Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/53

 omitted from it; some of them, such as oxygen and hydrogen, because they were as yet undiscovered, and others, such as the metals, because they were believed to be compounds.

Among the chemical elements, it became customary after the time of Newton to include light-corpuscles. That something which is confessedly imponderable should ever have been admitted into this class may at first sight seem surprising. But it must be remembered that questions of ponderability counted for very little with the philosophers of the period. Three-quarters of the eighteenth century had passed before Lavoisier enunciated the fundamental doctrine that the total weight of the substances concerned in a chemical reaction is the same after the reaction as before it. As soon as this principle came to be universally applied, light parted company from the true elements in the scheme of chemistry.

We must now consider the views which were held at this time regarding the nature of heat. These are of interest for our present purpose, on account of the analogies which were set up between heat and electricity.

The various conceptions which have been entertained concerning heat fall into one or other of two classes, according as heat is represented as a mere condition producible in bodies, or as a distinct species of matter. The former view, which is that universally hell at the present day, was advocated by the great philosophers of the seventeenth century. Bacon maintained it in the Novum Oryanum: "Calor," he wrote, “est motus expansiviis, cohibitus, et nitens per partes minores." Boyle affirmed that the “Nature of Heat” consists in "a various, vehement, and intestine commotion of the Parts among themselves." Hooke declared that "Heat is a property of a body arising from the motion or agitation of its parts." And Newton asked: “Do not