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The Boy Mechanic: Volume 1 by Popular Mechanics

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any convenient blocks which will place it midway. The walls of the
muffle should be about 1/2 in. thick, and the dimensions should
allow at least 1 in. of space all around for the passage of heat
between it and the walls of the kiln. By the time the clay of the
kiln is well dried, it will be found that it has all shrunk away
from the iron about 3/8 in. After removing all the paper, pack
this space-top, bottom and sides with moist ground asbestos. If
the cover of the pail has no rim, it may be fastened to the
asbestos and clay lining by punching a few holes, passing wire
nails through and clinching them. Fit all the parts together
snugly, take out the plugs in the top and bottom, and your kiln is
ready for business. The handle of the pail will be convenient for
moving it about, and it can be set on three bricks or some more
elaborate support, as dictated by fancy and expense.

The temperature required for baking earthenware is 1250
degrees--1310 degrees, C.,; hotel china, 1330 degrees; hard
porcelain, 1390 degrees-1410 degrees. These temperatures can not
be obtained in the above kiln by means of the ordinary Bunsen
burner. If will be necessary either to buy the largest size
Bunsen, or make one yourself, if you have the materials. If you
can get a cone which can be screwed into an inch pipe, file the
opening of the cone to 1/16 in. diameter, and jacket the whole
with a 2-1/2-in. pipe. The flame end of this burner tube should be
about 4-1/2 in. above the cone opening and should be covered with
gauze to prevent flame from snapping back. When lighted, the point
of the blue flame, which is the hottest part, should be just in
the hole in the bottom of the kiln. Such a burner will be cheaply
made and will furnish a kiln temperature of 1400 degrees, but it
will burn a great deal of gas.

A plumber's torch of medium size will cost more in the beginning,
but will be cheaper in operation. Whatever burner is used, the
firing should be gradual, and with especial caution the first
time. By experiment you will find that a higher temperature is
obtained by placing a 1-in. pipe 2-ft. long over the lid hole as a
chimney. It would be still more effective to get another iron
pail, 2 in. wider than the kiln, and get a down draft by inverting
it over the kiln at whatever height proves most suitable. --G. L.

** How to Make a Small Medical Induction Coil [63]

The coil to be described is 3-1/2 in., full length of iron core,
and 3/4 in. in diameter.

Procure a bundle of small iron wire, say 1/4 in. in diameter, and
cut it 3-1/2 in. long; bind neatly with coarse thread and file the
ends smooth (Fig. 1). This done, make two wood ends, 1-1/4 by
1-1/4 in. and 3/8 in. thick, and varnish. Bore holes in the center
of each so the core will fit in snugly and leave about 1/4 in.
projecting from each end (Fig. 1).

After finishing the core, shellac two layers of thick paper over
it between the ends; let this dry thoroughly. Wind two layers of
bell magnet wire over this, allowing several inches of free wire
to come through a hole in the end. Cover with paper and shellac as
before. Wind about 1/8 in. of fine wire, such

[Illustration: Medical Induction Coil]

as used on telephone generators, around the coil, leaving long
terminals. Soak the whole in melted paraffin and let cool; bind
tightly with black silk.

The vibrator is made of a piece of thin tin to which is soldered
the head of an iron screw and on the other side a small piece of
platinum, which can be taken from an old electric bell (Fig. 2).

Of course, a regulator must be had for the vibrator; this can be
accomplished by bending a stout piece of copper wire as shown. The
connections and the base for setting up are shown in the figures.
--Contributed by J. T. R., Washington, D. C.

** Mechanical Trick With Cards [63]

The following mechanical card trick is easy to prepare and simple
to perform:

First, procure a new deck, and divide it into two piles, one
containing the red cards and the other the black ones, all cards
facing the same way. Take the red cards, square them up and place
in a vise. Then, with a plane, plane off the upper right hand
corner and lower left hand corner, as in Fig. 1, about 1/16 in.

Then take the black cards, square them up, and plane off about
1/16 in. on the upper left hand corner and lower right hand
corner, as in Fig. 2.

Next restore all the cards to one pack, taking care to have the
first card red, the next black, and so on, every alternate card
being the same color. Bend the pack so as to give some spring to
the cards, and by holding one thumb on the upper left-hand corner

[Illustration: Card Trick]

all the cards will appear red to the audience; place thumb in the
center at top of pack and they will appear mixed, red and black;
with thumb on upper right-hand corner all cards appear black. You
can display either color called for.
--Contributed by Ralph Gingrich, Chicago.

** How to Make a Rain Gauge [64]

An accurate rain gauge may be easily constructed from galvanized
iron, as shown in the sketch herewith. The funnel, A, overlaps and
rests on the body, B, and discharges into the tube, C, the area of
which is one-tenth that of the top of the funnel. The depth of the
water in C is thus ten times the actual rainfall, so that by
measuring it with a stick marked off in tenths of an inch, we
obtain the result in hundredths of an inch.

A good size to make the rain gauge is as follows: A, 8 in.
diameter; C, 2.53 in. ; length of C, about 20 in. It should be
placed in an exposed location, so that no inaccuracy will occur
from wind currents. To find the fall of snow, pour a known

[Illustration: Rain Gauge]

of warm water on the snow contained in the funnel and deduct the
quantity poured in from the total amount in the tube.
--Contributed by Thurston Hendrickson, Long Branch, N.J.

** How to Make an Aquarium [64]

In making an aquarium, the first thing to decide on is the size.
It is well not to attempt building a very large one, as the
difficulties increase with the size. A good size is 12 by 12 by 20
in., and this is inexpensive to build.

First buy one length of 3/4 by 1/8-in. angle iron for the frame,
F, Fig. 1. This can be obtained at any steel shop and should cost
about 20 cents. All the horizontal pieces, B, should be beveled 45
degrees at the ends and drilled for 3/16 in. stove bolts. The
beveling may be done by roughing out with a hacksaw and finishing
with a file. After all the pieces are cut and beveled they should
be drilled at the ends for the 3/16-in. stove bolts, C. Drill all
the horizontal pieces, B, first and then mark the holes on the
upright pieces, A, through the holes already drilled, thus making
all the holes coincide. Mark the ends of each piece with a figure
or letter, so that when they are assembled, the same ends will
come together again. The upright pieces, A, should be countersunk
as shown in the detail, and then the frame is ready to assemble.

After the frame has been assembled take it to glazier and have a
bottom made of skylight glass, and sides and ends of double-thick
window glass. The bottom glass should be a good fit, but the sides
and ends should be made slightly shorter to allow the cement, E,
to form a dovetail joint as shown. When the glass is put in the
frame a space, D, will be found between the glass and the
horizontal pieces, B, of the frame. If this were allowed to remain
the pressure of the water would spring the glass and cause a leak
at E; so it is filled up with plaster of paris.

The cement, E, is made as follows: Take 1 gill of plaster of
paris, 1 gill of litharge, 1 gill of fine white sand, and 1/3 of a
gill of finely powdered rosin. Mix well and add boiled linseed oil
and turpentine until as thick as putty. Let

[Illustration: Detail of Aquarium Frame]

the cement dry three or four days before putting any water in the

In choosing stock for the aquarium it should be remembered that a
sufficient quantity of vegetable life is required to furnish
oxygen for the fish. In a well balanced aquarium the water
requires renewal only two or three times a year. It is well to
have an excess of plants and a number of snails, as the snails
will devour all the decaying vegetable matter which would
otherwise poison the water and kill the fish.

[Illustration: Aquarium Finished]

If desired, a centerpiece (A, Fig. 2) can be made of colored
stones held together by cement, and an inverted jar can be
supported in the position shown at B. If the mouth of the jar is
below the surface of the water it will stay filled and allow the
fish to swim up inside as shown. Some washed pebbles or gravel
should be placed on the bottom, and, if desired, a few Chinese
lilies or other plants may be placed on the centerpiece.

** Homemade Pneumatic Lock [65]

Mount an old bicycle hand-pump, A, on the door by means of a metal
plate, B, having a swinging connection at C. Fasten the lever, D,
to the door knob, and make a hinge connection with the pump by
means of a piece of sheet

[Illustration: Pneumatic Door-Opener]

brass, E, soldered to the end of the cylinder. All this apparatus
is on the inside of the door and is connected by a small rubber
tube, F, to a secret mouthpiece placed at some convenient
location. A small piece of spring brass, screwed to the door
frame, will open the door about 1/2 in. when the operator blows in
the mouthpiece, or if the door is within reach of the mouthpiece,
the operator may push the door at the same time that he blows,
thus doing away with the spring, which is only used to keep the
door from relocking.

One way of making the air connection with the outside is to bend
the tube F around and stick it through the keyhole. Few burglars
would ever think to blow in the keyhole.
--Contributed by Orton E. White, Buffalo, N. Y.

** A Homemade Water Motor [66]

In these days of modern improvements, most houses are equipped
with a washing machine, and the question that arises in the mind
of the householder is how to furnish the power to run it
economically. I referred this question to my husband, with the
result that he built a motor which proved so very satisfactory
that I prevailed upon him to give the readers of Amateur Mechanics
a description of it, hoping it may solve the same question for

A motor of this type will develop about 1/2 hp. with a water
pressure of 70 lb. The power developed is correspondingly
increased or decreased as the pressure exceeds or falls below
this. In the latter case the power may be increased by using a
smaller pulley. Fig. 1 is the motor with one side removed, showing
the paddle-wheel in position; Fig. 2 is an end view; Fig. 3 shows
one of the paddles, and Fig. 4 shows the method of shaping the
paddles. To make the frame, several lengths of scantling 3 in.
wide by 1 in. thick (preferably of hard wood) are required. Cut
two of them 4 ft. long, to form the main supports of the frame,
AA, Fig. 1 ; another, 2 ft. 6 in. long, for the top, B, Fig. 1;
another, 26 in. long, to form the slanting part, C, Fig. 1; and
another, D, approximately 1 ft., according to the slant given C.
After nailing these together as shown in the illustration, nail
two short strips on each side of the outlet, as at E, to keep the
frame from spreading.

