Physical and Metaphysical Inquiries (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1806. Excerpt: ... NOTE On Mr Leslie'j Inquiry into the Nature and Propagation of Heat. When the foregoing sheets were copying for the press, I obtained a sight of Mr Leslie's Inquiry into the nature and propagation of Heat. His experiments seem to have been very ingeniously conducted, and he possesses eminent mathematical skill. I cannot, however, admit the conclusion he draws respecting the identity of light and heat. Independent of the difference betwixt their chemical effects, which he is unable to reconcile, the characters of heat and light are as opposite as any two things can be. The former is entirely a homogeneous body, as far as has been discovered by its effects: the latter is composed of different varieties, which put on distinct appearances, and are found to possess different chemical powers. The sirst has an attraction for all matter indiscriminately, and a repulsion to none: the last discovers objects only by its repulsions or reflections. The motion of the one is uniformly swift, and always proceeds in straight lines: but the motion of the other appears to be irregular, and it passes equally by the bended tube as the straight line. Light has only the capacity of pasting through a certain class of bodies, which it performs with equal velocity as through void space: heat passes through all bodies, but with very different degrees of motion; sometimes with extreme slowness. It is impossible that heat mould be light in a state of combination; for in this state it produces no heat at all. What a vast accumulation of the particles of light are combined in a candle; yet it has not the smallest degree of sensible heat till it be lighted. When this takes place, the heat appears along with the light; because, on the dissolution of the combination, these powers are set ...