328 PHYSICAL SCIENCE 



due to three causes. The earth itself contains moisture which it 

 forces out at the surface ; it includes also air which in the dark 

 ness of the subterranean wintry cold is condensed into moisture 

 by the principle of interchangeability, whereby one element passes 

 into another, the earth in its interior resolves itself into moisture. 

 If it be urged that the rivers are too vast to draw their supplies 

 from these sources, the ready answer comes that the internal 

 reservoir is quite spacious enough for the purpose, and that it 

 might as well be matter of surprise that, with all the winds that 

 constantly blow, the supply of air does not fail, or that a single 

 wave of the sea should be left to follow so many breakers. If 

 the questioner, still unsatisfied, should demand to know how water 

 is produced, he is met with the query how air is produced on earth. 

 There are in nature four elements, and he is rtot entitled to ask 

 where one of them comes from. Each is a fourth part of nature, 

 and it is obvious that what has an element as its source cannot 

 fail. Hence the philosopher in pronouncing water to be an 

 element has given it enough, and more than enough, of strength. 

 In short, rain may give rise to a torrent, but not a river flowing 

 steadily between its banks. Heavy rains will swell such a river, 

 but cannot produce it. 



Having, as he believed, cleared the ground in this way, Seneca 

 proceeds to consider the distribution of water within the earth. 

 He opines that as in our body, so in the earth, there are channels 

 by which both air and liquids flow. He states his conviction 

 that the earth contains not only veins of water, but also large 

 streams, and in a later part of the volume he speaks of both 

 underground rivers, huge lakes, and a hidden sea from which 

 rivers at the surface are supplied (154, 233, 235). He is aware 

 that some of these subterranean reservoirs contain fish, about 

 which he has some incredible tales to tell. He makes mention 

 of rivers that sink underground and reappear, as if a matter for 

 great astonishment. But examples of it may be found in many 

 limestone districts, where the solution of the rock by underground 

 water has given rise to tunnels, passages, and caverns into which, 

 when their roofs give way, surface streams may be engulfed, to 

 break out again from other openings at lower levels (141). The 

 author concludes this part of his argument by asking if anybody 

 is ignorant that there are some standing waters which have no 

 bottom, whence, he contends, it is shown that this water is the 

 perpetual source of large rivers. 



The various kinds of taste possessed by natural waters are then 

 discussed, and some marvellous illustrations are given of their 

 effects. Allusion is made to medicinal springs, to petrifying 

 waters, to some with extraordinary dyeing properties, and to 