Cut two pieces 30 in. long. Lay these on the sides of the frame
with their center lines along the line FF, which is 15 in. from
the outside top of the frame. They are shown in Fig. 2 at GG. Do
not fasten these boards now, but mark their position on the frame.
Two short boards 1 in. wide

[Illustration: Detail of Homemade Waterwheel]

by 1 in. thick (HH, Fig. 2) and another 1 in. by 1-1/2 in. (I,
Fig. 2) form a substantial base.

Cut the wheel from sheet iron 1/16 in. thick, 24 in. in diameter.
This can be done roughly with hammer and chisel and then smoothed
up on an emery wheel, after which cut 24 radial slots 3/4 in. deep
on its circumference by means of a hacksaw. On each side of the
wheel at the center fasten a rectangular piece of 1/4-in. iron 3
by 4 in. and secure it to the wheel by means of four rivets; after
which drill a 5/8 in. hole through the exact center of the wheel.

Cut 24 pieces of 1/32-in. iron, 1-1/2 by 2-1/2 in. These are the
paddles. Shape them by placing one end over a section of 1-in.
pipe, and hammer bowl shaped with the peen of a hammer, as shown
in Fig. 4. Then cut them into the shape shown in Fig. 3 and bend
the tapered end in along the lines JJ, after which place them in
the slots of the wheel and bend the sides over to clamp the wheel.
Drill 1/8-in. holes through the wheel and sides of the paddles and
rivet paddles in place. Next secure a 5/8-in. steel shaft 12 in.
long to the wheel about 8 in. from one end by means of a key. This
is done by cutting a groove in the shaft and a corresponding
groove in the wheel and fitting in a piece of metal in order to
secure the wheel from turning independently of the shaft. Procure
two collars or round pieces of brass (KK, Fig. 2) with a 5/8-in.
hole through them, and fasten these to the shaft by means of set
screws to prevent it from moving lengthwise.

Make the nozzle by taking a piece of 1/2-in. galvanized pipe 3-1/2
in. long and filling it with babbitt metal; then drill a 3/16-in.
hole through its center. Make this hole conical, tapering from
3/16 in. to a full 1/2 in. This is best done by using a square
taper reamer. Then place the nozzle in the position shown in Fig.
1, which allows the stream of water to strike the buckets full in
the center when they reach the position farthest to the right.
Take the side pieces, GG, and drill a 1-in. hole through their
sides centrally, and a 1/4-in. hole from the tops to the 1-in.
holes. Fasten them in their proper position, with the wheel and
shaft in place, the shaft projecting through the holes just
mentioned. Now block the wheel; that is, fasten it by means of
wedges or blocks of wood until the shaft is exactly in the center
of the inch holes in the side pieces. Cut four disks of cardboard
to slip over the shaft and large enough to cover the inch holes.
Two of these are to be inside and two outside of the frames (one
to bear against each side of each crosspiece). Fasten these to the
crosspieces by means of tacks to hold them securely. Pour melted
babbitt metal into the 1/4-in. hole to form the bearings. When it
has cooled, remove the cardboard, take down the crosspieces, and
drill a 1/8-in. hole from the top of the crosspieces through the
babbitt for an oil-hole.

Secure sufficient sheet zinc to cover the sides of the frame. Cut
the zinc to the same shape as the frame and let it extend down to
the crosspieces EE. Tack one side on. (It is well to tack strips
of heavy cloth--burlap will do--along the edges under the zinc to
form a water-tight joint.) Fasten the crosspiece over the zinc in
its proper position. Drill a hole through the zinc, using the hole
in the crosspiece as a guide. Then put the wheel in a central
position in the frame, tack the other side piece of zinc in place
and put the other crosspiece in place. Place the two collars
mentioned before on the shaft, and fasten so as to bear against
the crosspieces, in order to prevent the wheel and shaft from
moving sidewise. If the bearings are now oiled, the shaft should
turn easily and smoothly. Fasten a pulley 4 or 6 in. in diameter
to the longest arm of the shaft.

Connect the nozzle to a water faucet by means of a piece of hose;
place the outlet over a drain, and belt the motor direct to the
washing-machine, sewing machine, ice-cream freezer, drill press,
dynamo or any other machinery requiring not more than 1/2 hp.

This motor has been in use in our house for two years in all of
the above ways, and has never once failed to give perfect
satisfaction. It is obvious that, had the wheel and paddles been
made of brass, it would be more durable, but as it would have cost
several times as much, it is a question whether it would be more
economical in the end. If sheet-iron is used, a coat of heavy
paint would prevent rust and therefore prolong the life of the
motor. The motor will soon pay for itself in the saving of laundry
bills. We used to spend $1 a month to have just my husband's
overalls done at the laundry, but now I put them in the machine,
start the motor, and leave them for an hour or so. At the end of
this time they are perfectly clean, and I have noticed that they
wear twice as long as when I sent them to the laundry.

** How to Make Silhouettes [68]

Photography in all branches is truly a most absorbing occupation.
Each of us who has a camera is constantly experimenting, and
everyone of us is delighted when something new is suggested for
such experiments.

[Illustration: Making a Silhouette with the Camera]

To use a camera in making silhouettes select a window facing north
if possible, or if used only at times when the sun is not on it,
any window will do, says the Photographic Times. Raise the window
shade half way, remove any white curtains there may be, and in the
center of the lower pane of glass paste by the four corners a
sheet of tissue paper that is perfectly smooth and quite thick, as
shown in the sketch at B. Darken the rest of the window, shutting
out all light from above and the sides. Place a chair so that
after being seated the head of the subject will come before the
center of the tissue paper, and as near to it as possible, and
when looking straight before him his face will be in clear profile
to the camera.

Draw the shades of all other windows in the room. Focus the camera
carefully, getting a sharp outline of the profile on the screen.
Do not stop down the lens, as this makes long exposure necessary,
and the subject may move. Correct exposure depends, of course, on
the lens, light and the plate. But remember that a black and white
negative is wanted with as little detail in the features as
possible. The best plate to use is a very slow one, or what is
called a process plate.

[Illustration: Sample Silhouette]

In developing get all possible density in the high lights, without
detail in the face, and without fog. Printing is best done on
contrasty development paper with developer not too strong.

The ideal silhouette print is a perfectly black profile on a white
ground. With a piece of black paper, any shape in stopping off
print may be made as shown at C in the sketch.

** How to Make a Galvanoscope [68]

A galvanoscope for detecting small currents of electricity can be
made from a coil of wire, A; a glass tube, B, full of water; a
core, C; and a base, D, with binding posts as shown. The core C,
which is made of iron and cork, is a trifle lighter than the water
it displaces and will therefore normally remain in the top of the
tube; but as soon as a current of electricity passes through the
coil, the core is drawn down out of sight. The current required is
very small, as the core is so nearly balanced that the least
attraction will cause it to sink.

The glass tube may be a test tube, as shown in Fig. 2, or an empty
developer tube. If one has neither a test tube nor developer tube,
an empty pill bottle may be used. The washers at the ends of the
coil can be made of fiber, hard rubber, or wood; or can be taken
from an old magnet. The base may be made of wood or any other
insulating material and should have four short legs on the bottom.
Make the coil of single-covered wire about No. 18 and connect ends
to binding posts as shown in Fig. 2.

The core is made by pushing a small nail through a piece of cork.
It should be made so that it will rise slowly when placed under
water. Some filing may be necessary to get the weight just right,
but it should be remembered that the buoyancy of the core can be
adjusted after the parts are assembled, by pressing the cork in
the bottom of the test tube. This causes compression in the water
so that some is forced into the upper cork, reducing its
displacement and causing it to sink. The lower cork is then slowly
withdrawn, by twisting, until the core slowly rises.

[Illustration: Galvanoscope]

The instrument will then be adjusted ready for use. Connect the
binding posts to a single cell of battery--any kind will do, as a
slight current will answer. On completing

[Illustration: Interior View]

the circuit the core will descend; or put in a switch or push
button on one of the battery wires. If the button be concealed
where the operator can reach it, the core will obey his command to
rise or fall, according to his control of the current. This is a
mysterious looking instrument, the core being moved without
visible connection to any other part.

** Lubricating Sheet Metal [69]

To lubricate sheet metal mix 1 qt. whale oil, 1 lb. white lead, 1
pt. water and 3 oz. finest graphite. Apply with a brush before the
metal enters the dies.

** An Optical Top [69]

One of the latest optical delusions, and one not easy to explain,
is Benham's color top. Cut out the black and white disk shown in
the figure, and paste on a piece of stiff cardboard. Trim the
edges of the cardboard to match the shape of the disk, and make a
pinhole in the center. Cut the pin in half and push it through
from the under side until the head of the pin touches the
cardboard. Spin slowly in a strong light and some of the lines
will appear colored. The colors appear different to different
people, and are changed by reversing the rotation.

[Illustration: An Optical Top]

** Card Trick with a Tapered Deck [70]

Another simple trick to perform but one not easily detected, is
executed by using a tapered deck of cards as shown in Fig. 1. A
cheap deck of cards is evened up square, fastened in a vise and
planed along the edge in such a manner that all the pack will be
tapered about 1/16 in. This taper is exaggerated in the
illustration which shows

[Illustration: Cards from a Tapered Deck]

one card that has been turned end for end.

