The Dial Telegraph of Brk mei, for many years in use with satisfactory results on tile French railways, is an apparatus operated on the same prin ciple as that of Wheatstone and Cooke, but embodies a number of substan tial improvements. Figure 26 is a diagram of the connections of the dial telegraph devised by Siemens and Halske. In this apparatus, an import ant condition in the operation of this system will be the exact synchronism of the ratchet-wheels at the two stations. To save the cost of batteries, the dial telegraph is commonly operated with the aid of the magneto-electric apparatus of Siemens and Halske referred to above.
Prinling Telegraphs.. .Worse System. —Of the printing telegraphs, that of Morse is the most widely used. Figure 31- col. 57) shows one of the forms of the Morse register. An armature, o,over the poles of the electro-magnet,E,E, is attached to one extremity of a lever, nn' , pivoted on a fulcrum near its centre. The other end of the lever carries a steel point which at each de pression of the armature, o, presses upon a ribbon of paper introduced be tween the rollers, W, (This ribbon is omitted in the illustration for the purpose of clearness.) The style will remain in contact with the paper ribbon as long as the armature is held down, and will be withdrawn from it by the action of the retracting spring, h, whenever the armature is freed from the attraction of the electro-magnet by the breaking of the circuit. There is thus formed a series of dots and dashes, the latter being pro duced by a more prolonged contact of the style with the paper; and these characters, in certain arbitrary combinations, constitute the telegraphic alphabet. For moving the rollers, W, W', which g-uide the paper ribbon, either a spring or a train of wheel-work actuated by a weight, as shown, may be employed. For sending the Morse characters the keys (j5/. 57, Jigs. 32, 33) are employed. The relay (Jig. 34) serves to throw into the circuit the current of a strong local battery by which the signals are recorded.
Figures 37 and 38 exhibit the mode of arranging a line of tele graphic communication between two terminal and 1.WO intermediate sta tions, with the Morse instrument as the chemical printer. The letters o, c, o, care the open-circuit keys (compare jig. 32); b, b, the batteries; and A, C, D, B, the electro-magnets of the recording apparatus. In Figure 37 all the keys are seen to be in contact with the parts o, but no current passes, because the circuit is broken at the points c, c. If, now, station D wishes
to speak, the key of this station is pressed down on c, and the D-batterv is thus closed. All the Morse instruments included in the main line, ex cept that at D itself, will now receive the current, which will travel in the course indicated by the arrows, while at the same time their local batteries will not be called into action. Various other arrangements of line are in Ilse, some operated upon the open-circuit and others upon the closed-circuit plan (see p. 349), for details of which the reader should consult special treatises 013 the electric telegraph.
Bain System. —In place of the style used for recording- the characters as just described, Bain 0847-1848) employed electro-cheinical decomposi tion. By this plan the record appears as a series of colored marks upon the paper. To this end, he passes the paper ribbon on which the record is to be made through a trough containing a solution formed of water six parts, sulphuric acid one part, and two parts of a saturated solution of yel low prussiate of potash. In this mode of recording, no pressure of the style iipon the paper is necessary, and the relay may be dispensed with. The chemical telegraph also may be worked more rapidly than the usual method of printing-. On the other hand, the dry writer has the advantage of greater reliability and cleanliness, the message being free from the risk of blotting or of being entirely missing in places, owing to the accidental absence of solution. In Figure 36 is shown a dry writer in which a small printing wheel carried on the extremity of the lever, b, and dipping and constant] V revolving beneath the surface of the solution in the color trough, c, presses against the paper ribbon when the armature of the electro-inag- net is attached.
s reduce the number of signals, and especially to lessen the time required to transmit the Morse signals? StOhrer of Leipsic devised a double-style apparatus on the 'Morse principle, the register being furnished with two electro-magnets actuating separate writing-levers, making two rows of dots and dashes, but recording on the same paper ribbon. BY this arrangement he was enabled to employ four elementary signals instead of two in constructing the alphabet. StOlirer's apparatus has been used to some extent in Bavaria, but its advantages have not been found to be so decided as to cause its general adoption.