar or a condenser discharges 
through a coil of wire, the spark which takes place 
does not consist simply of a single spark passing in one 
direction only, but is really made of a number of 
separate sparks passing alternately in opposite directions 
at the tremendous rate of from one hundred thousand 
to one million times per second. 

A Tesla high frequency coil opens a field of 
wonderful possibilities to the amateur experimenter and brings 
innumerable weird and fascinating experiments within 
his reach. 

The Tesla coil described in the following pages will 
give sparks of high frequency electricity two or three 
inches long from the secondary, when used in 
connection with a two inch spark induction coil. If used in 
connection with a small high potential wireless 
transformer, the high frequency discharge can be increased 
to six or eight inches. 

A Tesla coil, suitable for use with a smaller spark 
coil, say one capable of giving sparks from one-half to 
one inch in length can be made by following the same 
plans but cutting all of the dimensions in half. Make 
the secondary six inches long and one and one-half 
inches in diameter instead of twelve inches long and 
three inches in diameter, etc. 

.. figure:: images/Image171.jpg
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   :alt: FIG. 171.—Secondary Tube. 
   
   FIG. 171.—Secondary Tube. 

**The Secondary** winding consists of a single layer 
of No. 28 B. & S. Gauge double cotton covered wire 
wound over a cardboard tube, twelve inches long and 
and three inches in diameter. The tube must be 
thoroughly dried before using it, by baking in an oven. A 
coat of shellac, both inside and out, will avoid the 
possibility of having to rewind the tube because of the wire 
becoming loose, due to drying out of the tube later. 
The wire should be wound on in a smooth, even layer 
to within about one-quarter of an inch from the ends 
and given a coat of hot paraffine when finished. The 
ends of the tube are fitted with circular wooden heads 
having a half inch flange. 

**The Base** is a rectangular piece of wood, fifteen 
inches long and six inches wide. 

The secondary is supported in position by two hard 
rubber uprights, four inches high, seven-eighths of an 
inch wide and one-half an inch thick. A round-headed 
brass wood screw is passed through the top part of 
each of the supports into the centre of each one of the 
wooden secondary heads. High frequency currents 
are very hard to insulate and wood does not possess 
sufficient insulating value to fit it for use as supports. 
Hard rubber or glass are the most satisfactory 
materials for the supports. 

.. figure:: images/Image172.jpg
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   :alt: FIG. 172.—Details of the Secondary Heads. 
   
   FIG. 172.—Details of the Secondary Heads. 

The secondary terminals are connected to two brass 
rods, five inches long and having a small brass ball at 
the upper end, mounted on the top of each of the hard 
rubber supports. 

The lower ends of the hard rubber supports are 
fastened to the base by means of screws passing upwards 
through the base into a threaded hole in the bottom of 
each support. 

.. figure:: images/Image173.jpg
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   :alt: FIG. 173.—Details of the Primary Head.
   
   FIG. 173.—Details of the Primary Head.

The secondary passes through the centre of the 
primary. The primary consists of eight turns of heavy 
copper wire wound around a wooden drum or frame. 
The wire should be No. 8 or No. 10 B. & S. Gauge. 
Flat copper or brass ribbon one-quarter of an inch 
wide can be used in place of the wire. The stranded 
copper wire, consisting of seven No. 22 B. & S. Gauge 
wires twisted together and commonly employed for 
wireless aerials can be used to good advantage in 
winding the primary, the idea of using a large wire, 
stranded wire, or ribbon being to obtain a conductor 
having as much surface as possible. High frequency 
currents travel only on the surface of wires and 
conductors. A hollow tube is just as good a conductor 
for high frequency currents as a solid rod of the same 
diameter. 

.. figure:: images/Image174.jpg
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   :alt: FIG. 174.—Primary Cross Bar. 
   
   FIG. 174.—Primary Cross Bar. 

.. figure:: images/Image175.jpg
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   :alt: FIG. 175.—Front View of the completed Tesla Coil. 
   
   FIG. 175.—Front View of the completed Tesla Coil. 

.. figure:: images/Image176.jpg
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   :alt: FIG. 176—Side View of the completed Tesla Coil. 
   
   FIG. 176—Side View of the completed Tesla Coil. 

The heads of the primary drum are wooden rings, 
seven inches in diameter outside, four and one-half 
inches inside and one-half an inch thick. Six cross 
bars, two and one-half inches long, three-quarters of 
an inch thick and one-half an inch wide are required 
to support the wire. They are spaced equidistantly 
around the rings and held in position by means of 
brass screws passing through the rings. Do not use 
iron screws, because iron is magnetic and should be 
entirely avoided in the construction of a Tesla coil. 
Small notches should be cut in the outside edge of 
the cross bars to accommodate the wires. The wires 
should pass around the drum in the form of a spiral 
with one-quarter to five-sixteenths of an inch space 
between the turns. The completed drum will somewhat 
resemble a squirrel cage. The ends of the primary 
winding should terminate in two large binding posts 
mounted on the primary heads. The heads are 
fastened to the centre of the base by a couple of large 
wood screws passing upwards though the bottom. 

.. figure:: images/Image177.jpg
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   :alt: FIG. 177.—Diagram of connections for operating the Coil. 
   
   FIG. 177.—Diagram of connections for operating the Coil. 

The illustration in Figure 177 shows how to connect 
the Tesla coil. The primary should be in series with a 
condenser and a spark gap. The condenser should 
consist of two or three Leyden jars or several glass plates 
coated with tinfoil. It is impossible to determine just 
how much capacity the condenser should have in 
advance, because the length of the conducting wires, 
adjustment of the spark gap, etc., will have considerable 
effect. The condenser is connected directly across the 
terminals of the spark coil. The spark gap may 
consist of two one-eighth inch brass rods supported by 
two double binding posts mounted on a small wooden 
block. 

The induction coil should be as large as possible. 
When the coil is set in operation it will charge the 
condenser and a white, snappy spark should pass 
across the gap. If the fingers are brought near to one 
of the secondary terminals of the Tesla coil, a small, 
reddish purple spark will jump out to meet them. It 
will be necessary to adjust the apparatus very 
carefully before a spark of any considerable length can be 
obtained. Changing the length of the spark gap and 
the size of the condenser will undoubtedly produce 
results. It may also be possible to lengthen the high 
frequency spark by disconnecting one of the wires from 
the primary binding posts on the Tesla coil and 
connecting the wire directly to some one of the primary 
turns. A very small change in some one of the 
connections may produce considerable result. The 
purpose of the adjustments is to tune the circuit in the 
same manner that a wireless outfit is tuned by altering 
the capacity of the condenser or varying the number 
of turns in the helix. 

