42 .1. W. Greehj — (jeof/raphy of the Air. 



science of meteorology, while one alone stands as the exponent ' 

 of the " natnral philosophy '' of meteorology. 



To me it seems that it could not have failed to impress any 

 interested reader who has followed the late publications on the 

 convectional theory that, in order to clear the ground for definite 

 meteorological discussion, it is necessary to determine the exact 

 meaning of the various technical terms employed by the various 

 writers. Whether from looseness of verbiage originally or from 

 the not infrequent habit of disputants when worsted to change 

 their ground by claiming to be misunderstood, we find that 

 some writers are umvilling either to stand by their first criticisms 

 or to openly abandon them ; they prefer to explain away their 

 defective statements and gradually shift around to positions 

 almost diametrically opposed to those originally assumed. 



The generally accepted theory as to cyclones attributes their 

 initiator}^ formation to an unequal distribution of temperature 

 with resulting mean diminution of pressure, and the movement 

 of the air from places of high to places of low pressure, the 

 lower air ascending with a g3'ratory motion, while air jDarticles 

 moving from opposite directions form couples which produce 

 rotation. When energetic motions raise the ascending air to 

 such a height that the temperature, cooled dynamically in as- 

 cending, goes below the dew-point, then the great store of latent 

 heat thereby set free becomes, it is assumed, the main source of 

 energy in maintaining the upward convectional movement. The 

 subsidiary causes are attributed to the diminution of j^ressure on 

 the collapse of the vapor, and also to the direct absorption of 

 the sun's heat at the upper cloud surface. 



In anticyclones a slow gyratory descending motion of the air is 

 , assumed. Ferrel considers the cyclone and anticyclone one sys- 

 tem, and believes that air fiowing into the cyclone from a " high " 

 at the ground passes out into the higher atmospheric strata. 



Dr. Hann has put forth the hypothesis that the genesis of 

 cyclones and anticyclones may be sought in the general atmos- 

 pheric circulation through a difference of temperature of the air 

 from the equator to the poles. He speaks of a congestion in the 

 upper or anti-trade Avinds, where the air heaps up to a great 

 height, this being the cause of the anticyclones ; and he main- 

 tains that the low temperature of the " high " is due to ground 

 radiation, and that no part of the high pressure is the result of 

 low temperature. 



