268 SEE— TEMPERATURE, SECULAR COOLING [Apriv 20, 



Like Plato he recognized water and air as entering into the 

 bowels of the globe, through hollows, caverns and fissures; and 

 there, in contact with the internal heat, giving rise to imprisoned 

 vapor, which develops such force that it brings on an earthquake. 

 He fully recognized the prevalence of earthquakes in maritime 

 regions, and on this point his views have been adopted by Strabo 

 and Pliny. 



In the time of Aristotle the universe was conceived as made up 

 of four elements, fire, air, water, and earth. But the Greeks 

 noticed the evaporation of water, and its precipitation from the 

 clouds in the form of rain, hail and snow ; and they recognized that 

 there was some process by which it became invisible, and was after- 

 wards condensed into clouds and precipitated by atmospheric 

 agencies. Aristotle does not usually distinguish vapor of steam 

 from air, though occasionally he calls steam ar/Ltt?, while ordinary 

 wind is called ave^io^ . He must have conceived the two vapors 

 as passing by some unknown process one into the other. 



Accordingly when he says vapor, air, or wind, we are often to 

 understand not only atmospheric air, but also a mixture of vapor of 

 steam. Since such vapor is seen to be emitted by volcanoes, as in 

 the case he mentions of the ^olian Island Hiera, now called Vul- 

 cano, he naturally and correctly reasons that it was the cause of 

 that violent outbreak.^ In like manner Aristotle holds that vapor 

 is the cause of the agitation of the earth even when no surface 

 eruption occurs. He recognized therefore that the tension of elastic 

 vapor seeking to diffuse itself in the atmosphere may become so 

 powerful as to overcome the confining rocks of the earth's crust, 

 and bring on an earthquake, even though none escapes to the sur- 

 face, but the whole of it remains hidden in the earth. In this view 

 he is followed by Lucretius, Strabo, and Pliny. How much more 



* Paulus Orosius (Lib. LV., Cap. 20) says that this island, which was 

 often called Thermessa by the ancients, arose from the sea in the year 571 

 B.C. A passage in Thucydides (Lib. III., §88) shows that it was in exis- 

 tence in 427 B.C. (cf. Strabo's Geography, Bohn's Transl., vol. i, p. 417, 

 footnote). This date of 571 B.C. is consistent with the date given by Aris- 

 totle. Pliny's statement (Lib. II., Cap. 89; Vol. i, p. 118) is incorrect, and 

 may perhaps be explained by a transcriber's error, or by some confusion of 

 Pliny himself. Perhaps Thermessa was confounded with Therasia near 

 Thera. 