.. figure:: images/Image178.jpg
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   :alt: FIG. 178.—Plate Glass Condenser. 
   
   FIG. 178.—Plate Glass Condenser. 

There are many interesting experiments which may 
be performed with the aid of a Tesla coil which space 
does not permit of describing here. The weird and 
strange beauty of the Tesla discharge is most evident 
when it takes place in the dark. 

High frequency currents do not produce a shock. If 
you hold a piece of metal in your hand and bring it 
near one of the secondary terminals, you can take the 
shock of a high-frequency coil, throwing a spark 
several inches long without feeling any sensation 
except that of a slight warmth. 

CHAPTER XVIII. AN EXPERIMENTAL WIRELESS TELEPHONE. 
--------------------------------------------------

Many of the readers of this book are probably 
"wireless experimenters" who have constructed 
their own wireless telegraph apparatus, but not many 
have ever built a wireless telephone set. The 
arrangement described in the following chapter may be built 
by almost any boy and will prove a very interesting 
and instructive piece of apparatus. It is of no real 
practical value as a wireless telephone, owing to the fact 
that the distance over which it will transmit intelligible 
speech is limited to 150 to 300 feet. However if you 
have a chum who lives next door or across the street 
or within the distance named above, it is easily 
possible for you to construct a wireless telephone which 
will enable you to remain in your own rooms and hold 
a conversation with each other, without any connecting 
wires. 

.. figure:: images/Image179.jpg
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   :alt: FIG. 179.—When a Bar Magnet is plunged into a Hollow Coil of Wire, a Momentary Current of Electricity is Generated. 
   
   FIG. 179.—When a Bar Magnet is plunged into a Hollow Coil of Wire, a Momentary Current of Electricity is Generated. 

The instruments depend for operation upon what is 
known as magnetic induction. Michael Faraday, who 
was a famous English scientist, discovered in 1831 that 
if a magnet is suddenly plunged into a hollow coil of 
wire, a momentary current of electricity is generated in 
the coil. You can try this experiment for yourself by 
connecting a galvanometer with a hollow coil of wire 
and then suddenly plunging a bar magnet into the coil.

If you observe closely you will notice that the needle 
of the galvanometer is deflected, this indicating that 
a current has passed through the circuit. The 
galvanometer should of course be far enough away so that 
the needle is not affected directly by the magnetism 
of the bar magnet itself. 

.. figure:: images/Image180.jpg
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   :alt: FIG. 180.—Magnetic Phantom showing the Lines of Force about a Bar Magnet. 
   
   FIG. 180.—Magnetic Phantom showing the Lines of Force about a Bar Magnet. 

As long as the bar magnet is motionless, it will 
not induce any current in the coil. As soon as it is 
moved however, the currents are set up. The 
mechanical work done in moving the magnet is really the 
source of electrical energy. The medium which 
changes the mechanical energy into electricity is called 
the magnetic field. The real nature of a magnetic 
field is very hard to explain and not easily 
understood. It is a peculiar state or condition of the space 
in the immediate neighborhood of a magnet. It is 
possible to show its existence by placing a sheet of 
cardboard over a magnet and then sprinkling iron 
filings over the surface of the cardboard. If the 
cardboard is tapped slightly, the filings will settle down 
in curving lines, forming a magnetic "phantom." The 
curved lines into which the filings form themselves, 
represent the paths of the lines of force which make 
up the magnetic field. The illustration in Figure 180 
shows the magnetic phantom about a bar magnet. 

When the space in the neighborhood of a wire or a 
coil of wire through which a current of electricity is 
passing is examined by means of some iron filings 
sprinkled on a sheet of cardboard, it is found that a 
similar state of affairs exists there and that it also 
possesses a magnetic field. 

This can be readily shown by punching a small hole 
in the centre of a sheet of cardboard or stiff paper and 
passing a wire which is carrying a strong current of 
electricity through the hole at right angles to the 
surface of the cardboard. Sprinkle some iron filings on 
the cardboard and they will arrange themselves in 
circles around the wire, forming a magnetic phantom 
giving definite proof to the eyes of the existence of the 
magnetic field. 

Some of my readers may have begun to wonder 
what a magnetic field has to do with the operation of 
the wireless telephone. It has already been explained 
that this particular type of wireless telephone depends
upon magnetic induction for its operation. It is 
necessary to have some sort of a conception of the magnetic
field before you will be able to understand magnetic 
induction.

.. figure:: images/Image181.jpg
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   :alt: FIG. 181.—Magnetic Phantom about a Coil of Wire carrying a current. 
   
   FIG. 181.—Magnetic Phantom about a Coil of Wire carrying a current. 

In order that you may gain an idea of how the 
instruments work, suppose that two coils of wire, A and 
B, are connected as shown in Figure 182. The coil A 
is connected in series with a set of batteries and a 
telegraph key. The other coil B is connected to a 
telephone receiver. The coils are placed parallel to 
each other and only a few inches apart. When the 
key is pressed so that the circuit is complete and the 
battery current flows through the coil A, it creates a 
magnetic field in the vicinity of the coil and lines of 
force are set up in the immediate neighborhood. 

The lines of force will travel through and about coil 
B and **induce in it a current of electricity**. The electric 
current will cause a sound like a click in the telephone 
receiver. When a telephone transmitter is substituted 
for the key and words are spoken into the mouthpiece, 
the current passing through the coil from the battery 
will be varied in accordance with the vibrations of the 
voice. The changes in the current will produce changes 
in the magnetic field set up by the coil and the 
changes in the magnetic field will produce a varying 
current in the coil B so that the words will be distinctly 
repeated by the receiver connected to B. 

.. figure:: images/Image182.jpg
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   :alt: FIG. 182.—Illustrating the Principle of the Induction Wireless Telephone. 
   
   FIG. 182.—Illustrating the Principle of the Induction Wireless Telephone. 

