Fig. 35. Details of Magnets.
A soft iron yoke Y, 2 1/2 x 7/8 x 1/4 inches, connects the bottom of the magnets and supports them in an upright position. An 8-32 machine screw passing upward through the base and yoke holds them firmly. The base is preferably of hard rubber 4 x 3 1/4 x 3/4 inches.
Fig. 36. Details of Moving Parts.
The moving parts are illustrated in Fig. 36. The main spring, D, is a strip of spring steel, 2 1/8 inches long, 1/2 inch wide, and 1/32 inch thick. The soft iron armature, A, is fastened to the spring by means of two small 4-36 machine screws. M is a piece of brass rod, 1 1/2 inches long, bent in the form of a hook and threaded with a 4-36 die to screw in a similarly threaded hole in the back of the armature A. The hooked portion of M is fitted with a small piece of hard rubber rod, R, to insulate it where it comes into contact with the spring, G. The spring, D, carries a second hook, E, riveted to the center of the spring 1 5/8 inches from the lower end. The hook, which is about 3/8 inch long, passes through a hole in the top of the spring, F, and engages it so that it is set in operation by the vibratory motion of the spring, D. The spring, F, is 1 3/4 inches long, 5/16 inch wide, and ir 1/64 inch thick. It carries a platinum rivet 3/4 inch from its lower end. The spring, G, is 2 1/2 inches long, 5/16 inch wide and 1/64 inch thick. A heavy platinum rivet is fastened 2 1/4 inches from the lower end. An elongated hole, 1/4 inch long and 3/16 inch wide, permits the hook, M, to pass through the opening. A 5/32 inch hole, 1 1/4 inches from the bottom, allows the adjusting screw to pass through and make contact with the platinum rivet on the spring, F.
Two rectangular pieces of brass, O, 1 1/4 x 1/2 x 5/16 inches are fastened to the base to support the springs.
Fig. 37. Details of Standard and Screws.
The standard, U, supporting the adjusting thumbscrews is a piece of 3/8-inch brass, 2 1/2 inches high. It tapers from 1 1/2 inches at the bottom to 3/4 inch at the top. A hole 2 1/4 inches from the bottom is threaded with a 10-32 tap to receive the thumbscrew, B. A second hole 1 1/4 inches from the base is threaded with an 8-32 tap to fit the adjusting screw, S.
Both of the adjusting thumbscrews carry heavy platinum points. The standard is held upright to the base by means of two machine screws passing through the base.