File:Decorators Assistant - telegraph.png

Electric Telegraphs in Present Use.

Of all the adaptations of scientific discovery, in modern times, to the exigencies of everyday life, by far the most important, next to steam-locomotion, is undoubtedly that of voltaic electricity to the purposes of telegraphic communication. To trace the successive steps by which the practical employment of the electro-telegraphic arrangements now in use have been arrived at, would far exceed the space we are enabled to devote to the subject; suffice it, however, in justice to the early labours of previous discoverers, to notice, that there seems to be but little indeed in any of the more modern systems, however dignified by high-sounding names, or fortified by legislative protection, in the shape of "royal letters patent," to distinguish them, as regards any novelty of principle, from the first contrivance adopted by various inventors, including Ronalds, Alexander, Morse, and Davy, who already, in 1839, specified his Patent Electro-Magnetic Telegraph, in which he used clockwork, acted upon by electro-magnets, producing a step-by-step motion, similar to the seconds’ hand of a watch or clock, the signals being registered by dots upon a prepared fabric placed in the machine; whilst that of Alexander, of Edinburgh, in 1837, was put into operation by means of a key to be pressed down by the finger of the operator, connected with the end of the conducting wire, which dips into a cup of mercury when the key is depressed, and completes the electric circuit. It is with no unfriendly feeling that we have thus prefaced the description we are now about to lay before our readers of the latest of the electric dial-telegraphs, namely, that of Mr. Nott, which, we understand, is now being erected at the House of Commons for the instantaneous conveyance of messages from the various committee-rooms to the messengers’ lobby.

Our engraving represents a front view of the dial with its alphabetical circles and pointer; and on the other side is a view of the interior of the instrument with the dial-plate removed, in order to show the arrangement of the electro-magnets, connecting wires, toothed wheel, and pallet movement, alarum detent, and index. The rim of the dial is marked with four concentric circles, containing four several series of the letters of the alphabet, and two inner circles of numbers. With each successive tick of the ratchet-wheel, the hand or index moves through one division of the circles, there being ninety-six equal divisions; and as each of these divisions is marked with a letter, the hand is made to stop in its circuit at any one of the divisions at pleasure, and thus to point to any particular letter of the word intended to be conveyed by the distant correspondent. For this purpose, a key resembling that of a piano-forte is employed. The pointed end of one of the wires in communication with one element of a voltaic battery, is, by depressing the key, made to dip into a cup of mercury in metallic connection with the other element or metal plate; and a galvanic circuit being thus alternately completed and broken, by the rapid depression and liberation of the key, the index or pointer at the receiving station is advanced step by step to any required division on the dial. In our engraving, D and E are two electro-magnets fixed on the upright backboard F. A ratchet-wheel G, carrying an arbor (c), is placed in the same plane as the magnets; two levers (H H) are supported on pivots in the brackets I I, and, in order to render the action of these levers simultaneous, they are connected at a point immediately over the arbor c, by a link (a); from the ends of these levers are suspended by joints, two pallets (b c), which are pressed into the teeth of the ratchet-wheel G by delicate springs; the extent of the action of the pallets, as they are raised by the attraction of the magnets, is limited by the stops d e, causing a dead-beat movement of the apparatus. When the key K is depressed by the operator, the levers H H are attracted by the magnets D E, causing the palletsdc to be raised; the pallet b catching a tooth on the ratchet-wheel, moves the index s through the space of one division. The signal, which it is necessary to give to the correspondent at the distant station, as an intimation that a message is about to be transmitted, is conveyed in the usual way, by causing a bell or alarum (sic) to sound; and this is effected by a slight modification of the contrivance hitherto adopted in most of the preceding electric telegraphs, for a similar purpose, namely, by the action of a lever, which, being raised by the attractive force of an additional electro-magnet, comes in contact with the short arm of another lever, which strikes on a bell; and, by a repetition of the action, produces any required number of sounds, the conventional meaning of which may have been previously arranged and agreed upon.

In all this modification of previously existing apparatus, we recognise considerable ingenuity of detail; but nothing of an approach towards obviating the disturbing effects of atmospheric electric currents, or of the other now well-known disadvantages attending the transmission of the galvanic current through very long lengths of wire. In this arrangement we have still the trouble and uncertainty attendant on all the systems as yet introduced, wherein the message has to be deciphered letter by letter— a necessarily slow, and, at the very best, unsatisfactory process. In our next number, we purpose giving a description of the latest improvements of a far-preferable system of electro-telegraphic communication— namely, of self-registering electric telegraphs, for some time past in use in America, and now on the eve of introduction into this country.

The system of "deflected needles" hitherto employed, and which the above arrangements are intended to supersede, we shall now endeavour to explain to the general reader by means of the accompanying diagrams, illustrative of the general principle on which the "needle telegraphs” are constructed. If a permanently magnetised needle be nicely poised on a pivot, and, consequently, be left to tun freely like that of the mariners’ compass, in what is termed the magnetic meridian, it will, of course, point nearly north and south. Now, if a long wire, connected with the two ends of a voltaic battery, be made to pass transversely over the needle, or if, as is usually the case in practice, the needle be so placed as to be freely suspended within a coil or helix of the same wire, the instant the voltaic current is made to pass along the wire, the permanently magnetised needle will be forced or deflected from its natural position, and will move with considerable velocity either to the right or to the left, according as the voltaic current is made to enter the helix or coil, from one or other pole ‘of the battery. By this means, the needle may be caused, at any distance, to point in two contrary directions, its tendency to perform a complete revolution, in either direction, being prevented by two small ivory studs or pins against which it strikes, alternately, with some degree of force. Supposing, therefore, the small needle be made to strike, for instance, once to the right and once to the left, this signal may be understood to designate the letter A of the alphabet; once to the right and twice to the left, the letter B; twice to the right, and again twice to the left, the letter C, and so on; by varying and combining the number and direction of its motions, it will easily be understood that a great variety of preconcerted signals may be given. The working of this system of Electro-Telegraphs necessarily requires great nicety of manipulation, close attention, and \considerable practice on the part of the operator. There are likewise other disadvantages ‘attending the use of the deflected-needle telegraphs.

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