318 PROCEEDINGS OF THE AMERICAN ACADEMY. 



in opposite directions, and distinctly indicate a circulation of the wind 

 around two cyclonic centres passing along the equator, and an outflow 

 from high pressures half-way between them. The lower chart, headed 

 " Upper Winds," shows the hours of greatest frequency of each wind 

 direction in the upper air between 2,500 and 10,000 meters. These 

 times were determined by observations of clouds at Blue Hill, and from 

 hourly wind records on the Siintis in Switzerland. Cloud strata at three 

 different levels between 3,000 and 1 0,000 meters above Blue Hill each 

 gave a result similar to the other. This is indicated by heavy arrows in 

 the chart.* The observations on the Santis at an elevation of 2,500 

 meters are indicated by the light arrows in the same diagram. There 

 are no observations available at these heights south of the equator, but 

 the observations north of the equator indicate a circulation very different 

 from that at the earth's surface. There is apparent at this height only 

 one cyclonic and one anticyclonic circulation. The low pressure in the 

 cold-air cyclone of night persists at these levels, and probably with in- 

 creased intensity, while the low pressure in the warm-air cyclone of day 

 has been replaced by a high pressure and an anticyclonic circulation. 



* Annals of the Astron. Observatory of Harvard College, XXX. Ft. iv., 415 and 

 419. 



