HIGH FREQUENCY AND HIGH POTENTIAL CURRENTS. 153

iron. Upon the rim are wound several layers of line, wellannealed iron wire, which, when wound, is passed throughshellac. The armature wires are wound around brass pins,wrapped with silk thread. The diameter of the armature wirein this type of machine should not be more than £ of the thick-ness of the pole projections, else the local action will be con-siderable.

Fig. 98 represents a larger machine of a different type. Thefield magnet of this machine consists of two like parts whicheither enclose an exciting coil, or else are independently wound.

Fig. 97.

Each part lias 480 pole projections, the projections of one facingthose of the other. The armature consists of a wheel of hardbronze, carrying the conductors which revolve between the pro-jections of the held magnet. To wind the armature conductors,I have found it most convenient to proceed in the followingmanner. I construct a ring of hard bronze of the required size.This ring and the rim of the wheel are provided with theproper number of pins, and both fastened upon a plate. Thearmature conductors being wound, the pins are cut off and theends of the conductors fastened by two rings which screw to the