To make a simple galvanometer as in Fig. 1, get an old brass watch case with one of the brass plates removed. In the centre of this drill a very small hole to suit an end-stone, such as jewellers use in watches. Then cut a piece of brass to fit across the diameter of the plate, 1/8 in. wide and 3/32 in. thick. Drill a hole at each end, and get two small brass pillars for the ends, about 1/4 in. long by 1/8 in. in diameter, to raise the cross-bar from the plate. Then drill a central hole in the bar, and put an endstone in this. Taper a piece of watch spring each end from the centre to form a pointer, drill a 1/32 -in. hole in the middle of it, fit a shaft in tight to the hand, and magnetise the pointer; pivot the shaft at the endstones. Next cut a piece of tin to the shape of Fig. 2, lap it with silk tape, varnish, and lap again with about 8 ft. or 9 ft. of No. 28 S.W.g. silk-covered wire. Next get a piece of spring steel, 1/16 in in diameter by l 1/4 in. long, magnetise it, and fasten in cross section to the horseshoe magnet after taping and varnishing. Fasten these two magnets to the back of the brass plate by means of a short piece of ebonite and small screws at the ends. Drill two holes at each side of the case for the reception of two terminals, and connect as shown in Fig. 1. A scale, also, graduated as shown, should be affixed.

Fig. 1.

Watch-case Galvanometer.