The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

CONDUCTING POWER OF TELEGRAPH WIRES. 515
Battery of 144 pairs plates: No. 18. No. 16.
100 miles.....................5~.............. 41~
90......................37......................
80...................... 38~....................
70 "......................40~..................
65............41...............
Battery of plates: No. 18. No. 16.
100 miles 72 pr. plates..........23~......................30~
100 " 84..........26~......................
100 " 96..........281.....................
100 " 102......... 0~......................
According to the above experiments a wire, No. 18, has
capacity to conduct a given voltaic current 65 miles, and No.
16, 100 miles. Suppose the conductibility of iron wire, Nos.
8 and 10, have equal powers as Nos. 16 and 18 of copper,
respectively; on a line of 300 miles No. 8, iron wire, can be
worked successfully, but the No. 10 could be worked but 195
miles; or, if No. 10 wire can work maximum 300 miles, No.
8 could be worked 461 miles. These facts clearly prove a
very great advantage in the use of the larger size wire for telegraphic purposes. This is an important matter, and it is
worthy of being very gravely considered by companies having
lines on long routes, where long circuits are required. For example, suppose a line to be 900 miles long, using No. 10 wire,
a size common on American lines, the practical circuits would
be about 300 miles each. If the wire be No. 8, a circuit of
461 miles can be as effectually operated, with a battery of a
little more intensity than that employed for the 300 miles circuit, and, therefore, the line of 900 miles can be operated in
two circuits of 450 miles each. In the use of the larger wire
there will be economy, resulting from its increased strength.
There will also be a saving of expenses in three years, by the
lessening of repeating stations, sufficient to pay for the additional
cost of No. 8 wire for the 900 miles of line.
CONDUCTING POWER OF TELEGRAPH WIRES.
Considering the above-mentioned facts, and others observed
in my experience, I am convinced that the larger conductor is
the best for telegraphic purposes, pecuniarily and electrically
considered. On the Bengal lines, No. 1 iron rods are used for
conductors, and those lines are successfully worked in long circuits. The philosophy establishing the surface as the part, on
or through which the current moves, adds further proof in favor
of the larger wire. In practical telegraphing we have had
many proofs establishing the advantage of full metallic surface.
In Pittsburg, and many other cities, where great quantities of
coal are daily burned, the sulphurous vapors arising from such
fuel, in a very short time, corrodes the iron wire, leaving but