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 magnetization of soft iron, formed the three great steps in the history of the electric telegraph.
M. Ampère suggested the employment of the discovery of Oersted as early as 1830, and this suggestion was acted upon by Prof. Ritchie, in a model telegraph exhibited by him at the Royal Institution.
Ampère’s plan, however, was far from possessing the simplicity so essential to an instrument designed for practical use; not less than thirty pairs of conducting wires were necessary according to his scheme for maintaining a telegraph communication.
Baron Schilling in 1832 and 1833, following the idea originated by Ampère, proposed a similar form of telegraph in which there were as many of these galvanometers, each with its appropriate circuit, as there were letters or signs to be used in the various communications, 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 indication 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 twenty-five needles to be acted upon as in Ampère’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 the needle the screen was removed, and the letter brought into sight.
M. Alexander, however, effected one great improvement in substituting a single wire to which one end of all the coils was joined for the several return wires existing in the previous invention of M. Schilling.
At a later period this gentleman undertook a series of experiments with a view to the establishment of a communication by means of a single wire, but some mechanical difficulties appear to have arrested his progress.