198 WATER. [Lesson xxix. 



Water, as a fluid, is governed by several laws 

 peculiarto itself, to notice all of which would require 

 a volume : one of its most curious properties is, 

 that its pressure, or force, varies in the proportion, 

 of its depth, without any regard to its breadth : if 

 it were not for this remarkable property, it would 

 be impossible for ships, or any other vessels, to put 

 out to sea, for if the lateral pressure varied with 

 the breadth, it is evident that every sailing vessel 

 would be forced against the nearest shore with 

 great violence, and, of course, there would be an 

 insuperable bar in the way of navigation. 



As it would be absolutely impossible to mnke a 

 calculation of the quantity of subterraneousWaters, 

 I shall not attempi it ; but as it is a much easier 

 matter to have an idea of the enormous quantity 

 of Water on the earth's surface contained in seas, 

 we will here set about it. It is a reasonable sup- 

 position that of the earth's surface two-thirds are 

 seas : now if we suppose one common depth to 

 be the tenth part of a mile, we shall find that there 

 is Water sufficient to cover the whole globe to the 

 height of six hundred feet ; and if this Water were 

 reduced into one mass, it would form a globe of 

 more than sixty miles diameter. 



In reflecting upon the various changes of Water, 

 we have a curious kind of perpetual motion placed 

 in view : Vapours are raised from the ocean, by 

 means of the sun and other agents in the process 

 of evaporation ; and these are transported by the 

 winds,. 8cc. through every climate. The progress of 



these 



