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 bra.s.s 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 bra.s.s 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 + electricity.

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

** How to Receive Wireless Telegraph Messages with a Telephone [92]

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,

[Ill.u.s.tration: 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 ill.u.s.tration: 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,

[Ill.u.s.tration: 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]

[Ill.u.s.tration: 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 Inst.i.tution 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 b.u.t.ton or other small object.

The device thus arranged, and placed on the windowsill of the car, will indicate the acceleration and r.e.t.a.r.dation 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 second.

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-Sh.e.l.l 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 gla.s.s requires a steady hand. When you do not have a graduate at hand, a half egg-sh.e.l.l with a small hole p.r.i.c.ked in the end will serve better than a funnel. Place the sh.e.l.l 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,

[Ill.u.s.tration: 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

[Ill.u.s.tration: 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 sh.o.r.e 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.

[Ill.u.s.tration: 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.