insulated wire, about No. 36 B. & S. gauge in size. This should be
carefully removed and wound upon a spool for future use. Replace the
wire with some ordinary cotton-covered magnet wire, about No. 24 or 25
B. & S. gauge, winding it on very carefully and smoothly. Connect one
end of the winding to the pin leading to the insulated pin by soldering
it. This pin is the one at the end of the shaft opposite to that one to
which the spur gear is fastened. Connect the other end of the wire to
the pin at the same end of the shaft as the gear. This pin is grounded,
that is, connected to the frame.
An ordinary telephone magneto gives a very high voltage current. The
voltage may vary from twenty-five to several hundred, depending upon how
fast the machine is run. This is due to the fact that the armature
winding is composed of a very large number of turns of wire. The more
turns that are placed on the armature, the higher its voltage will be.
The current or amperage of a large telephone magneto wound with a large
number of turns of fine wire is very low. Too low in fact to be used for
anything except ringing a bell or testing. Winding the armature with
fewer turns of large wire reduces the voltage and increases the amperage
so that the current will light a small lamp or may be used for other
purposes. The winding does not change the principle of the magneto, it
merely changes its amperage and voltage.
The magneto may be mounted on a wooden base-board and screwed to a
table, so that the handle may be turned without inconvenience. A small
strip of copper, called a brush, should be fastened to the base with a
screw and brought to bear against the end of the insulated pin. The
brush should be connected to a binding-post with a piece of wire. A
second wire leading to a binding-post should be connected to the frame
of the magneto. When the handle is turned rapidly, currents may be drawn
from the two binding-posts.
The current is of the kind known as alternating, that is to say, it
flows first in one direction, then reverses and flows in the other.
In order to make the machine give direct current, it must be fitted with
a commutator. This is somewhat difficult with some magnetos but the
following plan may be carried out in most cases. Cut a small fiber
circle or disk about one inch in diameter from sheet fiber
three-sixteenths of an inch thick. Cut a small hole in the center, just
large enough so that the fiber will slip very lightly over the end of
the shaft from which the insulated pin projects. Two small commutator
sections similar to that shown in Figure 253 must be cut from
sheet-brass or sheet-copper. The three long ears shown in the drawing
are bent back around the fiber and squeezed down flat with a pair of
pincers so that they grip the fiber very tightly and will not slip. One
ear on one section should be bent over the back down to the hole, where
it will connect with the shaft. The other section of the commutator is
connected to the insulated pin by a drop of solder. In this manner, one
end of the winding is connected to one section of the commutator and the
other end to the other section. The commutator should fit tightly on the
end of the shaft so that it will not twist. The dividing line between
the section should be parallel to a line drawn to the axis of the actual
armature coil. When the iron parts of the armature are nearest the poles
of the horseshoe magnets in their revolution, the slot in the commutator
should be horizontal.
When the magnet is provided with a commutator, it may also be run as a
motor by connecting it to a battery. In order to operate it either as a
dynamo or a motor, however, it must first be fitted with a pair of
brushes. They are shown in detail in Figure 253. They are made from two
small strips of sheet-copper bent as shown and mounted on a small wooden
block. They must be adjusted to bear against the commutator so that when
the dividing line between the two sections is horizontal, the upper
brush bears against the upper section and the lower brush against the
lower section. The two brushes form the terminals of the machine. They
should be connected to binding-posts.
[Illustration: Fig. 254.—The Complete Generator.]
In order to operate the dynamo properly and obtain sufficient current
from it to operate a couple of small incandescent lamps, it will have to
be provided with a pulley mounted on the end of the shaft after the gear
wheel has been removed. The dynamo may then be driven at high speed by
connecting it to a sewing-machine with a belt, or the back wheel of a
bicycle from which the tire has been removed.
The completed dynamo is shown in Figure 254. The voltage and amperage of
the dynamo will depend upon the machine in question, not only upon the
size of the wire but also upon the size of the machine, the speed at
which it is run, and the strength of the horseshoe magnets. It is
impossible to tell just what the current will be until it is tested and
tried.
A 10-Watt Dynamo
Probably few experimenters fully understand how almost impossible it is
to construct a dynamo, worthy of the name as such, without resort to
materials and methods employed in the commercial manufacture of such
machines. Practical telegraph instruments, telephones, etc., can be
constructed out of all sorts of odds and ends, but in order to make a
real dynamo it is necessary to use certain materials for which nothing
can be substituted.
_The field magnets_ must be soft gray cast-iron except in special
instances.
_The wire_ used throughout must be of good quality and must be new.
The necessity for good workmanship in even the smallest detail cannot be
overestimated. Poor workmanship always results in inefficient working.
No dynamo will give its stated output continuously and safely unless the
materials and workmanship are up to a high standard.
Since castings must be used as field magnets, a pattern is necessary to
form the mould for the casting. Pattern work is something requiring
skill and knowledge usually beyond the average experimenter. A lathe is
necessary in order to bore or tunnel the space between the ends of the
field magnet into which the armature fits.
It may be possible for several boys to club together and have a pattern
made by a pattern-maker for building a dynamo. Then by using the lathe
in some convenient shop or manual training school secure a field magnet
and armature for a really practical small dynamo.
[Illustration: Fig. 255.—Details of the Field Casting.]
For these reasons, I have described below a small dynamo of about ten
watts output, the castings for which can be purchased from many
electrical dealers with all machine work done at an extremely low price.
The field magnet shown in Figure 255 is drawn to scale and represents
the best proportions for a small "overtype" dynamo of ten to fifteen’
watts output.
The dimensions are so clearly shown by the drawings that further comment
in that respect is unnecessary.
The armature is of the type known as the "Siemen’s H." It is the
simplest type of armature it is possible to make, which is a feature of
prime importance to the beginner at dynamo construction, although it is
not the most efficient form from the electrical standpoint. The armature
in this case is also a casting and therefore a pattern is required.
[Illustration: Fig. 256.—Details of the Armature Casting.]
The patterns for both the field and the armature are of the same size
and shape as shown in Figures 255 and 256. They are made of wood, and
are finished by rubbing with fine sandpaper until perfectly smooth and
then given a coat of shellac. The parts are also given a slight "draft,"
that is, a taper toward one side, so that the pattern may be withdrawn
from the mould.
The patterns are turned over to a foundry, where they are carefully
packed in a box, called a "flask," full of moulder’s sand. When the
patterns are properly withdrawn, they will leave a perfect impression of
themselves behind in the sand. The mould is then closed up and poured
full of molten iron. When the iron has cooled the castings are finished
except for cleaning and boring.
The shaft is a piece of steel rod, three-sixteenths of an inch in
diameter, and four and one-half inches in length.
The portion of the field into which the armature fits is bored out to a
diameter of one and five-sixteenth inches. Considerable care is
necessary in performing this operation in order not to break the field
magnet apart by taking too heavy a cut.
[Illustration: Fig. 257.—Details of the Commutator.]
The armature should be turned down to a diameter of one and one-quarter
inches or one-sixteenth of an inch smaller than the tunnel in which it
revolves between the field magnets. The center of the armature is bored
out to fit the shaft.
Figure 257 shows a two-part commutator for fitting to an armature of the
"Siemen’s H" type. It consists of a short piece of brass tubing fitted
on a fiber core and split length-wise on two opposite sides, so that
each part is insulated from the other.
The fiber is drilled with a hole to fit tightly on the shaft. It is then
placed in a lathe and turned down until a suitable piece of brass tube
can be driven on easily.
Two lines are then marked along the tube diametrically opposite. A short
distance away from each of these lines, and on each side of them, bore
two small holes to receive very small wood screws. The screws should be
counter-sunk. It is very important that none of the screws should go
into the fiber core far enough to touch the shaft.
The commutator may then be split along each of the lines between the
screws with a hacksaw. The saw-cut should be continued right through the
brass and slightly into the insulating core. The space between the
sections of the commutator should be fitted with well-fitting slips of
fiber, glued in.
The commutator should now be trued up and made perfectly smooth.
[Illustration: Fig. 258.—Diagram showing how to connect the Armature
Winding to the Commutator.]
The commutator is provided with a small brass machine screw threaded
into each section near the edge as shown in Figure 257. These screws are
to receive the ends of the armature winding and so facilitate
connections.
The commutator, shaft and armature are assembled as shown in Figure 258.
The armature may be held to the shaft by a small set screw or a pin. The
commutator should fit on the shaft very tightly so that it will not slip
or twist.
Every part of the armature and shaft touched by the armature winding
must be insulated with paper which has been soaked in shellac until
soft. The armature must be left to dry before winding.
The armature should next be wound with No. 20 B. & S. gauge
single-cotton-covered magnet wire. Sufficient wire should be put on to
fill up the winding space completely. Care should be taken, however, not
to put on too much wire or it will interfere with the field magnets and
the armature cannot revolve. After winding the armature, test it
carefully to see that the wire is thoroughly insulated from the iron.
[Illustration: Fig. 259.—Details of the Wooden Base.]
