The first piece, or main part of the frame, is made from brass, 3/4 in. wide and 16 in. long, bent into an oblong shape and the ends soldered or bolted together.  If the ends are to be soldered, before doing so drill four 1/4-in. holes 1 in. from the ends and insert the ends of the axles.  The other two pieces are 1/2-in. wide and of the dimensions shown in the sketch.  These pieces are riveted in the middle of the oblong frame, each in its proper place.  The motor is now bolted, bottom side up, to the top of the piece fastened to the frame lengthwise.  A trolley, Fig. 3, is made from a piece of clock spring, bent as shown, and a small piece of tin soldered to the top end for a brush connection.  A groove is made in the tin to keep the trolley wire in place.

The trolley wire is fastened to supports made of wood and of the dimensions given in Fig. 4.  The trolley should be well insulated from the frame.  The parts, put together complete, are shown in Fig. 5.  Run a belt from the pulley on the motor to the grooved wheel on the axle, as shown in Fig. 6, and the locomotive is ready for running.

In making the connections the travel of the locomotive may be made more complicated by placing a rheostat and controlling switches in the line, so that the engine can be started and stopped at will from a distance and the speed regulated.  Automatic switches can be attached at the ends of the line to break the circuit when the locomotive passes a certain point.

One connection from the batteries is made to the trolley wire and the other to a rail.  The connection for the motor runs from one binding post to the trolley and this connection must be well insulated to avoid a short-circuit.  The other binding-post is connected to the frame.

The cost of making the wheels and purchasing the track will not be over $1.50.  The track can be made from strips of tin put in a saw cut made in pieces of wood used for ties.  This will save buying a track.  —­Contributed by Maurice E. Fuller, San Antonio, Texas.

** Demagnetizing a Watch [166]

A test can be made to know if your watch is magnetized by placing a small compass on the side of the watch nearest the escapement wheel if the compass pointer moves with the escapement wheel the watch is magnetized.  A magnetized watch must be placed in a

[Illustration:  Watch Demagnetizer]

coil that has an alternating current of electricity flowing through it to remove the magnetism.  A demagnetizer can be made as shown in the illustration.  Two end pieces for the coil are made as shown in Fig. 1 from 1/4-in. wood.  These ends are fastened together, Fig. 2, with cardboard 3 in. long glued to the inside edges of the holes cut in them.  Wind upon the spool thus formed about 2 lb. of No. 16 cotton-covered copper wire.  As it will be necessary to place a 16-cp. lamp in series with the coil, both the coil and lamp can be mounted on a suitable base and connected as shown in Fig. 3.  The current, which must be 110 volt alternating current, is turned on the lamp and coil and the magnetized watch slowly drawn through the opening in the center of the coil.  —­Contributed by Arthur Liebenberg, Cincinnati, O.