C.—Upright.
Fig. 1.
For the dial you will require a piece of wood similar to the base, but measuring 5 inches by 4 inches. One end of this should be rounded as shown in B, [Fig. 1]. Drill a hole (F) right through this dial, 3 inches from the bottom and 21⁄2 inches from either side. As a piece of wire will have to revolve easily in this hole, take great care to cut it cleanly. In the lower end of the dial cut out two notches (G H), each according to the measurements in B, [Fig. 1], i.e. 3⁄4-inch deep and 1⁄2-inch wide. Each notch must be 3⁄4-inch from its side of the dial.
The upright is very easily made, being simply a strip of wood 31⁄2 inches by 1 inch (C, [Fig. 1]). In this drill a hole (K) 3 inches from the end and 1⁄2-inch from either side, taking the same care as with the hole in the dial.
Having thus prepared the several pieces of the framework, the dial should be glued into its groove. A small square block of wood glued into the angle formed by the base and the dial will insure the latter’s being perfectly perpendicular. The upright will be fixed in its place later.
To proceed with the more delicate part of the work. Cut a piece of cardboard, fairly thin in texture, 5 inches long and 1 inch wide, and bend it into the shape of an oblong hoop. Upon the hoop or bobbin wind about half an ounce of fine cotton-covered copper wire, size No. 36, which can be obtained from any electrician. Wind this wire very carefully and evenly, but not tightly, leaving about 4 inches free at either end (A, [Fig. 2]).
The next thing to be made is a magnetized needle, which can be easily done as follows. Take a piece of ordinary watch spring, an inch long, and make it red hot. When in this condition drill a hole through the center, and when it is cooler round the ends, as in B, [Fig. 2]. Heat it once more to a red heat and then plunge into cold water to harden. The needle must now be magnetized by being drawn several times firmly across the pole of a strong magnet, care being taken that it is always drawn in the same direction.
The pointer (C, [Fig. 2]) should be made in a similar manner, except that it must not be magnetized, and should be at least twice as large as the needle. Through the hole in the magnetized needle pass a couple of inches of straight stout wire, and with a little solder, or even sealing-wax, fasten the needle as shown in B, [Fig. 2].
