16,374. Lake, H. W., [Lindquist, D. L.]. July 15. Electro-magnets. - Relates to alternating- current electro-magnets having secondary coils or conductors in which currents of different phase are induced from the primary coils, and the invention consists in proportioning the ohmic resistance of the secondary conductors in accordance with the frequency of the supply current, so that the armature is held without chattering and with a selected (preferably minimum) current consumption. An electro-magnet is first constructed for a predetermined minimum tractive force, and the ohmic resistance of the secondary conductors is then varied until chattering stops. From this initial magnet, other magnets which are required to operate on circuits of different frequency are constructed by choosing or adjusting the ohmic resistances of the secondary conductors in the direct ratio of the frequencies. One construction of magnet for use with an electric brake is shown in Figs. 1 and 3. Two movable cores or armatures 9, 10 are arranged within the primary coil 11; each core is composed of sets of laminµ, some of which are enclosed in sleeves 14, 15 of German silver &c. forming the secondary conductors. The minimum tractive force may be governed by constructing the armatures so as to produce an air-gap 17, Fig. 7, between the cores in the attracted position; the dimensions of the air-gap may be varied. In a modification, Fig. 8, a single secondary conductor 18 is inserted in the end of each core, and the faces are made convex so that the cores are free to rock and adjust themselves in the magnetic field. One core only may be movable, and the secondary conductor may be placed either on the fixed or movable core. A condenser may be interposed in the secondary circuit as well as the ohmic resistance.