This experiment is very easy to perform and may be 
carried out by almost any boy with the materials he 
probably already has around his shop. Twenty-five to 
thirty turns of magnet wire of almost any size wound 
around one end of a cardboard tube three or four 
inches in diameter will serve as the coil A. A similar 
coil wound around the tube five or six inches away, an 
ordinary telephone transmitter and receiver and two 
or three dry cells form all the rest of the equipment 
desired. Words spoken into the transmitter connected 
to the coil A will be distinctly heard in the telephone 
receiver connected to the coil B, although there is no 
connection between the two coils other than the 
**magnetic field**. Such an outfit as this is of course only 
experimental and intended solely for the purpose of 
demonstrating the principles of operation of the larger 
outfit. If it is desired to make a practical set for 
talking over a considerable distance it will be necessary 
to make coils much larger in diameter and to build 
them so they contain a larger number of turns. 

.. figure:: images/Image183.jpg
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   :alt: FIG. 183.—Showing how the Coils may be formed by winding around nails set in a circle in the Floor. 
   
   FIG. 183.—Showing how the Coils may be formed by winding around nails set in a circle in the Floor. 

Large coils can be made by drawing a circle about 
four feet in diameter on the floor of your shop. Then 
drive a number of small nails around the circle about 
three inches apart. This arrangement will serve as a 
form to wind the coil. After the winding is completed 
you can pull a few of the nails out and lift it off and 
you will have a circular coil four feet in diameter. 
Two coils will be required. They should be made of 
No. 20 B. & S. Gauge cotton covered wire. Each coil 
should contain about seventy-five turns of wire. About 
three pounds of wire will be required for each coil. 
After winding the coils should be tied with string or 
tape about every six inches so that they will not come 
apart. The nails can then be pulled out of the floor 
and the coil is ready for use. If it is intended to 
subject the coils to any amount of handling, it is a good 
idea to secure two large hoops such as girls use for 
rolling along the sidewalk, about four feet in diameter. 
Then make the coils exactly the same diameter as the 
hoops and when they are finished bind them to the 
hoops with tape. Two binding posts may be mounted 
on each of the hoops and the terminals of the coil 
connected to them. 

Two coils are required in order to establish a 
complete wireless telephone system, one at each station. 
Each coil may be used for both sending and receiving 
messages. Each station should be arranged as in 
Figure 184. The transmitter should be of the type known 
as "long distance." The switch is a two point switch. 

.. figure:: images/Image184.jpg
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   :alt: FIG. 184.—Circuit Diagram showing how the Coil is connected so as to serve for either transmitting or receiving. 
   
   FIG. 184.—Circuit Diagram showing how the Coil is connected so as to serve for either transmitting or receiving. 

It is a good plan to use two telephone receivers 
mounted on a head band so that both ears can be used 
and the hands left free to manipulate the switch. If a 
set of telephone receivers wound to a high resistance 
for wireless telegraph purposes is used it will greatly 
increase the range of the outfit. 

Six to eight first class dry cells will be required to 
form the battery. A push button is placed in series 
with the transmitter so that the battery current will be 
consumed only when the button is pressed. This makes 
it necessary to push the button when sending a 
message. When the lever of the two point switch rests on 
the contact A the circuit is completed for transmitting. 
When the lever rests on B the telephone receivers are 
connected to the coil and the apparatus is ready for 
receiving a message. 

If the apparatus is used only for demonstrating 
purposes, a camera tripod will be found very convenient 
for supporting the coils. The transmitter and switch 
can be fastened to the top of the tripod and the 
batteries placed in a box on the ground. It is absolutely 
necessary that the coils be perfectly parallel to each 
other when messages are being transmitted back and 
forth. It is well to start with the coils comparatively 
close to each other, say ten or twelve feet at first, and 
then gradually increase the distance. 

Coils approximately four feet in diameter and 
containing about seventy-five turns of wire will transmit 
and receive messages about one hundred and fifty feet. 
The range can be increased slightly by using more 
batteries. If too much battery is used, however, the 
telephone transmitter will become very hot and is liable 
to burn out. 

It is impossible, of course, to "call up" over a set of 
wireless phones such as these. If you succeed in 
getting your set to work satisfactorily with your chum 
across the street and wish to talk to him it will be 
necessary for you to arrange some predetermined time. 

In order to operate your phone place the switch lever 
on the contact A. Hold your finger tightly against the 
push button so that the circuit is completed and talk 
slowly and distinctly into the transmitter. The 
transmitter will operate the best when the mouthpiece 
points on a level with your mouth. The lips should be 
about one inch away from the mouthpiece. Speak in a 
low even tone. The switch at your friend's station 
should be resting on B. When you finish speaking 
throw your switch to B and listen in your telephone 
receivers. The operator at the other station should 
throw his switch to A and push the button. He may 
then talk to you. 

CHAPTER XIX. MISCELLANEOUS EXPERIMENTS AND APPARATUS. 
-----------------------------------------------------

ELECTROLYSIS. 
`````````````

Liquid which will conduct a current of 
electricity is called an **electrolyte**. All electrolytes 
are compounds, that is, they consist of more than one 
substance. When an electric current passes through 
a liquid it decomposes it. This process of 
decomposition is called **electrolysis**. 

Pure water is not a conductor of electricity. If 
sulphuric acid is added to water, the mixture become an 
electrolyte and will conduct. If an electric current is 
passed through water containing sulphuric acid, it will 
decompose the water. 

.. figure:: images/Image185.jpg
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   :alt: FIG. 185.—Apparatus for Electrolysis Experiment. 
   
   FIG. 185.—Apparatus for Electrolysis Experiment. 

Water is composed of oxygen and hydrogen and so 
bubbles of oxygen and hydrogen gas will rise from the 
liquid. 

Figure 185 illustrates a very simple arrangement for 
decomposing acidulated water into oxygen and 
hydrogen gases. 

It consists of a bottle with the bottom broken out, 
and provided with a cork fitted snugly into the neck. 
Two glass tubes pass through the cork. A small piece 
of platinum wire is sealed into the inside end of each 
glass tube. The platinum wires are connected to 
copper wires leading out of the lower ends of the tubes. 

If the bottle is inverted and filled with a dilute 
solution of sulphuric acid, the current from two or three 
dry cells will decompose the water. The battery 
should be connected to the wires running through the 
glass tubes. 

Bubbles of gas will rise from the platinum wires. 
Oxygen gas will rise from the positive wire or 
electrode and hydrogen gas from the negative electrode. 

If two test tubes are filled with acidulated water and 
then inverted over the wires, the tubes will collect the 
gas. In a few minutes it will be noticed twice as much 
hydrogen as oxygen has been generated. 

If copper or brass electrodes &re used the acid will 
attack the positive one and a chemical action will take 
place which will prevent the liberation of any 
appreciable amount of oxygen, unless an excessive amount 
of current is passed through. 

ELECTROPLATING. 
```````````````

Electroplating consists of coating bodies with metal 
by means of an electric current. 

