734 THE POPULAR SCIENCE MONTHLY. 



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 em- 

 phasized by language were regarded as fundamental distinctions 

 in nature, or first principles, which they made the basis of dis- 

 cussion, 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 con- 

 sideration. 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 reject- 

 ing all but the first four of these, either because they are not act- 

 ive 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 ele- 

 mentary combinations which agree with the four apparently ele- 

 mentary 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 tend- 

 ency 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 natu- 

 ral motions upward, and water and earth have their natural 



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