HIGH FREQUENCY AND HIGH POTENTIAL CURRENTS. 379

casting a a, the two parts of which are brought together andclamped to the outer edge of the conductor d.

The core for the held magnet is built up of two circular partsh h, formed with annular grooves i, which, when the two partsare brought together, form a space for the reception of the ener-gizing coil <j. The hubs of the cores are trued off, so as to fitclosely against one another, while the outer portions or flangeswhich form the polar faces j ,t, are reduced somewhat in thick-ness to make room for the conductor n, and are serrated on theirfaces. The number of serrations in the polar faces is arbitrary ;

Fro. 200.

but there must exist between them and the radial portions ofthe conductor d certain relation, which will be understood byreference to Fig. 207 in which n n represent the projections orpoints on one face of the core of the field, and s s the points ofthe other face. The conductor n is shown in this figure in sectiona a' designating the radial portions of the conductor, and b theinsulating divisions between them. The relative width of theparts a a' and the space between any two adjacent points n n ors s is such that when the radial portions a of the conductor an*passing between the opposite points n s where the field is strong-est, the intermediate radial portions a' are passing through the