(From α, neg. and to cut or divide). An atom. It is a particle of matter exceedingly-small; indeed the elementary particles of which bodies consist. Asclepiades taught that atoms were the pri-mordia of all things, and that they were not perceptible to our senses, but only to our understandings; that they had no qualities, for the qualities of bodies which they compose, depend on the order, figure, and number, of many atoms joined together; and this last circumstance, he proves by observing, that a lump of silver is white, but if filed down it is black; and horns of goats are black when whole, but white if filed down. Galen says, that Asclepiades, adhering to the sentiments of Democritus and Epicurus with regard to the principles of bodies, had only changed the former names of things, calling atoms molecules, and a vacuum, pores. Molecules were, however, divisible, but atoms not. This doctrine has been generally admitted as sufficiently probable, though incapable of demonstration, and with greater facility, as' no important consequence is derived from it. Kant has, however, endeavoured to subvert it, by substituting what he calls the dynamic philosophy, changing the word atoms to powers, and real objects to their effects. Mr. Mitchell and Dr. Priestley, many years since, endeavoured to produce a similar change in the fundamental principles of philosophy, by transferring the sensation of resistance from matter, to a medium surrounding it, rather than to the ultimate atoms of the corpuscularian philosophers. Kant's system is very popular in Germany.