No. 1,diameter⅜ in.,length over all1⅛ in.
No. 2,”¾ in.,”1¼ in.
No. 3,”1 in.,”1⅜ in.

The brass ends should be neatly turned true and lacquered.

63. Bobbin. 64. Winding Bobbin.

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.

Thieves and Fire

Thieves and Fire.—It would be difficult to name two subjects demanding more attention and forethought from the housewife than the means to be adopted for protecting her household from the incursions of thieves and the horrors of fire. Some years ago, the well-known inventor of Chubb’s locks published a little book on these topics, from which we have taken the liberty of condensing a few paragraphs which are full of import to the safety of the dwelling and its inmates.

First with regard to thieves. Chubb remarks that most of the house-robberies so common in all large towns are effected through the common street-door latches in ordinary use being opened by false keys. It is a notorious fact that thousands are made year after year, but which do not afford the least security, as they are all so made that any one key will open the whole. Burglars are sometimes assisted by dishonest servants, but are more often unaided in this way. Frequently some coal-cellar window is left conveniently unbarred, although all other windows and doors are barred and bolted; or perhaps all the windows have safety-fasteners but one, which, of course, will be the one used by the burglars. Beggars or hawkers are often in the pay of thieves, endeavouring to get information—that may not be used perhaps for a long time; and such visitors should never be allowed inside one’s house, though their visits are too often encouraged by the weakness of the domestics.