wind pressure; for these reasons additional strength is required.
Speaking generally, the practical and economical spacing of poles
requires that wires, to be strong enough to meet the above conditions,
shall have a diameter not less than .08 inch, if of hard-drawn copper,
and .064 inch, if of iron or steel. The honor of developing ways of
drawing copper wire with sufficient tensile strength for open-air uses
belongs to Mr. Thomas B. Doolittle of Massachusetts.

Lines whose lengths are limited to a few miles do not require a
conductivity as great as that of copper wire of .08-inch diameter. A
wire of that size weighs approximately 100 pounds per mile. Less than
100 pounds of copper per mile of wire will not give strength enough
for use on poles; but as little as 10 pounds per mile of wire gives
the necessary conductivity for the lines of the thousands of telephone
stations in towns and cities.

Open wires, being exposed to the elements, suffer damage from storms;
their insulation is injured by contact with trees; they may make
contact with electric power circuits, perhaps injuring apparatus,
themselves, and persons; they endanger life and property by the
possibility of falling; they and their cross-arm supports are less
sightly than a more compact arrangement.

Grouping small wires of telephone lines into cables has, therefore,
the advantage of allowing less copper to be used, of reducing the
space required, of improving appearance, and of increasing safety. On
the other hand, this same grouping introduces negative advantages as
well as the foregoing positive ones. It is not possible to talk as far
or as well over a line in an ordinary cable as over a line of two open
wires. Long-distance telephone circuits, therefore, have not yet been