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 cylinder, and the limit of exhaustion was thereby much extended. The invention was well received at the time, but is now almost forgotten.

Siemens had been trained as a mechanical engineer, and, although he became an eminent electrician in later life, his most important work at this early stage was non-electrical; indeed, the greatest achievement of his life was non-electrical, for we must regard the regenerative furnace as his magnum opus. Though in 1847 he published a paper in Liebig's Annalen der Chemie on the 'Mercaptan of Selenium,' his mind was busy with the new ideas upon the nature of heat which were promulgated by Carnot, Clayperon, Joule, Clausius, Mayer, Thomson, and Rankine. He discarded the older notions of heat as a substance, and accepted it as a form of energy. Working on this new line of thought, which gave him an advantage over other inventors of his time, he made his first attempt to economise heat, by constructing, in 1847, at the factory of Mr. John Hick, of Bolton, an engine of four horse-power, having a condenser provided with regenerators, and utilising superheated steam. Two years later he continued his experiments at the works of Messrs. Fox, Henderson, and Co., of Smethwick, near Birmingham, who had taken the matter in hand. The use of superheated steam was, however, attended with many practical difficulties, and the invention was not entirely successful, but it embraced the elements of success; and the Society of Arts, in 1850, acknowledged the value of the principle, by awarding Mr. Siemens a gold medal for his regenerative condenser. Various papers read before the Institution of Mechanical Engineers, the Institution of Civil Engineers, or appearing in Dingler's Journal and the Journal of the Franklin Institute about this time, illustrate the workings of his mind upon the subject. That read in