consist of a pair of No. 14 B. & S. gage hard-drawn copper wires, tinned, twisted, and insulated either with okonite or with three separate, closely woven braids of cotton impregnated with a moisturerepellent compound. The thickness of the rubber compound in the former case should be 32-inch, and of the furnished cotton insulation in the latter case not less than 1-inch. In place of a twisted pair, however, bare open wires may be used. The drop wires are joined to the line wires as shown in Fig. 87, A being the method employed for a series connection, and B that for a bridging connection. McIntire sleeves, c, are used in the former case, and clamps s in the latter case.

Protection.-Pole lines should be protected from lightning by placing on every tenth pole a lightning rod composed of No. 6 galvanized iron wire. This should extend at least 12 inches above the

FIG. 87.-Method of Joining Drop Wires to Line Wires in Series and Bridging Connections

pole and be soldered to a ground rod or plate at the base. The wire should run perfectly straight and be fastened to the pole by galvanized-steel staples spaced 1 foot apart.

Poles may be protected from the weather and

at the same time improved in appearance by painting them after the line is finished, with two coats of lead and linseed oil having a dark olivegreen color.

Humming of the wires may be prevented by wrapping that portion of them at the insulators with

S

m

FIG. 88. Device to Prevent Humming of the Line Wires

soft rubber rr, Fig. 88, and over this placing a covering of sheet lead m. The tie wire s is similarly treated, and the cushion thus formed for the line wire absorbs its vibrations and so does away with the humming..

At curves and corners the line wire at the inner end of a cross-arm may, in case it becomes loosened from its insulator, fall off and, by coming in contact with other wires, do considerable damage. To prevent the wire from falling, an iron guardarm should be screwed to the crossarm so as to catch the wire in case of its insulator breaking or its tie wire becoming loosened.

Telephone Cables.-These are gen- ble erally composed of No. 19 B. & S. gage soft-drawn copper wires covered with dry paper and twisted in

pairs, the bunch being encased in a lead sheath about inch thick, as shown in Fig. 89. The pairs are twisted to overcome inductance; and to distinguish between the conductors of a pair the insulation on one of them is usually marked in some peculiar way. Specifications for dry-paper cables call

for a capacity between conductors of not over o.08 microfarad (see Appendix) per mile; a conductivity of not less than 98 per cent. that of pure copper; an ohmic resistance of not more than 47 ohms per mile at a temperature of 60° F.; and an insulation resistance of each conductor of at least 500 megohms (see Appendix) per mile. Cables

are thus made containing from 5 to 300 pairs of conductors in lengths of 800 and 1,000 feet. A 200-pair cable of No. 19 wires has an outside diameter of only about 2 inches. Iron wires are never formed into telephone cables.

Stringing the Cable is done by first fixing clamps n, Fig. 90, to the sides of the poles a short distance below the cross-arms. A suspension cable c, usually composed of 7 strands of galvanized steel wires, is then run from clamp to clamp and bolted in place as indicated. The cable and reel as received from the manufacturer are next mounted at one end of the line, as shown at m, Fig. 91, and by means of a manila-hemp rope r, Fig. 92, secured to the free end of the cable and led through pulleys a temporarily fastened to the poles just below the suspension clamps, and terminating in a windlass h mounted at a distance along the line from the reel equal to the length of the cable on the reel, the cable is pulled in position. An iron cap c, Fig. 93, screwed to the end of the cable sheath, facilitates the fastening of the pulley rope. The windlass is operated by horse-power as shown. When all the cable on one reel has been strung, the process is repeated, the next reel being set up at the terminus of the first length. Such a case is illustrated in Fig. 91.

Cable Hangers are attached to the cable as the latter is drawn off the reel, and, as the cable is pulled along, the hangers slide over the suspension cable the end of which is temporarily lowered on