If the insulation is correct, paint the whole armature with thick
shellac varnish and bake it in a warm oven to set the shellac.
Figure 258 is a diagram showing how the winding is made and connected.
It is wound about the armature, always in the same direction, just as if
the armature were an ordinary electro-magnet.
The ends of the winding are each connected to one of the commutator
sections by scraping the wire and placing it under the screws.
The winding space in the field magnet should be shellacked, and
insulated with brown paper by wrapping the core with a strip of paper
and covering the bobbin ends with circular pieces made in two halves.
The field magnet is wound full of No. 20 B. & S. gauge
single-cotton-covered wire. The wire should be put on in smooth, even
layers and the winding space completely filled up.
[Illustration: Fig. 260.—The Pulley and Bearings.]
The base for the dynamo is a piece of hard wood, five inches long, four
inches wide, and five-eighths of an inch thick.
The bearings are small brass castings of the dimensions shown in Figure
260. It is necessary first to make a wooden pattern and send it to the
foundry for the castings.
The bearings are fastened to the projecting arms on the field casting by
means of machine screws eight-thirty-seconds of an inch in thickness.
The field magnet should not be screwed down on to the base until the
armature runs easily and truly in the tunnel.
The brushes are made from thin gauge sheet-copper according to the shape
and dimensions shown in Figure 261.
They are bent at right angles and mounted on the base on either side of
the commutator with small round-headed wood screws.
The completed dynamo is shown in Figure 262. One end of the shaft is
provided with a small pulley to accommodate a small leather belt.
[Illustration: Fig. 261.—The Brushes.]
The dynamo is connected as a "shunt" machine, that is, one terminal of
the field magnet is connected to one of the brushes, and the other
terminal to the other brush.
A wire is then led from each of the brushes to a binding-post.
A shunt 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.
The dynamo just described should have an output of from 10 to 15 watts
and deliver about 6 volts and 1 3/4 to 2 1/2 amperes.
In order to secure current from the dynamo it will first be necessary to
magnetize the field by connecting it to several batteries.
[Illustration: THE JUNIOR DYNAMO MOUNTED ON A LONG WOODEN BASE AND
BELTED TO A GROOVED WHEEL FITTED WITH A CRANK SO THAT THE DYNAMO CAN BE
RUN AT HIGH SPEED BY HAND POWER. THE ILLUSTRATION ALSO SHOWS A SMALL
INCANDESCENT LAMP CONNECTED TO THE DYNAMO SO THAT WHEN THE CRANK IS
TURNED THE LAMP WILL LIGHT.]
It will be found that the dynamo will also operate as a very efficient
little motor, but that on account of having a two-pole armature it must
be started by giving the shaft a twist.
[Illustration: Fig. 262.—Complete Dynamo.]
It can be used as a generator for lighting small lamps, electro-plating,
etc., but cannot be used for recharging storage cells on account of
having a two-pole armature.
The dynamo may be driven with a small water motor or from the
driving-wheel of a sewing-machine.
Before the machine will generate as a dynamo, it must be connected to a
battery and run as a motor. This will give the field the "residual
magnetism" which is necessary before it can produce current itself.
CHAPTER XVIII AN ELECTRIC RAILWAY
No toys loom up before the mind of the average boy with more appeal to
his love of adventure than do railway cars and trains. In England, the
construction and operation of miniature railways is the hobby not only
of boys but of grown men, and on a scale that is hardly appreciated in
this country.
The height of ambition of many boys is not only to own a miniature
railway system but to build one. For some unknown reason, none of the
boys’ papers or books have heretofore given any information on this
interesting subject. The car shown in Figure 263 is such that it can be
easily built by any boy willing to exercise the necessary care and
patience in its construction.
The first operation is to cut out the floor of the car. This is a
rectangular piece of hard wood, eight inches long, three and one-quarter
inches wide and one-half of an inch thick. Its exact shape and
dimensions are shown in Figure 264.
The rectangular hole cut in the floor permits the belt which drives the
wheels to pass down from the counter-shaft to the axle.
[Illustration: Fig. 263.—Complete Electric Railway operated by Dry
Cells. Note how the Wires from the Battery are connected to the Rails by
means of the Wooden Conductors illustrated in Figure 277.]
The two pieces forming the wheel-bearings are cut out of sheet-brass
according to the shape and dimensions shown in Figure 265. The brass
should be one-sixteenth of an inch thick. The two projecting pieces at
the top are bent over at right angles so that they can be mounted on the
under side of the car floor by small screws passing through the holes.
The holes which form the bearings for the ends of the axles upon which
the wheels are mounted should be three inches apart. The bearings cannot
be placed in position on the under side of the car floor until the
wheels and axles are ready, but when this work is done, care should be
taken to see that they line up and come exactly opposite to each other.
[Illustration: Fig. 264.—Details of the Floor of the Car.]
The wheels themselves cannot be made by the young experimenter unless he
has a lathe. They are flanged wheels, one and one-eighth inches in
diameter, and are turned from cast iron or brass. Such wheels can be
purchased ready made, or it may be possible to obtain from some broken
toy a set which will prove suitable.
[Illustration: Fig. 265.—Details of the Bearing which supports the Wheel
and Axle.]
Each shaft is composed of two pieces of "Bessemer" rod held together by
a short piece of fiber rod having a hole in each end into which one end
of each piece of iron rod is driven. The wheels fit tightly on the other
end of each of these pieces. They should be spaced so as to run on rails
two inches apart.
[Illustration: Fig. 266.—The Wheels and Axle.]
The purpose of the fiber rod is to insulate the halves of the axle from
each other. The electric current which operates the car is carried by
the two rails which form the track, and if the axles were made in one
piece or the halves joined together so as to form an electrical
connection, the battery furnishing the current would be short-circuited,
because the current would pass along the two rails and across the axles
instead of through the motor.
One pair of wheels are fitted with a grooved pulley one inch in
diameter.
It is hardly necessary to say that the wheels and axles should be
perfectly aligned, and should run true.
[Illustration: Fig. 267.—The Motor.]
The motor used to drive the car will prove more satisfactory if
purchased ready made. A self-starting three-pole motor similar to that
shown in Figure 267 will serve very nicely. The wooden base should be
removed and the motor screwed down firmly to the floor of the car as in
Figure 268.
One terminal of the motor is connected to one of the bearings, and the
other terminal to the other bearing.
The motor is belted to a countershaft so that it will have sufficient
power to move the car. It cannot be directly connected or belted to the
axle, because the speed of a small motor is so high that it has
comparatively little turning power or _torque_. The speed must be
reduced and the torque increased before it will drive the car.
The countershaft consists of two grooved pulleys mounted upon an axle
running in two bearings mounted upon the floor of the car. The bearings
are made from a strip of heavy sheet-brass, bent at right angles and
fastened to the car floor with small screws. The large pulley, _A_, is
one inch and one half in diameter and the small pulley, _B_, is
five-sixteenths of an inch in diameter. The countershaft is mounted in
such a position that a belt may be run from the small pulley, _B_, to
the pulley mounted on the axle of one pair of wheels. A belt is also run
from the small pulley on the motor to the large pulley, _A_, on the
countershaft. The pulleys must all be carefully lined up so that the
belts will run in their grooves without danger of slipping out.
[Illustration: Fig. 268.—The Complete Truck of the Car without the
Body.]
The shield on the platform at each end of the car is made of sheet-iron
or tin. Two small projections on the bottom are bent over at right
angles and used to secure the shields in position by driving a small
tack through them into the floor of the car.
The steps on either side of each platform are also made by bending
strips of sheet-iron or tin and fastening them to the car with small
nails or tacks.
The coupler consists of a strip of tin having a small hook soldered to
the end so that a trail car may be attached if desirable.
[Illustration: Fig. 269.—Pattern for the Sides and Ends of the Car.]
The car is now ready for testing, and when held in the hand so that the
wheels are free to run, two cells of dry battery should be found all
that is necessary to drive them at a fair rate of speed. The two wires
leading from the battery should be connected to the bearings, one wire
leading to each bearing. It will require more than two cells, however,
to drive the wheels properly when the car is on the track, All moving
parts should run freely and smoothly. The car may be used just as it is,
but if fitted with a body and a top it will present a much more
realistic appearance.
The sides and ends of the car body are made of sheet-iron or tin. Figure
269 shows the pattern and dimensions for these parts. They may be made
from one piece of metal eighteen and one-half inches long and three and
three-quarters inches wide. The doors and windows are cut out with a
pair of tin-snips. The small projections along the top are bent down at
right angles and the roof is fastened to them. The dotted lines indicate
the places for bending these projections and also the sides and ends of
the car.
[Illustration: Fig. 270.—The Roof of the Car.]
The roof is made in two pieces. It also is sheet-iron or tin. The roof
proper is eight inches long and four inches wide. It has a hole five and
one-half inches long and one and three-quarters inches wide cut in the
center. A number of small projections are left and bent upward to
support the deck and to form imitation ventilators. The deck is six
inches long and two and one-quarter inches in width. It is placed in
position on the roof and fastened by soldering. The roof is fastened to
the sides and ends of the car by soldering. It must be bent slightly to
conform with the curve at the top of the front and the rear of the car.
