| Fig. 58. | Fig. 59. |
113. Horseshoe Electro-Magnet. Fig. 58. Bend soft iron wires, and make a bundle of them. If you wish to wind the wire around spools, the bundle cannot be very large. It will be found best to make the bundle about ⅜ in. in diameter, and not to use the spools. Strong paper should be wrapped once or twice around the legs of the horseshoe, and the insulated wire, say 4 layers, can then be wound directly upon this. ([See § 115] for method of making connection between the coils.) It is a little troublesome to wind wire upon a horseshoe like this, and for [App. 85]. Spools are handier, because each can be wound separately, and then be slipped in place. The ends of the horseshoe should be filed smooth.
114. Electro-Magnet. Fig. 59. An ordinary iron staple is useful as the core of a small magnet. One like this is shown also in Fig. 94, used as a telegraph sounder. It takes some time to wind 4 layers of wire on to each leg of the staple, so be sure to [see § 115] about the method of winding. In Fig. 59 the half-hitches ([§ 110]) are not shown. Coat the finished coils with paraffine.
Fig. 60.
115. Method of Joining Coils. Fig. 60. If A and B represent the two cores of a horseshoe electro-magnet, the coils must be joined in such a manner that the current will pass around them in opposite directions, in order to make them unlike poles. The current is supposed to pass around B, Fig. 60, in the direction taken by clock hands, while it passes around A in an anti-clockwise direction. The inside ends, [§ 123], of the coils may be twisted together, or fastened under a screw-head. In Fig. 60 one coil is shown to be a continuation of the other.