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 TELEGRA PHS. 509
in this line, in consequence of the well-known inconveniences of
submarine cables, which are the greater here, as the lines from
Cagliari to Malta, and from Malta to Corfu, are each nearly
600 kilometres (about 375 miles), much longer than any previously existing. I, therefore, deem it useful to exhibit, in
some detail, the effects which have been observed, the consequences which result therefrom for the service, and the importance of discovering a remedy.
The submarine cable between Cagliari and Malta is composed of a very fine copper wire, around which are twisted six
similar wires of equal fineness, all in free contact with one
another, so that if one or more of them should break, the transmission would not be interrupted. The seven wires together
form a cord of about two millimetres (1-16 inch) in diameter,
covered with a gutta-percha case of two millimetres, and a
second envelope of tarred hemp. Eighteen iron wires, two millimetres in diameter, twisted in an extended spiral, enclose the
whole, and form the outer covering of the cable, the total
diameter of which is thus carried to 14 millimetres (about 2
inch), and weight 547 kilogrammes per kilometre (about 2,000
pounds per mile). The two extremities of the cable, both at
Malta and Cagliari, are fastened to two pieces of wire on the
land, each 5 kilometres (about 3 miles) long.
After the experiments made in England, and elsewhere, to
diminish the difficulties which were foreseen, it was decided to
employ for transmission induced electrical currents, with piles
of a large surface, and a special apparatus to change the direction of the current alternately.
In spite of all these precautions, the following effects have
been experienced:
If the transmission is made too rapidly, the signals are so
uncertain as to become unintelligible; it is better, therefore,
to be very slow in making them. But several inconveniences
result from this. Such a degree of special skill is required in
the operator, that among the employes at Malta, for instance,
only one was able to transmit the signals satisfactorily. Pauses
of nearly a second must be made, so that scarcely 75 signals
can be transmitted in a minute-that is to say, but two or three
words-while on the land lines the average transmission in the
same time is 280 signals, or perhaps ten words.
Besides-principally to avoid the difficulty of a current
generated in the opposite direction, called return current-the
apparatus is so arranged, that during the transmission from one
side, nothing can be received from the other, nor can the current be interrupted. The operator to whom the message is