[Illustration: Fig. 271.—The Completed Car.]
The car when completed will appear as in Figure 271.
The track is made of smooth spring steel, one-half inch wide and either
No. 20 or No. 22 gauge in thickness.
[Illustration: Fig. 272.–Details of a Wooden Tie.]
The wooden ties are three and one-half inches long, three-quarters of an
inch wide and three-eighths of an inch thick. Each tie has two saw-cuts,
exactly two inches apart across the top face. This part of the work is
best performed in a miter-box so that the cuts will be perfectly square
across the ties. A saw should be used which will make a cut of such a
size that the steel track will fit tightly into it.
The distance between the two rails of the track, or the "gauge," as it
is called, is two inches.
[Illustration: Fig. 273.–Arrangement of Track.]
The track is assembled as in Figure 273. The spring steel is forced into
the saw-cuts in the ties by tapping with a light wooden mallet. The ties
should be spaced along the track about three inches apart. The work of
laying the track must be very carefully done so that the car wheels will
not bind at any spot. Curves should not be too sharp, or the car will
not pass around.
The track may be laid out in a number of different shapes, some of which
are shown in Figure 274.
[Illustration: Fig. 274.—Three Different Patterns for laying out the
Track.]
A circle is the easiest form of track to make. In laying out a circle or
any sort of curved track, the outside rail must necessarily be made
longer than the inside one.
The oval shape is a very good form to give the track in a great many
cases, especially where it is desirable for the car to have a longer
path than that afforded by a circle.
[Illustration: Fig. 275.—Details of the Base of the Cross-over.]
In order to make a figure-eight out of the track, a crossing, or
"cross-over," as it is sometimes called, will be required. This is shown
in Figure 275. A cross-over permits two tracks to cross each other
without interference. It consists of a wooden base, eight inches square
and three-eighths of an inch thick. Four saw-cuts, each pair exactly
parallel, and two inches apart, are made at right angles to each other
across the top surface of the base, as shown in the illustration.
The track used on the cross-over is semi-hard hoop-brass, one-half of an
inch wide and of the same gauge as the steel track. The brass is more
easily bent than the steel and is used for that reason, it being
practically impossible to bend the steel track at right angles without
snapping it.
Four pieces of the brass, each five inches long, are bent at right
angles exactly in the center. Four short pieces, each one and one-half
inches long, will also be required.
[Illustration: Fig. 276.—The Completed Cross-over.]
The cross-over is assembled as shown in Figure 276. The strips marked
_D_ are strips of very thin sheet-brass or copper. The purpose of these
strips is to connect the ends of the track on the cross-over to the ends
of the track forming the figure-eight so that the cross-over will not be
a "dead" section, that is, a section of track where the car cannot get
any current.
The long strips, bent at right angles to each other and marked _A_, _A_,
_B_, _B_, in the illustration, are forced into the saw-cuts in the base
over the strips marked _D_.
The small pieces, _C_, _C_, _C_, _C_, are placed in between the long
strips, leaving a space between so that the flanges of the car wheels
can pass. The pieces, _C_, _C_, _C_, _C_, should form a square open at
the corners. The two long strips, _A_, _A_, should be at opposite
corners diagonally across the square. _B_ and _B_ should occupy the same
relative position at the other corners. _A_ and _A_ are connected
together and _B_ and _B_ are connected together by wires passing on the
under side of the base.
The ends of the track forming the figure-eight are forced into the
saw-cuts at the edges of the base so that they form a good electrical
connection with the small strips marked _D_.
It is quite necessary to use care in arranging a figure-eight track, or
there will be danger of short-circuiting the batteries. The outside
rails of the figure-eight, distinguished by the letter _B_ in the
illustration, should be connected together by the cross-over. The inside
rails, marked _A_, should also be connected together by the cross-over.
In order to make a good mechanical and electrical connection between the
ends of the rails when two or more sections of track are used in laying
out the system, it is necessary to either solder the rails together or
else use a connector such as that shown in Figure 277.
This consists of a small block of wood having a saw-cut across its upper
face and a piece of thin sheet-brass set into the cut. The two rails are
placed with their ends abutting and one of these connectors slipped up
from beneath and forced on the rails. The piece of thin brass set into
the wooden block serves to make an electrical connection between the two
rails and also to hold them firmly in position. A small screw and a
washer placed outside the track and passing through the brass strip will
allow a battery wire to be conveniently attached.
[Illustration: Fig. 277.—A Connector for joining the Ends of the Rails.]
The steel rails should be occasionally wiped with machine oil or
vaseline to prevent rusting, and also to allow the car to run more
freely wherever the flanges of the wheels rub against the rails in
passing around a curve.
Four dry cells or three cells of storage battery should be sufficient to
operate the car properly. If it is desirable, a small rheostat may be
included in the battery circuit, so that the speed of the car can be
varied at will. The motor and the wheels should be carefully oiled so
that they will run without friction. The belts should not be so tight
that they cause friction or so loose that they allow the motor to slip,
but should be so adjusted that the motor runs freely and transmits its
power to the wheels.
The car may be made reversible by fitting with a small current reverser,
but unless the reverser is carefully made the danger of loss of power
through poor contacts is quite considerable. If the car is fitted with a
reverser the handle should be arranged to project from the car in a
convenient place where it can be easily reached by the fingers and the
car sent back or forth at will.
A railway system such as this can be elaborated and extended by adding
more than one car to the line or such features as bridges and stations.
[Illustration: Fig. 278.—A Bumper for preventing the Car from leaving
the Rails.]
The ends of a blind section of track, that is, a straight piece of track
not part of a circle or curve so that the car can return, should be
fitted with a track bumper, to prevent the car leaving the rails.
[Illustration: Fig. 279.—A Design for a Railway Bridge.]
No dimensions are given in Figures 279 and 280, showing designs for a
bridge and a station, because they are best left to be determined by the
scale upon which the railway system is to be extended.
[Illustration: Fig. 280.—A Design for a Railway Station.]
Both the bridge and the station are very simple. The bridge is built
entirely of wood, with the exception of the steel rails.
The station may be made out of thin wood, such as cigar-box wood. The
doors, windows, etc., may be painted on the walls. If this is carefully
done, it will give a very realistic appearance to your station.
CHAPTER XIX MINIATURE LIGHTING
Miniature lighting is a field of many interesting possibilities for the
young experimenter. Any labor expended along this line will result in
something far more useful from a practical standpoint than almost any of
the other things described in this book.
Miniature lights, operated from batteries, may be used in various ways;
to light dark corners, hallways, or other places where a light is often
temporarily wanted without the accompanying danger and nuisance of
matches or kerosene lamps.
Miniature lighting has only been made practical by the tungsten filament
lamp. The filament, or wire inside the globe, which becomes hot and
emits the light when the current is turned on, is made of _tungsten_ in
a tungsten lamp. In the earlier lamps, it was made of carbon. The carbon
lamp is now seldom used and is highly inefficient when compared to the
tungsten.
*A Carbon Lamp* consumes about three and one-half watts of current for
each candle-power of light, whereas a small tungsten lamp uses only
about one watt per candle-power small tungsten lamp uses only about one
watt per candle-power. The tungsten lamp is therefore three times as
efficient as a carbon lamp, and when used on a battery of equal voltage
it is possible to obtain the same amount of light with one-third of the
current that would be required by a carbon lamp.
[Illustration: Fig. 281.—Miniature Carbon Battery Lamp.]
Carbon lamps similar to that shown in Figure 281 are made in a number of
different voltages. The lowest voltage that it is practically possible
to make a carbon lamp for is three and one-half. A three-and-one-half
volt carbon lamp is designed to be operated on small dry cells such as
flashlight batteries. The E. M. F. of a dry cell is about one and
one-half volts, but when three small dry cells of the flashlight type
are connected in series and used to operate a lamp, their voltage
"drops," and the available E. M. F. is only about three and one-half
volts.
Four-volt carbon lamps are intended to be operated on large dry
batteries or wet cells because they do not lose their voltage as quickly
as small dry cells. The table below gives the voltage and candle-power
of the various small carbon lamps which are carried in stock by most
electrical dealers or supply houses:
*MINIATURE CARBON BATTERY LAMPS*
3.5 volts for flashlight batteries
4 volts. 2 candle-power
5.5 volts for flashlight batteries
6 volts. 2 candle-power
6 volts. 4 candle-power
8 volts. 4 candle-power
10 volts. 6 candle-power
*Tungsten Lamps* are made for voltages as low as one and one-half, and
will light on one cell of dry battery. The range of voltages is quite
wide and varied. A few of the most common sizes are given below:
*MINIATURE TUNGSTEN BATTERY LAMPS*
1.5 volts. for one dry cell
2.5 volts. for two-cell flashlight battery
2.8 volts. for two-cell flashlight battery
3.5 volts. for three-cell flashlight battery
3.8 volts. for three-cell flashlight battery
4 volts. 4 candle-power
6 volts. 2 candle-power
6 volts. 4 candle-power
6 volts. 6 candle-power
6 volts. 8-10-12-16-20-24 candle-power
[Illustration: Fig. 282.—Miniature Tungsten Battery Lamp.]
