460 THE PHYSICAL GEOGRAPHY OF THE SEA. 



inosphere ordained to move without resistance, the air from these 

 null belts would carry with it. to the polar calms the easterly mo- 

 tion which it had acquired from the earth in its motion around 

 its axis at these null belts. Were this motion so impressed, the 

 wind would arrive, rushing with an hourly velocity about the 

 polar calm places of 700 miles in the arctic, and 800 in the ant- 

 arctic. Such a velocity would impart a centrifugal force sufficient 

 to keep the air away from the poles and produce almost a vacuum 

 there. In this state of things, the same air would continue to 

 revolve about the poles were not some other agent, such as heat, 

 brought in to expand and drive it away. Being expanded and 

 puffed out above the general atmospherical level, but retaining its 

 velocity — for the supposition is that it moves without friction — 

 and returning through the upper regions, it would flow back as it 

 went, viz., as a westerly wind, and arrive at its null belt in the di- 

 rection of the meridian. But the wind has friction, and is resisted 

 in every movement ; the atmosphere partakes of the spheroidal 

 form, which has been impressed upon the earth itself by its axial 

 rotation. That form is to it the form of stability. The water 

 at the pole is 13 miles nearer to the centre of the earth than the 

 water at the equator ; but there is not on that account any tend- 

 ency in the sea to flow back from the equator toward the jDoles ; 

 neither is there any tendency to motion one way or the other in 

 the atmospherical ocean by reason of the oblateness of its surface. 

 To produce the polar and equatorial movements of the air, there 

 must be an agent both at the equator and the poles to prevent such 

 stability by constantly disturbing equilibrium there, and that agent 

 is heat ; therefore, whatever be the degree of polar depression due 

 the barometer in consequence of axial rotation, such depression 

 could, of itself, produce neither trade nor counter-trade wind ; it 

 could no more produce currents in the air than in the sea, nor 

 could axial rotation produce a high barometer at one pole, a low 

 barometer at the other ; consequently, the difference in the press- 

 ure of the atmosphere about the two poles, as shown by the dia- 

 gram (§ 858), can not be ascribed to the influence of axial rotation. 

 It is doubtless due to the excess in antarctic regions of aqueous 

 vapor and its latent heat. 



862. The arctic circle lies chiefly on the land, the antarctic on 

 the water. As the winds enter one, they are loaded with vapor; 



