n6 PHYSICAL SCIENCE BK. in 



does not flow. Surface water comes from rain ; 

 spring water from a natural fountain. There is, 

 however, nothing to prevent surface and spring 

 water in the same spot. This we see in Lake 

 Fucinus, into which the streams drain all the 

 rainfall of the surrounding mountains, while there 

 are also large springs concealed under the surface 

 of the lake itself. So, even when the torrents 

 discharge into it in winter, it preserves its appear 

 ance unaltered. 



IV 



LET us inquire therefore, in the first place, how the 

 earth can contain sufficient water to maintain the 

 unbroken flow of the rivers, and where such a vast 

 quantity of water comes from. We are surprised 

 that the ocean is not sensible of the additional water 

 derived from rivers. It is no less surprising that 

 the earth is not sensible of the loss of all the water 

 that issues from it. What is it that has so filled it 

 up that it can from its hidden recesses furnish such 

 quantities and continually make good the loss as 

 it does ? Whatever explanation we give regarding 

 a river must apply also to streams and springs. 



SOME are of opinion that the earth receives back 

 all the water it has lost. The sea, therefore, does 

 not get larger, because it does not assimilate the 

 water that runs into it, but forthwith restores it to the 

 earth. For the sea water returns by a secret path, 



