To fill the Bobbins with Wire.--For this purpose, No 28 wire should be used, which is better if varnished or paraffined. The bobbins should be neatly covered with paper over the copper tube and inside of ends, to prevent any possibility of the wire touching the bobbin itself; the bobbin is best filled by chucking it on a mandrel in the lathe, or a primitive winding apparatus may be made by boring a hole through the sides of a small box, fit a wire crank and wooden axle to this, and push the bobbin on the projecting end--thus (Fig. 64): _a_, crank; _b_, box; _c_, bobbin; _d_, axle. The box may be loaded to keep it steady; on any account do not attempt to wind the wire on by hand--the bobbin must revolve. Leave about 1½ in. of wire projecting outside the hole _d_, in end of bobbin, and wind the wire on carefully and quite evenly, the number of layers being respectively 6, 8, and 10; the last layer must finish at the same end as the first began, and is best fastened off by a silk or thread binding, leaving about a 3 in. piece projecting. Both bobbins must be wound in the same direction, turning the crank from you, and commencing at the end nearest the box. The bobbins must now be firmly pushed on the part _a b_ of the magnet, and the two pieces of wire projecting through the hole _c_ soldered together. To put the Bell together.--First screw on the bell. This should be supported underneath by a piece of ¼ in. iron tube, long enough to keep the edge of the bell ⅜ to ⅝ in. above the backboard. Cut off the hammer-rod, so that when the head is on it will come nearly as low as the bell screw, and in a line with it. Make a hole in the backboard, and drive the armature post in tightly--it must be driven in so far that when the magnet is laid upon the backboard, the centre of the magnet iron and the armature are the same height. Place the magnet so that when the armature is pressed against it, the hammer-head all but touches the bell; screw it into its place by a wooden bridge across the screw passing between the bobbins. By afterwards easing this screw, any little adjustment can be made. The armature spring should tend to throw the hammer-head about ⅝ in. from the bell. The contact-post should be so placed that when the armature touches the magnet, there is a slight space between the platinum point on the screw and the platinum on the spring. In putting in the posts, a piece of copper wire must be driven in with them to attach the wire to. One post can be moved round a little either way to alter the tension of the spring; the screw in the other post can be turned in or out, to just allow the proper break to take place. By screwing it in and out, the ear will soon judge where the bell rings best. (Volk.) Those desiring further information on batteries, telephones, and all electrical matters, are referred to the Third Series of ‘Workshop Receipts,’ where diffuse instructions are given.