The proper chemicals, a small tank and a suitable 
source of current are the only apparatus required. The 
process may be outlined as follows: Thoroughly clean 
the article to be electroplated so as to remove all grease 
and dirt. Attach it to the negative pole of the battery 
and suspend it in an electrolyte composed of some 
chemical salt of the metal to be deposited. In order to 
maintain the strength of the solution, a piece of metal 
of the kind to be deposited is attached to the positive 
electrode. 

A tank for plating small articles such as keys, rings, 
knives, etc., may be made out of a square glass battery 
jar by providing it with a wooden moulding fitted 
around the top edge to support the conductor rods. 
The rods are made of brass or copper and are threaded 
at one end so as to be provided with binding posts. 
The centre rod is the one from which the articles to 
be plated are suspended. They should be attached to 
it by means of a thin copper wire. The two outside 
rods support the anodes. The anodes are sheets of 
metal of the kind to be deposited which, in the case of 
copper plating, would be copper, in a case of silver 
plating silver, nickel for nickel plating, etc. 

.. figure:: images/Image186.jpg
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   :alt: FIG. 186.—Electroplating Tank. 
   
   FIG. 186.—Electroplating Tank. 

Objects which are to be plated must be free from all 
traces of dirt or grease or the plating will not be 
uniform because it will not stick to the dirty spots. 

Articles made of plaster, wax, etc., which are not 
conductors of electricity can be plated by first covering 
with powdered graphite. Articles of iron, steel, zinc 
and tin cannot be silver or gold plated unless first 
covered with a thin coating of copper. 

A single storage cell is an excellent source of current 
for electroplating. A rheostat should be placed in the 
circuit so that the current can be regulated. The 
negative pole should be connected to the centre rod from 
which the articles are suspended. The positive pole is 
connected to the rods supporting the anodes. 

The tank should be filled with electrolyte to within 
about an inch of the top. The articles to be plated and 
also the anodes should be completely submerged. 

The electrolyte used for copper plating is simply a 
solution of copper sulphate in water. The electrolyte
for nickel plating is composed of one part of nickel 
sulphate dissolved in twenty parts of water to which one 
part of sodium bisulphate is added. 

Articles which have been electroplated must be 
buffed to give them a bright polish. 

ELECTRIC CURRENT GENERATED BY HEAT.
``````````````````````````````````` 

If the point of contact between two dissimilar metals 
is heated, a current of electricity will be generated. 

This principle was discovered nearly one hundred 
years ago by a scientist named Seebeck, and has 
resulted in many attempts on the part of inventors to 
utilize the heat of the sun's rays in producing 
electricity. 

.. figure:: images/Image187.jpg
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   :alt: FIG. 187.—Generating Electric Current by Heat. 
   
   FIG. 187.—Generating Electric Current by Heat. 

An interesting experiment illustrating the 
production of electricity by heat can be easily performed with 
very simple apparatus. An alcohol lamp, candle or 
source of heat, a piece of copper, a steel needle and a 
galvanometer or a telephone receiver are all that are 
necessary. 

The galvanometer or the telephone receiver, 
whichever is used, is for the purpose of detecting the electric 
current. 

Connect the needle and the piece of copper, which 
should preferably be a small sheet, to the galvanometer 
or telephone receiver. Hold the copper sheet over the 
flame of the alcohol lamp until it is quite hot and then 
touch the hottest portion with the point of the needle. 
Enough current will be generated to produce a click In 
the telephone receiver or to cause the galvanometer 
needle to move. The needle should be pressed against 
the copper tightly enough so that the point cuts 
through the scale or oxide on the surface and makes a 
good electrical contact with the metal underneath. 

Various devices for the production of electricity 
consisting of a large number of strips of dissimilar metals 
in contact with one another and arranged so that they 
can be easily heated have been invented. They are 
called "thermopiles." 

A HANDY LIGHT.
`````````````` 

Figure 188 shows a simple and handy form of light 
which utilizes the current from a home made primary 
cell. It consists of a glass fruit jar, fitted with a tight 
wooden top. A miniature porcelain socket and a 1.5 
volt tungsten lamp are mounted on top. 

The battery is arranged so that the zinc element can 
be drawn up out of the solution when the light is not 
in use and any waste thereby prevented. The zinc 
electrode consists of a strip of that metal fastened onto 
the lower end of a brass rod by means of two threaded 
nuts. The upper end of the rod passes through a small 
metal collar on the top of the cover, provided with a 
thumb-screw so that when the electrode is lifted up 
out of the solution it may be clamped firmly in that 
position. 

The zinc strip should not be so long that it will not 
clear the solution when raised up if the jar is about 
half filled. 

.. figure:: images/Image188.jpg
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   :alt: FIG. 188.—A Handy Light. 
   
   FIG. 188.—A Handy Light. 

The positive electrode is a battery carbon mounted 
on the lower end of a brass rod. The brass rod in this 
case is not movable because the carbon can remain in 
the solution indefinitely without any waste. 

The joint between the brass rods and the electrode 
should be coated with paraffine so that the chemicals 
in the solution will not cause any corrosion. The rods 
should be connected to the lamp socket. When the 
zinc is lowered into the solution, the lamp will be 
lighted by the current generated. 

The electrolyte should be that described as the 
"bichromate" solution on page 34 of Vol. I of this 
book. 

