THE ATMOSPHERE. 79 



winds come from the northwest (^ 106), and consequently there 

 they revolve about it with 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 Cap- 

 ricorn (Plate I., p. 70). These arrows are intended to represent 

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

 the polar side of these calms. 



114. 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, Reid, Piddington, and others, viz., 

 that all rotary storms in the northern hemisphere revolve as do 

 the w^hirlwinds about the north pole, viz., from right to left, and 

 that all circular gales in the southern hemisphere revolve in the 

 opposite direction, as does the whirl about the south pole. 



How can there be any connection between the rotary motion 

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

 caused here by local agents ? 



That there is probably such a connection has been suggested 

 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 § 172, into the rela- 

 tions between magnetism and the circulation of the atmosphere ; 

 for, although the theory of heat satisfies many 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. 



115. Some of its Meteorological Agencies. — So far, we see 

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

 department in the economy of nature, has its offices to perform, 

 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. 



To distribute moisture over the surface of the earth, and to 

 temper the climate of different latitudes, it would seem, are two 

 great offices assigned by their Creator to the ocean and the air. 



When the northeast and southeast trades meet and produce the 

 equatorial calms (§ 104), the air, by this time, is heavily laden 

 with moisture, for in each hemisphere it has traveled obliquely 



