A Story of the Telegraph

by John Murray

In both of these telegraphs, all that was required in addition to the indicating apparatus and conducting wires, was a contrivance by which the connection 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. One pole of the battery being connected to the return or common wire, the other pole of the battery 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 instrument, and return by the common wire to the Voltaic battery. The keys bore the same letters as the needles to which they were connected, so 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 of 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 unexpected development of the electric telegraph in the hands of these gentlemen led each one who was in possession of any title to the merit of having believed in and experimented upon the possibility to produce his title, or to have it eagerly put forward by his friends and fellow countrymen.

Although the principal facts necessary to the construction of an electric telegraph had been known ever since 1821, yet it was not until the general establishment of railways that telegraph wires could be safely carried to any great distance.

Moreover, the importance of the invention was by no means understood.

In 1837 the experiments of Cooke and Wheatstone, which had been progressing for more than a twelvemonth, appeared so far successful as to induce them to apply for a patent for their inventions.

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 axis in a horizontal line. The needles when at rest hung vertically, by reason of a slight preponderence given to the 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 pair of finger keys for making the connections with the battery was placed through two of the wires at once, that is to say, of the wire 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 connecting the coils, and the second wire to the battery again.

Two needles were in this manner deflected at once, and it will be obvious, that the current would pass in opposite directions around their coils, and, consequently, that the deflection must be in contrary directions. The needles would, therefore, converge either above or below their line of centre 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 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 plan was recognized by which the number of wires requisite for 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.