AN EXPERIMENTAL ARC LAMP.
````````````````````````` 

An arc lamp is operated by causing an electric 
current to pass between two carbon rods. If the voltage 
is high enough, carbon vapor will form between the 
rods when they are separated a short distance. It 
requires an E. M. F. of approximately fifty volts to 
produce and maintain an arc. 

A six volt storage battery will heat a pair of sharp 
pointed carbons to incandescence and produce a light 
somewhat similar to the electric arc. 

.. figure:: images/Image189.jpg
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   :alt: FIG. 189.—Experimental Arc Lamp. 
   
   FIG. 189.—Experimental Arc Lamp. 

Ordinary carbon rods such as those used in flashlight 
batteries will serve very nicely for a "battery arc lamp." 
The ends should be filed to sharp points. Figure 189 
shows a simple method of mounting the carbons. The 
lower one is soldered to a piece of brass strip by taking 
advantage of the brass cap pressed over the upper end 
of flashlight battery carbons. 

The upper carbon is mounted on the forward end of 
a brass lever which is pivoted near the back end so that 
an adjustable counterweight may be used to regulate 
the pressure on the point of contact between the two 
carbons. 

If the carbons are touching lightly and are connected 
to a strong battery of six volts or more, the point of 
contact will be heated to incandescence and will 
produce a dazzling white light. 

A real arc lamp for operation on the 110 volt 
current, in series with a bank of lamps, may be constructed 
on this same scheme by using larger carbons and 
eliminating the counterweight. The upper arm should be 
pivoted in the same manner but should move stiffly so 
that it will remain in any position in which it is set. 

If the 110 volt current is used, the carbons should be 
brought together and then separated a short distance. 
The current will continue to flow across and will form 
an arc producing a very powerful purplish white light. 
The arc will consume the carbons quite rapidly and 
also generate a great deal of heat. Therefore if it is 
intended to use the light for any length of time it is 
advisable to fasten the carbons by means of a clamp 
so that they may be easily replaced. 

A MAGNETIC DIVER.
````````````````` 

This is a mystifying piece of apparatus to those who 
do not know its secret. The little diver apparently 
travels up and down from the bottom of a jar full of 
water to the surface at a word of command. 

The diver consists of a small glass test tube about 
two inches long having the figure of a man painted 
upon it. The lower end is closed by a very small cork 
through which is pushed a large iron tack with the 
head on the outside. The test tube contains just 
enough water to float head up even with the surface of 
the water. The exact amount of water required to just 
permit enough buoyancy for the diver to rise again to 
the surface after he has been to the top will have to be 
determined by careful experiment. 

The jar containing the diver should be set on a table 
having a drawer in which a pair of powerful 
electromagnets can be placed directly under the jar. The 
electro-magnets are connected to a strong battery and 
a switch located under the rug or carpet and so 
arranged that it may be closed by stepping on it lightly 
and without attracting attention. If the diver does not 
have too much bouyancy the attraction between the 
tack and the electro-magnets when the switch is closed 
should be sufficient to cause him to descend to the 
bottom of the jar. When the current is turned off the 
diver should rise again. 

.. figure:: images/Image190.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 190.—The Magnetic Diver. 
   
   FIG. 190.—The Magnetic Diver. 

THE MAGNETIC FISH. 
``````````````````

The same sort of a scheme employed in the Magnetic 
Diver may be used for producing a magnetic fish which 
will swim around and around a pan of water.

.. figure:: images/Image191.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 191.—The Magnetic Fish. 
   
   FIG. 191.—The Magnetic Fish. 

It consists of a small wooden fish having a magnetised 
sewing needle attached to the under side. The fish is 
placed in a bowl of water on a table having a drawer in 
which a pair of electro-magnets mounted on a rotating 
wooden arm may be placed so that they swing around 
directly underneath. A piece of strong twine wrapped 
around an empty spool and attached to the centre of 
the arm makes it possible to rotate the magnets by 
pulling on the string. When the magnets are 
connected to a battery they will exert a strong magnetic 
pull upon the needle fastened to the fish and if slowly 
rotated will cause the latter to follow slowly around 
the bowl. 

A MAGNETIC CLOWN.
````````````````` 

Small figures of men or animals cut out of sheet iron 
will perform many amusing acrobatic feats when under 
the influence of a magnet. 

.. figure:: images/Image192.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 192.—The Magnetic Clown. 
   
   FIG. 192.—The Magnetic Clown. 

Such figures are easily cut out of an old tin cracker 
box with a pair of snips or strong shears. A realistic 
appearance may be secured with the aid of a little paint. 

A tin clown having a sharply pointed hat, hands and 
feet will do all sorts of stunts when hanging from the 
poles of a horseshoe magnet. If several clowns are 
made they can be caused to hold hands, stand on each 
others heads, jump up in the air, etc. 

AN ELECTRIC BREEZE. 
```````````````````

If a sewing needle is connected to one of the 
discharge rods of a static machine and the point of the 
needle is presented to the flame of the candle while the 
machine is in operation, the flame will be repelled just 
as if a breeze or current of air were issuing from the 
needle. This is caused by the "brush" discharge which 
takes place whenever high voltage electricity has a 
chance to escape from a sharp point or edge. The 
brush discharge will be much more marked if the 
condensers or Leyden Jars are not connected to the 
discharge rods. The "electric breeze" can be felt if the 
point of the needle is brought near to the side of the 
face. It is necessary that the needle and the wire 
connecting it to the static machine be very carefully 
insulated from all surrounding objects which might 
dissipate the electricity before it has an opportunity to 
escape from the needle point. 

.. figure:: images/Image193.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 193.—An Electric Breeze. 
   
   FIG. 193.—An Electric Breeze. 

A STATIC MOTOR.
``````````````` 

This is a motor operated by the electricity from a 
static machine. It does not possess any appreciable 
amount of power and must be very carefully built and 
balanced in order to operate. 

It consists of four celluloid "ping-pong" balls, B, B, 
B, B, covered with tinfoil and mounted on opposite 
ends of two wooden spokes. The balls should be at 
right angles to each other as shown in the illustration. 
The spokes pass through a cork. The cork is mounted 
on a wire spoke or knitting needle passing through its 
centre and supported in small notches in the top of two 
upright wooden bearings. The device must be very 
carefully balanced so that the slightest impulse will 
cause it to spin and so that there will not be any dead 
centre. 

The upright bearings are mounted on a wooden base. 
Two other tinfoil covered balls A, A, are supported on 
glass or rubber insulating rods at opposite ends of the 
base on a level with the axle and in such a position 
that the balls B, B, B, B, almost touch A and A as they 
swing past. 

.. figure:: images/Image194.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 194.—The Static Motor. 
   
   FIG. 194.—The Static Motor. 

Connect A and A each to one discharger rod on the 
Wimshurst machine. Start the machine and give the 
axle of the static motor a twist. As the balls B, B go 
past A and A they will receive a charge of electricity 
which will cause them to repel each other until they 
have swung past the other ball on the opposite side 
and discharge their electricity in return for a charge 
of the opposite sign. 

