INTRODUCTION. 19 



of the globe. Let us then pour water upon it until 

 the surface of the water should equal that part which 

 •is exposed, and it is clear the average depth of the 

 one would be equal to the average height of the 

 other. But if we increase the quantity of 'water 

 until the proportion is as three to one, it is evident 

 the depth will have increased in the same ratio. We 

 may, therefore, with high probability, conclude that, 

 as the greatest height of the land is about five miles, 

 the greatest depth of the water does not much 

 exceed twelve or thirteen ; while the average depth 

 may be about two or three. 



Every one is aware of the saltness of the sea. 

 It has been assumed that its object is to prevent 

 stagnation and putrescence. But this reason does 

 not appear to be the correct one, for large masses 

 of fresh water, such as inland lakes, do not stag- 

 nate. Strictly speaking, however, water cannot 

 putrefy ; when a small body of it becomes offensive, 

 it is on account of the decomposition of vegetable 

 or animal matters contained in it. But organized 

 substances will decompose, and consequently become 

 offensive in salt water as well as in fresh, as may 

 be easily proved by experiment. Perhaps the 

 reason for the Ocean's saltness may be the increase 

 of its weight without the increase of its bulk; for 

 the decrease of specific gravity of so large a portion 

 of the globe would materially affect the motions 

 of the earth, and perhaps derange the whole con- 

 stitution of things. The increase of its specific 

 gravity makes it more buoyant, and every one is 

 aware with how much less effort a bather swims in 



