73 



TELEGRAPH, ELECTRIC. 



TELEGRAPH, ELECTRIC. 



man undertook a series of experiments, with a view to the establish- 

 ment of a communication by means of a single wire ; but some 

 mechanical difficulties appear to have arrested his progress. In both 

 of these telegraphs all that was requisite, in addition to the indicating 

 apparatus and conducting wires, was a contrivance by which the con- 

 nection of the voltaic batteries could be made with any pair of wires in 

 the former, and with any single wire and the return-conductor in the 

 latter of the two inventions. In M. Alexander's instrument, a set of 

 keys resembling those of a pianoforte, and corresponding to the number 

 of needles, was arranged' on a frame or table. One pole of the battery 

 being connected to the return or common wire, the other pole was 

 joined to a plate of metal, or to a trough of mercury, extending beneath 

 all the keys. On depressing any key, the wire belonging to it, which 

 was continued to the end over the battery connection, was brought 

 into contact with this bar or trough. The current would then flow along 

 the conducting wire, around the multiplier-coil in the distant instru- 

 ment, and return by the common wire to the voltaic battery. The 

 keys bore the same letters as the needles to which they were con- 

 nected, BO that the operator communicated any letter by pressing down 

 the corresponding key. 



In these two instruments no use was made of the power which 

 exists of determining the deflection of the needle to either side, by 

 merely reversing the connections of the battery. 



We have thus traced the history of the telegraph up to the point at 

 which it first assumed the practical form in Cooke and Wheatstone's 

 inventions ; but what had been accomplished remained either unknown 

 or was known only to a few leading men of science, until the unex- 

 pected development of the electric telegraph in the bauds of those 

 gentlemen led each one who was in possession of any title to the 

 merit of having believed in, and experimented upon, its posnibility, 

 to produce his title, or to have it eagerly put forward by his friends 

 and fellow-countrymen. 



In June, 1837, the experiments of Messrs. Cooke and WheaUtone, 

 which had been progressing for more than a twelvemonth, appeared so 

 far successful as to induce them to apply for a patent for their inven- 

 tions. The principal pointa of novelty in this patent were the use of a 

 much smaller number of needles to denote all the required bignals, the 

 employment of the temporary magnetism excited by the current in 

 soft iron, to ring an alarum ; and the reciprocal arrangement by which 

 the invention was rendered practically applicable to a long line of com- 

 munication. In explaining the invention, Mr. Cooke (' Telegraphic 

 Railways ') says : ' If a magnetic needle were placed parallel and near 

 to any part of a conducting wire, which we will suppose to be laid 

 down between London and Blackwall, the transmission of an electric 

 current from a voltaic battery would cause the needle to change its 

 position, so a.i to stand during the continuance of the current at right 

 angles to the wire, being turned in one direction or the other according 

 to the course of the current. If this deflexion of the needle were 

 limited by two fixed stops placed respectively at the two sides of one of 

 its poles, the motion of that pole to one stop might evidently consti- 

 tute one signal, and it* motion to the other stop another signal." 

 Such an apparatus is shown in jig. 1, the dial upon which the signals 



Flg.I. 



are represented being removed. In this cut a may be supposed to 

 represent the battery, and 1 1 the conducting wire, which is formed 

 behind tin- dial into a coil e: ddi* the front or index needle, mounted 

 upon an axis passing through the coil, another needle on the same axis 



Fi. 3. 



being within the coil. The front needle carries upon its extremity, 

 which comes through the dial, an index or pointer e. The arrown 

 indicate the direction of the current required to deflect the magnet to 



the position indicated in the figure ; and a current in the opposite 

 direction would produce a deflexion towards the opposite side. While 

 no current passes through the wire, the maguet and pointer remain 

 vertical. The next cut (fig. 2) represents three such instruments 

 complete, and connected together by wires enclosed in tubes, which 

 may be of any required length. One of these may be supposed to be 

 at the Minories, the next at an intermediate station, and the third at 

 Blackwall; and as each is provided with a battery, and a handle 

 (beneath the dial) by which the conducting wire may be connected 

 with it at pleasure, the attendant at every station at which such an 

 instrument is placed can instantaneously communicate the signal to 

 " stop " or to "go on " to all the other stations ; attention being 

 previously engaged by ringing a bell, placed above the dial. Fig. 3 



Vig. 3. 



J 



represents a dial, in which, by the combination of four such 

 magnets and pointers, all the letters of the alphabet may be expressed 

 by pointing one or two needles towards them ; and of course a larger 

 or smaller number of signals might be made on the same principle if 

 necessary. A telegraph with two pointers, showing eight signals, is 

 considered by Mr. Cooke to be sufficient for all ordinary purposes. 

 The wires, where several are used, are covered with some insulating 

 material (such as a mixture of cotton and caoutchouc), and combined 

 into a rope and enclosed in an iron tube, which may be either buried 

 beneath the surface of the earth or supported above it. 



The instrument which was brought into use on the Great 

 Western Railway shortly after the date of the patent, contained five 

 needles, arranged with their axes in a horizontal line. The needles 

 when at rest hung vertically, by reason of a slight preponderance 

 given to their lower ends. Each coil was-connected with one of the 

 long conducting wires at one end, and was united at the other with a 

 rod of metal, which joined together the similar ends of all the coils. 

 The current was transmitted from the opposite end of the wires 

 (where a set of ,five pairs of finger-keys, for making the connections 

 with the battery, was placed) through two of the wires at once. That 

 is to y, one of the wires, of which one key was pressed down, served 

 to convey the current from one pole of the battery to the distant 

 instrument, while the key of a second wire being brought into contact 

 with the other pole, the current returned by the rod of metal con- 

 necting the coils and the second wire to the battery again. Two 

 needles were in this manner deflected at once, and it will lie obvious 

 that the current would pas in opposite directions around their coils, 

 and consequently that the deflections must be in contrary directions. 

 The needles would therefore converge, either above or below their line 

 of centres, as one or other of the pair of keys belonging to each wire 

 was depressed. Fixed stops were so placed on each side of the needles 

 as to limit their motion, and when resting against them, the needles 

 were parallel to two converging lines, at the point of intersection of 

 which a letter was placed. (Fig. 3.) This was the signal indicated by the 

 movement of the needles. In a similar manner, as lines were drawn 

 diverging from the centre of each axis, mutually crossing one another, 

 a number of points of intersection were formed, at each of which was 

 a letter or signal. Any of these letters could be indicated by the 

 simultaneous movement of two needles, so that a communication could 

 be carried on with certainty and tolerable rapidity. At the same time 

 a |. Ian was .recognised, by which the number of wires requisite fur 

 maintaining a communication might be reduced, by using one of them 

 at times as a return wire only, there being no needle in connection 

 with this one. One needle could by the use of this wire be deflected 

 by itself either to the right or left, and thus of course each would 

 furnish two signals, in addition to those formed by its simultaneous 

 deflection with any other. The instruments at the two stations were 

 always rendered reciprocating ; that is, at each end of the line were 

 placed an instrument, a set of finger-keys, and a voltaic battery, so 

 that either station could transmit or receive a signal. By an ingenious 

 arrangement, the keys, on being released after depression, were made 

 to resume by themselves the position necessary to enable that which 

 had been the signalling station to become the recipient. By this 

 means messsages and answers, or words and their acknowledgments, 

 could follow one another without the necessity for any intervening 

 adjustment of the instruments. 



The bell or alarum which was to be rung, when the attention of the 



