I9IS.] IN AIR CIRCULATION OF THE GLOBE. 189 



sation. Unlike the latter, which is determined by the measure of 

 the vertical component of its fall, the contact cooling is in' direct 

 ratio to the time the layer of air rests upon the snow-ice surface. 

 Conditions of calm therefore favor cooling and descent of air cur- 

 rents, as high wind velocity, does the warming and consequent re- 

 tardation or even reversal of the descending current. It is not sur- 

 prising, therefore, that the strophic glacial storms are initiated in 

 calm conditions, " work themselves up " or become accelerated to 

 accord with the acceleration of velocity of bodies sliding upon in- 

 clined surfaces (here further accelerated by increasing slope toward 

 the margins), and bring about their own extinction when the air 

 passes over the surface too rapidly for surface cooling to exceed 

 or equal adiabatic warming. The sudden check in the outward 

 flow of air, which is one of the most striking features of these 

 strophic movements, in turn promotes new surface cooling and 

 causes the precipitation of fresh snow within the zone of near con- 

 tact to ice, thus often taking place with the sun but little obscured. 

 In the automatic recurrence of similar movements the glacial anti- 

 cyclone thus bears considerable resemblance to the hydraulic ram. 



The Lines of Evidence for Fixed Glacial Anticyclones. 



The Earlier Evidence. — The observational evidence which in 

 earlier papers was adduced in support of the existence of the glacial 

 anticyclone above continental glaciers, was drawn chiefly from the 

 then available reports upon exploration of the inland-ice masses of 

 Greenland, Antarctica, and Northeast Land (Spitzbergen). This 

 evidence may be profitably summarized under the following heads : 



1°. Centrifugal flow of surface air currents above inland-ice 

 masses. 



2°. Outward (centrifugal) sweeping of surface snow largely 

 derived from the central areas, and its deposition and accumulation 

 as a marginal fringe about the inland-ice. 



3°. Snow in large part wind-driven above the sloping portions 

 of the ice mass. 



4°. Sudden warming of the air at the end of the blizzard— 

 foehn effect in descending currents. 



5°. Behavior of upper air currents and movements of the cirri. 



