Fig. 17.
Fig. 18.
Fig. 19.Saw an ordinary spool, C, into two parts. One-half of C will serve as the outside case for the button. The part to be pressed with the finger is a short length of ¼ in. dowel. To keep this from falling out of the hole in C, a short piece of wire nail, N, has been put through a small hole in its lower end. A slot, F, has been burned or cut into the underside of C, so that N can pass up and down in it when D is raised and lowered. The rod, D, rests upon A, one of the contacts. This is a straight piece of tin, cut as shown in Fig. 17, the narrow part being ¼ in. wide and 1¼ in. long. The wide part is ¾ in. wide and 1 in. long. The other contact, B, is the same size as A. A deep groove, a little over ¼ in. wide, is cut into the base so that the narrow part of B can be bent down below the end of A. The base shown is 4 × 2½ × ⅞ in. The spool, C, is fastened to the base by 2 screws or wire nails put up through the base, their positions being shown by the dots at E, Fig. 17. X and Y, Fig. 18, are 2 screw binding-posts. It is evident that the current cannot pass from X to Y, unless the button, D, be pressed down so that the end of A will touch B.
48. Sifter for Iron Filings. Fig. 20. In making magnetic figures with iron filings, it is an advantage to have the particles of iron fairly small and uniform in size. A simple sifter may be made by pricking holes in the bottom of a pasteboard pill-box with a pin. The sifter may be put away with the filings in it, provided you turn it upside down.
Fig. 20.
49. Sifter for Iron Filings. Fig. 21. Punch small holes in the cover of a tin box with a small wire nail. If you have occasion to use sifters for other purposes, the different sizes can be made by using larger and smaller nails to punch the different tin covers. But one size of nail should be used for one sifter.