TERRESTEIAL PHENOMENA. 49 



always flowed, but there was a time when the places where 

 they flow were dry, for their work has an end but Time has 

 none." * He concludes that rivers are produced and destroyed, 

 that the same regions of the Earth are not always the same, 

 land or sea, as the case may be, and that everything changes 

 in course of time.t 



In Meteorol. iii. c. 7, Aristotle treats of materials found 

 beneath the surface of the Earth. He says that, just as 

 there are two exhalations, the vaporous and the dry or smoke- 

 like, so also there are two kinds of substances in the Earth 

 itself. The first kind includes those substances which are 

 merely dug out of the Earth and have been formed as a 

 result of "complete burning" of the dry exhalation, e.g., 

 infusible kinds of stones and realgar, red and yellow ochres, 

 sulphur, and the like ; substances of this kind are generally 

 stones or coloured powders. The second kind includes those 

 obtained by regular mining operations, and are produced, in 

 some way, from the vaporous exhalation, e.g., fusible or 

 malleable substances, like gold, iron, and bronze, t By iron 

 and bronze, Aristotle clearly means the ores from which 

 this metal and alloy are respectively obtained ; in Meteorol. 

 iv. c. 6, he incidentally gives some account, to be discussed 

 later, of iron and its conversion into steel. 



The distinction made between the different kinds of 

 mineral substances, in Meteorol. iii. c. 7, is almost equivalent 

 to the recognition of a class of ores and another of metals. 

 Aristotle's coloured powders or pigments include some ores, 

 e.g., the ochres include oxide of iron and red lead, and 

 realgar (red sulphide of arsenic, the Sandarache of the 

 ancient Greeks) is an ore of arsenic. All these pigments 

 were well known to the ancient Greeks. 



Aristotle attempts to explain the production of gold and 

 other metallic deposits in the earth. His explanation is by 

 no means clear, but he seems to mean that the vaporous 

 exhalation, enclosed more particularly in rocks, is compressed 

 and solidified and appears as a separate body, like dew or 

 hoar-frost. The metallic substances exist before the con- 

 densation takes place. All, except gold, can be affected by 

 the action of fire and contain earth, for they contain a dry 

 exhalation. § This shows, as far as it can be understood, 

 that he believed that the vaporous exhalations from which 



* Meteorol. i. c. 14, s. 31. f Ibid, i c. 14, b. 32. 



I Ibid. iii. c. 7. § Ibid. iii. c. 7, 



E 



