washer of the magnet, as shown in Fig. 180, run up and over the boom pulley J, then through screw-eye G, and tied to the second drum.
Figure 176 shows how the dry-cell may be strapped to the base board in front of the mast, and how the wires that connect the electro-magnet, switch, and cell should be twisted around the hoisting cable, part way, and the remainder of their length allowed to hang. Be sure to cut the wires long enough to reach from a table-top down to the floor. Use flexible wire if you can get it.
By mounting the base upon spool wheels, your derrick can be moved along a table-top. Spool-ends may be used for the wheels, and can either be screwed to the edge of the base, or be fastened upon axles as the wheels of the Electric Motor Truck are fastened (Figs. 203 and 208).
How the Derrick Works. It is probably unnecessary to explain that a load is picked up by throwing over the switch lever to the contact point and closing the circuit, and that it is dropped by throwing off the switch lever and opening the circuit—which causes the electro-magnet to lose its magnetism.
A Toy Shocking Machine. The little shocking machine shown in Fig. 187 is a harmless toy with which you can have an endless amount of fun when entertaining friends. The shock it produces is not severe, but strong enough to make your friend's arm and wrist muscles twitch, and perhaps cause him to dance. Large shocking coils contract the muscles to such an extent that it is impossible to let.
