Page:Dictionary of National Biography volume 60.djvu/442

 very typical of his farsightedness into the practical utility of any known scientific fact. His ‘polar clock’ was another instance of this trait of his genius. When Brewster discovered that the plane of polarisation of the light from the sky is always 90° from the sun, Wheatstone devised a clock by which it was possible to tell the hour of the day by the light from the sky though the sun might be invisible.

It was by this skill in turning knowledge to practical account that Wheatstone gave to the electric telegraph the character which it now possesses. Though his inventions in other branches of science are as numerous as they are various, it is in connection with the electric telegraph that the name of Wheatstone will always live. He was not the ‘inventor’ of the electric telegraph. Indeed no one can lay claim to that title. Stephen Gray [q. v.] in 1727 suspended a wire seven hundred feet long on silk threads, and on applying an excited glass tube to one end electrification was observed at the other, but he did not send messages. Advances were made from that time by many men of science, who saw more or less clearly the great possibilities before them. Omitting the pioneer claims of Lomond, Sömmering, and others of the last century, the names connected with early development of the practical telegraph are Froment in France, Gauss, Weber, and Steinheil in Germany, Sir Francis Ronalds [q. v.] and Edward Davy [q. v.] in England, Morse and Vail in America. But to Wheatstone, with his coadjutor (Sir) William Fothergill Cooke [q. v.], is due the merit of having been the first to render it available for the public transmission of messages. In 1834, shortly after being appointed professor of experimental physics at King's College, London, Wheatstone began experimenting on rate of transmission of electricity along wires. For this purpose about half a mile of copper wire was insulated by suspension in the vaults under the college, and three interruptions of this circuit were made by three pairs of brass knobs with a small interval between them. One of these interruptions was in the middle point of the conductor, and the other two near the ends. A Leyden jar was discharged through the wire, and the interval of time between the occurrence of the sparks at the ends and the occurrence of the spark at the middle was measured by noting the displacement of the image of the middle spark in a mirror revolving at a known speed. It was calculated from results of this experiment that the velocity of an electric disturbance along a wire was about two hundred and fifty thousand miles per second, a result differing from the true speed of one hundred and eighty-six thousand miles per second not very widely, considering the difficulties of observation in an experiment of this kind. From this research he passed on to the transmission of messages by electricity, and, in conjunction with Cooke, he elaborated the five-needle telegraph, and then the two-needle telegraph, the first that came into general use. Wheatstone's fertility of scientific resource led the partners on to many new developments—the letter-showing dial telegraph in 1840, the type-printing telegraph in 1841, and the magneto-electric dial telegraph, a subsequent extension of the same to type-embossing, and, lastly, the automatic transmitting and receiving instruments by which messages are sent with such great rapidity.

He was the first to appreciate the importance of reducing to a minimum the amount of work to be done by the current at the receiving station by diminishing as far as practicable the mass, and therefore the inertia, of the moving parts; this was beautifully exemplified in that marvel of ingenuity the magneto-electric letter-showing telegraph, commonly adopted for private telegraphic communication.

From 1837 Wheatstone appears to have devoted a good deal of time to submarine telegraphy, and in 1844 experiments were made in Swansea Bay, with the assistance of J. D. Llewellyn. Wheatstone also had a share in the perfecting of the magneto-electric machines which have culminated in the modern dynamo. In 1837 he devised a method of combining several armatures on one shaft so as to generate currents which were continuous instead of intermittent, and in 1867 he described to the Royal Society a method of making such machines self-exciting as to their magnetism by the use of a shunt circuit; the use of a main circuit for the same purpose had been described by Werner Siemens one month earlier, but the machine described by Wheatstone had been constructed for him by Mr. Stroh in the preceding summer. Wheatstone was also inventor of a system of electro-magnetic clocks for indicating time at any number of different places united on a circuit.

Among other accomplishments Wheatstone had an extraordinary facility in deciphering hieroglyphics and cipher despatches. He himself invented a cryptograph or secret despatch writer, which is supposed to be indecipherable. Wheatstone's miscellaneous inventions are too numerous to mention here in detail. They related, among other things, to electric chronographs, apparatus for making instruments record automatically;