Page:Popular Science Monthly Volume 34.djvu/754

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next, water the next, and earth the lowest. The reasons urged in support of these conclusions appear to us absurd enough.

By Aristotle, as by other Greek philosophers, the contrasts emphasized by language were regarded as fundamental distinctions in nature, or first principles, which they made the basis of discussion, and from which they sought to deduce general truths. Aristotle enumerates ten such principles as enunciated by the Pythagoreans—limited and unlimited, odd and even, one and many, right and left, male and female, rest and motion, straight and curved, light and darkness, good and evil, square and oblong—and from oppositions of this kind he deduced his doctrine of the four elements.

"We seek," Aristotle writes, "the principles of sensible things, that is, of tangible bodies. We must take, therefore, not all the contrarieties of quality, but those only which have reference to the touch. Thus, black and white, sweet and bitter, do not differ as tangible qualities, and must therefore be rejected from our consideration. Now, the contrarieties of quality which refer to the touch are these: hot, cold; dry, wet; heavy, light; hard, soft; unctuous, meager; rough, smooth; dense, rare." Then, after rejecting all but the first four of these, either because they are not active and passive qualities, or because they are combinations of the first four, and concluding for these reasons that the four retained must be elements, he proceeds: "Now, in four things there are six combinations of two; but the combinations of two opposites, as hot and cold, must be rejected. We have, therefore, four elementary combinations which agree with the four apparently elementary bodies: fire is hot and dry; air is hot and wet (for steam is air); water is cold and wet; earth is cold and dry."

In a similar way, by considering light as opposite to heavy, Aristotle justifies his conclusion that levity is a quality of a body, and that bodies are absolutely heavy or absolutely light. "Former writers," he says, "have considered heavy and light relatively only—taking cases where both things have weight, but one is lighter than the other, and they imagined that in this way they defined what was absolutely heavy and light." Fire and air, according to Aristotle, were absolutely light, with fire the lighter of the two; while water and earth were absolutely heavy, with earth the heavier of the two. In another place he writes, "Heavy and light are, as it were, the embers or sparks of motion"; and hence he concluded that the tendency of light bodies to rise, like the tendency of heavy bodies to fall, was an inherent quality.

Subsequently Aristotle recognized a fifth element in nature. In his book "On the Heavens" he wrote: "The simple elements must have simple motions; and thus fire and air have their natural motions upward, and water and earth have their natural