Below is a small wooden hut, in which a person is employed to observe the movements of the machine. On the eminence nearest to this, another person is to repeat these movements, and a third to write them down. The time taken up for each movement is twenty seconds, of which, the motion alone is four seconds; the other sixteen the machine is stationary. Two working models of this instrument were executed at Frankfort, and sent by Mr. W. Playfair, to the Duke of York; and hence, the plan and alphabet of the machine came to England.
This telegraph consisted of six octagonal boards, each of which was poised upon a horizontal axis in a frame that surrounded it, in such a manner that each octagonal board might be placed either with its flat side towards the spectator, or edgeways, when the board became invisible owing to the distance. An officer's cabin was placed underneath, provided with a telescope pointed to the next station. By a simple mode of working, these six boards made 36 changes, which are adequate for all occasions. Experience has shown that this plan of telegraph, which was deemed at the time of its introduction to be an improvement upon the design of M. Chappe, previously described, was, in reality, inferior to it in simplicity and clearness; consequently the latter has been since adopted by the British government, under such improved modifications as great practical conversancy in the subject must necessarily produce.
There is probably no subject which has exercised more of the ingenuity of scientific men than that of telegraphic communication; and we are convinced that a description of the various schemes for that object, would alone All a volume like the present We shall therefore confine our notice to a very few of them; and, in preference, to such as are upon a totally different principle from each other.
Telegraphic communication, (the ingenious Mr. Vallance observes,) has hitherto been a mean of intercourse that was serviceable only during those portions of the enlightened half of the twenty-four hours, when clear weather admitted of uninterrupted vision for a distance of about ten miles. It has been frequently proposed to remedy this disadvantage, (so far as related to the absence of light, that is,) by nocturnal telegraphs; for the lamps of which, gas seemed so admirably adapted. But as this would do nothing towards lessening the interruption which wet and foggy weather occasion, it has not been thought worth while to incur the expense of it; and as it has also been supposed impossible that these interruptions could be obviated, we have sat down under the impression, that communications, rapid as are those of the telegraph under favourable circumstances, must remain dependent, to a degree that would ever prevent the principle from being rendered available to the purposes of commercial and domestic communication. But this impression is erroneous, - there being a well known principle, by the aid of which information may be communicated equally well during darkness and the most foggy weather, as in daylight and clear wea ther.
The putting of this principle into execution, will of course be incomparably more expensive than laying down a line of telegraphs; but as the revenue it may be made to bring in will, (to use M. Dupin's observation relative to our domestic policy,) render this expenditure but an additional instance of that "economy, well understood, which knows how to make sacrifices bordering almost on prodigality, in order to reap afterwards, with usury, the fruits of its advances," the amount of it in no wise diminishes the attention the principle deserves.
"It has long been known," adds Mr. Vallance, "that an incompressible liquid, confined in a pipe, might be caused to move through the whole length of that pipe, by operating on it at either end, whether the pipe was one mile or one hundred miles long. (It was proved by Bossuet, for a distance of three miles, about half a century ago.) But although this has long been known, and although it offers a mean of symbolic intercourse which would alike be independent both of darkness and cloudy days, yet it has been unthought of as n principle of instantaneous transmission." The mode proposed by Mr Vallance, of carrying the principle into practice, may be thus briefly explained.
A pipe of small calibre is to be laid from one to the other of the places, between which, (as hitherto termed,) telegraphic communication is to be effected. This pipe, (effectually secured against leakages,) is to be kept constantly filled with water, by apparatus which both empties it of air and guards against (or rather counteracts) contraction and expansion. Each end of this pipe is connected to apparatus, which will cause any movement of the water inside it, to act on and move a hand. This hand may point out and indicate letters, or numbers, or words, painted on a dial plate; though it will be better to cause it to indicate them when placed in a line. In connexion with telegraphic apparatus, is always understood a vocabulary, connecting the symbols with certain meanings. The principle of this method will admit of either letters, numbers, words, or sentences, being used. Having thus explained the principle of Mr. Vallance's plan, we must refer the reader for the details of it to a pamphlet by the author, published by Wightman, London, 1825, entitled, Description of a Method of Telegraphic Communication. A variety of suggestions for the employment of the electric fluid acting upon wires extended from the places in communication, have been made from time to time.
In one of these the intelligence is communicated by means of sound, produced by the collision of bodies in opposite states of electricity; these bodies consist of a series of small balls, suspended at the extremities of metallic conductors by slender chains, and a series of numbered bells hung within their space of action. The author of this plan, who is an anonymous contributor to a scientific journal, illustrates his proposed scheme by the following example:-
"Let a metallic wire, coated with a non-conducting substance, be extended under ground between any two given places, which, for the sake of experiment, may be two separate apartments in the same house; one of which may be denominated A, and the other B. In the apartment A place an electrical machine, and to the extremity of the wire in B a little ball, suspended by means of a very slender chain, within whose sphere of action there is a common bell. Now, by connecting the wire in A with the conductor of the machine, the electric fluid will pass instantaneously along it, and charge the ball in B, through the medium of its little chain, which flies off immediately to the uninsulated bell, to discharge its surplus of electric matter, and recover its equilibrium. The force by which it is attracted or impelled towards the bell is quite sufficient to produce the sound required; it is an experiment which I have often made, and with invariable success. Let this bell be numbered 1, and have a series of them up to 10, with separate and distinct metallic conductors, it is evident to a demonstration that, by a combination and the successive excitement of these simple numbers, the whole of those at present made use of in our most improved telegraph and signal books, together with their corresponding meanings, may be conveyed from the apartment A to B with the greatest accuracy, and with the speed of thought.
"Thus, by this simple and inexpensive means, (by two electrical machines, and a double series of wires with their appendages,) say between Portsmouth or Plymouth and London, news of the greatest political importance may be conveyed in a few minutes, by a gentleman connected with the apparatus at either of these places; he has only to excite the wires which correspond to each individual number of the telegraph made to him by the common flag signals, which will, in almost the same instant of time, affect their corresponding in London, and give the necessary intelligence in a series of numbers, whose symbols will be found by referring to the signal books now in use.
Domestic telegraphs (which are now very common) are designed to prevent the trouble of calling for certain articles in a dwelling-house, and to dispense with one-half of the journeys of the servants in answering bells. They are made in a variety of ways, but usually consist of two circular indexes or dials, equally divided into a given number of parts, and marked on these divisions, with the names of such things or necessaries as are generally wanton in a house, such as dinner, tea, supper, coals, lights, carriage, horse, etc. These indexes exactly correspond, and are provided with hands, the axes of which pass through pulleys of equal diameter; a wire or chain extends from the pulley of one of them, fixed in the sitting room, to another fixed in the kitchen, or servants' hall. The pulley of the latter contains a spring, and that of the former a ratchet wheel and catch, so that if the hand of the sitting room index be turned, it also turns that of the servants' room an equal portion of a revolution, and thereby points to the same word. The pull is lifted off the ratchet after it if used, by touching a pin, when the spring in the other pulley draws the chain or wire round it, and so returns both the hands to their original place at o.
The attention of the servant is called by the ringing of a bell.