Perfect connection is absolutely necessary for telephone, telegraph, or annunciator work, and where there is a lightning-arrester and the line is not working well, the trouble may often lie in the poor contact of lead and brass or copper, or possibly in using wire that is too fine. Lead is a very poor conductor, and a fine wire would act as a check. For a test, first insert a piece of copper wire to see that the line is working properly; then use lead wire of sufficient size to carry the current as well as the copper did. The action of metals and wire, as current retarders, will be explained in the chapter on resistance and resistance-coils. For general commercial use the base-blocks of all lightning-arresters should be made of porcelain, slate, or some of the composition non-conductors, such as moulded mica, silex and shellac, or fibre. As these are not always available, wood, with a covering of mica, will answer every purpose and can be readily adapted for use. The apparatus pictured in Fig. 19 is known as a single-pole lightning-arrester, and is the simplest form of this kind of electrical paraphernalia. In Fig. 20 a double-pole arrester is shown. This is constructed in the same manner as described for the single one. The block is five inches long, two inches wide, and half or five-eighths of an inch thick. A countersunk hole is made in the middle of all the lightning-arrester blocks through which a screw can be passed to hold the apparatus fast in any desired location. In Fig. 21 another form of fuse is shown. It is made from a piece of mica three-quarters of an inch wide and four inches long, two pieces of thin sheet-copper, and a piece of lead fuse-wire. The copper is three-quarters of an inch wide, and one piece of it is bent in the form of a [V], as shown at A in Fig. 21. One end of the mica strip is dropped in the [V], and with a pair of pliers the [V] is closed up by pinching it at the bottom. To further insure its staying in place, the top and end, or open edges, should be soldered. Punch a small hole through the copper ends, at the inside edge, slip the ends of the fuse-wire in them, and touch the union with a drop of solder to insure perfect contact. With shears and file cut a [U] from the side of one copper band and from the end of the other; these will allow the copper ends to pass under the heads of screws, thus avoiding the necessity of removing the entire screw from the block in order to set the fuse in place. [Illustration: FIG. 19 FIG. 20 FIG. 21 FIG. 22 FIG. 23 FIG. 24 FIG. 25 FIG. 26 LIGHTNING-ARRESTERS AND FUSE-BLOCKS]