To find the approximate amount of current drawn from a battery by a
tungsten lamp, divide the candle-power by the voltage and the result
will be the current in amperes. For example, a 6 v. 2 c. p. lamp will
require, 2 divided by 6, or one-third of an ampere.
Six-volt tungsten lamp giving a light greater than six candle-power are
only used on storage batteries and are employed principally for
automobile lighting.
The filament of a tungsten lamp is much longer than that of a carbon
lamp and is usually in the form of a spiral or helix, as shown in Figure
282.
The bases of battery lamps, the base being the lower portion of the
lamp, which is made of brass and fits into a socket or receptacle, are
made in three different styles: _miniature_, _candelabra_, and
_Ediswan_.
[Illustration: Fig. 283.—Lamps fitted respectively with Miniature,
Candelabra, and Ediswan Bases.]
The miniature and candelabra bases have a threaded brass shell on the
outside and a small brass contact-button on the bottom. They are similar
except in respect to size. The miniature base is smaller than the
candelabra. The Ediswan base is a plain brass shell having two pins on
the side and two contacts on the bottom. This type of base is only used
in this country on automobiles. The miniature and the candelabra bases
are standard for battery lighting. The miniature base has many
advantages over the candelabra for the young experimenter, and should be
adopted in making any of the apparatus described in this chapter. These
three bases are shown in Figure 283.
[Illustration: Fig. 284.—Miniature Flat-Base Porcelain Receptacle.]
In order to form a good electrical connection between the lamp and the
power wires some sort of a receptacle or socket is necessary. The most
common arrangement for this purpose is the miniature flat-base porcelain
receptacle shown in Figure 284. This type of receptacle is used in
places where it can be permanently fastened in position with two small
screws.
[Illustration: Fig. 285.—Weather-proof and Pin-Sockets.]
The devices shown in Figure 285 are known respectively as a porcelain
weather-proof socket and a pin-socket. Sockets similar to the
weather-proof socket are also made of wood. The weather-proof sockets
are used in places where the light is to be exposed out-of-doors, as for
instance on a porch. The small metal parts are sealed in the porcelain
and entirely protected.
The pin-sockets and the wooden sockets are used principally on Christmas
trees or in decorative outfits where lamps are hung in festoons. The
flat-base receptacle, the pin-socket, and also the wooden socket will be
found very useful in making the apparatus described farther on in this
chapter.
*The Wires* used to carry the current in a miniature lighting system may
be of the sort known as _annunciator_ or _office_ wire if the wires are
to be run entirely indoors. The wire should not be smaller than No. 16
B. & S. gauge. When the wires are run outdoors, on a porch, or in some
other place exposed to the weather, the wire used should be
rubber-covered. Hanging lights or lights intended to be adjustable
should be connected with "flexible conductor." This is made of a number
of very fine wires braided together and insulated with silk. The wires
used in a lighting system should not in any case be longer than it is
necessary to have them. When a battery is connected to a system of wires
it is found that the voltage at the end of the wires is much lower than
at a point near the battery. This is called voltage "drop," and is much
greater as the wires grow longer. A light placed at the end of two very
long wires will not burn as brightly as it would if connected to the
same battery by means of short wires.
*Switches* can be made by following the suggestions given in Chapter
VII. Suitable switches can be purchased for a few cents at a most any
electrical house and will prove very much neater and efficient. They
should preferably be of any of the types shown in Figure 286.
*The Batteries* used for miniature lighting may be made up of storage
cells, dry cells or carbon cylinder cells. Storage cells will prove the
most satisfactory, provided that the experimenter has some convenient
means of recharging them or of having them recharged. Storage cells will
be found of especial value wherever it is desirable to operate several
lights from one battery.
Carbon cylinder cells are only suitable where one cell is to be operated
at a time. If more than one is used, the battery is liable to become
polarized and the lamps will not burn brightly. Carbon cylinder
batteries are very inexpensive to renew, and will be found the cheapest
method of lighting a small tungsten lamp.
[Illustration: Fig. 286.—Types of Battery Switches suitable for
Miniature Lighting.]
If lamps requiring more than two amperes are to be operated on dry
cells, the latter should be connected in series-multiple, as shown in
Figure 69. Two sets of dry cells connected in series-multiple will give
more than twice the service of a single set.
Lamps may be connected either in multiple or in series, provided that
the proper voltages of both battery and lamps are used.
When they are to be connected in multiple, the voltage of the lamps
should be the same as that of the battery. When they are to be used in
series, the voltage of the lamps multiplied by the number used should
equal the voltage of the battery. For example, suppose that you wish to
use a number of six-volt lamps on a six-volt storage battery. In that
case they must be connected in multiple. But if it should be that the
lamps are only two-volt lamps and you wish to operate three of them on a
six-volt battery you will have to place them in series.
[Illustration: Fig. 287.—How Lamps are Connected in Multiple.]
[Illustration: Fig. 288.—How Lamps are Connected in Series.]
It is sometimes desirable to arrange a lamp and two switches so that it
can be turned off or on from either switch independently of the other.
This is called "three-way wiring," and is a very convenient method of
arranging a light in a hallway. If one switch is placed at the top of a
stairway and the other switch at the bottom, a person can pass upstairs
or downstairs, light the lamp ahead, and turn it out as he passes the
last switch, no matter in which direction the previous user of the light
may have gone.
The switches are two-point switches, and the circuit should be arranged
as in Figure 289.
The switch-levers should always rest on one of the contacts and never be
left between, as shown in the drawing.
[Illustration: Fig. 289.—Three-way Wiring Diagram. The Light may be
turned off or on from either Switch.]
They are represented that way in the illustration in order not to
conceal the contacts.
Small brackets made of brass and similar to that shown in Figure 290 are
for sale at many electrical supply houses, and will add a very realistic
appearance to a miniature lighting plant.
[Illustration: Fig. 290.—A Lamp Bracket for Miniature Lighting.]
Brackets may be constructed after the plan shown in Figure 291. A wooden
socket or a pin-socket is mounted on the end of a small piece of brass
tubing which has been bent into the shape shown in the illustration. The
other end of the tube is set into a wooden block so that the bracket may
be mounted on the wall. The wires from the socket lead through the brass
tube and through the back or top of the block.
[Illustration: Fig. 291.—A Home-made Bracket.]
Hanging lights may be arranged by fitting a wooden socket and a lamp
with a reflector as shown in Figure 296. The reflector consists of a
circular piece of tin or sheet-aluminum having a hole in the center
large enough to pass the base of a miniature lamp. The circle is then
cut along a straight line from the circumference to the center. If the
edges are pulled together and lapped the circular sheet of metal will
take on a concave shape and form a shade or reflector which will throw
the light downwards. The overlapping edges of the reflector should be
soldered or riveted together. The reflector is slipped over the base of
the lamp, a small rubber or felt washer having been placed over the base
next to the glass bulb so that the reflector will not break the lamp.
The lamp is then screwed into a socket and allowed to hang downwards
from a flexible conductor.
[Illustration: Fig. 292.—A Hanging Lamp.]
A very pretty effect can be secured by drilling the edges of a reflector
full of small holes about three-sixteenths of an inch apart and then
hanging short strings of beads from the holes. The beads should form a
hanging fringe around the edge of the reflector, and if they are of
glass, a pleasing brilliancy is produced. Figure 293 shows how to make
the reflector.
[Illustration: Fig. 293.—How the Reflector is made.]
The batteries for a miniature lighting plant may be located in a closet,
under a stairway, or in some other out-of-the-way place. Wires from
there may be extended to various parts of the house, such as hallways,
closets, the cellar stairs, over a shaving-mirror in the bath-room or in
any dark corner where a light is often temporarily needed. The wires can
be run behind picture-mouldings or along the surbase and be almost
entirely concealed.
[Illustration: Fig. 294.—A Three-Cell Dry Battery for use in
Hand-Lanterns, etc.]
*Small Batteries* consisting of three small dry cells enclosed in
cardboard box, as shown in Figure 294, are on the market, and may be
bought at prices ranging from thirty to forty cents, depending upon the
size and the maker. One of the most convenient and practical sizes of
this type of battery has the dimensions shown in the illustration, and
with its aid it is possible to construct a number of very useful
electrical novelties and household articles in the shape of portable
electric lamps, etc. These batteries are quite small and are only
intended to operate very small lamps. Only one lamp should be used on
each battery at a time, and it should not be allowed to burn long. Some
of these batteries will give ten to fourteen hours of intermittent
service but if allowed to burn continuously would only light the lamp
for about five hours at the most. It is much the better plan to use them
only for a few minutes at a time, and then turn the light off and allow
the battery to recuperate.
