1909.] BY MEANS OF KITES AND BALLOONS. 25 



as compiled by Hann, give the mean gradient up to 3,000 meters 

 as .45 degree Centigrade per 100 meters, while at twice this altitude 

 the temperature change is .70 degree Centigrade per 100 meters. 



Witliin the moist stratum itself, observations on the relative 

 humidity show that the yearly minimum at the earth's surface occurs 

 in the summer months. The result is that condensation begins at 

 higher levels in summer than in winter. The temperature gradient 

 responds to these conditions, being greater nearer the earth's surface 

 and less near the upper region of the moist stratum in summer than 

 in winter. Values closely approximating the adiabatic rate are often 

 found for the first 500 meters above sea level in the summer months. 

 Comparison of the mean temperature gradients as observed in 

 Europe and in this country, at Mt. Weather and Blue Hill, points 

 to the fact that condensation takes place at lower levels in western 

 Europe than here. This is reasonable when the comparatively dry 

 surface conditons which obtain on our continent are taken into 

 consideration. 



It follows from the above that the moist or storm stratum is : 

 (i) Deeper in summer than in winter, (2) deeper over a conti- 

 nent than over the ocean or smaller land areas. Convection cur- 

 rents are more sluggish where the relative humidity at the surface 

 is low and therefore the barometric changes are less pronounced : 

 (i) In summer than in winter, (2) in continental than in insular 

 climatic conditions. Upon these considerations alone we should 

 expect the deeper storms to be the less intense, but this is not in 

 general true and another factor, viz., the velocity of the upper 

 westerly winds, must be taken into consideration. By storm inten- 

 sity is meant the suddenness of the changes brought about by the 

 passage of the storm — probably best measured by the barometric 

 changes. 



These upper currents apparently control the rate of motion of the 

 storms. Their velocities are found to vary with altitude, increasing 

 up to heights of 10,000 or 12,000 meters. They also vary with 

 the seasons. At an altitude of 3,000 to 5,000 meters their mean 

 velocity for January is found to be fully one and a half times the 

 mean for July. It follows that, for a given season, the deeper 

 storms move faster, i. e., continental and insular climatic conditions 