It is evident that any card reversed in this way can be easily
separated from the other cards in the pack, which makes it
possible to perform the following trick: The performer spreads the
cards out, fan-like, and asks an observer to withdraw a card,
which is then replaced in any part of the pack. After thoroughly
shuffling the cards the performer then holds the deck in both
hands behind his back and pronouncing a few magic words, produces
the card selected in one hand and the rest of the pack in the
other. This is accomplished by simply turning the deck end for end
while the observer is looking at his card, thus bringing the wide
end of the selected card at the narrow end of the pack when it is
replaced. The hands are placed behind the pack for a double
purpose, as the feat then seems more marvelous and the observers
are not allowed to see how it is done.

In prize games, players having the same score are frequently
called upon to cut for low to determine which shall be the winner,
but a fairer way is to cut for high as a person familiar with the
trick shown in Fig. 2 can cut the cards at the ace, deuce, or
three spot, nearly every time, especially if the deck is a new
one. This is done by simply pressing on the top of the deck as
shown, before cutting, thus causing the increased ink surface of
the high cards to adhere to the adjacent ones. A little practice
will soon enable one to cut low nearly every time, but the cards
must be grasped lightly and the experiment should be performed
with a new deck to obtain successful results.
--Contributed by D.B.L., Chicago.

** A Constant-Pressure Hydrogen Generator [70]

By fitting three bottles, A, B, C, with rubber stoppers and
connecting with glass tubes as shown in the sketch, hydrogen or
other gases produced in a similar manner may be generated under
constant pressure. In making hydrogen, bottle B is partly filled
with zinc nodules formed by slowly pouring melted zinc into water.
Hydrochloric acid is then poured in the small funnel, thus partly
filling bottles A and C. When the acid rising from C comes in
contact with the zinc, hydrogen gas is generated and fills bottle
B. The gas continues to generate until the pressure is sufficient
to force the acid back down the tube into bottle C, when the
action ceases. As fast as the gas is used the acid rises in the
tube and generates more, thus keeping the pressure nearly
constant, the pressure depending on the difference between the
levels of the acid in bottle A and bottle B. As this device is
easily upset, a ring-stand should be used to prevent its being
broken, or if it is to be a permanent apparatus it may be mounted
on a substantial wooden base. This apparatus may also be used for
preparing acetylene gas or almost any gas which requires a mixture
of a solid and liquid in its preparation.
--Contributed by C. S. J., Detroit.

** Restoring Tone to a Cracked Bell [71]

Many a bell with a deadened tone due to a cracked rim, can be
given its original clear ringing sound by sawing out the crack
with a common hacksaw. Make the saw cut along the line of the
crack. The opening caused by the saw will allow the free vibration
of the metal.
--Contributed by F. W. Bently, Jr., Huron, S. Dak.

** How to Make a Paper Phonograph Horn [71]

Secure a piece of tubing about 1-3/4 in. long that will fit the
connection to the reproducer, and wrap a quantity of heavy thread
around one end as shown in the enlarged sketch A, Fig. 1. Form a
cone of heavy paper, 9 in. long and 3 in. in diameter, at the
larger end with the smaller end to fit the diameter of the tube A,
making it three-ply thick and gluing the layers together. Attach
this cone on the tube A where the thread has been wrapped with
glue, as shown in Fig. 2. Fig. 2 is also an enlarged sketch. Make
ten pieces about 1 ft. 10 in. in length and 3 in. wide from the
thin boards of a biscuit or cracker box. Cut an arc of a circle in
them on a radius of 2 ft. (Fig. 3). Make a 10-sided stick, 12 in.
long, that will fit loosely in the tube A, to which nail the 10
pieces as shown in Fig. 4, connecting the bottom by cross pieces,
using care to keep them at equal distances apart and in a circle
whose diameter is about 2 ft.

[Illustration: Detail of Phonograph Horn]

The cone is placed over the stick as shown by the dotted lines in
Fig. 4 and temporarily fastened in position. Cut out paper
sections (Fig. 5) that will cover each space between the 10
pieces, allowing 1 in. on one side and the top, in which to cut
slits that will form pieces to overlap the next section and to
attach with glue. Fasten the sections all around in like manner.
The next course is put on in strips overlapping as shown at B,
Fig. 6. Finish by putting on sections in the same way as the first
course, making it three-ply thick. Remove the form, trim to suit
and glue a piece of paper over the edge. When the glue is
thoroughly hardened, put on two coats of white and one of blue
paint, shading it to suit and striping it with gold bronze.

** How to Make a Hygrometer [71]

A homemade hygrometer, for determining the degree of moisture in
the atmosphere, is shown in the accompanying sketch and consists
of a board, A, with a nail at each end to hold the silk thread B.
A second piece of silk thread, C, is tied to the center of B and
connects with an indicating hand or pointer supported by the
bracket D. The axle on which the pointer revolves consists of a
piece of round wood, about the size of a lead-pencil, with a pin
driven in each end. A piece of tin, E, is cut V-shaped at each end
and bent up at the ends to form bearings for the pins. The silk
thread C is fastened to the wooden axle and is wrapped one or two
turns around it, so that when

[Illustration: The Hygrometer]

the thread is pulled the pointer will move on the scale. It will
be noticed that the thread B is not perfectly straight, but bends
toward D. For this reason a very small shrinkage of B, such as
occurs when the atmosphere is dry, will cause an increased
movement of C, which will be further increased in the movement of
the pointer. An instrument of this kind is very interesting and
costs nothing to make.
--Contributed by Reader, Denver.

** The Protection of a Spring Lock [72]

After shutting the front door and hearing the spring lock snap
into its socket, most people go off with a childlike faith in the
safety of their goods and chattels. But the cold fact is that
there is scarcely any locking device which affords less protection
than the ordinary spring lock. It is the simplest thing in the
world for a sneak thief to slip a thin knife between the
door-casing and the strip, push back the bolt, and walk in.

Fortunately, it is equally easy to block that trick. Take a narrow
piece of tin 3 or 4 in. long, bend it at right angles throughout
its length, and tack it firmly in the angle between the casing and
strip, so as to make it impossible to reach the bolt without
tearing off the strip.

Another way is to drive nails through the strip at intervals of
half an inch, enough to protect the bolt from being meddled with.

** A Controller and Reverse for a Battery Motor [72]

Secure a cigar or starch box and use to make the base, B. Two
wood-base switches, S S, are cut off a little past the center and
fastened to the base with a piece of wood between them. The upper
switch, S, is connected to different equal points on a coil of
wire, W, while the lower switch, S, is connected each point to a
battery, as shown. The reverse switch, R, is made from two brass
or copper strips fastened at the top to the base with screws and
joined together by a piece of hard rubber or wood with a small
handle attached. Connect wires A to the armature and wires F to
the field of the motor. By this arrangement one, two or three and
so on up until all the battery cells are used and different points
of resistance secured on the coil of wire. The reverse lever when
moved from right to left, or left to right, changes the direction
of the armature in the motor from one way to the other.
--Contributed by J. Fremont Hilscher, Jr., West St. Paul, Minn.

[Illustration: Motor Reverse and Controller]

** How to Build a Grape Arbor [73]

A grape arbor made of white pine, put together as shown in the
sketch, will last for several years. The 2 by

[Illustration: Grape-Arbor Trellis]

4-in. posts, A, are 7 ft. long. The feet, B, are made 2 by 4 in.,
4 ft. long, and rest on a brick placed under each end.

** How to Make a Toy Steam Engine [73]

A toy engine can be easily made from old implements which can be
found in nearly every house.

[Illustration: Toy Steam Engine Assembled]

The cylinder A, Fig. 1, is an old bicycle pump, cut in half. The
steam chest D, is part of the piston tube of the same pump, the
other parts being used for the bearing B, and the crank bearing C.
The flywheel Q can be any small-sized iron wheel; either an old
sewing-machine wheel, pulley wheel, or anything available. We used
a wheel from an old high chair for our engine. If the bore in the
wheel is too large for the shaft, it may be bushed with a piece of
hard wood. The shaft is made of heavy steel wire, the size of the
hole in the bearing B.

[Illustration: Valve Motion and Construction of Piston]

The base is made of wood, and has two wood blocks, H and K, 3/8
in. thick, to support bearing B, and valve crank S, which is made
of tin. The hose E connects to the boiler, which will be described
later. The clips FF are soldered to the cylinder and nailed to the
base, and the bearing B is fastened by staples.

The valve motion is shown in Figs. 2 and 3. In Fig. 2 the steam is
entering the cylinder, and in Fig. 3 the valve B has closed the
steam inlet and opened the exhaust, thus allowing the steam in the
cylinder to escape.

The piston is made of a stove bolt, E, Fig. 2, with two washers,
FF, and a cylindrical piece of hard wood, G. This is wound with
soft string, as shown in Fig. 3, and saturated with thick oil. A
slot is cut in the end of the bolt E, to receive the connecting
rod H. The valve B is made of an old bicycle spoke, C, with the
nut cut in half and filed down as shown, the space between the two
halves being filled with string and oiled.

The valve crank S, Fig. 1, is cut out of tin, or galvanized iron,
and is moved by a small crank on the shaft. This crank should be
at right angles to the main crank.

[Illustration: Engine in Operation]

The boiler, Fig. 4, can be an old oil can, powder can, or a syrup
can with a tube soldered to it, and is connected to the engine by
a piece of rubber tubing. The heat from a small gas stove will
furnish steam fast enough to run the engine at high speed. This
engine was built by W. G. Schuh and A. J. Eustice, of Cuba, Wis.

** Writing with Electricity [74]

Soak a piece of white paper in a solution of potassium iodide and
water for about a minute and then lay it on a piece of sheet
metal. Connect the sheet metal with the negative or zinc side of a
battery and then, using the positive wire as a pen, write your
name or other inscription on the wet paper.

[Illustration: Electrolytic Writing]

The result will be brown lines on a white background.
--Contributed by Geo. W. Fry, San Jose, Cal.

** To Photograph a Man in a Bottle [74]

Neither a huge bottle nor a dwarfed man is necessary for this
process, as it is merely a trick of photography, and a very
amusing trick, at that.

