THE TELEGRAPH.
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.
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.