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 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