Tho old-fashioned telegraph, which was in common use before the
wonderful invention of the electro-magnetic telegraph by Morse, was an
arrangement for the communication of intelligence by signals, or
movements, previously agreed upon; which signals represented letters,
words, or ideas, which could thus be transmitted from one station to
another, as far as the signals could be seen. It was first devised in
France, about 1793 or 1794, and soon became extensively adopted and used
in other nations. A good idea of its appearance may be formed from the
cut below. It consisted of a mast, or frame, in connection with
shutters, or sliding-boards, worked by ropes pulled like bell-ropes, and
exhibiting, in all, sixty-three signals; by which were represented the
nine digits, the letters of the alphabet, and several generic words:
and, sometimes, to these were added other signals, expressive of entire
phrases. The observers at these telegraphs were not expected to keep
their eye constantly at the glass, but to look only every five minutes
for the signal to make ready. The telescopes used for observation, were
commonly what are called Dolland’s achromatics, which possess no
recommendation but their enlarged field, and their freedom from
prismatic colors in that field; points of no consequence in looking
through a fixed glass at a fixed and circumscribed object. Sometimes a
common and powerful spy-glass was found sufficient. In the use of this
kind of telegraph, dead flats or levels were found to be universally
unfavorable; and generally stations were found to be useless nearly in
the proportion of the miles of dead flat looked over. On the contrary,
stations between hill and hill, looking across a valley, or a series of
valleys, were found to be mostly clear; and water surfaces were found to
produce fewer obscure days than land in any situation. The period least
favorable of the same day was an hour or two before and after the sun’s
passage of the meridian, particularly on dead levels, where the play of
the sun’s rays on the rising exhalations, renders distant vision
exceedingly obscure. The tranquillity of the morning and evening were
ascertained to be the most favorable hours for observation.
[Illustration: THE SIGNAL TELEGRAPH.]
The old line of this kind of telegraph between London and Portsmouth,
had twelve stations; and another chain from London to Yarmouth, had
nineteen stations. The distances of the stations averaged about eight
miles, yet some of them extended to twelve or fourteen; and the lines
were often increased by circuits, for want of commanding hights. After
about twenty years’ experience, they found they could calculate on about
two hundred days on which signals could be transmitted throughout the
day; about sixty others on which they could pass only part of the day,
or at particular stations; and about one hundred days in which few of
the stations were visible to each other. A message from London to
Portsmouth, was usually transmitted in about fifteen minutes; but, by an
experiment tried for the purpose, a single signal has been transmitted
to Plymouth and back again in _three minutes_, which, by the telegraph
route, is at least five hundred miles. In this instance, however, notice
had been given to make ready, and every captain was at his post to
receive and return the signals. The progress was at the rate of one
hundred and seventy miles in a minute, or three miles a second, or three
seconds at each station; a rapidity truly wonderful for so imperfect an
apparatus! And yet, clumsy and slow-moving as all this now seems to us,
it was the best telegraph known before the invention of Morse. In
contrast to it, let us turn to the latter.