*An Electric Hand-Lantern* is a very convenient device which is quite
simple to make. It consists of a wooden box large enough to receive a
three-cell battery, such as that shown in Figure 295. The back of the
box should open and close on hinges and be fastened with a hook so that
the battery may be easily removed for renewal.
[Illustration: Fig. 295.—An Electric Hand-Lantern.]
A three-and-one-half-volt tungsten lamp is mounted on the front of the
lantern and connected with the battery and a switch so that the light
can be turned on and off at will. The switch may be placed at the top of
the box so that the fingers of the same hand used to carry the lantern
may be used to turn the light on and off. The lantern is fitted with a
leather strap at the top, to be convenient for carrying.
*The Ruby Lantern* shown in Figure 296 is somewhat similar in
arrangement to the lantern just described, which may be used both as a
hand-lantern and a ruby light for developing photographs.
[Illustration: Fig. 296.—An Electric Ruby Lantern.]
It consists of a wooden box to hold a three-cell dry battery, and is
provided with a handle so that it may be easily carried. A switch by
which to turn the lamp on and off is mounted on the side of the box.
The light is furnished by a three-and-one-half-volt tungsten lamp
mounted on the front of an inclined wooden board arranged as shown in
the illustration so as to throw the light downward. The sides and bottom
of the box are grooved near the front edges so that a piece of ruby
glass may be inserted. Ruby glass for this purpose may be purchased at
almost any store dealing in photographers’ supplies.
The top is provided with a shield which is fastened in position by means
of four small hooks after the glass is in place. The shield is used in
order to prevent any white light from escaping through the crack between
the glass and the top of the box. A ruby lamp of this sort must be made
absolutely "light-tight" so that the only light emitted is that which
passes through the ruby glass. If any white light escapes it is liable
to fog and spoil any pictures in process of development.
[Illustration: Fig. 297.—The Electric Ruby Lamp with Glass and Shield
Removed.]
By removing the ruby glass and the shield, as shown in Figure 297, the
light is changed into a hand-lantern. The back of the box should be made
removable so that the battery can be replaced when worn out.
*A Night-Light* arranged to shine on the face of the clock so that the
time may be easily told during the night without inconvenience is shown
in Figure 298.
[Illustration: Fig. 298.—An Electric Night-Light for telling the Time
during the Night.]
It consists of a flat wooden box containing a three-cell dry battery and
having a small three-and-one-half-volt tungsten lamp mounted on the top
in the front with room for a clock to stand behind. The battery and the
lamp are connected to a switch so that the light may be turned on and
off. By attaching a long flexible wire and a push-button of the
"pear-push" type it is possible to place the light on a table and run
the wire with the push-button attached over to the bed so that one may
see the time during the night without getting up. The bottom of the box
should be made removable so that a new battery may be inserted when the
old one is worn out.
*The Watch-Light* is in many ways similar to the clock light just
described—but is smaller. It consists of a box just large enough to
receive a three-cell flashlight battery. A piece of brass rod is bent
into the form of a hook or crane from which to suspend the watch.
[Illustration: Fig. 299.—A Watch-Light.]
The light is supplied by a three-and-one-half-volt tungsten flashlight
bulb mounted on the top of the box in front of the watch. If desirable,
the light may be fitted with a small shade or reflector so that it
shines only on the dial and not in the eyes. The figures on the face of
the timepiece can then be seen much more plainly.
The lamp is mounted in a small wooden socket or a pin-socket passing
through a hole in the top of the box, so that the wires are concealed. A
small push-button is located in one of the forward corners of the box,
so that when it is pressed the lamp will light. Two small binding-posts
mounted at the lower right-hand corner of the box are connected directly
across the terminals of the switch, so that a flexible wire and a
push-button can be connected, and the light operated from a distance.
*An Electric Scarf-Pin* can be made by almost any boy who is skillful
with a pocket-knife. The material from which the pin is made may be a
piece of bone, ivory, or meerschaum. It is carved into shape with the
sharp point of a penknife and may be made to represent a skull, dog’s
head, an owl, or some other simple figure. The inside is hollowed out to
receive a "pea" lamp. Pea lamps with a cord and a plug attached as shown
in Figure 300 may be purchased from almost any electrical supply house.
The lamp is a miniature carbon bulb about one-eighth of an inch in
diameter. The eyes, nose, and mouth of the figure are pierced with small
holes, so that when the lamp is lighted the light will show through the
holes. The figure should be carved down thin enough to be translucent
and light up nicely.
[Illustration: Fig. 300.—A "Pea" Lamp attached to a Flexible Wire and a
Plug.]
A large pin is cemented or otherwise fastened to the back of the figure
so that it can be placed on the necktie or the lapel of the coat. The
lamp is removed from the socket of an electric flashlight and the plug
attached to the pea lamp screwed into its place. The pea lamp is
inserted inside the figure and bound in place with some silk thread.
Then when the button is pressed on the flashlight case, the pin will
light up and tiny beams of light will shoot out from the eyes, nose, and
mouth of the figure.
[Illustration: Fig. 301.—Four Steps in Carving a Skull Scarf-Pin. 1. The
Bone. 2. Hole drilled in Base. 3. Roughed out. 4. Finished.]
The drawings in Figure 301 show how to carve a skull scarf-pin. It is
made from a cylindrical piece of bone about five-eighths of an inch long
and three-eighths of an inch in diameter. The first operation is to
drill a hole three-eighths of an inch deep into the bottom. The hole
should be large enough in diameter to pass the pea lamp.
[Illustration: Fig. 302.—The Completed Pin ready to be connected to a
Battery by removing the Lamp from a Flashlight and screwing the Plug
into its Place.]
Then carve the eyes and nose and teeth. The drawings will give a good
idea of the steps in this part of the work. Next round off the top of
the skull. Bore a small hole in the back to receive the pin. Put the
light inside of the skull, and after it is bound in position the
scarf-pin is finished.
CHAPTER XX MISCELLANEOUS ELECTRICAL APPARATUS
HOW ELECTRICITY MAY BE GENERATED FROM HEAT
For the past century there has been on the part of many scientists and
inventors a constant endeavor to "harness the sunlight." The power which
streams down every day to our planet is incalculable. The energy
consumed in the sun and thrown off in the form of heat is so great that
it makes any earthly thing seem infinitesimal. We can only feel the heat
from a large fire a few feet away, yet the scorching summer heat travels
90,000,000 miles before it reaches us, and even then our planet is
receiving only the smallest fractional part of the total amount
radiated.
Dr. Langley of the Smithsonian Institute estimated that all the coal in
the State of Pennsylvania would be used by the sun in a fraction of a
second if it were sent up there to supply energy.
Perhaps, some day in the future, electric locomotives will haul their
steel cars swiftly from city to city by means of electricity, generated
with "sun power." Perhaps energy from the same source will heat our
dwellings and furnish us light and power.
This is not an idle dream, but may some day be an actuality. It has
already been carried out to some extent. A Massachusetts inventor has
succeeded in making a device for generating electricity from sun energy.
The apparatus consists of a large frame, in appearance very much like a
window. The glass panes are made of violet glass, behind which are many
hundred little metallic plugs. The sun’s heat, imprisoned by the violet
glass, acts on the plugs to produce electricity. One of these generators
exposed to the sun for ten hours will charge a storage battery and
produce enough current to run 30 large tungsten lamps for three days.
[Illustration: Fig. 303.—How the Copper Wires (_C_) and the Silver Wires
(_I_) are twisted together in Pairs.]
The principle upon which the apparatus works was discovered by a
scientist named Seebeck, in 1822. He succeeded in producing a current of
electricity by heating the points of contact between two dissimilar
metals.
Any boy can make a similar apparatus, which, while not giving enough
current for any practical purpose, will serve as an exceedingly
interesting and instructive experiment.
Cut forty or fifty pieces of No. 16 B. & S. gauge German silver wire
into five-inch pieces. Cut an equal number of similar pieces of copper
wire, and twist each German silver wire firmly together with one of
copper so as to form a zig-zag arrangement as in Figure 303.
[Illustration: Fig. 304.—Wooden Ring.]
Next make two wooden rings about four inches in diameter by cutting them
out of a pine board. Place the wires on one of the rings in the manner
shown in Figure 305. Place the second ring on top and clamp it down by
means of two or three screws.
[Illustration: Fig. 305.—Complete Thermopile. An Alcohol Lamp should be
lighted and placed so that the Flame heats the Inside Ends of the Wires
in the Center of the Wooden Ring.]
The inner junctures of the wires must not touch each other. The outer
ends should be bent out straight and be spaced equidistantly. The ring
should be supported by three iron rods or legs. The two terminals of the
thermopile as the instrument is called, should be connected to
binding-posts.
Place a small alcohol lamp or Bunsen burner in the center, so that the
flame will play on the inner junctures of the wires. A thermopile of the
size and type just described will deliver a considerable amount of
electrical energy when the inside terminals are good and hot and the
outside terminals fairly good.
