Page:Popular Science Monthly Volume 12.djvu/350

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energy had previously been recognized, or involved in the dispute as to the intimate constitution of heat, may be inferred from what has been already given of the history of heat theory. But in 1822, M. A. Seguin, in a letter to Sir J. F. W. Herschel,[1] explicitly asserted it in support of the dynamical existence of heat, and in explanation of the work obtained from caloric in the steam-engine. The view of the subject he claimed to have derived, some years before, from his uncle, the celebrated Montgolfier.

Soon after he restated these considerations in a letter to Sir David Brewster,[2] wherein, by a perfectly legitimate course of reasoning, and in a very lucid manner, he showed that the accepted teachings of the calorists led to a violation of this principle of the conservation of energy. For, quoting his own language:

"If we suppose, indeed, that at each stroke of the piston of a high-pressure steam-engine the quantity of caloric employed is represented exactly by the elevation of temperature of the water of condensation, abstracting all loss, it follows that we have lost nothing in obtaining a very great effect, and that, if it were possible (which is supposable)[3] to condense the caloric contained in a mass M into another represented by Mx, in such a manner that it may be reduced into vapor at the primitive pressure, we may, by means of a small quantity of caloric, produce an indefinite number of oscillations."

He expressly stated, therefore, that after a mechanical effect had been produced through any given thermal agency, as in a steam engine, only that quantity of molecular motion or heat which had not been thus appropriated would remain as heat.

To him, therefore, most undeniably belongs the credit of having first publicly urged the principle of the conservation of energy against the materiality of heat, and of having considered in this connection the reverse phenomenon of the performance of work by thermal agencies.

The only indefinite or erroneous particular in his statement was that arising from the rather incautious introduction of molecular hypothesis. His leading argument was thoroughly scientific, but the oversight or neglect to refer explicitly to the disturbing effect which latent as distinguished from sensible heat might exert upon the experimental verification of his principles, served afterward as a point of attack upon the accuracy of his reasoning in general, and an opportunity, abundantly improved, to detract from his true merit as an early supporter of the mechanical theory of heat.

This criticism depends upon and applies with still greater justice

  1. Published in the Edinburgh Philosophical Journal, x., p. 280.
  2. Published in the Edinburgh Journal of Science, iii., p. 276, 1825.
  3. A particular instance of this supposition will be seen in our account of Carnot's engine.