The action is as follows :—The type-disc is turned round by alter nately transmitting and interrupting the current until the proper letter is brought into the proper position to be struck, when, the hammer being released, it presses the typo on the paper. The drawing rollers immediately jerk the papers forward through a space equal to that of one letter, when the type-disc is again moved onward to the next letter required, which is struck in like manner, and so with all the rest of the letters in the message. The hammer usually strikes by the force of a spring, which Is released by the train which acts upon the drawing-rollers. The mechanism is eo contrived that the hammer cannot strike while the type-disc is in motion, but falls as soon as a pause is made, that is, when the right letter is brought into position. The types are inked by means of a small roller smeared with printing ink, which, as the typo-disc revolves, presses lightly against their sur faces. Or a ribbon of carbonic ink transfer-paper may be drawn round between the type-disc and the white paper ribbon. Numerous variations have been made in the type-printing telegraph, the beat known of which is by Mr. Bain. In this machine the types were arranged on the edge of the disc or wheel, radiating from its centre; and the printing of any one upon the cylinder was effected by the movement forward of the entire type-wheel and its axis, by a crank and connecting gear in the printing train, instead of one punch or type only being struck down by the printing-hammer, in impressing a signal. It was also proposed to use two clocks at the two communicating sta tions, to rotate the type-wheels with a uniform motion. These clocks, having been adjusted to exactly the same rate, and being started from the lame signal, would bring continually, at each station, similar type opposite to the paper-cylinders at the same moment. The action of this part of the apparatus is exactly analogous to that of Mr. Ronalda', already described. A hand or index revolving on a dial in front of the machine, at the same rate asi the type-wheel, indicates to the operator the signals which are successively in a position ready for printing in his own instrument, and therefore, if the clocks go accurately together, in a similar position in his correspondent's Instrument. At the same time this fund, by coming in contact. In its revolution with a pin, placed by the operator opposite to any signal that he wishes to print, complete. the electric circuit at this moment, and by so doing store the type-wheel, and releases the printing-train at each station. A similar figure laving thus been impressed on the cylinder at the two ends of the line, the operator removes the pin, and replaces it opposite the next signal he requires to send. The moment the phi is removed, arid the circuit therefore broken, the hands and type-wheels at each station resume their evolution's which are again checked by — — — — the contact of the hand and pin as before. It should be stated that the idea of the two clocks, as well as that of the printing-telegraph, was borrowed from Wheatstone Bain'e sinle.inde.r telegraph, which was the instrument proposed by Lim for practical nee, consisted of two hollow cylindrical coils of wire, placed horizontally a short distance apart, with their axes in the same line. Between them a small bar-magnet was fixed across a delicate spring, which in front passed through the dial-plate of the instrument, and was turned up to form an index. The two coils were connected, so that an electric current entering from the line wire would pose through both. When this was the case, the bar-magnet would be attracted towards one coil, while at the same time it would be repelled by the other. These actions tended to carry the magnet to the same side, as far as the spring to which it was attached and a fixed stop would allow of its moving. The reversal of the current inverted the effects of the coils, and the magnet would then pass to the other side. The combinations of these two movements represented the carious letters and signals, they being denoted to the observer by the index on the dial of the instrument. The movement of the index to the left denoting the letter t, and to the right the letter v, this instrument obtained the name of and v Telegraph.' In 1842, Mr. Bain patented his proposed plan for working an electric telegraph by means of an earth battery. At one end of the line he buried in moist earth a large plate of zinc, and at the other cud plate of copper, iron, or other substance such as coke or charcoal, which might act the part of a negative plate to the zinc. Then, on connecting these distant plates with a wire insulated from the earth, a current of electricity would constantly pass from the one plate to the other. Indeed, the distant plates connected with the wire, as above described, may be regarded merely as a battery of one pair of plates, separated by a very wide interval of exciting material, represented by the earth. It was at first supposed by Mr. Bain that this current
would be applicable to all telegraphic purposes, but subsequent experi ments showed that it was available only for a few miles of distance ; its intensity not being sufficient to enable it to travel through any great length of wire. In some cases, where a constant current of low inten sity is required, this earth battery might be of use.
In 1843, Mr. Cooke introduced the mode of extending the wires between distant places, so that their insulation from one another, and from the earth, might be maintained without. the expense and difficulty hitherto incurred ; before this period the wires having been covered with cotton, and insulated by coating them with shell-lac, resin, or pitch, bad been laid down in pipes of wood or iron. It was now proposed to insulate the wires by suspending them in the air upon posts or standards of wood or iron, the wires not coming in actual contact with any part of the standard, but passiug through rings of porcelain or earthenware. [Glass was afterwards found to be the best insulator.] The standards were usually fixed at from forty to sixty yards asunder, and at each quarter of a mile a stouter post was placed, to bear the winding or straining apparatus. This was a simple winding-reel, con nected with a ratchet-wheel and click to prevent its recoil, after the wire had been strained up by its means. The intermediate posts within each quarter of a mile only supported the wire, without. refer ence to its tension, which depended solely on the winding posts. Instead of the copper wires hitherto employed, iron wires of a larger size were now used. By the adoption of this method of extending the conducting wires, the cod of construction of an electric telegraph was reduced nearly one-half, and at the same time the risk of imperfect insulation was diminished. So long as the wires were buried in tubes beneath the ground, it was always deemed prudent to add a return wire, extending from one end of the line to the other ; as it was found very difficult to render the insulation sufficiently good to enable the earth itself to be used as half of the circuit. The tendency of the electric fluid to escape from the wires in the tubes to the earth, was much greater than to another wire lying in the same tube, so that the latter plan was always adopted. But when the suspended conductors came into operation, the insulation was rendered so complete, that the earth was subsequently in all cases need to return the current, by which means an economy of one wire throughout the whole line was effected. In addition to this, another advantage was gained by the suspension of the wires, In the facility with which accidental errors or injuries wore discovered and rectified. While the tubes were in use, it was necessary to supply, at about each quarter of a mile along the line, a proving or testing post, within which the wires were brought ' up to a box, so as to afford the means of examining any of them as to their insulation and conducting power. For this purpose, Mr. Cooke had invented an instrument called the detector, by which the perfect state of each wire could be tested, and the position of any error or fault discovered with considerable accuracy. Still, with all these appliances, the detection and repair of any derangement of tire wires demanded considerable skill, and led to no small expense. But when the wires wero in sight throughout, any contact or fracture was at once visible, and was easily and quickly repaired.
We must here pause in the attempt to trace the history of this great invention through the medium of its patents. The reader who ns desirous of pursuing the subject in this way, is referred to one of the valuable volumes printed by order of the Connnissioners of Patents, entitled Abridgments of Specifications relating to Electricity and Magnetism, their Generation and Applications' (1S59). This volume contains an introduction of xciii. pages, and an abstract of patents extending to 728 pages, exclusive of a copious index. A single speci men of this index will show the extent of patent influence that has been exerted down to the year 1857. For example : under ' Tele graphs ' (Electric), we have for acoustic telegraphs, 14 patents ; copying telegraphs, 8 ; dial telegraphs, 65 ; embossing, 1; gold leaf, 2 ; mag neto-electric, 23 ; marking, 33 ; needle, 39 ; pointer, 32 ; portable, 7 ; printing, 44; and recording telegraphs, 5 patents ; while the compo nent parts of electric telegraphs are the subjects of separate patents under distinct heads, such as alarums, telegraphic, 76 patents; insula tors, 42 patents ; galvanic batteries, nearly three columns of names.