having a diameter of 0.08 inch and a breaking strength of about 325 pounds, being the most usual.

For a common return wire used in place of the ground when there are a number of instruments connected together, a No. 8 copper wire is desirable. This usually affords best protection from foreign noises when not grounded. Telephone connection by means of a common return conductor is cheaper than the use of complete metallic lines, but does not afford such freedom from inductive disturbances.

Copper line wire should be hard drawn, uninsulated, and have a conductivity of at least 97 per cent. that of pure copper. Iron line wire should be thoroughly annealed and double galvanized. Iron wire is made in several varieties commonly known as "Extra Best Best," "Best Best," and "Steel." "Extra Best Best" or "E. B. B." wire is made of the very best material and has the highest conductivity of any iron; its breaking strength is about 2.7 times its weight per mile. "Best Best" or "B. B." wire is harder than the "E. B. B." and of less conductivity, but is stronger; its breaking strength is 3.3 times its weight per mile. "Steel" wire is stronger than those previously mentioned, but has poor conductivity; it has a breaking strength of about 4.5 times its weight per mile. The properties of both copper and iron wires are recorded in tables in the Appendix.

Stringing the Line Wires is usually done by aid

of a running board and rope and a team of horses. The rope is carried over the cross-arms of the poles for a distance of about 1,500 feet and its end fastened through the center hole c of the running board, Fig. 75. At this end of the line are mounted the reels containing the wires, and one end of each wire is fastened to the board through the holes a, e, s, n, etc. The horses are then hitched to the other end of the rope and started, and as they walk away they pull the board and wires over the crossarms. On each pole a lineman guides the board and wires over the cross-arm, and when the reels

FIG. 75.-Running Board Used in Stringing Telephone Line Wires

are empty the wires are temporarily fastened and the process repeated with full reels until the entire course is covered. In stringing wires over crossarms below the top one, a divided running board is used, one half of it passing each side of the pole.

In case but one or two line wires are to be strung, the running board and team may be dispensed with, the running rope being then tied directly to a wire and pulled over as many cross-arms as possible by hand.

The line wires are finally drawn tight by means of clamps and tackle, Fig. 76, until the sag in inches between the adjacent poles corresponds to the figures given in the following table for the tempera

ture and length of span in feet dealt with. If the wires are drawn tighter than there indicated, they are liable to contract and break in cold weather,

FIG. 76. Elevation and Plan of Clamps and Tackle Used in Pulling up the Line Wires

and if allowed a greater deflection they will swing in the wind and eventually break at the insulators.

Each line wire is tied to its insulator as shown in

Fig. 77, the tie wire m being from 16 to 22 inches

in length and of the same size and material as the line wire n n. On straight lines the line wires are placed on the inner sides of the insulators, excepting the two wires next to the pole, which are placed

n

n

FIG. 77.—Method of Tying the Line Wire to its Insulator

FIG. 78.-Position of the Line Wires on the Insulators in Straight Lines

FIG. 79.-Position of the Line Wires on the Insulators at Curves

FIG. 80.-The Standard Western Union Joint for Connecting Iron Wires

outside to afford greater clearance of the pole. On curves, the line wires are placed so that the strain draws them against the insulators. These two cases are shown respectively in Figs. 78 and 79. Joints in iron wires are made as in Fig. 80, which

shows what is known as the "Standard Western Union" joint. Joints in copper wires are made with McIntire copper sleeves, Fig. 81, each hole in

FIG. 81. McIntire Sleeve for Connecting Copper Wires

the sleeve being no more than 0.01 inch larger than the wire with which it is used. The ends of the copper wires to be joined are inserted in the respective halves of the sleeve from opposite ends, so that each wire projects one-quarter inch beyond

FIG. 82.-Pliers for Use in Connection with McIntire Sleeves

the sleeve. The ends are then turned over, and by means of McIntire pliers, Fig. 82, the sleeve and wire are twisted as in Fig. 83.

Dead-Ending a copper line wire on its last insu

FIG. 83.-Copper Wire Joint as Made by a McIntire Šleeve

lator for the purpose of connecting it to a cable or to a station instrument is done as in Fig. 84, the line wire being first slipped through a McIn