First, photograph the person to be enclosed in the bottle against
a dark plain background and mark the exact position on the ground
glass. Let the exposure be just long enough to show the figure
distinctly. Then place an empty bottle against a dark background
and focus so as to have the outlines of the bottle enclose those
of the man. Let this exposure be about twice the length of the
first, and the desired result is obtained.

** A Musical Windmill [74]

Make two wheels out of tin. They may be of any size, but wheel A
must be larger than wheel B. On wheel A fasten two pieces of wood,
C, to cross in the center, and place a bell on the four ends, as
shown. The smaller wheel, B, must be separated from the other with
a round piece of wood or an old spool. Tie four buttons with split
rings to the smaller wheel, B. The blades on the wheels should be
bent opposite on one wheel from the others so as to make the
wheels turn in different directions. When turning, the buttons
will strike the bells and make them ring constantly.

[Illustration: Musical Windmill]

** Optical Illusions [74]

By giving the page a revolving or rinsing motion the three
circular figures printed on the next page appear to rotate. The
best effect will be produced by laying the book down flat on the
desk or table and revolving, first

[Illustration: Move These Figures Rapidly with a Rinsing Motion]

in one direction and then in the opposite direction, in such a way
that any given point on the page will describe a circle of about
1/2 in. diameter. Fig. 1 then appears to rotate in the same
direction as the revolution; Fig. 2 appears to revolve in the
opposite direction, and Fig. 3 appears to revolve sometimes in the
same direction and at other times in the opposite direction.

A curious effect can be produced with Fig. 1 by covering up Figs.
2 and 3 with a piece of plain paper and laying a coin or other
small object on the paper. If the vision is then concentrated on
the coin or other object while same is being revolved, Fig. 1 will
be seen to rotate.

** Barrel-Stave Hammock [75]

A hammock made of barrel staves is more comfortable than one would
think, considering the nature of the material employed in making
it. Good smooth staves should be selected for this purpose, and if
one cares to go to little trouble a thorough sandpapering will
make a great improvement. Cut half circles out of each stave, as
shown at AA, and pass ropes around

[Illustration: Cheap and Comfortable]

the ends as shown at B. When finished the weight will then be
supported by four ropes at each end, which allows the use of small
sized ropes, such as clothes lines. A hammock of this kind may be
left out in the rain without injury.
--Contributed by H.G.M., St. Louis, Mo.

** A Singing Telephone [75]

Those who have not already tried the experiment may be interested
to know that a telephone may be made to sing by holding the
receiver about 1/16 in. from the transmitter, as shown in the
illustration. The experiment will

[Illustration: To Make a Telephone Sing]

work well on most telephones, but not on all.

When the receiver is placed in the position shown it acts like an
ordinary buzzer, and the function of the transmitter will then be
that of an interrupter. The slightest movement of the transmitter
diaphragm will cause an increased movement of the receiver
diaphragm. This in turn will act on the transmitter, thus setting
up sympathetic vibrations between the two, which accounts for the

** A Microscope Without a Lens [76]

Nearly everyone has heard of the pin-hole camera, but the fact
that the same principle can be used to make a microscope, having a
magnifying power of 8 diameters (64 times) will perhaps be new to
some readers. To make this lensless microscope, procure a wooden
spool, A (a short spool, say 1/2 or 3/4 in. long, produces a
higher magnifying power), and enlarge the bore a little at one
end. Then blacken the inside with india ink and allow to dry. From
a piece of thin

[Illustration: Detail of Lensless Microscope]

transparent celluloid or mica, cut out a small disk, B, and fasten
to the end having the enlarged bore, by means of brads. On the
other end glue a piece of thin black cardboard, C, and at the
center, D, make a small hole with the point of a fine needle. It
is very important that the hole D should be very small, otherwise
the image will be blurred.

To use this microscope, place a small object on the transparent
disk, which may be moistened to make the object adhere, and look
through the hole D. It is necessary to have a strong light to get
good results and, as in all microscopes of any power, the object
should be of a transparent nature.

The principle on which this instrument works is illustrated in
Fig. 2. The apparent diameter of an object is inversely
proportional to its distance from the eye, i. e., if the distance
is reduced to one-half, the diameter will appear twice as large;
if the distance is reduced to one-third, the diameter will appear
three times as large, and so on. As the nearest distance at which
the average person can see an object clearly is about 6 in., it
follows that the diameter of an object 3/4 in. from the eye would
appear 8 times the normal size. The object would then be magnified
8 diameters, or 64 times. (The area would appear 64 times as
large.) But an object 3/4-in. from the eye appears so blurred that
none of the details are discernible, and it is for this reason
that the pin-hole is employed.

Viewed through this microscope, a fly's wing appears as large as a
person's hand, held at arm's length, and has the general
appearance shown in Fig. 3. The mother of vinegar examined in the
same way is seen to be swarming with a mass of wriggling little
worms, and may possibly cause the observer to abstain from all
salads forever after. An innocent-looking drop of water, in which
hay has been soaking for several days, reveals hundreds of little
infusoria, darting across the field in every direction. These and
hundreds of other interesting objects may be observed in this
little instrument, which costs little or nothing to make.

** How to Make a Telegraph Key and Sounder [76]

The sounder, Fig. 1, is made from an old electric-bell magnet, D,
fastened to a wooden base. The lever, A, can be made of brass and
the armature, C, is made of iron. The pivot, E, is made from a
wire nail and is soldered to A. It should be filed to a point at
each end so as to move freely in the bearings, B, which are pieces
of hard wood. The spring, H, is fastened at each end by pins, bent
as shown, and should not be too strong or the magnet will be
unable to move the armature.

[Illustration: SOUNDER-A. brass: B. wood: C. soft iron; DD. coils
wound with No. 26 wire: E. nail soldered on A; FF. binding posts:
H spring]

The stop, K, is a wire nail driven deep enough in the base to
leave about 1/8 in. between the armature and the magnet. The
binding posts, F, may be taken from old dry batteries and are
connected to the two wires from the magnet by wires run in grooves
cut in the base.

The base of the key, Fig. 2, is also made of wood and has two
wooden bearings, E, which are made to receive a pivot, similar to
the one used in the sounder. The lever of the key is made of brass
and has a hardwood knob, A, fastened near the end. A switch, D,
connects with the pivot at F and can be either made from sheet
brass, or taken from a small one-point switch. The binding posts
are like those of the sounder, and are connected to the contacts,
K, by wires run in grooves cut in the wood.

[Illustration: KEY-A. wood; B. brass or iron soldered to nail; C.
brass; D. brass: E. wood: F. connection of D to nail; HH. binding

** How to Make a Music Cabinet [77]

A neat music cabinet can be made as shown in the accompanying
sketch. Each side, AA, Fig. 1, is cut from a board about 36 in. in
length and 16 in. wide. Both are alike and can be cut from the
same pattern. As the front legs curve out a little the main body
of the boards AA should be 15 in. wide. The back, B, should be
about 22 in. long by 16 in. wide and set in between sides AA. Cut
the top, C, 16 in. long and 14-1/2 in. wide. The bottom must be
the same length as the top and 13-1/2 in. wide.

The door, D, can be made panel as shown, or a single piece, 16 in.
wide and about 20 in. long. All material used is to be made from
boards that will dress to 3/4 in. thick.

[Illustration: How to Make a Music Cabinet]

Shelving may be put in as shown in Fig. 2 and made from 1/4-in.
material. Make 12 cleats, E, 13-1/2 in. long, from a strip of wood
1/2 by 3/4 in., with a groove 1/4 by 1/4 in. cut in them. Fasten 6
cleats evenly spaced on the inside of each of the sides, AA, with
3/4-in. brads. This will give seven spaces for music and as the
shelves are removable two places can be made into one.

** Easily Made Wireless Coherer [77]

A good wireless coherer may be made with very little expense, the
only materials necessary being a glass tube, two corks: a
magnetized needle and a quantity of iron and silver filings. Push
a piece of wire through one cork and place in the bottom of the
tube, as shown in the sketch.

Pour in the filings and insert the top cork with the needle pushed

[Illustration: Detail of Coherer]

from above. The point of the needle should barely touch the
filings and by slightly agitating the tube the iron filings will
separate from the silver and cling to the magnetized needle, as

In operation, the device must stand on end and should be connected
in the circuit as shown in the sketch. When the electrical waves
strike the needle, the conductivity of the filings is established
and a click is heard in the receiver.
--Contributed by Carl Formhals, Garfield, Ill.

** One-Wire Telegraph Line [78]

The accompanying wiring diagram shows a telegraph system that
requires no switches and may be operated with open-circuit
batteries on a one-wire

[Illustration: Diagram of One-Wire Line]

line with ground connections at each end. Any telegraph set in
which the key makes double contact can be connected up in this
--Contributed by R. A. Brown, Fairport, N. Y.

** How to Make a Water Rheostat [78]

A water rheostat may be made by fitting a brass tube with a cork,
through which a piece of wire is passed. The brass tube may be an
old bicycle hand pump, A (see sketch), filled with water. Pushing
the wire, B, down into the water increases the surface in contact,
and thus decreases the resistance. An apparatus of this kind is
suitable for regulating the current from an induction coil, when
the coil is not provided with a regulator, and by using a piece of
pipe instead of the tube, it can be used to regulate the speed of
a motor.

When the pipe is used, a piece of brass or copper rod should be
substituted for the wire, in order to increase the surface. Adding
salt to the water will decrease the resistance, and, when used
with a motor, will give a greater speed.
--Contributed by John Koehler, Ridgewood, N. J.

[Illustration: Diagram of One-Wire Line Water Rheostat]

** Electric Door-Opener [78]

A very convenient and efficient device for unlocking any door
fitted with a spring lock is shown in the accompanying sketches. A
fairly stiff spring, A, is connected by a flexible wire cord to
the knob B. The cord is also fastened to a lever, C, which is
pivoted at D and is released by a magnetic trigger, E, made from
the armature and magnet of an old electric bell.

