diameter. Slip one of these on to the bolt next to the head, and the other one next to the nut, as shown in Fig. 188.
Three layers of the coarse wire should be wound on first, for
The Primary-Coil. Pierce a hole through one cardboard end, stick the wire through it, and allow about 5 inches to project upon the outside; then commence winding the wire upon the core, placing each turn close to the preceding turn. When the opposite end of the bolt has been reached, wind back to the starting point, then work back to the other end again. There will be in the neighborhood of 175 turns in the three layers. Cut off the wire so there will be a 5-inch projection, and stick the projecting end through a hole in the cardboard end. This completes the primary-coil (Fig. 189).
Before winding the small wire on top of the primary-coil, to form
The Secondary-Coil, wrap the primary-coil with a layer of bicycle tape, or glue several layers of paper around the coil. Then wind on the small wire as you did the coarser wire, being very careful to get it on evenly and smoothly. Wind eleven layers on the coil, and run the end of the eleventh layer out through the cardboard end (Fig. 190). There should be about 100 turns of this wire to the layer, or 1100 turns in all.
A crank arrangement can be rigged up to make the winding easier, but with patience, and by doing the work slowly, the wire can be wound almost as well by hand.
