28 BLAIR— EXPLORATION OF THE UPPER AIR [March s, 



sary to distinguish it from temporary inversions frequently found 

 in the lowest of the three strata described. The existence of the 

 permanent inversion is a well established and interesting fact. Of 

 the many balloons sent into it, only a few have been followed 

 all the way up with the theodolite, consequently the wind velocities 

 have been but little observed. The winds are found to be variable 

 and of low velocity, 3.5 meters per second has been observed. This 

 is in pronounced contrast to the prevailing west winds of extremely 

 high velocity which characterize the layer just below it. Leading 

 meteorologists still differ as to the explanation of this warm stratum. 

 Their opinions may be found in the October i, 1908, number of 

 Nature in the form of a report of the discussion organized on this 

 subject by the committee of Section A of the British Association. 



Isothermal charts, such as the one for the first two weeks in 

 August, 1908 (Fig. 6), illustrate the change in the upper air tem- 

 peratures with the time. The daily rise and fall of temperature is 

 seen to extend to about 1,500 meters above the surface. Super- 

 posed upon this and somewhat complicated by it is an aperiodic 

 change which follows the passage of high and low barometer over 

 the station. This sort of change extends up to the permanent inver- 

 sion. Still a third change in temperatures aloft with time has an 

 annual period. The time of greatest cold occurs near the earth's 

 surface in January, at an altitude of 5,000 to 7,000 meters it comes 

 in March and April, 7,000 to 9,000 meters in July, and 9,000 to 

 11,000 meters in September. 



Means of temperature records from 581 balloon ascensions made 

 by Teisserenc de Bort show that the greatest annual fluctuation in 

 temperature occurs at an altitude of 6,000 meters above sea level, 

 i. e., about the base of the second stratum above mentioned. From 

 this level up the annual fluctuation decreases gradually. Almost as 

 great a change occurs at the base of the lower stratum, i. e., near 

 the earth's surface. In this layer the fluctuation reaches a minimum 

 at an altitude of 3,000 meters. These facts compel us to set aside 

 the idea not long ago prevalent that, at an altitude 7,000 to 9,000 

 meters above sea level, the temperature should be constant through- 

 out the year. 



Special interest attaches to the particular study of the peculiari- 



