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LECTURE LX.

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Pythagoras , great as lie was in some other departments of science, reasonedrespecting physical effects in a manner too mathematical and visionary, toallow him much claim to be ranked among those, who have studied to inves-tigate the minute operations of nature.

Anaxagoras was so far from confining himself to the supposition of fourelements, which was most generally received by the philosophers of antiquity,that he imagined the number of elements nearly if not absolutely infinite.He conceived that the ultimate atoms, composing- every substance, were ofthe same kind with that substance, and his system was thence called thehomoeomeria; it erred perhaps less from the truth than many of the moreprevalent opinions. Democritus, adopting the sentiments of Leucippus , proposeda still more correct theory of the constitution of matter, supposing it to beultimately so far homogeneous, that the weight of its atoms was proportionalto their bulk. lie asserted that the forms of these atoms were different anilunalterable; that they were always in motion, and that besides their primi-tive difference of form, they were also susceptible of a variety in the modeof their arrangement. The space not occupied by the atoms of matter, heconsidered as a perfect vacuum.

As Thales had supposed water to be the first principle of all things, andAnaximenes air, so Heraclitus lixed on lire as the foundation of his system,attributing to it the property of constant motion, and deriving all kinds ofgrosser matter from its condensation in different degrees. This doctrine waswholly unsupported by any thing like reason or observation.

Plato introduced into philosophy a variety of imaginations, which re-sembled the fictions of poetry much more than the truths of science.He maintained, for example, that ideas existed independently of the humanmind, and of the external world, and that they composed beings of differentkinds, by their union with an imperfect matter. It is observed by Bacon , inhis essay on the opinions of Parmenides , that the most ancient philosophers)Empedocles, Anaxagoras, Anaximenes, Heraclitus, and Democritus , sub-mitted their minds to things as they found them; but that Plato made theworld subject to ideas, and Aristotle made even ideas, as well as all otherthings, subservient to words; the minds of men beginning to be occupied, in

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