.. cleardoublepage::
 
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   Any of the Following 

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   Practical Books 

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   COLE & MORGAN 

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   Publishers of the Arts and Sciences Series 

   \P.O. Box 473 New York, N. Y. 

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   **The Boy Electrician**

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   Practical Plans for Electrical Toys and Apparatus, with an Explanation 

   of the Principles of Everyday Electricity. 

   .. vspace:: 2

   **By ALFRED P. MORGAN.**

   .. vspace:: 2

   Author of "Wireless Telegraph Construction for Amateurs" and "Wireless 

   Telegraphy and Telephony," etc. 

   .. vspace:: 2

   **With full-page Illustrations and 324 Working Drawings and Diagrams**
   
   **by the author. 8vo., Cloth, Net Price, $2.00.**

.. figure:: images/TheBoyElectrician.jpg
   :align: center
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   :alt: Book Cover The Boy Electrician

This is the age of electricity. The most fascinating of all 
books for a boy must therefore be one dealing with the 
mystery of this ancient force and modern wonder, even a 
mere list of whose services is impossible. The best qualified 
of experts to instruct boys, Alfred P. Morgan, has in a book 
far superior to any other of its kind told not only how to 
make all kinds of motors, telegraphs, telephones, batteries, 
etc., and to do so economically, but has explained the principles
upon which these depend for operation, and how the 
same thing is done in the every-day world be well 
presented and so attractive is this really great book that it will 
be an education for any bright boy to have it, as well as 
the best kind of a moral safeguard, by leaving no time or 
thought for evil, and a means of future benefit beyond the 
power of any one to reckon. Glancing over the pages of 
this book, one cannot but be impressed by the excellent 
illustrations, clearness of expression and the large number 
of subjects that are covered. It is beyond doubt the best 
book in this line that has ever been written or published. 
It is a book that will delight every boy who has a leaning 
towards electrical experiments. The author writes in a clear 
and chatty style and while he has a thorough 
technical knowledge of his subject he has succeeded 
in treating it in a simple manner 
so that it is readily intelligible to his young readers. 

   .. vspace:: 2

.. container:: center medium

   **Among the Chapter Headings and Contents are:**

Magnets and Magnetism—Static Electricity—Static Electric Machines—Cells and Batteries—Electro-Magnetism and Magnetic Induction—Electrical Units—Electrical Appurtenances—Electrical Measuring Instruments—Bells, Alarms and Annunciators—Electric Telegraphs—Microphones and Telephones—Induction Coils—Transformers—Wireless Telegraphy—Wireless Telephony—Electric Motors—Dynamos—An Electric Railway—Miniature Lighting—Miscellaneous Electrical Apparatus. 

   .. vspace:: 2

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   **READ WHAT HAS BEEN SAID OF IT.**

"Even a casual glance through the many pages of the book does not fail to 
emphasize the fact that Mr. Alfred P. Morgan has indeed succeeded well in giving the 
juvenile electricians a work that has long been sought."—Popular Electricity. 

"We have no hesitation in commending the book to the attention of the juvenile 
audience for which it is intended."—Boston Post. 

"A great book for enterprising boys. Bright boys will highly appreciate it and feel 
like thanking the wideawake publishers for putting such a reliable and interesting 
work in the field."—New Haven Journal. 

"The book covers the subject of electricity thoroughly in all its phases and is a 
splendid acquisition to any boy’s library."—Detroit Times. 

"In this age of electricity a book like the present one is both fascinating and valuable 
especially to boys. The book is attractive with its many illustrations and will prove 
of much educational value for any bright boy."—Zion’s Herald. 

"This is an admirably complete and explicit handbook for young boys who fall under 
the spell of tinkering with electrical apparatus."—Boston Transcript. 

"Well presented and attractive this book will be a source of great benefit and delight 
for any bright boy."—New Orleans Times-Picayune. 

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   **Price, $2.00, Postpaid**

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   COUNTLESS OTHER MAGAZINES, NEWSPAPERS AND LIBRARIES HAVE 
   
   ENDORSED THIS GREAT BOOK. SEND FOR A COPY NOW. 

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.. clearpage::

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   **Experimental Wireless Construction**

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   **EIGHTY-SIX PAGES NINETY-THREE ILLUSTRATIONS**

   .. vspace:: 2

   **Only 25 Cents, Postpaid**

.. figure:: images/ExperimentalWirelessConstruction.jpg
   :align: center
   :scale: 50 %
   :alt: Book Cover Experimental Wireless Construction 

Here at last is the book which every young 
experimenter interested in constructing his 
own wireless apparatus has been looking for. 

A book which tells how to build apparatus 
which anyone would be proud to own. It is 
a more advanced book than "Wireless Construction 
and Installation for Beginners," 
and describes apparatus which is much more 
elaborate and sensitive. The instruments 
have all been the subject of considerable experimental 
work and study. All the apparatus has been put to 
practical test and carefully improved by clever experts. 
By purchasing this book you get the benefit of vast 
knowledge and experience and are enabled 
to build far better instruments than by 
following your own designs and haphazard 
methods. 

.. vspace:: 2

THE TREMENDOUS POPULARITY OF
THIS VALUABLE LITTLE BOOK IS ONLY 
AN INDICATION OF ITS GREAT WORTH. 

.. vspace:: 2

It has only been on the market a short time, 
yet the sales will undoubtedly soon reach a 
point which would indicate that experimenters unquestionably 
consider, that in proportion to its size, it is the best book on the 
market. 

It does not describe any old or obsolete forms of wireless apparatus but only the 
latest types of aerials, spark coils, keys, gaps, condensers, 
helixes, oscillation transformers, loose couplers, tuning coils, 
detectors, loading coils, variable condensers, 
aerial switches, etc. 

.. vspace:: 2

IT IS ONE OF THE MOST DETAILED AND THOROUGH BOOKS EVER PUBLISHED. 

.. vspace:: 2

The information is all intensely practical. Complete directions and dimensions 
are given. Nothing is left to be guessed at. The book must really be seen to be 
appreciated. 

.. container:: center large

   .. vspace:: 2

   **Partial Contents**

   .. vspace:: 2

Chapter I.—THE AERIAL. The Location of the Station. The Construction of 
an Operating Bench. The Aerial and Ground. The Supports or Masts. Types 
of Aerials. How to Erect an Aerial. Protection from Lightning, Etc. 