When the circuit is completed by means of a secret contact device
outside the door, the magnet, F, pulls down the armature, which
releases the trigger and allows the spring to open the lock. If
there are metal numbers on the outside of the door they may be
used for the secret contact, if desired,

[Illustration: Apparatus Placed on Inside of Door]

but if there are no numbers on the door, a small contact-board may
be constructed by driving about 12 brass headed tacks into a thin
piece of wood and making connections at the back as shown in the
wiring diagram.

In this particular diagram the tacks numbered 1 and 7 are used for
unlocking the door, the others being connected with the
electric-bell circuit as indicated, for the purpose of giving an
alarm should anybody try to experiment with the secret contacts.
By means of a pocket knife or other metal article the operator can
let himself in at any time by connecting the tacks numbered 1 and
7, while a person not knowing the combination would be liable to
sound the alarm. Of course, the builder of this device may choose
a combination of his own and may thus prevent anybody else from
entering the door, even those who read this description.
--Contributed by Perry A. Borden, Gachville, N. B.

[Illustration: Wiring Diagram]

** How to Tighten a Curtain-Roller Spring [79]

A common table fork can be used to hold the little projection on
the end of a curtain roller for tightening the spring. Hold the
fork firmly with one hand while turning the roller with the other.
Do not let go of the fork until the little catches are set in
position to prevent the spring from turning, or else the fork may
be thrown off with dangerous force.

** Alarm Clock Chicken Feeder [79]

An automatic poultry feeder, which will discharge the necessary
amount of corn or other feed at any desired time, may be made by
using an alarm clock as shown in the sketch. A small wire trigger
rests on the winding key and supports the swinging bottom of the
food hopper by means of a piece of string which connects the two.
When the alarm goes off the trigger drops and allows the door to
open, thus discharging the contents of the hopper.

After the device has been in operation for some time the hens will
run to the feeder whenever the. bell rings.
--Contributed by Dr. H. A. Dobson, Washington, D. C.

[Illustration: Will Open or Close Circuit as Desired]

** Homemade Disk-Record Cabinet [79]

Select some boards that have a nice grain and about 1 in. thick
and 12-in. wide. Cut the end pieces each 36-in. long and trim down
the edges so as to make them 11-3/8 in. wide. The top board is
made 28-in. long and full 12-in. wide. The three shelves are cut
25-in. long and the edges trimmed so they will be 11-3/8 in. wide.
The distance between the bottom of the top board and the top of
the first shelf should be 3 in. Two drawers are fitted in this
space, as shown in Fig. 1. A series of grooves are cut 1/4 in.

[Illustration: Cabinet Holding 32 Records]

1/4 in. deep and 3/4 in. apart on one side of the top and bottom
shelves, as shown in Fig. 2, and on both sides of the middle
shelf. The shelves should be spaced 9-5/8 in. for 10-in. records
and 5-5/8 in. for 6-in. records. A neat scroll design is cut from
a board 25 in. long to fill up and finish the space below the
bottom shelf.
--Contributed by H. E. Mangold, Compton, Cal.

** A Battery Rheostat [80]

In a board 7 in. long and 5 in. wide bore holes about 1/4 in.
apart, in a semicircle 2 in. from the bottom, and cut notches in
top end to correspond with the holes. From a piece of brass a
switch, C, is cut with a knob soldered on at the end. Nails for
stops are placed at DD. Two binding-posts are placed in board at A
and B. With about 9 ft. of fine iron wire attach one end to the
bottom of post A and run through first hole and over in first
notch to back of board and then through second hole and over
second notch and so on until E is reached, where the other end of
wire is fastened. Connect switch to post B.
--Contributed by Edmund Kuhn, Jr., East Orange, N. J.

[Illustration: Battery Rheostat]

** Automatic Time Switch [80]

This device may be used to either open or close the circuit at any
desired time. An alarm clock is firmly fastened to a wooden
bracket and provided with a small wood or metal drum, A, to which
is fastened a cord, B. The other end of the cord is tied to the
switch handle so that when the alarm goes off the switch is either
opened or closed, depending on whether the cord is passed over
pulley C or pulley D.

When the cord is passed over pulley C, as shown in Fig. 1, the
circuit will be closed when the alarm goes off, but if it is
passed over D the circuit will be opened. Pulley D is fastened to
a piece of spring steel, E, which in operation is bent, as shown
by the dotted lines, thus causing the switch to snap open quickly
and prevent forming an arc.
--Contributed by Douglas Royer, Roanoke, Va.

[Illustration: Will Open or Close Circuit as Desired]

** How to Make a Rotary Pump [81]

[Illustration: Details of Rotary Pump]

A simple rotary pump is constructed on the principle of creating a
vacuum in a rubber tube and so causing water to rise to fill the
vacuum. Figs. 3, 4 and 5 show all the parts needed, excepting the
crank and tubing. The dimensions and description given are for a
minimum pump, but a larger one could be built in proportion.

Through the center of a block of wood 4 in. square and 7/8 in.
thick (A, Figs. 1, 2 and 3) saw a circular opening 2-7/8 in. in
diameter. On each side of this block cut a larger circle 3-1/4 in.
in diameter, having the same center as the first circle (Fig. 3).
Cut the last circles only 1/4 in. deep, leaving the first circle
in the form of a ridge or track 3/8 in. wide, against which the
rubber tubing, E, is compressed by wheels. Bore two 1/4 in. holes
(HH, Fig. 1) from the outside of the block to the edge of the
inner circle. Put the rubber tube, E, through one of these holes,
pass it around the track and out through the other hole. Notice
the break (S) in the track; this is necessary in order to place in
position the piece holding the wheels.

Fig. 4 shows the wheel-holder, B. Make it of hard wood 3-1/8 in.
long, 1 in. wide and a little less than 7/8 in. thick, so that it
will run freely between the sides (Fig. 5) when they are placed.
Cut two grooves, one in each end, 1 in. deep and 1/2 in. wide. In
these grooves place wheels, CC, to turn on pins of stout wire.
These wheels should be 3/4 in. in diameter. When placed in the
holder their centers must be exactly 2 in. apart, or so arranged
that the distance between the edge of the wheels and the track (K,
Fig. 1) is equal to the thickness of the tubing when pressed flat.
If the wheels fit too tightly, they will bind; it too loose, they
will let the air through. Bore a hole through the middle of the
wheel-holder and insert the crankpin, D, which should be about 1/2
in. in diameter. The crankpin should fit tightly; if necessary
drive a brad through to keep it from slipping.

In the sides (Fig. 5) bore a hole in the center of the crankpin to
run in loosely. Now put all these parts together, as shown in the
illustration. Do not fasten the sides too securely until you have
tried the device and are sure it will run smoothly. For the crank
a bent piece of stout wire or a nail will serve, though a small
iron wheel is better, as it gives steadiness to the motion. In
this case a handle must be attached to the rim of the wheel to
serve as a crank. The drive wheel from a broken-down eggbeater
will do nicely. For ease in handling the pump, a platform should
be added.

To use the pump, fill the tube with water and place the lower end
of the tube in a reservoir of water. Make a nozzle of the end of a
clay pipe stem for the other end of the tube. Then turn the crank
from left to right. The first wheel presses the air out of the
tube, creating a vacuum which is immediately filled with water.
Before the first wheel releases the tube at the top, the other
wheel has reached the bottom, this time pressing along the water
that was brought up by the first wheel. If the motion of the
wheels is regular, the pump will give a steady stream. Two feet of
1/4-in. tubing, costing 10 cents, is all the expense necessary.
--Contributed by Dan H. Hubbard, Idana, Kan.

** How to Make a Fire Screen [82]

[Illustration: FIG.2 Made of Strap Iron]

A screen which will not interfere with the radiation of the heat
from the fire, and will keep skirts and children safe can be made
at little expense out of some strap iron. The screen which is
shown in Fig. 1, stands 20 in. high from the base to the top
crosspiece and is made of 3/4 by 1/4-in. and 1/2 by 1/4-in. iron.
The top and bottom pieces marked AA, Fig. 1, are 3/4 by 1/4 in.
and are 30 in. long, bent at an angle to fit the fireplace 7 in.
from each end, as shown in Fig. 2. The three legs marked BBB, Fig.
1, are of the same size iron and each leg will take 34 in. of
material. In shaping the feet of these three pieces give them a
slight tendency to lean toward the fire or inside of screen, says
a correspondent in the Blacksmith and Wheelwright. In the two
cross bars 1 in. from each end, A in Fig. 2, mark for hole and 3
in. from that mark the next hole. Take the center of the bar, B,
15 in. from each end, and mark for a hole, and 3-1/2 in. on each
side mark again and 3-1/2 in. beyond each of these two, mark

Mark the legs 2-3/4 in. from the bottom and 2 in. from the top and
after making rivet-holes rivet them to the cross bars, AA, Fig. 1.

Cut six pieces, 17-1/2 in. long and punch holes to fit and rivet
onto the remaining holes in cross bars, AA, Fig. 1. Clean it up
and give it a coat of black Japan or dead black.

** Trap for Small Animals [82]

This is a box trap with glass sides and back, the panes of glass
being held in place by brads placed on both sides. The animal does
not fear to enter the box, because he can see through it: when he
enters, however, and touches the bait the lid is released and,
dropping, shuts him in. This is one of the easiest traps to build
and is usually successful.

[Illustration: Trap]

** Homemade Grenet Battery [83]

Procure an ordinary carbon-zinc, sal-ammoniac battery and remove
the zinc rod. If the battery has been used before, it is better to
soak the carbon cylinder for a few hours to remove any remaining
crystals of sal-ammoniac from its pores.

