i9o6.] SEE— THE CAUSE OF EARTHQUAKES. 293 



In " De Rerum Natura," Lib. VI, 680 et seq., we read, accord- 

 ing to Munro's translation : 



" And now at last I will explain in what ways yon flame roused to fury 

 in a moment blazes forth from the huge furnaces of ^tna. And first the 

 nature of the whole mountain is hollow underneath, underpropped through- 

 out with caverns of basaltic rocks. Furthermore, in all caves are wind and 

 air; for wind is produced when the air has been stirred and put in motion. 

 When this air has been thoroughly heated and raging about has imparted 

 its heat to all the rocks round, wherever it comes in contact with them, 

 and to the earth, and has struck out from them fire burning with swift 

 flames, it rises up and then forces itself out on high, straight through the 

 gorges; and so carries its heat far and scatters far its ashes and rolls on 

 smoke of a thick pitchy blackness and flings out at the same time stones 

 of prodigious weight; leaving no doubt that this is the stormy force of 

 air. Again the sea to a great extent breaks its waves and sucks back its 

 surf at the roots of that mountaift. Caverns reach from this sea as far as 

 the deep gorges of the mountain below. Through these you must admit 

 (that air mixed up in water passes; and) the nature of the case compels 

 (this air to enter in from that) open sea and pass right within and then 

 go out in blasts and so lift up flame and throw out stones and raise clouds 

 of sand; for on the summit are craters, as they name them in their own 

 language ; what we call gorges and mouths." 



In one important part of this passage, the text is corrupt and 

 the context, therefore, supplied ; yet there is absolutely no doubt, 

 from preceding passages stating that the sea penetrates the land, 

 that Lucretius held that the mountain is hollow, the water filters 

 through the crevices and cracks in the rocks, until it comes into con- 

 tact with the subterranean fires which convert it into vapors that 

 give rise to the explosive violence witnessed in the eruptions of 

 ^tna. 



We shall see hereafter that Aristotle describes a volcanic eruption 

 as due to the urging blast of pent-up vapor, but it does not seem that 

 he gave any satisfactory explanation of how the vapor developed 

 within the earth's crust. 



§ 9. Lucretius' views on earthquakes. 



" Now mark and learn what the law of earthquakes is. And first of 

 all take for granted that the earth below us as well as above is filled in 

 all parts with windy caverns and bears within its bosom many lakes and 

 many chasms, cliffs and craggy rocks ; and you must suppose that many 

 rivers hidden beneath the crust of the earth roll on with violence waves 

 and submerged stones ; for the very nature of the case requires it to be 

 throughout like to itself. With such things then attached and placed below, 

 the earth quakes above from the shock of great falling masses, when under- 



