84 THE PHYSICAL GEOGRAPHY OF THE SEA. 



forward as wind, and ascends as in a calm ; about this calm disc, 

 therefore, there should be a whirl, in which the ascending column 

 of air revolves from right to left, or against the hands of a watch. 

 At the south pole the winds come from the northwest (§ 137), and 

 consequently there they revolve about it ii^ith the hands of a watch. 

 That this should be so will be obvious to any one who will 

 look at the arrows on the polar sides of the calms of Cancer and 

 Capricorn (Plate I., p. 75). These arrows are intended to repre- 

 sent the prevailing direction of the wind at the surface of the earth 

 on the polar side of these calms. 



156. It is a singular coincidence between these two facts thus 

 deduced, and other facts which have been observed, and which 

 have been set forth by Redfield, E-eid, Piddington, and others, 

 viz., that many of the rotary storms in the northern hemisphere 

 revolve as do the whirlwinds about the north pole, viz., from right 

 to left, and that all circular gales in the southern hemisphere re- 

 volve in the opposite direction, as does the whud about the south 

 pole. 



157. How can there be any connection between the rotary mo- 

 tion of the wind about the pole, and the rotary motion of it in a 

 gale caused here by local agents? 



158. That there is probably such a connection has been sug- 

 gested by other facts and circumstances, and perhaps I shall be 

 enabled to make myself clearer when we come to treat of these 

 facts and circumstances, and to inquire farther, as at § 299, into 

 the relations between magnetism and the circulation of the atmos- 

 phere ; for, although the theory of heat satisfies the conditions of 

 the problem, and though heat, doubtless, is one of the chief agents 

 in keeping up the circulation of the atmosphere, yet it can be made 

 to appear that it is not the sole agent. 



159. Some of its Meteoeological x\gencies. — So far, we 

 see how the atmosphere moves ; but the atmosphere, like every 

 other department in the economy of nature, has its offices to per- 

 form, and they are many. I have already alluded to some of them ; 

 but I only propose, at this time, to consider some of the meteoro- 

 logical agencies at sea, which, in the grand design of creation, have 

 probably been assigned to this wonderful machine. 