The truncated, conical zinc required is known as a fuller's zinc
and can be bought at any electrical supply dealer's, or, it may be
cast in a sand mold from scrap zinc or the worn-out zinc rods from
sal-ammoniac batteries. It should be cast on the end of a piece of
No. 14 copper wire. Amalgamation is not necessary for the zinc one
buys, but if one casts his own zinc, it is necessary to amalgamate
it or coat it with mercury. This may be done as follows:

Dip a piece of rag in a diluted solution of sulphuric acid (water
16 parts, acid 1 part); rub the zinc well, at the same time
allowing a few drops of mercury to fall on a spot attacked by the
acid. The mercury will adhere, and if the rubbing is continued so
as to spread the mercury, it will cover the entire surface of the
zinc, giving it a bright, silvery appearance.

Next procure what is known as a wire connector. This is a piece of
copper tube about 1-1/2 in. long having two thumb screws, one on
each end on opposite sides (Fig. 2). The upper screw is to connect
the battery wire, the lower one to raise and lower the zinc. The
battery is now complete, and the solution (Fig. 1) must be
prepared. Proceed as follows:

In 32 oz. of water dissolve 4 oz. potassium bichromate. When the
bichromate has all dissolved, add slowly, stirring constantly, 4
oz. sulphuric acid. Do not add the acid too quickly or the heat
generated may break the vessel containing the solution. Then pour
the solution into the battery jar, until it is within 3 in. of the
top. Thread the wire holding the zinc through the porcelain
insulator of the carbon cylinder and also through the wire
connector. Pull the zinc up as far as it will go and tighten the
lower thumb screw so that it holds the wire secure. Place the
carbon in the jar. If the solution touches the zinc, some of it
should be poured out. To determine whether or not the zinc is
touched by the solution, take out the carbon and lower the zinc.
If it is wet, there is too much liquid in the jar. The battery is
now ready for use.

To cause a flow of electricity, lower the zinc until it almost
touches the bottom of the jar and connect an electric bell or
other electrical apparatus by means of wires to the two binding

This battery when first set up gives a current of about two volts.
It is useful for running induction coils, or small electric
motors. When through using the battery, raise the zinc and tighten
the lower thumb screw. This prevents the zinc wasting away when no
current is being used.
--Contributed by H. C. Meyer, Philadelphia.

[Illustration: Fig.1 Details of Homemade Battery]

** Door-Opener for Furnace [83]

The accompanying diagram shows an arrangement to open the coal
door of a furnace. When approaching the furnace with a shovelful
of coal it is usually necessary to rest the shovel on the top of
the ash door, while the coal door is being opened. With my device
it is only necessary to press the foot pedal, which opens the
door. After putting in the coal, pressing the pedal closes the
door. The pulley in the ceiling must be placed a little in front
of the door, in order to throw the door open after lifting it from
the catch. A large gate hinge is used to hold the pedal to the
--Contributed by Edward Whitney, Madison, Wis.

[Illustration: Furnace Door Opener]

** How to Make an Efficient Wireless Telegraph [84]

A simple but very efficient wireless telegraph may be constructed
at slight cost from the following description:

The sending apparatus consists of nothing but an induction coil
with a telegraph key inserted in the primary circuit, i. e., the
battery circuit. This apparatus may be purchased from any
electrical-supply house. The price of the coil depends upon its
size, and upon the size depends the distance signals can be
transmitted. If, however, one wishes to construct his own coil he
can make and use, with slight changes, the jump-spark coil
described elsewhere in this book. This coil, being a 1-in. coil,
will transmit nicely up to a distance of one mile; while a 12-in.
coil made on the same plan will transmit 20 miles or even more
under favorable conditions.

Change the coil described, as follows: Insert an ordinary
telegraph key in the battery circuit, and attach two small pieces
of wire with a brass ball on each, by inserting them in the
binding-posts of the coil as shown at B B". Of these two terminal
wires one is grounded to earth, while the other wire is sent aloft
and is called the aerial line. This constitutes all there is to
the sending apparatus.

Now for the receiving apparatus. In the earlier receiving
instruments a coherer was used, consisting of a glass tube about
1/8-in. diameter, in which were two silver pistons separated by
nickel and silver filings, in a partial vacuum. This receiver was
difficult of adjustment and slow in transmission. An instrument
much less complicated and inexpensive and which will work well can
be made thus:

Take a 5-cp. incandescent lamp and break off the tip at the dotted
line, as shown in Fig. 5. This can be done by giving the glass tip
or point a quick blow with a file or other thin edged piece of
metal. Then with a blow-torch heat the broken edges until red hot
and turn the edges in as seen in Fig. 6. Remove the carbon
filament in the lamp and bend the two small platinum wires so they
will point at each other as in Fig. 6, W W. Screw the lamp into an
ordinary wall socket which will serve as a base as in Fig. 7. Make
a solution of 1 part sulphuric acid to 4 parts of water, and fill
the lamp about two-thirds full (Fig. 7). This will make an
excellent receiver. It will be necessary to adjust the platinum
points, W W, to suit the distance the message is to be worked. For
a mile or less the points should be about 1/16 in. apart, and
closer for longer distances.

The tuning coil is simply a variable choking coil, made of No. 14
insulated copper wire wound on an iron core, as shown in Fig. 7.
After winding, carefully scrape the insulation from one side of
the coil, in a straight line from top to bottom, the full length
of the coil, uncovering just enough to allow a

[Illustration: Aerial]

good contact for the sliding piece. The tuning is done by sliding
the contact piece, which is made of light copper wire, along the
convolutions of the tuning coil until you can hear the signals.
The signals are heard in a telephone receiver, which is shown
connected in shunt across the binding posts of the lamp holder
with one or two cells of dry battery in circuit, Fig. 7.

[Illustration: Details]

The aerial line, No.6 stranded, is run from binding-post B through
the choking or tuning coil, and for best results should extend up
50 ft. in the air. To work a 20-mile distance the line should be
100 or 150 ft. above the ground. A good way is to erect a wooden
pole on a house or barn and carry the aerial wire to the top and
out to the end of a gaff or arm.

To the end of the aerial wire fasten a bunch of endless loops made
of about No. 14 magnet wire (bare or insulated), attaching both
ends to the leading or aerial wire. The aerial wire should not
come nearer than 1 ft. at any point to any metal which is

Run a wire from the other binding post, A, to the ground and be
sure to make a good ground connection.

For simple experimental work on distances of 100 ft. only, an
ordinary automobile spark coil can be used in place of the more
elaborate coil, Figs. 1 to 4.

The above-mentioned instruments have no patents on them, and
anyone is at liberty to build and use them. The writer does not
claim to be the originator, but simply illustrates the above to
show that, after all, wireless is very simple when it is once
understood. The fundamental principles are that induction travels
at right angles, 90 degrees, to the direction of the current. For
an illustration, if a person standing on a bridge should drop a
pebble into the water below, after contact he would note circles
radiating out over the surface of the water. These circles, being
at right angles, 90 degrees, to the direction of the force that
caused the circles, are analogous to the flow of induction, and
hence the aerial line, being vertical, transmits signals
horizontally over the earth's surface.

** Beeswax for Wood Filler [85]

When filling nail holes in yellow pine use beeswax instead of
putty, as it matches the color well.

** How to Make a Lathe [86]

A small speed-lathe, suitable for turning wood or small metal
articles, may be easily made at very little expense. A lathe of
this kind is shown in the cut (Fig. 1), where A is the headstock,
B the bed and C the tailstock. I run my lathe by power, using an
electric motor and countershaft, but it could be run by foot power
if desired. A large cone pulley would then be required, but this
may be made in the same manner as the small one, which will be
described later.

[Illustration: Assembled Lathe Bed and Bearing Details]

The bed of the machine is made of wood as shown in Figs. 2 and 3,
hardwood being preferable for this purpose. Fig. 2 shows an end
view of the assembled bed, and Fig. 3 shows how the ends are cut
out to receive the side pieces.

The headstock, Fig. 6, is fastened to the bed by means of carriage
bolts, A, which pass through a piece of wood, B, on the under side
of the bed. The shaft is made of 3/4-in. steel tubing about 1/8
in. thick, and runs in babbitt bearings, one of which is shown in
Fig. 5.

To make these bearings, cut a square hole in the wood as shown,
making half of the square in each half of the bearing. Separate
the two halves of the bearing slightly by placing a piece of
cardboard on each side, just touching the shaft. The edges which
touch the shaft should be notched like the teeth of a saw, so as
to allow the babbitt to run into the lower half of the bearing.
The notches for this purpose may be about 1/8 in. pitch and 1/8
in. deep. Place pieces of wood against the ends of the bearing as
shown at A and B, Fig. 4, and drill a hole in the top of the
bearing as shown in Fig. 4.

The bearing is then ready to be poured. Heat the babbitt well, but
not hot enough to burn it, and it is well to have the shaft hot,
too, so that the babbitt will not be chilled when it strikes the
shaft. If the shaft is thoroughly chalked or smoked the babbitt
will not stick to it. After pouring, remove the shaft and split
the bearing with a round, tapered wooden pin. If the bearing has
been properly made, it will split along the line of the notched
cardboard where the section of the metal is smallest. Then drill a
hole in the top as shown at A, Fig. 5, drilling just deep enough
to have the point of the drill appear at the lower side. This
cavity acts as an oil cup and prevents the bearing from running

The bolts B (Fig. 5) are passed through holes in the wood and
screwed into nuts C, which are let into holes

[Illustration: FIG. 6 Headstock Details]

D, the holes afterward being filled with melted lead.

This type of bearing will be found very satisfactory and may be
used to advantage on other machines. After the bearings are
completed the cone pulley can be placed on the shaft. To make this
pulley cut three circular pieces of wood to the dimensions given
in Fig. 6 and fasten these together with nails and glue. If not
perfectly true, they may be turned up after assembling, by rigging
up a temporary toolrest in front of the headstock.

