This consists of fifty feet of the finest silk-covered copper wire wound on a frame of card two inches long, half an inch broad, three-eighths deep in the open part.
An edge or flange of card, three-eighths of an inch wide, is attached to it at each side to keep the wire in its place. The frame may be of thin wood or ivory, and the winding of the wire commences at the lower left corner, and it is coiled from left to right, as the hands of a watch would move in the same plane. (Fig. 214.)
Fig. 214.
The coil.
Two inches of each end of the coil wire are now stripped of their silk covering by being rubbed with sand-paper. The coil is mounted in the frame by inserting its lower edge or flange in the groove, so that the lower part or floor of the inside of the coil is level with that of the frame, as shown below, and it is now ready to receive the magnetized needle. (Fig. 215.)
Fig. 215.
The coil fitted into frame.