2}+C^{2}[omega]^{2} + 1/2(RS-LC[omega]^{2}
\/ \/

The quantities are

R = Resistance in ohms
L = Inductance in henrys
C = Mutual (shunt) capacity in farads
[omega] = 2[pi]_n_ = 6.2832 times the frequency
S = Shunt leakage in mhos

The quantity _S_ is a measure of the combined direct-current
conductance (reciprocal of insulation resistance) and the apparent
conductance due to dielectric hysteresis.

NOTE. An excellent paper, assisting such study, and of immediate
practical value as helping the understanding of cables and their
reasons, is that of Mr. Frank B. Jewett, presented at the
Thousand Islands Convention of the American Institute of
Electrical Engineers, July 1, 1909.

Chapter 43 treats cables in further detail. They form a most
important part of telephone wire-plant practice, and their uses
are becoming wider and more valuable.

Possible Ways of Improving Transmission. Practical ways of improving
telephone transmission are of two kinds: to improve the lines and to
improve the apparatus. The foregoing shows what are the qualities of
lines and the ways they require to be treated. Apparatus treatment, in
the present state of the art, is addressed largely to the reduction of
losses. Theoretical considerations seem to show, however, that great
advance in apparatus effectiveness still is possible. More powerful
transmitters--and more _faithful_ ones--more sensitive and accurate
receivers, and more efficient translating devices surely are possible.
Discovery may need to intervene, to enable invention to restimulate.

In both telegraphy and telephony, the longer the line the weaker the
current which is received at the distant end. In both telegraphy and
telephony, there is a length of line with a given kind and size of
wire and method of construction over which it is just possible to send
intelligible speech or intelligible signals. A repeater, in
telegraphy, is a device in the form of a relay which is adapted to
receive these highly attenuated signal impulses and to re-transmit
them with fresh power over a new length of line. An arrangement of two
such relays makes it possible to telegraph both ways over a pair of
lines united by such a repeater. It is practically possible to join up
several such links of lines to repeating devices and, if need be, even
submarine cables can be joined to land lines within practical limits.
If it were necessary, it probably would be