The tail stock (Fig. 7) is fastened to the bed in the same manner
as the headstock, except that thumb nuts are used on the carriage
bolts, thus allowing the tail stock to be shifted when necessary.
The mechanism of the center holder is obtained by using a 1/2-in.

[Illustration: FIG.7 Details of Tailstock]

pipe, A, and a 1/2-in. lock nut, B, embedded in the wood. I found
that a wooden tool-rest was not satisfactory, so I had to buy one,
but they are inexpensive and much handier than homemade tool rest.
--Contributed by Donald Reeves, Oak Park, Ill.

** To Use Old Battery Zincs [87]

When the lower half of a battery zinc becomes eaten away the
remaining part can be used again by suspending it from a wire as
shown in the cut. Be sure and have a good connection at the zinc
binding post and cover that with melted paraffin. This prevents
corrosion, which would otherwise occur from the action of the sal
ammoniac or other chemical. The wire may be held at the top by
twisting it around a piece

[Illustration: Showing Zinc Suspended]

of wood or by driving a peg through the hole in the porcelain
--Contributed by Louis Lauderbach, Newark, N.J.

** Callers' Approach Alarm [87]

This alarm rings so that callers approaching the door may be seen
before they ring the bell and one can exercise his pleasure about
admitting them.

If one has a wooden walk, the alarm is easy to fix up. Take up
about 5 ft. of the walk and nail it together so as to make a
trapdoor that will work easily. Place a small spring under one end
to hold it up about 1/4 in. (A, Fig. 2). Nail a strip of tin along
the under side of the trap near the spring and fasten another
strip on the baseboard, so that they will not touch, save when a
weight is on the trap. Connect up an electric bell, putting the
batteries and bell anywhere desired, and using rubber-covered

[Illustration: Alarm Rings When Caller Approaches]

wire outside the house, and the alarm is complete.

When a person approaching the house steps on the trap, the bell
will ring and those in the house can see who it is before the door
bell rings.
--Contributed by R. S. Jackson, Minneapolis, Minn.

** Easy Method of Electroplating [88]

Before proceeding to electroplate with copper, silver or other
metal, clean the articles thoroughly, as the least spot of grease
or dirt will prevent

[Illustration: Electroplating Apparatus]

the deposit from adhering. Then polish the articles and rub them
over with a cloth and fine pumice powder, to roughen the surface
slightly. Finally, to remove all traces of grease, dip the
articles to be plated in a boiling potash solution made by
dissolving 4 oz. American ash in 1-1/2 pt. of water. Do not touch
the work with the hands again. To avoid touching it, hang the
articles on the wires, by which they are to be suspended in the
plating bath, before dipping them in the potash solution; then
hold them by the wires under running water for ten minutes to
completely remove every trace of the potash.

For plating with copper prepare the following solution: 4 oz.
copper sulphate dissolved in 12 oz. water; add strong ammonia
solution until no more green crystals are precipitated. Then add
more ammonia and stir until the green crystals are re-dissolved
giving an intense blue solution. Add slowly a strong solution of
potassium cyanide until the blue color disappears, leaving a clear
solution; add potassium cyanide again, about one-fourth as much in
bulk as used in the decolorizing process. Then make the solution
up to 2 qt. with water. With an electric pressure of 3.5 to 4
volts, this will give an even deposit of copper on the article
being plated.

A solution for silver plating may be prepared as follows: Dissolve
3/4 oz. of commercial silver nitrate in 8 oz. of water, and slowly
add a strong solution of potassium cyanide until no more white
precipitate is thrown down. Then pour the liquid off and wash the
precipitate carefully. This is best done by filling the bottle
with water, shaking, allowing precipitate to settle and then
pouring off the water. Repeat six times. Having finished washing
the precipitate, slowly add to it a solution of potassium cyanide
until all the precipitate is dissolved. Then add an excess of
potassium cyanide--about as much as was used in dissolving the
precipitate--and make the solution up to 1 qt. with water. This
solution, with an electric pressure of 2 to 4 volts, will give a
good white coat of silver in twenty minutes to half-an-hour; use 2
volts for large articles, and 4 volts for very small ones. If more
solution is required, it is only necessary to double all given

Before silver plating, such metals as iron, lead, pewter, zinc,
must be coated with copper in the alkaline copper bath described,
and then treated as copper. On brass, copper, German silver,
nickel and such metals, silver can be plated direct. The deposit
of silver will be dull and must be polished. The best method is to
use a revolving scratch brush; if one does not possess a buffing
machine, a hand scratch brush is good. Take quick, light strokes.
Polish the articles finally with ordinary plate powder.

The sketch shows how to suspend the articles in the plating-bath.
If accumulators are used, which is advised, be sure to connect the
positive (or red) terminal to the piece of silver hanging in the
bath, and the negative (or black) terminal to the article to be
plated. Where Bunsen cells are used, the carbon terminal takes the
place of the positive terminal of the accumulator. --Model

** An Ingenious Electric Lock for a Sliding Door [89]

The apparatus shown in Fig. 1 not only unlocks, but opens the
door, also, by simply pressing the key in the keyhole.

In rigging it to a sliding door, the materials required are: Three
flat pulleys, an old electric bell or buzzer, about 25 ft. of
clothesline rope and some No. 18 wire. The wooden catch, A (Fig.
1), must be about 1 in. thick

[Illustration: Electric Lock for Sliding Door]

and 8 in. long; B should be of the same wood, 10 in. long, with
the pivot 2 in. from the lower end. The wooden block C, which is
held by catch B, Can be made of a 2-in. piece of broomstick. Drill
a hole through the center of this block for the rope to pass
through, and fasten it to the rope with a little tire tape.

When all this is set up, as shown in Fig. 1, make a key and
keyhole. A 1/4 in. bolt or a large nail sharpened to a point, as
at F, Fig. 3, will serve for the key. To provide the keyhole, saw
a piece of wood, I, 1 in. thick by 3 in. square, and bore a hole
to fit the key in the center. Make a somewhat larger block (E,
Fig. 3) of thin wood with a 1/8-in. hole in its center. On one
side of this block tack a piece of tin (K, Fig. 3) directly over
the hole. Screw the two blocks together, being careful to bring
the holes opposite each other. Then, when the point of the key
touches the tin, and the larger part (F, Fig. 3) strikes the bent
wire L, a circuit is completed; the buzzer knocks catch A (Fig.
1), which rises at the opposite end and allows catch B to fly
forward and release the piece of broom-stick C. The weight D then
falls and jerks up the hook-lock M, which unlocks the door, and
the heavier weight N immediately opens it.

Thus, with a switch as in Fig. 3, the door can only be opened by
the person who has the key, for the circuit cannot be closed with
an ordinary nail or wire. B, Fig. 2, shows catch B, Fig. 1,
enlarged; 0, Fig. 2, is the cut through which the rope runs; H,
Fig. 1, is an elastic that snaps the catch back into place, and at
G the wires run outside to the keyhole.

This arrangement is very convenient when one is carrying something
in one hand and can only use the other. Closing the door winds up
the apparatus again.
--Contributed by E. H. Klipstein, 116 Prospect St., East Orange,
New Jersey.

** Parlor Magic for Winter Evenings [90]

You are seated in a parlor at night, with the lights turned low.
In front of you, between the parlor and the room back of it, is an
upright square of brightly burning lights, surrounding a perfectly
black space. The magician stands in front of this, in his shirt
sleeves, and after a few words of introduction proceeds to show
the wonders of his magic cave.

Showing you plainly that both hands are empty, he points with one
finger to the box, where immediately appears a small white china
bowl. Holding his empty hand over this bowl, some oranges and
apples drop from his empty hand into the bowl. He removes the bowl
from the black box, or cave, and hands its contents round to the
audience. Receiving the bowl again, he tosses it into the cave,
but it never reaches the floor--it disappears in midair.

The illusions he shows you are too many to retail at length.
Objects appear and disappear. Heavy metal objects, such as forks,
spoons and jackknives, which have been shown to the audience and
which can have no strings attached to them, fly about in the box
at the will of the operator. One thing changes to another and back
again, and black art reigns supreme.

Now all this "magic" is very simple and requires no more skill to
prepare or execute than any clever boy or girl of fourteen may
possess. It is based on the performance of the famous Hermann, and
relies on a principle of optics for its success. To prepare such a
magic cave, the requisites are a large soap box, a few simple
tools, some black paint, some black cloth, and plenty of candles.

The box must be altered first. One end is removed, and a slit,
one-third of the length from the remaining end, cut in one side.
This slit should be as long as the width of the box and about five
inches wide. On either side of the box, half way from open end to
closed end, should be cut a hole, just large enough to comfortably
admit a hand and arm.

Next, the box should be painted black both inside and out, and
finally lined inside with black cloth. This lining must be done
neatly-no folds must show and no heads of tacks. The interior must
be a dead black. The box is painted black first so that the cloth
used need not be very heavy; but if the cloth be sufficiently
thick, no painting inside is required. The whole inside is to be
cloth-lined, floor, top, sides and end.

[Illustration: Candle stand]

Next, the illumination in front must be arranged. If you can have
a plumber make you a square frame of gas-piping, with tiny holes
all along it for the gas to escape and be lit, and connect this by
means of a rubber tube to the gas in the house, so much the
better; but a plentiful supply of short candles will do just as
well, although a little more trouble. The candles must be close
together and arranged on little brackets around the whole front of
the "cave" (see small cut), and should have little pieces of
bright tin behind them, to throw the light toward the audience.
The whole function of these candles is to dazzle the eyes of the
spectators, heighten the illusion, and prevent them seeing very
far into the black box.

Finally, you must have an assistant, who must be provided with
either black gloves or black bags to go over his hands and arms,
and several black drop curtains, attached to sticks greater in
length than the width of the box, which are let down through the
slit in the top.

