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276 thing to be corporeal, they consider that only to be a void in which there is absolutely nothing; so that it can be to no purpose to shew that the air is something. This epitome shews sufficiently how widely apart from one another are the antient and modern significations of a void, since it now implies such a rarefaction of the air as can be obtained through the air-pump; and, as rarefaction cannot be carried beyond 300 times, no proof can be afforded of the possible existence of a void. Aristotle objects to those who maintained that the void is identical with any space filled with air, "for, if the air be driven out, the space will clearly, he observes, be a void, in a stricter sense than it was, since it will no longer be full of air." But it would be foreign to the purport of these notes to inquire further into the opinions of that age; it may be inferred, however, from what has been adduced, that Aristotle, although he refused corporeity to the air, was not a very consistent supporter either of the plenum or vacuum.

Note 4, p. 102. Every sonorous body, &c.] This passage is a summary of all that physiology has now to offer upon sound and hearing; but although it might have been surmised that sound is vibration of the air, caused by a sonorous body and conveyed, by successive undulations, to the organ of hearing, yet, as the internal ear was then unknown, it is a surprising assumption that air must be contained within the organ, in order that the