─────────────────────────────────────────────────────────────────── Size of Coil A B C ─────────────────────────────────────────────────────────────────── 1/4 in. 8 in. 4 in. 1 1/8 in. ─────────────────────────────────────────────────────────────────── 1/2 in. 8 1/4 in. 4 1/2 in. 1 1/8 in. ─────────────────────────────────────────────────────────────────── 1 in. 10 1/4 in. 4 1/2 in. 1 1/4 in. ───────────────────────────────────────────────────────────────────
*The Base* of the coil is a box eight inches long, four inches wide and one and one-eighth inches deep. It is made in the form of a hollow box. Give the base a coat of stain, preferably some dark color, such as mahogany, and then a coat of shellac or varnish.
The wooden heads should be stained black.
The parts of the interrupter are shown in Figure 115. They cannot be made by every experimenter on account of the tools required, but can be purchased very cheaply from concerns dealing in material for experimenters.
*The Standard* is a piece of hexagonal brass rod one and three-sixteenths inches long and three-eighths of an inch in diameter. The lower end of the standard is tapped to receive an 8-32 machine screw. A hole is bored at right angles to the axis of the standard, one inch from the lower end and tapped to receive an 8-32 thumbscrew.
[Illustration: FIG. 115.—Details of the Interrupter. The Spring and Standard for the One inch coil should be made one-quarter of an inch longer.]
The Thumbscrew should be about seven-eighths of an inch long and be provided with a lock nut so that it can be fastened in position. The end of the thumb-screw is drilled with a small hole and a contact point driven in tightly. The contact point is usually a piece of platinum wire, but in the case of a small coil may be a piece of the special contact wire which is sold for just this purpose.
[Illustration: FIG. 116.—The tube.]
────────────────────────────────────────────────────────────────── Size of Coil Length of Tube Diameter of Tube ────────────────────────────────────────────────────────────────── 1/4 inch 4 1/4 inch 2 1/2 inch ────────────────────────────────────────────────────────────────── 1/2 inch 4 1/2 inch 2 1/2 inch ────────────────────────────────────────────────────────────────── 1 inch 6 1/2 inch 3 inch ──────────────────────────────────────────────────────────────────
*The Spring* is a piece of thin steel, three-eighths of an inch wide and two and one-eighth inches long. Several holes are drilled in it. The illustration shows the exact location of these holes. The holes A and C should be just large enough to allow an 8-32 machine screw to slip through. The hole B is just large enough to receive a piece of contact wire.