The marvellous development of telegraphy within the last generation has
called into existence a great variety of receiving instruments, each
admirable in its way. The Hughes, or the Stock Exchange instruments,
for instance, print the message in Roman characters; the sounders strike
it out on stops or bells of different tone; the needle instruments
indicate it by oscillations of their needles; the Morse daubs it in ink
on paper, or embosses it by a hard style; while Bain's electro-chemical
receiver stains it on chemically prepared paper. The Meyer-Baudot and
the Quadruple receive four messages at once and record them
separately; while the harmonic telegraph of Elisha Gray can receive as
many as eight simultaneously, by means of notes excited by the current
in eight separate tuning forks.
But all these instruments have one great drawback for delicate work,
and, however suitable they may be for land lines, they are next to
useless for long cables. They require a certain definite strength of
current to work them, whatever it may be, and in general it is very
considerable. Most of the moving parts of the mechanism are
comparatively heavy, and unless the current is of the proper strength to
move them, the instrument is dumb, while in Bain's the solution requires
a certain power of current to decompose it and leave the stain.
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