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,

[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.