THE 



PHYSICAL GEOGRAPHY OF THE SEA, 

 AND ITS METEOROLOGY. 



CHAPTER I. 



§ 1-55. — THE SEA AND THE ATMOSPHERE, 



§ 1. Our planet is invested with two great oceans ; one visi- 

 The tvo oceans of ^^^j the othcf invisible ; one underfoot, the other 

 air and water. Overhead; One entirely envelops it, the other cov- 

 ers about two thirds of its surface. All the water of the one 

 weighs about 400 times as much as all the air of the other. 



2. It is at the bottom of this lighter ocean where the forces 



Their meeting, which wc are about to studj are brought into play ; 

 to treat of the Physical Geography of the Sea, we must neces- 

 sarily refer to the phenomena which are displayed at the meeting 

 of these two oceans. Let us, therefore, before entering either of 

 these fields for study, proceed first to consider each one in some 

 of its most striking characteristics. They are both in a state of 

 what is called unstable equilibriuln ; hence the currents of one 

 and the winds of the other. 



8. As to their depth, we know very little more of the one than 

 Their depth, of the othcr ; but the conjecture that the average 

 depth of the sea does not much exceed four miles is probably 

 as near the truth as is the commonly received opinion that the 

 height of the atmosphere does not exceed 50 miles. If the air 

 were, like water, non-elastic, and not more compressible than this 

 non-elastic fluid, we could sound out the atmospherical ocean with 

 the barometer and gauge it by its pressure. The mean height 

 of the barometer in the torrid and temperate zones, at the level 

 of the- sea, is about 30 inches — rather under than over. Now, it 



A 



