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 
