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

MEDITERRANEAN TELEGRAPHS. 511
It is true that Faraday and Whitehouse have made experiments
touching the phenomena in question, but these experiments
have been made only on cables prepared for immersion and
coiled up in storehouses, or on submarine cables by uniting
different wires, in order to multiply the length, or by combining
them with long extensions of land lines. Now, in each of
these cases, the effect took place of an inverse current on the
cables or adjacent wires, whence resulted phenomena in the
transmission entirely different from those which are manifested
with a single current over a single wire of great length. Besides, if we have seen the great effect of the simple connection
of five kilometres of land wire on a submarine cable of 600
kilometres, how can we estimate the influence of the land wires
of so much greater length employed by the English experiments?
It seems to me that their reasons alone are sufficient to throw
great doubt on the certainty of the result obtained by those experiments; but the convincing proof of their insufficiency is
derived from a comparison of these results with those presented
by the Malta line, although in both cases, the apparatus was
the same and similarly arranged. While, in fact, we see an
operator of the first order obtain a maximum of 75 signals in a
minute, between Cagliari and Malta, on 600 kilometres, in the
English experiments of October, 1854, from 210 to 270 signals
in a minute (that is 6 or 8 words) were obtained, with currents
on a circuit of more than 8,000 kilometres, over the subterranean and submarine wires between London, Dumfries, and Dublin. The rapid increase of difficulties from the Cagliari and
Bona line, which is only 260 kilometres, to that of Cagliari and
Malta, which is 600, leads to the conclusion that the same difficulties must be much more considerable on a line of 3,000.
The reflections which naturally arise from the examination
of the facts in the case, show to how great a degree it is necessary to study profoundly these questions of vital importance to
the utility of great submarine lines. BONELL1."
The following table contains the proximate velocity of an
electric current on subaqueous conductors, based upon reliable
experiments, instituted on submarine and subterranean telegraphs.