WheatJtone'sAutematie Transmitter.—The speed of the ordinary Morse instrument is limited to the rapidity with which the hand of the operator can move the key, so as to preserve the proper spacing between the marks at the receiving instrument. We are indebted to sir Charles Wheatstone for 'an apparatus which trebles, and in some cases quadruples the carrying capacity of a wire, securing, at the same time, mechanical accuracy in the relative size of the dots, dashes, spaces, etc. To effect this, three differ ent instruments are required: First, there is a perforator, by which holes are punched in a paper slip to correspond with the signals required. The operator strikes three disks, the central one producing a central hole, which is of no avail electrically, only carrying forward the paper; the left-hand disk producing two holes, directly opposite to each other, on the sides of this central row; and that on the right producing two holes, placed diagonally to each other. The passage of the electric current is regulated by the posi tion of the outer holes. Those opposite each other admit of a momentary passage of the current through the "transmitter"—used in sending the message—while the holes diagonally placed produce a lengthened mark, corresponding to the dash. The follow ing diagram represents the word "and," as shown on the punched slip: The third portion of this instrument is the " receiver," in which the currents sent by the action of the punched slips in the transmitter are reproduced in the dots and dashes of the Morse code—the printing being, moreover, done with a mathematical accuracy keying by hand cannot attain. The speed of transmission depends on the length of line and state of the atmosphere; but the movement of the clock-work, both of trans mitter and receiver, is capable of adjustment to any speed below 120 words per minute. When the post-office took possession of the telegraphs in this country, the Wheatstone automatic instrument was in use at only four stations in the kingdom. It has since come into extended use; and one of its most successful applications is in the simultaneous transmission of news from London to a large number of towns. The punched ribbon is carried from one transmitter to the other, the circuit to Birmingham, Manchester, and Liverpool (on which the highest speed is attained) sending it first, and from that instru ment it passes to several others, each serving several towns. The adjustment of "resist ance," by which a message is run off simultaneously at Edinburgh, Glasgow, Dundee, and Aberdeen by one sending from London (and so through the various transmitters where this system of "express news circuits" is adopted), forms one of the most inter esting objects of study in the practical working of the telegraph in this kingdom. By combining the automatic transmission with Bain's principle of producing marks on chemically prepared paper, an American inventor has accomplished still higher speed, the lever action of the inking disk (fig. 1) being saved.
Other Instruments.—All that has been said as to the battery, the earth insulation, etc., is applicable to nearly every instrument now in use; the exception being several mag neto electric instruments, such as Wheatstone's "ABC," in which the use of s battery Is dispensed with, power being generaten ny two bobbins coiled upon an armature rotating continuously over the two poles of a permanert magnet. On the upper surface of this instrument is seen a circle of buttons corresponding to the letters of the alphabet, by means of which levers, arranged vertically in a circle, may be pressed down. These levers press a pitch chain into a series of indentations on the periphery of a metal disk, the chain having sufficient slack, so that, when a second lever is depressed, the first must be raised. A series of currents, corresponding to the number of letters between each lever pressed down, is sent into the line, and operating on twolittle bent magnets, moves forward a ratchet wheel, having a pointer on the same axis which shows the letter on a dial card. In this way the message is spelled out letter by letter, and as the instrument gives not an arbitrary sign, but the letter itself, it is much used in private telegraphs and for the smaller post-offices throughout the kingdom. The non-recording instrument most used in this country(excluding private telegraphs) is the single-needle instrument of Cooke and Wheatstone. It consists of an upright galvanometer, with astatic needles, one of which moves within the coil, and the other upon the front of the dial. The
needles are loaded at the lower end, to maintain them perpendicular when no current is passing. The instrument is worked by means of two keys, like those of a piano, a deflection of the needle to right or left being effected by depressing one or other of the keys. The signal is shown both on the sending and receiving instrument. The Morse alphabet is used, a deflection to the left corresponding to the dot, and one to the right representing the dash.
Acoustic the introduction of high-speed automatic instruments for the more important circuits, expert telegraphists in many cases dispensed with the reading of the printed slip, reading by the sound, which, by long practice, became a language perfectly intelligible to them. The great advantage of this was, that the use of the eye was obtained exclusively for the task of writing down the message. In sir Charles Bright's "bell" instrument, most admirable results, in point of speed, have been attained. The bells, different in sound, are placed at the two sides of an upright instru ment, so that the clerk, bending forward to write, may concentrate his attention on that duty, translating in his mind the tinkle of the hammers as they ring out their message. The bells are now worked in the Morse code—the left bell a dot, and the right bell a dash ; but when first introduced, the instrument had a code of its own, based on the desire to complete each letter as much as possible on one bell. A simpler acoustic tele graph has been brought into use in America (hence called the "American sounder") and in this country. This instrument is, shortly stated, the Morse without its wheel-work and ink-printing apparatus; and its whole construction is shown in fig. 1, omitting the inking disk. The use of the "sounder" has greatly increased in this country owing to its cheapness and efficiency. For a description of the type-printing and fee simile instru ments, on which great advances have been made of late years, we must refer our readers to the larger treatises on the telegraph and its history.
Duplex fact that two currents may be sent simultaneously (one from each end) has been long recognized by electricians, but the principle of the duplex was revived and patented by Stearns, an American, in 1872. At first the duplex-working was only tried on short circuits of 40 to 60 m.; but it has now become a matter of daily use on every busy circuit, long or short, both in this country and abroad. The principle of the duplex system is that the current sent on the depression of the key is divided into two parts, one-half being carried through one pair of coils in a differential galvanometer to the line, and the other half through the other pair of coils to a resistance coil, and thus to earth. The resistance of the latter is made exactly equal to that of the line-wire, and the instrument of the sender being so placed that this divided current presses equally in each direction, this instrument remains unaffected, while the armature at the other end responds to the signal sent. At the same time a telegraphist at the other end is sending a current, which is divided in like manner, and leaves his own instrument unaffected while operating on the armature of the first instrument. The two currents on the line wire assist or oppose each other in such a way as to affect the equilibrium in the differ ential galtuometer, but each operates only on the distant instrument. Duplex-working led to diplcx, that is, two messages passing over a wire in the same direction at once, and to this has followed quadruplex and multiplex telegraphy. Quadruplex working was first perfected in 1876 by Prescott, Edison, and Gerritt Smith, but the possibility of its being accomplished was suggested by Stark of Vienna, in 1855. It was introduced into Britain as a practical branch in 1878, and is now used from London to Liverpool, Dublin, and other towns. An illustration of the value of these additions to the wire power is afforded by a wire from Chicago to Pittsburg, 550 m., which is quadruplexed, and at Pittsburg branches off in two duplex circuits to Baltimore and Philadelphia, giving Chicago duplex communication with these two places. In the same way Middlesborough and West Hartlepool have been duplexed to London, on separate wires as far as Leeds, and quadruplex on one wire thence to London.