FIG. 3.
In 1828, likewise, Victor Triboaillet de Saint Amand proposed to construct a telegraph line between Paris and Brussels. This line was to be a subterranean one, the wire being covered with gum shellac, then with silk, and finally with resin, and being last of all placed in glass tubes. A strong battery was to act at a distance upon an electroscope, and the dispatches were to be transmitted by the aid of a conventional vocabulary based upon the number of the electroscope's motions.
Finally, in 1844, Henry Highton took out a patent in England for a telegraph working through electricity of high tension, with the use of a single line wire. A paper unrolled regularly between two points, and each discharge made a small hole in it, But this hole was near one or the other of the points according as the line was positively or negatively charged. The combination of the holes thus traced upon two parallel lines permitted of the formation of an alphabet. This telegraph was tried successfully over a line ten miles long, on the London and Northwestern Railway.
FIG. 4.
We have followed electrostatic telegraphs up to an epoch at which telegraphy had already entered upon a more practical road, and it now remains for us to retrace our steps toward those apparatus that are based upon the use of the voltaic current.
Prof. Dolbear observes that if a galvanometer is placed between the terminals of a circuit of homogeneous iron wire and heat is applied, no electric effect will be observed; but if the structure of the wire is altered by alternate bending or twisting into a helix, then the galvanometer will indicate a current. The professor employs a helix connected with a battery, and surrounding a portion of the wire in circuit with the galvanometer. The current in the helix magnetizes the circuit wire inclosed, and the galvanometer exhibits the presence of electricity. The experiment helps to prove that magnetism is connected with some molecular change of the magnetized metal.