The audience room should have only low lights; the room where the
cave is should be dark, and if you can drape portieres between two
rooms around the box (which, of course, is on a table) so much the

The whole secret of the trick lies in the fact that if light be
turned away from anything black, into the eyes of him who looks,
the much fainter light reflected from the black surface will not
affect the observer's eye. Consequently, if, when the exhibitor
puts his hand in the cave, his confederate behind inserts his
hand, covered with a black glove and holding a small bag of black
cloth, in which are oranges and apples, and pours them from the
bag into a dish, the audience sees the oranges and apples appear,
but does not see the black arm and bag against the black

The dish appears by having been placed in position behind a black
curtain, which is snatched swiftly away at the proper moment by
the assistant. Any article thrown into the cave and caught by the
black hand and concealed by a black cloth seems to disappear. Any
object not too large can be made to "levitate" by the same means.
A picture of anyone present may be made to change into a grinning
skeleton by suddenly screening it with a dropped curtain, while
another curtain is swiftly removed from over a pasteboard
skeleton, which can be made to dance either by strings, or by the
black veiled hand holding on to it from behind, and the skeleton
can change to a white cat.

But illusions suggest themselves. There is no end to the effects
which can be had from this simple apparatus, and if the operators
are sufficiently well drilled the result is truly remarkable to
the uninitiated. The illusion, as presented by Hermann, was
identical with this, only he, of course, had a big stage, and
people clothed in black to creep about and do his bidding, while
here the power behind the throne is but a black-veiled hand and
arm. It can be made even more complicated by having two
assistants, one on each side of the box, and this is the reason
why it was advised that two holes be cut. This enables an
absolutely instantaneous change as one uncovers the object at the
moment the second assistant covers and removes the other.

[Illustration: The Magic Cave]

It is important that the assistants remain invisible throughout,
and if portieres are impossible, a screen must be used. But any
boy ingenious enough to follow these simple instructions will not
need to be told that the whole success of the exhibition depends
upon the absolute failure of the audience to understand that there
is more than one concerned in bringing about the curious effects
which are seen. The exhibitor should be a boy who can talk; a good
"patter"--as the magicians call it--is often of more value than a
whole host of mechanical effects and helpers. It is essential that
the exhibitor and his confederate be well drilled, so that the
latter can produce the proper effects at the proper cue from the
former. Finally, never give an exhibition with the "cave" until
you have watched the illusions from the front yourself; so that
you can determine whether everything connected with the draping is
right, or whether some stray bit of light reveals what you wish to

** Reversing-Switch for Electrical Experiments [92]

A homemade reversing-switch, suitable for use by students of
electrical and engineering courses in performing experiments, is
shown in the diagram.

[Illustration: FIG.2 Suitable for Students' Use]

Referring to Fig. 1, A represents a pine board 4 in. by 4 in. and
a is a circular piece of wood about 1/4 in. square, with three
brass strips, b1, b2, b3, held down on it by two terminals, or
binding posts, c1, c2, and a common screw, d. Post c1 is connected
to d by means of an insulated wire, making them carry the same
kind of current (+ in the sketch).

About the center piece H moves a disk, held down by another disk F
(Fig. 2), which is fastened through the center piece to the wooden
base, A, by means of two wood screws. On the disk G are two brass
strips, e1 and e2, so arranged that, when handle K is turned to
one side, their one end just slips under the strips b1, b2, or b2,
b3, respectively, making contact with them, as shown in Fig. 2, at
L, while their other ends slide in two half-circular brass plates
f1, f2, held down on disk F by two other terminals, c3, c4, making
contact with them as shown at y, Fig. 2.

The action of the switch is shown in Fig. 1. Connect terminal c1
to the carbon of a battery, and c2 to the zinc. Then, if you turn
handle K to the right, so that the strips e1 and e2 touch b1 and
b2, respectively, terminal c3 will show +, and c1 -- electricity;
vice versa, if you turn the handle to the left so that e1 and e2
touch b2 and b3, respectively, terminal c3 will show - , and c4 +

The switch is easy to make and of very neat appearance.

** How to Receive Wireless Telegraph Messages with a Telephone

Any telephone having carbon in the transmitter (all ordinary
telephones have carbon transmitters) can be used to receive
wireless messages by simply making a few changes in the
connections and providing a suitable antenna. Connect the
transmitter and receiver in series with three dry cells and run
one wire from the transmitter to the antenna. Connect the other
transmitter wire to a water or gas pipe in order to ground it, and
then hold the receiver to your ear. Any wireless telegraph message
within a radius of one mile will cause the transmitter to act as a
coherer, thus making the message audible in the receiver.

By using an ordinary telephone transmitter and receiver and a
1/2-in. jump spark coil, a complete wireless telegraph station may
be made, which will send or receive messages for a radius of one
mile. The accompanying wiring diagram shows how to make the
connections. By putting in an extra switch three of the sending
batteries may be switched in when receiving,

[Illustration: Wiring Diagram for Wireless Telegraph]

thus obviating the necessity of an extra set of batteries.
--Contributed by A. E. Joerin.

** Connecting Up Batteries to Give Any Voltage [93]

Referring to the illustration: A is a five-point switch (may be
homemade) ; B is a one-point switch, and C and C1 are binding
posts. When switch B is closed and A is on No. 1,

[Illustration: Battery Switch]

you have the current of one battery; when A is on No. 2 you
receive the current from two batteries; when on No. 3, from three
batteries; when on No. 4, from four batteries, and when on No. 5,
from five batteries. More batteries may be connected to each point
of switch B.

I have been using the same method for my water rheostat
(homemade). I have the jars of water where the batteries are and
the current coming in at a and b.
--Contributed by Eugene F. Tuttle, Jr., Newark, Ohio.

** A Simple Accelerometer [93]

[Illustration: Accelerometer]

A simple accelerometer for indicating the increase in speed of a
train was described by Mr. A. P. Trotter in a paper read before
the Junior Institution of Engineers of Great Britain. The device
consists of an ordinary 2-ft. rule, A, with a piece of thread tied
to the 22-in. mark, as shown in the sketch, and supporting the
small weight, B, which may be a button or other small object.

The device thus arranged, and placed on the windowsill of the car,
will indicate the acceleration and retardation as follows: Every
1/2 in. traveled by the thread, over the bent portion of the rule,
indicates an increase of or decrease of velocity to the extent of
1 ft. per second for each second. Thus, it the thread moved 2-1/4
in. in a direction opposite to the movement of the train, then the
train would be increasing its speed at the rate of 4-1/2 ft. per

If the thread is tied at the 17-in. mark, then each half inch will
represent the mile per hour increase for each second. Thus if the
thread moves 1 in., it shows that the train is gaining 2 miles an
hour each second.

** An Egg-Shell Funnel [93]

Bottles having small necks are hard to fill without spilling the
liquid. A funnel cannot be used in a small opening, and pouring
with a graduate glass requires a steady hand. When you do not have
a graduate at hand, a half egg-shell with a small hole pricked in
the end will serve better than a funnel. Place the shell in an
oven to brown the surface slightly and it will be less brittle and
last much longer.
--Contributed by Maurice Baudier, New Orleans, La.

** Handy Electric Alarm [94]

An electric alarm which one may turn off from the bed without
arising combined with a light which may be turned on and off from
a lying position, so one can see the time, is the device of H. E.
Redmond, of Burlington, Wis. The alarm clock rests on a shelf, A,

[Illustration: Handy Electric Alarm]

which has a piece of metal, B, fastened in such a position that
the metal rod C, soldered to the alarm winder, will complete the
circuit and ring the bell. The two-point switch D is closed
normally at E, but may be closed at F any time desired, thus
turning on the small incandescent light G, which illuminates the
face of the clock. When the alarm goes off, the bell will continue
to ring until the switch is opened.

** To Keep Dogs and Cats Away from the Garbage-Can [94]

Last summer I was annoyed a great deal by dogs upsetting our
garbage can on the lawn, but finally executed a plan that rid the
yard of them in one afternoon.

I first secured a magneto out of an old telephone, then drove a
spike in a damp place under the porch, attached a wire to the
spike and ran the wire to one of the poles of the magneto. Then I
set the garbage-can on some blocks of wood, being careful not to
have it touch the ground at any point. I next ran a wire from the
other pole of the

[Illustration: Wiring]

magneto to the can, wrapping the wire around the can several
times. Then I sat down on the porch to wait.

It was not long before a big greyhound came along, putting his
forepaws on the top of the can to upset it. At the same instant I
gave the magneto a quick turn, which sent the dog away a very
surprised animal. This was repeated several times during the
afternoon with other dogs, and with the same result. --Contributed
by Gordon T. Lane, Crafton, Pa.

** How to Cross a Stream on a Log [94]

When crossing a water course on a fence rail or small log, do not
face up or down the stream and walk sideways, for a wetting is the
inevitable result. Instead, fix the eye on the opposite shore and
walk steadily forward. Then if a mishap comes, you will fall with
one leg and arm encircling the bridge. --C. C. S.

** Relay Made from Electric Bell [94]

It is not necessary to remove the adjusting-screw when changing an
electric bell into a relay. Simply twist it around as at A and
bend the circuit-breaking contact back as shown. It may be
necessary to remove the head of the screw, A, to prevent
short-circuiting with the armature.
--Contributed by A. L. Macey, New York City.

[Illustration: Relay]

** Foundry Work at Home [95]

** I The Equipment [95]

Many amateur mechanics who require small metal castings in their
work would like to make their own castings. This can easily be
done at home without going to any great expense, and the variety
and usefulness of the articles produced will make the equipment a
good investment.

With the easily made devices about to be described, the young
mechanic can make his own telegraph keys and sounders, battery
zincs, binding posts, engines, cannons, bearings, small machinery
parts, models and miniature objects, ornaments of various kinds,
and duplicates of all these, and many other interesting and useful

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