Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/56

 proved that the temperature of a body is without sensible influence on its weight.

Perhaps nothing in the history of natural philosophy is more amazing than the vicissitudes of the theory of heat. The true hypothesis, after having met with general acceptance throughout a century, and having been approved by a succession of illustrious men, was deliberately abandoned by their successors in favour of a conception utterly false, and, in some of its developments, grotesque and absurd.

We must now return to s'Gravesande's book. The phenomena of combustion he explained by assuming that when a body is sufficiently heated the light-corpuscles interact with the material particles, some constituents being in consequence separated and carried away with the corpuscles as flame and smoke. This view harmonizes with the theory of calcination which had been developed by Becher and his pupil Stahl at the end of the seventeenth century, according to which the metals were supposed to be composed of their calces and an element phlogiston. The process of combustion, by which a metal is changed into its calx, was interpreted as a decomposition, in which the phlogiston separated from the metal and escaped into the atmosphere; while the conversion of the calx into the metal was regarded as a union with phlogiston.

s'Gravesande attributed electric effects to vibrations induced in effluvia, which he supposed to be permanently attached to such bodies as amber. "Glass," he asserted,"contains in it, and has about its surface, a certain atmosphere, which is excited by Friction and put into a vibratory motion; for it attracts and