36S C. Abbe — Atmosjrfieric Radiation of 



of density and are caused by differences of pressure as modi- 

 fied by simple kinetic laws. The up rush of water at one 

 place and its downrush, as a whirlpool, at another place in a 

 swift stream is a vortex phenomenon in which temperature 

 and density have no part. The rise of the surface of a river 

 at any bend in the channel or at the junction with a tributary 

 stream is a kinetic phenomenon ; so also is the resulting surface 

 overflow to the right and left of the channel ; so also the slow 

 spiral circulation that goes on, in consequence of which the 

 surface water flows from the center out to the banks of the 

 river then down to the bottom of the channel and thence up 

 to the swift surface and back to the banks again. 



We must expect to find similar phenomena in the atmosphere 

 where, corresponding to the general current of a river, we 

 have a general circulation of air due to the greater warmth of 

 equatorial air and to the swift diurnal rotation of the whole 

 atmosphere about the polar axis. 



(a.) Ferrel was the first to show that the tropical belts of 

 high pressure are due — not to local cool air or to local density 

 — but to the interaction of pressures and that they would exist 

 if the atmosphere were a mass of incompressible fluid ; they 

 may be affected to some degree by various forms of resistance, 

 they may also be affected by temperatures due to local radia- 

 tion and convection, and also bj thermodynamic relations, but 

 all these are minor incidents subordinate to the action of the 

 hydro-dynamic laws that bring them into existence. 



(b.) Ferrel maintains that areas of high pressure with cold 

 anti-cyclonic winds give evidence of originating with upper 

 currents of air such as those that are conceived to flow out 

 from great cyclonic areas and be whirled toward each other; 

 Ferrel' s reasoning would justify his conclusion that there is 

 only sufficient energy in those whirls that are due to the general 

 circulation between the equator and the pole, to generate very 

 moderate high and low pressures but not the great barometric 

 depressions and elevations that characterize the low and high 

 areas. He therefore looks to the latent heat of the precipitated 

 vapor as not only maintaining the lows but furnishing the 

 energy that enables these to overflow as peri cyclones which by 

 interference among themselves give rise to the high areas. 



(e.) It has been shown by Prof. Finger of Yienna that 

 westerly winds have a tendency to rise above the earth's sur- 

 face due to their excess of centrifugal force, while easterly 

 winds having a deficiency tend to press down upon the earth's 

 surface; but these effects are inappreciable in our barometric 

 measurements and cannot be quoted as efficient mechanical 

 causes for the production of high or low pressure. 



