THE CHEMICAL ELEMENTS. 735 



motions downward. But, besides these motions, there is motion 

 in a circle, which is unnatural to these elements, but which is a 

 more perfect motion than the other, because a circle is a perfect 

 line, and a straight line is not ; and there must be something to 

 which this motion is natural. From this it is evident that there 

 is some essence of body different from those of the four elements, 

 more divine than those and superior to them. If things which 

 move in a circle move contrary to nature, it is marvelous or 

 rather absurd that this, the unnatural motion, should alone be 

 continuous and eternal ; for unnatural motions decay speedily. 

 And so from all this we must collect that, besides the four ele- 

 ments which we have here and about us, there is another removed 

 far off, and the more excellent in proportion as it is more distant 

 from us." This element was called the quinta essentia by Latin 

 writers, and the word quintessence in our own language frequently 

 brings to mind this singular conception, which, although so absurd 

 to us, held for ages a wonderful control over the human mind. 



It is not, however, our purpose to trace the influence of the 

 dynamical conceptions of Aristotle on the development of physical 

 science, interesting and instructive as such a study would be. We 

 are here dealing only with the conception of an element or prin- 

 ciple of material bodies, also involved in this reasoning ; and it is 

 obvious that this early conception of an element was not that of a 

 definite substance — as we now understand the word substance — 

 that is, something subsistens per se — but rather that of the 

 essentia or substantia which were supposed to underlie the 

 external attributes of bodies, and of which these last were merely 

 accidents. Earth was the underlying principle of all solid bodies, 

 whose multifarious forms were as familiar to Aristotle as to us. 

 So all liquid bodies were forms of water, and all aeriform bodies 

 manifestations of the all-diffusive air ; and the ancients, at times 

 even more acute than ourselves, made distinctions between con- 

 ditions, both of water and air, which we know are not essential. 



We know that flame is simply intensely heated gas rising in a 

 denser atmosphere ; but it was perfectly natural that the ancients 

 should regard such a startling effect as a manifestation of a fourth 

 condition of matter still lighter and more subtile than air, and 

 the conception of fire as a fundamental principle of nature once 

 formed, the phenomena of combustion appeared to them as direct 

 evidences of the escape of this principle of fire from the burning 

 bodies. 



The famous theory of phlogiston, advanced by Becher and Stahl 

 during the seventeenth century, was simply a development of 

 these views without any essential change. Phlogiston was merely 

 a new name for the fourth element of Aristotle. As by Aristotle 

 all combustible bodies were assumed to hold the principle of fire. 



