FOR HIGH LEVELS IN THE EARTh's ATMOSPHERE. 85 



On the other hand, practical difficulties will certainly be experienced, through 

 occasional inability to make kite ascensions at the proper hour of the day at a sufficient 

 number of stations. But it is to be expected that better results will be attained as the 

 technique of kite-flying develops. In any case it is very desirable that kite-observa- 

 tions be supplemented by observations of another character. Such supplementary ob- 

 servations are indeed supplied by the measurements of cloud heights and cloud veloci- 

 ties. But in order to utilize these we must make use of the Bjerknes theorem of 

 circulation as perfected by taking into account the earth's rotation. I hope soon 

 to return to the consideration of cloud-observations as supplementary to the high-level 

 charts, and also to the consideration of the importance of such charts in weather 

 prediction. 



