Fig. 82. Glass Compensating Strip.
Drill four 1/8-inch holes in a piece of window glass 6 inches long and 1 inch wide. The location of the holes is shown in Fig. 82. The two at the ends serve to mount the standards, A and B, and those at the center to fasten down the strip to the base. The holes are drilled with a small three-cornered file which has been broken off and set in a breast drill. The broken end should be used to drill the glass and be kept thoroughly lubricated with camphor and turpentine. With a little care and patience the holes may be drilled without breaking the glass.
Fig. 83. Details of "Hot Wire" Supports.
Two brass standards are fastened on each end of the glass. They are bent out of sheet brass and are 3/4 inch high and 3/8 inch wide. A brass spring of the same width and 1 1/4 inches long is clamped under one standard. The standard which holds the spring in position is tapped for a small thumbscrew which may be secured from a binding post. Solder a small brass pin to the top of the spring and another one to the top of the standard which is fastened at the opposite end of the glass strip. Some paper or rubber washers must be placed between the feet of the standards and the glass strip to prevent it from cracking when the screws are tightened.
For a station up to one-half K.W. in power the hot wire must be No. 40 B. S. gauge platinum. For larger stations a single No. 36 wire may be used or three No. 40 wires in parallel. The wire must be about 7 inches long. Stretch it between the standard, A, and the spring, C. Wrap the ends around the pins and solder them there, using as small amount of solder as possible. The tension of the wire, which should be taut, is adjusted with the thumbscrew.
Take a piece of the platinum wire about 1/2 inch long and make a little eyelet at one end. Wrap the straight end around the center of the long hot wire and tie a piece of silk in the eyelet.
Fig. 84. Details of Movement.