greater as its wires are closer together. The self-induction of a
telephone line is smaller as its wires are closer together. The
electromotive force induced by the capacity of a line leads the
impressed electromotive force by 90 degrees. The inductive
electromotive force lags 90 degrees behind the impressed electromotive
force. And so, in general, the natures of these two properties are
opposite. In a cable, the wires are so close together that their
induction is negligible, while their capacity is so great as to limit
commercial transmission through a cable having .06 microfarads per
mile capacity and 94 ohms loop resistance per mile, to a distance of
about 30 miles. In the case of open wires spaced 12 inches apart, the
limit of commercial transmission is greater, not only because the
wires are larger, but because the capacity is lower and the inductance
higher.

Table I shows-the practical limiting conversation distance over
uniform lines with present standard telephone apparatus.

TABLE I

Limiting Transmission Distances

+-----------------------------+----------------------+
| SIZE AND GAUGE OF WIRE | LIMITING DISTANCE |
+-----------------------------+----------------------+
| No. 8 B. W. G. copper | 900 miles |
| 10 B. W. G. copper | 700 miles |
| 10 B. & S. copper | 400 miles |
| 12 N. B. S. copper | 400 miles |
| 12 B. & S. copper | 240 miles |