BLAIR— AEROLOGY. 211 



zontal component of the wind speed shown is about 7.5 centimeters 

 per second. It would require a horizontal acceleration of 17 to 20 

 times this amount to sustain a bird or a well-constructed glider in 

 soaring flight, but together with the changes in direction in the 

 horizonal plane recorded by our instruments, vertical changes in 

 direction occur in these gusts which are really only a series of ex- 

 pansions and contractions in the moving air. 



When the air expands and contracts with sufficient rapidity, the 

 vibrations become audible. The use of these vibrations and pos- 

 sibly of aerial vibrations of still higher frequency in detecting the 

 presence of aircraft or as a means of communication between air- 

 craft or to receiving stations is outside the scope of this paper. 



The subject of atmospheric electricity and possibly closely con- 

 nected with it the loading of aircraft with liquid or solid H^O are 

 also matters of interest to the aeronaut. So far not much has been 

 done toward the solution of the problems arising from these atmos- 

 pheric conditions. It is likely that the solid formations, both crys- 

 talline and amorphous, occur more readily, if not altogether, on 

 electrically charged surfaces. 



U. S. Weather Bureau, 

 Washington, D. C. 