Chapter II.—SPARK COILS. The Construction of Spark Coils. A 1/4-inch Spark 
Coil. A 1/2-inch Spark Coil. A 1-inch Spark Coil. A 1 1/2-inch Coil. A 2-inch 
Coil. Sources of Current. Dry Cells. Storage Cells. Wireless Keys, Etc. 

Chapter III.—TRANSMITTING APPARATUS AND ITS CONSTRUCTION. 
Step-down Transformers. Spark Gaps. The Oscillation Condenser. Leyden Jars. 
Helixes. Oscillation Transformers, Etc. 

Chapter IV.—THE RECEIVING APPARATUS AND ITS CONSTRUCTION. A 
Silicon Detector. A Galena Detector. The Double Slide Tuning Coil. How to 
Make a Fixed Condenser. Building a Loose Coupler. The Loading Coil. How to 
Make a Variable Condenser, Etc. 

Chapter V.—ARRANGEMENT AND OPERATION OF THE APPARATUS. Aerial 
Switches. The Buzzer Test. Using More Than One Detector. 
Shunting the Detector. Complete Outfits. Portable Sets. The 
Operation of the Station, Etc. 
 
.. clearpage::

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   **LESSONS IN WIRELESS TELEGRAPHY**

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   FOURTH EDITION 

   72 Pages 66 Illustrations 

.. figure:: images/LessonsWirelessTelegraphy.jpg
   :align: center
   :scale: 50 %
   :alt: Book Cover Lessons in Wireless Telegraphy

A systematic course in the elementary principles. 
Written so you can understand it. In 35 lessons. 

\1.—Magnetism. 2.—Magnetic Induction. 3.—Primary and Secondary Cells. 4.—Electric Currents. 5.—Electromagnetism. 6.—Dynamo-Electric Machinery. 7.—The Induction Coil. 8.—The Transformer. 9.—Leyden Jars and Condensers. 10.—Electromagnetic Theory. 11.—Electric Waves. 12.—Principles of Wave Telegraphy. 13.—The Aerial. 14.—The Wireless Coil. 15.—The High Potential Transformer. 16.—The Oscillation Condenser. 17.—The Helix. 18.—Spark Gaps. 19.—The Key. 20.—Aerial Switches. 21.—Anchor Gaps. 22.—Detectors. 23.—Tuning Coils. 24.—Loose Couplers. 25.—Fixed Condensers. 26.—Variable Condensers. 27.—Telephone Receivers. 28.—Hot Wire Ammeter. 29.—Potentiometer. 30.—Dead End Losses and Switches. 31.—Distributed Capacity. 32.—Poulsen Arc. 33.—Receiving Undamped Waves. 34.—The Audion Amplifier. 35.—Hook-Ups.

.. container:: center medium

   **Price, 25 Cents, Postpaid**

If you want to understand your apparatus and how it works, you will need this 
book—over 15,000 copies in use. 

.. container:: center medium

   **Price, 25 Cents, Postpaid**

.. clearpage::

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   **Model Flying Machines**

   **HOW TO BUILD AND FLY THEM**

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   Will prove interesting and valuable. 

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   Have you ever built and flown a Model Racer? 

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   If not, you have missed something. 

   .. vspace:: 2

   Price, 25 Cents, Postpaid. 

.. figure:: images/ModelFlyingMachines.jpg
   :align: center
   :scale: 50 %
   :alt: Book Cover Model Flying Machines

Model Aeroplaning is one of the most fascinating and 
instructive of sports. 

Thousands of young men and boys have formed Model 
Aero Clubs and organized Flying Contests throughout the 
country. 

"MODEL FLYING MACHINES" of the *Arts and 
Sciences* series is the only book giving reliable data and 
instructions for the construction of practical Model 
Aeroplanes. 

IF YOU ARE A BEGINNER, this is the book that you ought to have. It will 
start you right. It tells how to build seven different types of machines, starting 
with the simplest Monoplane and finishing with several Long Distance Racing Models. 

IF YOU ARE INTERESTED IN MODEL AEROPLANING, this book will prove 
the one you have been looking for. Gives valuable "Kinks". Tells how to carve 
propellers, make winders, adjust and fly machines, etc. Fully illustrated with large 
size, detailed working drawings, showing the exact size of each part. Twelve 
full-page plates. 

Printed on first-class paper. Heavy cover in three colors. 

.. container:: center medium

   Sent postpaid by return mail upon receipt of 25 cents. 

   .. vspace:: 2

   **EVERY MODEL AVIATOR OUGHT TO HAVE A COPY**


.. clearpage::

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   **Wireless Construction and Installation for Beginners**

.. container:: center large

   .. vspace:: 2

   SEVENTY-THREE PAGES SIXTY-SEVEN ILLUSTRATIONS. 

   .. vspace:: 2

   (Second Edition.) 

   .. vspace:: 2

   A Practical Handbook giving detailed 
   instructions for the Construction and 
   Operation of a Boy’s Wireless Outfit. 

.. container:: center x-large

   .. vspace:: 2

   **Only 25c. Prepaid**

.. figure:: images/WirelessConstructionInstallation.jpg
   :align: center
   :scale: 50 %
   :alt: Book Cover

An indispensible book for the young wireless 
experimenter. It not alone shows how to build 
the various instruments but describes their 
actual workings and tells how to operate them. 

.. container:: center large

   .. vspace:: 2

   **EVERY BOY IS ADVISED TO**

   **SEND FOR A COPY**

   .. vspace:: 2

Written in a very clear and simple style, the 
book is invaluable to a beginner. He will be 
able with its aid to construct simple apparatus 
of the latest and approved type. The instruments 
described in the book have been the 
subject of considerable experimental work and special study. 
They are modeled along simple lines 
so that they will be easy and inexpensive to 
construct, but at the same time combine features 
which make them very sensitive and 
capable of receiving or transmitting messages 
greater distances than some more complicated 
apparatus. 

.. container:: center large

   **THIS BOOK, CONSIDERING ITS WORTH, IS A GIFT AT 25c.**

   .. vspace:: 2

There are no old or obsolete forms of wireless apparatus discussed, but only the latest 
types of tuning coils, receiving transformers, fixed condensers, keys, spark coils, 
detectors, etc. The book is illustrated by numerous detailed working drawings giving all 
dimensions. Several full-page views of the apparatus enable the beginner to fully 
comprehend the text. 