The current may be very easily detected by connecting the terminals to a
telephone receiver or galvanometer. By making several thermopiles and
connecting them in parallel, sufficient current can be obtained to light
a small lamp.
HOW TO MAKE A REFLECTOSCOPE
A reflectoscope is a very simple form of a "magic lantern" with which it
is possible to show pictures from post-cards, photographs, etc. The
ordinary magic lantern requires a transparent lantern slide, but the
reflectoscope will make pictures from almost anything. The picture
post-cards or the photographs that you have collected during your
vacation may be thrown on a screen and magnified to three or four feet
in diameter. Illustrations clipped from a magazine or newspaper or an
original sketch or painting will likewise show just as well. Everything
is projected in its actual colors. If you put your watch in the back of
the lantern, with the wheels and works exposed, it will show all the
metallic colors and the parts in motion.
[Illustration: Fig. 306.—A Reflectoscope.]
The reflectoscope, shown in Figure 306, consists of a rectangular box
nine inches long, six inches wide, and six inches high outside. It may
be built of sheet-iron or tin, but is most easily made from wood. Boards
three-eighths of an inch thick are heavy enough. The methods of making
an ordinary box are too simple to need description. The box or case in
this instance, however, must be carefully made and be "light-tight,"
that is, as explained before, it must not contain any cracks or small
holes which will allow light to escape if a lamp is placed inside.
A round hole from two and one-half to three inches in diameter is cut in
the center of one of the faces of the box.
The exact diameter cannot be given here because it will be determined by
the lens which the experimenter is able to secure for his reflectoscope.
Only one lens is required. It must be of the "double-convex" variety,
and be from two and one-half to three inches in diameter. A lens is very
easily secured from an old bicycle lantern. It should be of clear glass.
[Illustration: Fig. 307.—How the Lens is Arranged and Mounted.]
A tube, six inches long and of the proper diameter to fit tightly around
the lens, must be made by rolling up a piece of sheet-tin and soldering
the edges together. This tube is the one labeled "movable tube" in the
illustrations. A second tube, three inches long and of the proper
diameter to just slip over the first tube, must also be made. A flat
ring cut from stiff sheet-brass is soldered around the outside of this
second tube, so that it may be fastened to the front of the case by
three or four small screws in the manner shown. The hole in the front of
the box should be only large enough to receive the tube.
The lens is held in position near one end of the movable tube by two
strong wire rings. These rings should be made of wire that is heavy and
rather springy, so that they will tend to open against the sides of the
tube. It is a good plan to solder one of them in position, so that it
cannot move, and then put in the lens. After the lens is in position,
the second ring should be put in and pushed down against the lens. Do
not attempt to put the lens in, however, until you are sure that the
metal has cooled again after soldering, or it will be liable to crack.
[Illustration: Fig. 308.—A View of the Reflectoscope from the Rear,
showing the Door, etc.]
The back of the box contains a small hinged door about four inches high
and five and one-half inches long. The pictures that it is desired to
project on the screen are held against this door by two small brass
clips, as shown in Figure 308.
[Illustration: Fig. 309.—A View of the Reflectoscope with the Cover
removed, showing the Arrangement of the Lamps, etc.]
The light for the reflectoscope is most conveniently made by two
16-candle-power electric incandescent lamps. Figure 309 shows a view of
the inside of the box with the cover removed, looking directly down. The
lamps fit into ordinary flat-base porcelain receptacles, such as that
shown in Figure 310. Two of these receptacles are required, one for each
lamp. They cost about ten cents each.
[Illustration: Fig. 310.—A Socket for holding the Lamp.]
The reflectors are made of tin, bent as shown in Figure 311. They are
fastened in position behind the lamps by four small tabs.
It is possible to fit a reflectoscope with gas or oil lamp to supply the
light, but in that case the box will have to be made much larger, and
provided with chimneys to carry off the hot air.
The interior of the reflectoscope must be painted a dead black by using
a paint made by mixing lampblack and turpentine. The interior also
includes the inside of the tin tubes.
The electric current is led into the lamps with a piece of flexible
lamp-cord passing through a small hole in the case. An attachment-plug
is fitted to the other end of the cord, so that it may be screwed into
any convenient lamp-socket.
[Illustration: Fig. 311.—The Tin Reflector.]
The pictures should be shown in a dark room and projected on a smooth
white sheet. They are placed under the spring clips on the little door
and the door closed. The movable tube is then slid back and forth until
the picture on the screen becomes clear and distinct.
The lantern may be improved considerably by using tungsten lamps of 22
c. p. each in place of ordinary c. p. carbon filament lamps.
If four small feet, one at each corner, are attached to the bottom of
the case, its appearance will be much improved.
Very large pictures will tend to appear a little blurred at the corners.
This is due to the lens and cannot be easily remedied.
HOW TO REDUCE THE 110-v. CURRENT SO THAT IT MAY BE USED FOR
EXPERIMENTING
Oftentimes it is desirable to operate small electrical devices from the
110-v. lighting or power circuits. Alternating current can be reduced to
the proper voltage by means of a small step-down transformer, such as
that described in Chapter XIII. Direct current may be reduced by means
of a resistance. The most suitable form of resistance for the young
experimenter to use is a "lamp bank."
A lamp bank consists of a number of lamps connected in parallel, and
arranged so that any device may be connected in series with it.
The lamps are set in sockets of the type known as "flat-base porcelain
receptacles," such as that shown in Figure 310, mounted in a row upon a
board and connected as shown in Fig. 312.
The current from the power line enters through a switch and a fuse and
then passes through the lamps before it reaches the device it is desired
to operate. The switch is for the purpose of shutting the current on and
off, while the fuse will "blow" in case too much current flows in the
circuit.
The amount of current that passes through the circuit may be accurately
controlled by the size and number of lamps used in the bank. The lamps
may be screwed in or out and the current altered by one-quarter of an
ampere at a time if desirable.
The lamps should be of the same voltage as the line upon which they are
to be used. Each 8-candle-power, 110-v. carbon lamp used will permit
one-quarter of an ampere to pass. Each 16-candle-power, 110-v. lamp will
pass approximately one-half an ampere. A 32-candle-power lamp of the
same voltage will permit one ampere to flow in the circuit.
[Illustration: Fig 312.—Top View of Lamp Bank, showing how the Circuit
is arranged. A and B are the Posts to which should be connected any
Device it‘s desirable to operate.]
AN INDUCTION MOTOR
*An Induction Motor* is a motor in which the currents in the armature
windings are _induced_. An induction motor runs without any brushes, and
the current from the power line is connected only to the field. The
field might be likened to the primary of a transformer. The currents in
the armature then constitute a secondary winding in which currents are
induced in the same manner as in a transformer.
An induction motor will operate only on alternating current.
A small motor such as that shown in Figure 267, and having a three-pole
armature, is the best type to use in making an experimental induction
motor.
Remove the brushes from the motor and bind a piece of bare copper wire
around the commutator so that it short-circuits the segments.
A source of alternating current should then be connected to the
terminals of the field coil. If you have a step-down transformer, use it
for this purpose, but otherwise connect it in series with a lamp bank
such as that just described.
Place a switch in the circuit so that the current may be turned on and
off. Wind a string around the end of the armature shaft so that it may
be revolved at high speed by pulling the string in somewhat the same
manner that you would spin a top. When all is ready, give the string a
sharp pull and immediately close the switch so that the alternating
current flows into the field.
If this is done properly, the motor will continue to run at high speed,
and furnish power if desirable.
Most of the alternating-current motors in every-day use for furnishing
power for various purposes are induction motors. They are, however,
self-starting, and provided with a hollow armature, which contains a
centrifugal governor. When the motor is at rest or just starting, four
brushes press against the commutator and divide the armature coils into
four groups. After the motor has attained the proper speed, the governor
is thrown out by centrifugal force and pushes the brushes away from the
commutator, short-circuiting all the sections and making each coil a
complete circuit of itself.
ELECTRO-PLATING
Water containing chemicals such as sulphate of copper, sulphuric acid,
nitrate of nickel, nitrate of silver, or other metallic salts is a good
conductor of electricity. Such a liquid is known as an _electrolyte_.
It has been explained in Chapter IV that chemical action may be used to
produce electricity and that in the case of a cell such as that invented
by Volta, the zinc electrode gradually wastes away and finally enters
into solution in the sulphuric acid.
It is possible exactly to reverse this action and to produce what is
known as _electrolysis_. If an electrolyte in which a metal has been
"dissolved" is properly arranged so that a current of electricity may be
passed through the solution, the metal will "plate out," or appear again
upon one of the electrodes.
Electrolysis makes possible electro-plating and thousands of other
exceedingly valuable and interesting chemical processes.
More than one-half of all the copper produced in the world is produced
_electrolytically_.
Practically all plating with gold, silver, copper and nickel is
accomplished with the aid of electricity.
These operations are carried out on a very large scale in the various
factories, but it is possible to reproduce them in any boy’s workshop or
laboratory, with very simple equipment.
