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Among the most interesting of Siemens's investigations were his experiments on the influence of the electric light in promoting the growth of plants, carried out during the winter of 1880 in the greenhouses of Sherwood. These experiments showed that plants do not require a period of rest, but continue to grow if light and other necessaries are supplied to them. Siemens enhanced the daylight, and, as it were, prolonged it through the night by means of arc lamps, with the result of forcing excellent fruit and flowers to their maturity before the natural time in this climate.

While Siemens was testing the chemical and life-promoting influence of the electric arc light, he was also occupied in trying its temperature and heating power with an 'electric furnace,' consisting of a plumbago crucible having two carbon electrodes entering it in such a manner that the voltaic arc could be produced within it. He succeeded in fusing a variety of refractory metals in a comparatively short time:

thus, a pound of broken files was melted in a cold crucible in thirteen minutes, a result which is not surprising when we consider that the temperature of the voltaic arc, as measured by Siemens and Rosetti, is between 2,000 and 3,000 Deg. Centigrade, or about one-third that of the probable temperature of the sun. Sir Humphry Davy was the first to observe the extraordinary fusing power of the voltaic arc, but Siemens first applied it to a practical purpose in his electric furnace.

Always ready to turn his inventive genius in any direction, the introduction of the electric light, which had given an impetus to improvement in the methods of utilising gas, led him to design a regenerative gas lamp, which is now employed on a small scale in this country, either for street lighting or in class-rooms and public halls.

In this burner, as in the regenerative furnace, the products of combustion are made to warm up the air and gas which go to feed the flame, and the effect is a full and brilliant light with some economy of fuel. The use of coal-gas for heating purposes was another subject which he took up with characteristic earnestness, and he advocated for a time the use of gas stoves and fires in preference to those which burn coal, not only on account of their cleanliness and convenience, but on the score of preventing fogs in great cities, by checking the discharge of smoke into the atmosphere. He designed a regenerative gas and coke fireplace, in which the ingoing air was warmed by heat conducted from the back part of the grate; and by practical trials in his own office, calculated the economy of the system. The interest in this question, however, died away after the close of the Smoke Abatement Exhibition;and the experiments of Mr. Aiken, of Edinburgh, showed how futile was the hope that gas fires would prevent fogs altogether. They might indeed ameliorate the noxious character of a fog by checking the discharge of soot into the atmosphere; but Mr. Aiken's experiments showed that particles of gas were in themselves capable of condensing the moisture of the air upon them. The great scheme of Siemens for making London a smokeless city, by manufacturing gas at the coal-pit and leading it in pipes from street to street, would not have rendered it altogether a fogless one, though the coke and gas fires would certainly have reduced the quantity of soot launched into the air. Siemens's scheme was rejected by a Committee of the House of Lords on the somewhat mistaken ground that if the plan were as profitable as Siemens supposed, it would have been put in practice long ago by private enterprise.

>From the problem of heating a room, the mind of Siemens also passed to the maintenance of solar fires, and occupied itself with the supply of fuel to the sun. Some physicists have attributed the continuance of solar heat to the contraction of the solar mass, and others to the impact of cometary matter. Imbued with the idea of regeneration, and seeking in nature for that thrift of power which he, as an inventor, had always aimed at, Siemens suggested a hypothesis on which the sun conserves its heat by a circulation of its fuel in space. The elements dissociated in the intense heat of the glowing orb rush into the cooler regions of space, and recombine to stream again towards the sun, where the self-same process is renewed. The hypothesis was a daring one, and evoked a great deal of discussion, to which the author replied with interest, afterwards reprinting the controversy in a volume, ON THECONSERVATION OF SOLAR ENERGY. Whether true or not--and time will probably decide--the solar hypothesis of Siemens revealed its author in a new light. Hitherto he had been the ingenious inventor, the enterprising man of business, the successful engineer; but now he took a prominent place in the ranks of pure science and speculative philosophy.

The remarkable breadth of his mind and the abundance of his energies were also illustrated by the active part he played in public matters connected with the progress of science. His munificent gifts in the cause of education, as much as his achievements in science, had brought him a popular reputation of the best kind; and his public utterances in connection with smoke abatement, the electric light. Electric railways, and other topics of current interest, had rapidly brought him into a foremost place among English scientific men. During the last years of his life, Siemens advanced from the shade of mere professional celebrity into the strong light of public fame.