should be cut as shown in Fig. 2, so as to have four small pieces that can be bent out, leaving the projections as shown.  After wrapping three or four turns of paper around the bundle of wires the cardboard ends are put on with the projections inside, so the coils of wire will hold them in place.  About 70 turns of No. 24 gauge double covered magnet wire is first placed on the core, for the primary, and then 1,500 turns of No. 32 or 34 gauge double-covered wire is wrapped on top of the primary, for the secondary.  Sufficient length of wire must be left outside at each end of both windings to make connections.  The vibrator B, Fig. 1, and the support C are made from thin spring steel, about 1/8 in. wide, bent as shown and securely fastened to the cardboard end of the coil.  The armature is made from a soft piece of iron, about 3/16 in. in diameter and 1/16 in. thick, which is soldered to the end of the vibrator directly opposite the end of the core.  A small screw is fitted in the end of the support, C, for adjustment, which should be tipped with platinum and also a small piece of platinum placed where the screw will touch the vibrator, B.

One of the primary wires is connected to the screw support.  The vibrator, is connected to a flash lamp battery, D. The other primary wire is connected to a switch, S, which in turn is connected to the other terminal of the battery.  The switch, S, may be made from a 3/8-in. cork with the wires put through about 3/16 in. apart and allow them to project about 1/2 in.  The plate E is cut about 1/2 in. square from a piece of copper and is fastened to the heel of one shoe and connected with a wire from the secondary coil which must be concealed inside of the trouser leg.  The other secondary wire is connected through the coat sleeve to a finger ring, F. The vibrator screw must be properly adjusted.  When the vibrator is not working the armature should be about 1/16 in. from the core and directly opposite.

The coil when complete will be about 2-1/2 in. long and 1 in. in diameter.  The coil can be placed in an old box that has been used for talcum powder or shaving stick.  The space around the coil in the box can be filled with paper to keep it tight.

The coil and battery are carried in the pockets and the cork button put in the outside coat pocket, where it can be pressed without attracting attention.

** Experiment with Heat [134]

[Illustration:  Heat Experiment]

Place a small piece of paper, lighted, in an ordinary water glass.  While the paper is burning turn the glass over and set into a saucer previously filled with water.  The water will rapidly rise in the glass, as shown in the sketch.

** How to Attach a Combination Trunk Lock [134]

[Illustration:  Trunk Lock]

A small combination lock for chests can be purchased for a small sum of money and attached to a trunk cover after first removing the old lock as shown in Fig. 1.  It is necessary to add 1/2-in. to the thickness of the trunk lid or cover.  This may be done by placing a brass plate 1/8-in. thick on the outside and a board 3/8-in. thick on the inside.  The lock, brass plate, board and trunk cover are all securely riveted together.  The support for the dial is soldered to the brass plate.