i2 THJi! BOTTOM OF THE SEA. 



points as we desire. Suppose, .however, that the 

 conditions of our existence were su -h as to maintain 

 as constantly at the height of 16,00l) feet above the 

 sea-level ? In that case, our survey of the land 

 would be attended with the same degree of difficulty 

 as our attempts to delineate the floor of the ocean. 

 The highest mountains only would litt their summits 

 into our atmosphere, and those alone we should be 

 able to explore by the observation of actual contact. 

 The plummet, or some analogous instrument, would 

 have to be used for ascertaining the configuration of 

 the less elevated regions. This is precisely our case 

 in regard to the depths of the ocean. The regularity 

 of its surface enables us to make use of it as a common 

 point of departure Irom which to measure the relative 

 heiglits of difierent parts of the terrestrial surfac. 

 If sufficient water existed to cover all the land, our 

 globe would everywhere present the regular surface 

 of a sphere, or nearly so. Although this is not the 

 case, yet the great oceans, and all the seas communi- 

 cating with them, have the 'same level. 



The pressure of the air is pretty constant on every 

 point of the ocean-surface, and it is found to dimini.^h 

 in a certain ratio as we ascend in the atmosphere. 

 It must be remembered that the bottom of the at- 

 mospheric ocean rests on the surface o.' the watery 

 ocean. If we suppose the whole mass of water to 



