In 1516, Mr. itonalds, of Hammersmith, invented an electric tele graph, in which the use of frictional electricity was recurred to. This telegraph, which was shown to several scientific men at the date above given, was fully described by the inventor in a work published by him in 1823. Mr. Itonalda employed the divergence and collapse of a pair of pithdells as the telegraphic indication, in which respect the principle was the sane as that adopted by Mr. Lomond ; but to this simple apparatus, a distinct contrivance was appended, in order to render the communication more rapid and easy. A single wire, perfectly insulated by being suspended from silken strings, or buried in glass tubes, surrounded by pitch, and protected by wooden troughs, was eitcnded between tho two stations. From the end of this wire was suspended in front of the dial of a clock a pair of pith-balls, so that while the wire was charged the balls would remain divergent, but would instantly collapse, when the wire by contact with the earth, or with the hand of the operator, was discharged. A person at one end having therefore an electrical machine by which he could maintain the wire in an electrified state, and the pith-balls at the farther extremity consequently in a state of divergence,—had it of course in his power to give an instantaneous indication to an observer at that farther extremity by touching the wire with his hand, which, discharging the electricity, would allow the balls to col lapse for an instant. But instead of merely employing the successive movements of the pith-balls to denote the various signals, Mr. Ronal& added another apparatus for this purpose. Two clocks, very accu rately adjusted to the same rate of going, carried, instead of the ordinary seconds hand, light discs, on which the various letters of the alphabet, the figures, and other required signals were engraved. These discs turned with a regular step by step movement, behind a screen of metal, in which was made a small opening, sufficient to allow of one letter at a time being seen. As the discs turned round, each letter in succession would be visible through this space; and it is evident that if the clocks were started with the same signal visible, the movement of the discs would bring similar signals into view at the same time. One of these instruments was situated at each end of the communicating wire. The operator who was about to trans mit any communication, watched the dial of his clock until the letter he required was visible, and at that instant discharged the wire. The momentary collapse of the balls at the distant end would then warn the observer to note the letter visible on his instrument, which would form a part of the intelligence to be received. The successive letters or signals constituting any message were denoted iu this mauner Al the clock dials continued to turn round. In order to avoid the necessity for constant attention on the part of the observer, an arrangement was adopted by which a pistol could Lo fired by the spark at the farther end, to summon the attendant to his instrument. Various signals were also concerted beforehand, by the use of which the time necessary for the transmission of any intelligence was lessened. These experiments of Mr. Roualds' were made with the interven tion of several miles of wire, carried backward and forward across his grounds.
In 1819, Professor Oersted of Copenhagen made his great dis covery of the action of the galvanic current upon a magnetic-needle. He observed that when a current is passed along a wire, placed parallel and near to a magnetic needle, free to turn on its centre, the needle is deflected to one side or the other, according to the direc tion in which the current is transmitted. He further noticed that the position of the wire, whether above or below the needle, had an equal influence with the direction of the current in determining the side to which the deflection took place. [Esserno-D roams.] The power of a single wire in causing this deviation of a needle is but small, but this was remedied by the invention of the multiplier, or GALVANOMETER, by Professor Schweigger, in which the needle, being surrounded with many successive coils of insulated wire, is acted upon by the joint force of all. Under a somewhat different form, this dis
covery now forms the basis of the needle electric telegraph.
Very shortly after this important discovery had been made, Arago and Ampere in France, and Seebeck in Berlin, succeeded in rendering iron magnetic, by the passage of a galvanic current through a wire coiled around the iron, and Sturgeon in England produced the first electro-magnet [Eteesno-MeessTism.] It was found that, provided the iron to be magnetised were perfectly soft and pure, the magnetic property remained only during the actual transmission of the elec tricity, and was lost immediately on the interruption of the electric circuit. If the iron which was exposed to the influence of the galvanic current were combined with sulphur, carbon, or phosphorus, the magnetic power became to a greater or less extent permanent in it.
The invention of the voltaic battery, of the deflection of the needle. and of the magnetisation of soft iron, formed the three great steps in tho history of the electric telegraph.
M. Ampere suggested the employment of the discovery of Oersted as early as 1830, and this suggestion was acted upon by Professor Ritchie, in a model telegraph exhibited by him at the Royal institu tion. Ampere's plan however was far from possessing the simplicity so essential in an instnunent designed for practical use. Not less than thirty pairs of conducting wires were necessary, according to his scheme, for maintaining a telegraphic communication.
Baron Schilling also, in Prussia, in 1832 and 1S33, following the i lea originated by Ampare, proposed a similar form of telegraph, in which there were as many of these galvanometers, each with its approp iate circuit, as there were letters or signs to be used in the various com munications. In fact there were 30 needles and 72 wires. In 1833, Gauss and Weber proposed to employ the separate movements of a suspended bar as signals : but its indications must have been feeble, as they had to be observed through a telescope placed at some distance from the oscillating bar. In 1837, M. Alexander exhibited a model of a proposed form of telegraph, containing 25 needles, to be acted upon as in Ampere's arrangement. In this instrument a distinct needle was employed for the indication of each letter, these needles bearing at one end light screens of paper, which concealed from view a letter or figure, until by the deflection of tho needle the screen was removed, and the letter brought into sight. M. Alexander, however, effected one great improvement, in substituting a single return wire, to which one end of all the coils was joined for the several distinct return wires existiug in the previous invention of M. Schilling. At a later period this gentle 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 31. 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, so that the operator communicated any letter by pressing down the corresponding key.