xxv SPECIFIC GRAVITY 139 



equipoise with the water. For it always holds good 

 that, when the weights of the two are equal, neither 

 yields to the other ; but objects heavier than water 

 sink, those lighter are upborne. 



Now heavy and light do not refer to our judg- 6 

 ment of weight, but are relative to the medium 

 by which an object is to be supported. So when 

 water is heavier than the human body or than a 

 stone, it does not allow the inferior weight to sink. 

 So it comes to pass that in some lakes even stones 

 will not go to the bottom ; I mean hard solid 

 stones. There are many light pumice stones, 

 of which in Lydia whole islands that float are 

 composed. Theophrastus is my authority for 

 the statement. I have myself seen a floating 

 island in the lake near Cutiliae. Another is 

 carried about in the Vadimonian Lake, another 

 in the lake by Statonia. The island at Cutiliae 7 

 contains trees and grows grass, and yet it is 

 borne up by the water, and is wafted now in this 

 direction, now in that, not merely by wind, but 

 even by a mere air. So light the breath that moves 

 it that night and day it never remains stationary 

 in one spot. There are two reasons for it : first, 

 there is the weight of the water, which is medicated 

 and therefore heavy ; and then there is the portable 

 material of the island itself, which contains no solid 

 body, although it supports trees. Perhaps in the first 8 

 instance the thick liquid laid hold upon and made 

 fast light trunks and boughs scattered over the 

 surface of the lake. So also whatever rocks are 

 in the island, you will find porous and hollow. They 

 resemble those formed of moisture that has hardened 

 especially near the banks of medicinal springs ; in 

 such cases the scourings of the spring coalesce and 