.. container:: center large

   .. vspace:: 2

   **THE MOST THOROUGH AND COMPLETE ELEMENTARY WIRELESS**

   **CONSTRUCTION BOOK PUBLISHED**

   .. vspace:: 2

The pages on the construction and installation of aerials will be found to be of 
considerable help to the experimenter, for it is here that the most trouble is experienced 
by the beginner. The practical and helpful information on this subject is alone worth 
several times the cost of the book. 

.. container:: center large

   .. vspace:: 2

   **PARTIAL CONTENTS**

   .. vspace:: 2

Chapter I.—**WIRELESS TELEGRAPHY**. An intensely interesting subject; amateur 
wireless telegraphy; the purpose of the aerial and ground; the apparatus used to send 
messages; the apparatus used to receive messages. 

Chapter II.—**AERIALS AND GROUNDS**. Where to put up the aerial; types of 
aerials; the "T" aerial; the masts; the wire; insulators; leading in the wires; the 
ground. 

Chapter III.—**HOW TO BUILD AND OPERATE THE SIMPLEX DOUBLE SLIDE 
RECEIVING OUTFIT**. The tuning coil; the tube; the sliders; the fixed condenser; 
the detector parts; assembling the set; connecting the instruments; operation. 

Chapter IV.—**HOW TO BUILD THE SIMPLEX LOOSE COUPLER, DETECTOR 
AND CONDENSER**. The base; the primary; the secondary; the pillar; the switch; 
How to make the Simplex cat whisker detector; How to make the Simplex fixed condenser; How to connect the apparatus; How to tune with the loose coupler; How to adjust the detector. 

Chapter V.—**TELEPHONE RECEIVERS AND HEADBANDS.** 

Chapter VI.—**HOW TO BUILD THE SIMPLEX SPARK COIL.** The core; the secondary; the condenser; the coil heads; the base; the interrupter parts; the bridge. 

Chapter VII.—**HOW TO MAKE THE SIMPLEX KEY**. 

Chapter VIII.—**HOW TO CONNECT AND OPERATE THE APPARATUS**. How to connect and operate a complete wireless station; How to operate; the code, etc. 

.. clearpage::

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   **Three New Books on Home Made**
   
   **Electrical Apparatus**

   .. vspace:: 2

The Book you are now reading is only the first volume of "Home-made 
Electrical Apparatus." Written in a very clear and simple style, the other volumes 
are invaluable to the young experimenter. There are no old or obsolete forms 
of apparatus described but only the latest electrical devices, making them 

.. container:: center large

   **The Most Thorough and Complete Books for**
   
   **the Young Electrical Experimenter Published**

The partial Table of Contents below only gives a small idea of the interesting 
matter contained in these volumes. 

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   VOLUME II 

   72 Pages 55 Illustrations 

   Table of Contents 

Chapter VI—ELECTRICAL MEASURING INSTRUMENTS. Galvanometers, Ammeters, Voltmeters, etc. 

Chapter VII—CURRENT CONTROL DEVICES. How to Make a Pole Changing 
Switch or Current Reverser. How to Reverse Small Motors. Battery Rheostats. 

Chapter VIII—HOW TO MAKE A TELEGRAPH KEY AND SOUNDER. How to 
Install a Telegraph Line and Learn to Operate. Learning the Morse Code. 

Chapter IX—HOW TO MAKE AND INSTALL A TELEPHONE. 

Chapter X—MEDICAL COILS AND SHOCKING COILS. 

Chapter XI—THE CONSTRUCTION OF SPARK COILS. A one-quarter inch Coil, 
a one-half inch Coil, a one inch Coil. Experiments with Spark Coils. 

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   VOLUME III 

   80 Pages 73 Illustrations 

Chapter XII—HOW TO MAKE A DYNAMO-MOTOR. 

Chapter XIII—HOW TO MAKE A TOY BATTERY MOTOR. 

Chapter XIV—HOW TO BUILD AN ELECTRIC ENGINE. 

Chapter XV—MINIATURE BATTERY LAMP LIGHTING. 

Chapter XVI—COHERER OUTFITS FOR WIRELESS TELEGRAPHY. 

Chapter XVII—HOW TO BUILD A TESLA HIGH FREQUENCY COIL. Experiments with High Frequency Currents. 

Chapter XVIII—AN EXPERIMENTAL WIRELESS TELEPHONE. 

Chapter XIX—MISCELLANEOUS APPARATUS. Electrolysis of Water. Electro-Plating. Electricity from Heat. A Handy Light. An Experimental Arc Lamp. A Magnetic Diver. Magnetic Fish. A Magnetic Clown. An Electric Breeze. A Static Motor. 

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   **Price Postpaid, 25 Cents per Volume**

All three volumes can be supplied bound together with handsome cloth cover 
for $1.25 postpaid. 

.. clearpage::

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   **Parts and Materials**

.. container:: center large

   For Building the Apparatus Described in this Book 

We have received so many requests from our customers for 
information as to where they may obtain some of the materials required 
to build the apparatus described in this book, that we have made 
arrangements to supply same. Our business is essentially publishing, 
and we do not intend to go into the manufacture of, or to push the 
sale of apparatus or parts. Knowing, however, that many of our 
customers live where they are remote from cities or suitable supply 
houses, where they might obtain the necessary materials, we believe 
that the value of our books will be increased ten fold to the reader if 
we are in a position to furnish parts, etc. 

**M500**
    Complete Set of Parts for Dynamo illustrated in Figure 132 **$3.75**

Shipping Weight, 5 lbs. 

**M631**
    Complete Set of Parts for Tesla Coil **4.50**

Shipping Weight, 4 lbs. 

**M631A**
    Completed Tesla Coil **6.00**

Shipping Weight, 10 lbs. 

**M631B**
    Complete Tesla Coil Outfit, consisting of Tesla Coil, two-inch Spark Coil, Spark Gap and Leyden Jars **25.00**

Shipping Weight, 25 lbs. 

Please use list number when ordering. Include postage to 
pre-pay mailing charges, or we will ship by Express Collect. No parts 
supplied other than listed above. All prices subject to change 
without notice. Send for latest price list. 

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   **COLE & MORGAN, Inc.**

.. container:: center large

   .. vspace:: 2

   \P.O. Box 473, City Hall Sta. New York, N. Y.

.. vspace:: 2

.. pgfooter:: 