The proper chemicals, a tank, and a battery are the only apparatus
required. The current must be supplied by storage cells or a bichromate
battery because the work will require five or six amperes for quite a
long period.
A small rectangular glass jar will make a first class tank to hold the
electrolyte.
The simplest electro-plating process, and the one that the experimenter
should start with is copper-plating.
Fill the tank three-quarters full of pure water and then drop in some
crystals of copper-sulphate until the liquid has a deep blue color and
will dissolve no more.
Obtain two copper rods and lay them across the tank. Cut two pieces of
sheet copper having a tongue at each of two corners so that they can be
hung in the solution, as shown in Figure 313. Hang both of the sheets
from one of the copper rods. Connect this rod to the _positive_ pole of
the battery. These sheets are known as the anodes.
Then if a piece of carbon, or some metallic object is hung from the
other rod and connected to the _negative_ pole of the battery, the
electro-plating will commence. The apparatus should be allowed to run
for about half an hour and then the object hung from the rod connected
to the negative pole of the battery should be lifted out and examined.
It will be found thickly coated with copper. It is absolutely necessary
to have the poles of the battery connected in the manner stated, or no
deposit of copper will take place.
Objects which are to be electro-plated must be free from all traces of
oil or grease and absolutely clean in every respect, or the plating will
not be uniform, because it will not stick to dirty spots.
[Illustration: Fig. 313.—A Glass Jar arranged to serve as an
Electro-Plating Tank.]
Such articles as keys, key-rings, tools, etc., can be prevented from
rusting by coating with nickel.
Nickel-plating is very similar to copper-plating. Instead, however, of
having two copper sheets suspended from the rod connected to the
positive pole of the battery, they must be made of nickel.
The electrolyte is composed of one part of nickel-sulphate dissolved in
twenty parts of water to which one part of sodium-bisulphate is added.
This mixture is placed in the tank instead of the copper-sulphate. The
objects to be plated are hung from the copper rod connected to the
negative pole of the battery.
When the nickel-plated articles are removed from the bath they will have
a dull, white color known as "white nickel." When white nickel is
polished with a cloth wheel revolving at high speed, and known as a
buffing-wheel, it will assume a high luster.
HOW TO MAKE A RHEOSTAT
It is often desirable to regulate the amount of current passing through
a small lamp, motor, or other electrical device operated by a battery.
This is accomplished by inserting resistance into the circuit. A
rheostat is an arrangement for quickly altering the amount of resistance
at will.
A simple rheostat is easily made by fitting a five-point switch such as
that shown in Figure 95 with several coils of German-silver resistance
wire. German silver has much more resistance than copper wire, and is
used, therefore, because less will be required, and it will occupy a
smaller space.
A five-point switch will serve satisfactorily in making a rheostat, but
if a finer graduation of the resistance is desired it will be necessary
to use one having more points.
Two lines of small wire nails are driven around the outside of the
points, and a German-silver wire of No. 24 B. & S. gauge wound in
zig-zag fashion around the nails from one point to the other.
[Illustration: Fig. 314.—A Rheostat.]
The rheostat is placed in series with any device it is desirable to
control. When the handle is on the point to the extreme left, the
rheostat offers no resistance to the current. When the lever is placed
on the second point, the current has to traverse the first section of
the German-silver wire and will be appreciably affected. Moving the
handle to the right will increase the resistance.
If the rheostat is connected to a motor, the speed can be increased or
decreased by moving the lever back and forth.
In the same manner, the light from a small incandescent lamp may be
dimmed or increased.
A CURRENT REVERSER OR POLE-CHANGING SWITCH
A pole-changing or current reversing switch is useful to the
experimenter. For example, if connected to a small motor, the motor can
be made to run in either direction at will. A motor with a permanent
magnet field can be reversed by merely changing the wires from the
battery so that the current flows through the circuit in the opposite
direction. If the motor is provided with a field winding, however, the
only way that it can be made to run either way is by reversing the
field. This is best accomplished with a pole-changing switch.
Such a switch may be made by following the same general method of
construction as that outlined on pages 107 and 108, but making it
according to the design shown in Figure 315.
Motors such as those illustrated can be made to reverse by connecting to
a pole-changing switch in the proper manner.
The two outside points or contacts (marked _D_ and _D_) should both be
connected to one of the brushes on the motor. The middle contact, _C_,
is connected to the other brush.
One terminal of the field is connected to the battery. The other
terminal of the field is connected to the lever, _A_. _B_ connects to
the other terminal of the battery.
[Illustration: Fig. 315.—A Pole-Changing Switch or Current Reverser. The
Connecting Strip is pivoted so that the Handle will operate both the
Levers, A and B.]
When the switch handle is pushed to the left, the lever _A_ should rest
on the left-hand contact, _D_. The lever _B_ should make contact with
_C_. The motor will then run in one direction. If the handle is pushed
to the right so that the levers _A_ and _B_ make contact respectively
with _C_ and _D_ (right-hand), the motor will reverse and run in the
opposite direction.
A COMPLETE WIRELESS RECEIVING SET
Many experimenters may wish to build a wireless receiving set which is
permanently connected and in which the instruments are so mounted that
they are readily portable and may be easily shifted from one place to
another without having to disturb a number of wires.
The receiving set shown in Figure 316 is made up of some of the separate
instruments described in Chapter XIV, and illustrates the general plan
which may be followed in arranging an outfit in this manner.
[Illustration: COMPLETE RECEIVING SET, CONSISTING OF DOUBLE SLIDER
TUNING COIL, DETECTOR AND FIXED CONDENSER.]
[Illustration: COMPLETE RECEIVING SET, CONSISTING OF A LOOSE COUPLER IN
PLACE OF THE TUNING COIL, DETECTOR AND FIXED CONDENSER.]
The base is of wood, and is nine inches long, seven inches wide, and
one-half of an inch thick.
A double-slider tuning coil, similar to that shown in Figure 203, is
fastened to the back part of the base by two small wood-screws passing
upwards through the base into the tuner heads.
[Illustration: Fig. 316. A Complete Wireless Receiving Outfit.]
The fixed condenser is enclosed in a rectangular wooden block which is
hollowed out underneath to receive it and then screwed down to the base
in the forward right-hand corner.
The detector is mounted in the forward left-hand part of the base, and
in the illustration is shown as being similar to that in Figure 210. Any
type of detector may, however, be substituted.
The tuning coil may be replaced by a loose coupler if desirable, but in
that case the base will have to be made larger.
The telephone receivers are connected to two binding-posts mounted
alongside the detector.
The circuit shown in Figure 218 is the one which should be followed in
wiring the set. The wires which connect the various instruments should
be passed through holes and along the under side of the base so that
they are concealed.
HOW TO BUILD A TESLA HIGH-FREQUENCY COIL
A Tesla high-frequency coil or transformer opens a field of wonderful
possibilities for the amateur experimenter. Innumerable weird and
fascinating experiments can be performed with its aid.
When a Leyden jar or a condenser discharges through a coil of wire, the
spark which can be seen does not consist simply of a single spark
passing in one direction, as it appears to the eye, but in reality is a
number of separate sparks alternately passing in opposite directions.
They move so rapidly that the eye is unable to distinguish them. The
time during which the spark appears to pass may only be a fraction of a
second, but during that short period the current may have oscillated
back and forth several thousand times.
If the discharge from such 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 containing a larger number of turns, the secondary will
produce a peculiar current known as _high-frequency_ electricity.
High-frequency currents reverse their direction of flow or _alternate_
from one hundred thousand to one million times a second.
[Illustration: Fig. 317.—Illustrating the Principle of the Tesla Coil. A
Leyden Jar discharges through the Primary Coil and a High-Frequency
Spark is produced at the Secondary.]
High-frequency currents possess many curious properties. They 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. High-frequency currents do not produce a shock. If you hold a
piece of metal in your hand you can take the shock from a high-frequency
coil throwing a spark two or three feet long with scarcely any sensation
save that of a slight warmth.
The Tesla coil described below is of a size best adapted for use with a
two-inch or three-inch spark coil, or a small high-potential wireless
transformer. The purpose of the spark coil or the transformer is to
charge the Leyden jars or condenser which discharge through the primary
of the Tesla coil.
[Illustration: Fig. 318.—Details of the Wooden Rings used as the Primary
Heads.]
If the young experimenter wishes to make a Tesla coil which will be
suited to a smaller spark coil, for instance, one capable of giving a
one-inch spark, the dimensions of the Tesla coil herein described can be
cut exactly in half. Instead of making the secondary twelve inches long
and three inches in diameter, make it six inches long and one and
one-half inches in diameter, etc.
*The Primary* consists of eight turns of No. 10 B. & S. gauge copper
wire wound around a drum. The heads of the drum are wooden rings, seven
inches in diameter and one-half inch thick. A circular hole four and
one-half inches in diameter is cut in the center of each of the heads.
[Illustration: Fig. 319.—Details of the Cross Bars which support the
Primary Winding.]
The cross bars are two and one-half inches long, three-quarters of an
inch thick and one-half of an inch wide. Six cross bars are required.
They are spaced at equal distances around the rings and fastened by
means of a _brass_ screw passing through the ring. When the drum is
completed it should resemble a "squirrel cage."
Small grooves are cut in the cross bars to accommodate the wire. The
wires should pass around the drum in the form of a spiral and be spaced
about five-sixteenths of an inch apart.
The ends of the wire should be fastened to binding-posts mounted on the
heads.
*The Secondary* is a single layer of No. 26 B. & S. silk- or
cotton-covered wire wound over a cardboard tube, twelve inches long and
three inches in diameter.
The tube should be dried in an oven and then given a thick coat of
shellac, both inside and out, before it is used. This treatment will
prevent it from shrinkage and avoid the possibility of having to rewind
the tube in case the wire should become loose.
[Illustration: Fig. 320.—The Secondary Head.]
The secondary is fitted with two circular wooden heads just large enough
to fit tightly into the tube, having a half-inch flange, and an outside
diameter of three and seven-eighths inches.
*The Base* of the coil is fifteen inches long and six inches wide and is
made of wood.
The coil is assembled by placing the primary across the base and exactly
in the center. Two long wood-screws passing through the base and into
the primary heads will hold it firmly in position.
The secondary is passed through the center of the primary and supported
in that position by two hard rubber supports, four inches high,
seven-eighths of an inch wide and one-half of an inch thick. A brass
wood-screw is passed through the top part of each of the supports into
the secondary heads so that a line drawn through the axis of the
secondary will coincide with a similar line drawn through the axis of
the primary.
[Illustration: A COMPLETE COHERER OUTFIT AS DESCRIBED ON PAGE 274.]
[Illustration: THE TESLA HIGH FREQUENCY COIL.]
The supports are made of hard rubber instead of wood, because the rubber
has a greater insulating value than the wood. High-frequency currents
are very hard to insulate, and wood does not usually offer sufficient
insulation.
A brass rod, five inches long and having a small brass ball at one end,
is mounted on the top of each of the hard-rubber supports. The ends of
the secondary winding are connected to the brass rods.
[Illustration: Fig. 321.—End View of the Complete Tesla Coil.]
The lower end of each of the hard-rubber supports is fastened to the
base by means of a screw passing through the base into the support.
In order to operate the Tesla coil, the primary should be connected in
series with a condenser and a spark-gap as shown in Figure 324. The
condenser may consist of a number of Leyden jars or of several glass
plates coated with tinfoil. It is impossible to determine the number
required ahead of time, because the length of the connecting wires, the
spark-gap, etc., will have considerable influence upon the amount of
condenser required. The condenser is connected directly across the
secondary terminals of the spark coil.
When the spark coil is connected to a battery and set into operation, a
snappy, white spark should jump across the spark-gap.
If the hand is brought close to one of the secondary terminals of the
Tesla coil, a small reddish-purple spark will jump out to meet the
finger.
[Illustration: Fig. 322.—The Complete Tesla Coil.]
Adjusting the spark-gap by changing its length and also altering the
number of Leyden jars of condenser plates will probably increase the
length of the high-frequency spark. It may be possible also to lengthen
the spark by disconnecting one of the wires from the primary
binding-posts on the Tesla coil and connecting the wire directly to one
of any one of the turns forming the primary. In this way the number of
turns in the primary is changed and the circuit is _tuned_ in the same
way that wireless apparatus is tuned by changing the number of turns in
the tuning coil or helix.
[Illustration: Fig 323.—Showing how a Glass-Plate Condenser is built up
of Alternate Sheets of Tinfoil and Glass.]
The weird beauty of a Tesla coil is only evident when it is operated in
the dark. The two wires leading from the secondary to the brass rods and
the ball on the ends of the rods will give forth a peculiar _brush_
discharge.
If you take a piece of metal in your hand and hold it near one of the
secondary terminals, the brushing will increase. If you hold your hand
near enough, a spark will jump on to the metal and into your body
without your feeling the slightest sensation.
If one of the secondary terminals of the Tesla coil is _grounded_ by
means of a wire connecting it to the primary, the brushing at the other
terminal will increase considerably.
Make two rings out of copper wire. One of them should be six inches in
diameter and the other one four inches in diameter. Place the small ring
inside the large one and connect them to the secondary terminals. The
two circles should be arranged so as to be _concentric_, that is, so
that they have a common center.
The space between the two coils will be filled with a pretty brush
discharge when the coil is in operation.
[Illustration: Fig. 324.—A Diagram showing the Proper Method of
Connecting a Tesla Coil.]
There are so many other experiments which may be performed with a Tesla
coil that it is impossible even to think of describing them here, and
the young experimenter wishing to continue the work further is advised
to go to some library and consult the works of Nikola Tesla, wherein
such experiments are fully explained.
CONCLUSION
Unless the average boy has materially changed his habits, in recent
years, it matters not what the preface of a book may contain, for it
will be unceremoniously skipped with hardly more than a passing glance.
With this in mind, the author has tried to "steal a march" on you, and
instead of writing a longer preface, and including some material which
might properly belong in that place, has added it here in the nature of
a conclusion, thinking that you would be more likely to read it last
than first.
Some time ago, when in search for something that might be described in
this book, I thought of some old boxes into which my things had been
packed when I had dismantled my workshop before going away to college.
They had been undisturbed for a number of years and I had almost
forgotten where they had been put. At last a large box was unearthed
from amongst a lot of dusty furniture put away in the attic. I pried the
cover off and took the things out one by one and laid them on the floor.
Here were galvanometers, microphones, switches, telegraph keys,
sounders, relays, and other things too numerous to mention. They had all
been constructed so long ago that I was considerably amused and
interested in the manner in which bolts, screws, pieces of curtain rod,
sheet-iron, brass, and other things had been taken to form various parts
of the instruments. The binding-posts had almost in every case seen
service as such on dry cells before they came into my hands. The only
parts that it had been necessary to buy were a few round-headed brass
screws and the wire which formed the magnets. In several instances, the
latter were made so that they might be easily removed and mounted upon
another instrument. The magnets on the telegraph sounder could be
removed and fitted to form part of an electric engine or motor.
One particular thing which struck me very forcibly was the lack of
finish and the crudeness which most of the instruments showed.
Of course it was impossible to avoid the clumsy appearance which the
metal parts possessed, since they were not originally made for the part
that they were playing, but I wished that I had taken a little more care
to true up things properly or to smooth and varnish the wood, or that I
had removed the tool-marks and dents from the metal work by a little
filing.
If I had done so, I should now be distinctly proud of my work. That is
not to say that I am in the least ashamed of it, for my old traps
certainly served their purpose well, even if they were not ornamental
and were better back in their box. Perhaps I might be excused for
failing in this part of the work through lack of proper tools, and also
because at that time there were no magazines or books published which
explained how to do such things, and when I built my first tuning coils
and detectors nothing on that subject had ever been published. I had to
work out such problems for myself, and gave more thought to the
principles upon which the instruments operated than to their actual
construction.
The boys who read this book have the advantage of instructions showing
how to build apparatus that has actually been built and tested. You know
what size of wire to use and will not have to find it out for yourself.
For that reason you ought to be able to give more time to the
construction of such things. The purpose of this conclusion is simply a
plea for better work. The American boy is usually careless in this
regard. He often commences to build something and then, growing tired
before it is finished, lays it aside only to forget it and undertake
something else. _Finish whatever you undertake_. The principle is a good
one. Remember also that care with the little details is what insures
success in the whole.
If in carrying out your work, you get an idea, do not hesitate to try
it. A good idea never refused to be developed. It is not necessary to
stick absolutely to the directions that I have given. They will insure
success if followed, but if you think you can make an improvement, do
so.
Of course, such a book as this cannot, in the nature of things, be
exhaustive, nor is it desirable, in one sense, that it should be.
I have tried to write a book which, considered as a whole, would prove
to be exhaustive only in that it treats of almost every phase of
practical electricity.
The principle in mind has been to produce a work which would stimulate
the inventive faculties in boys, and to guide them until face to face
with those practical emergencies in which no book can be of any
assistance but which must be overcome by common sense and the exercise
of personal ingenuity.
The book is not as free from technical terms or phrases, as it lay in my
power to make it, because certain of those terms have a value and an
every-day use which are a benefit to the young experimenter who
understands them.
Any one subject treated in the various chapters of the "Boy Electrician"
may be developed far beyond that point to which I have taken it. The
railroad system could be fitted with electric signals, drawbridges, and
a number of other devices.
Many new ideas suggest themselves to the ready-witted American boy. I
shall always be pleased to hear from any boy who builds any of the
apparatus I have described, and, if possible, to receive photographs of
the work. I should be glad to be of any assistance to such a lad, but
remember that some of the drawings and text in this book required many
hours even to complete a small portion, and therefore please do not
write to ask how to build other apparatus not described herein. And, as
the future years bring new inventions and discoveries, no one now knows
but that, some day, perhaps I will write another "Boy Electrician."
THE END.