SQUIER— PHYSICAL ASPECTS. 169 



increase of elevation the temperature of the air decreased more or 

 less uniformly from whatever it was at the surface of the earth to 

 absolute zero at an elevation of perhaps 30 to 40 kilometers. Now 

 we know that this is not true, that at an elevation of only 10 to 12 

 kilometers at this latitude the temperature becomes substantially 

 constant with respect to increase of altitude, and, what is of even 

 greater intellectual interest, we can explain why it must be so. Only 

 a little while ago no one could say why the clouds never rose higher 

 than certain levels that were far below the known heights of the 

 atmosphere. Now we do know why this is true, as we also know 

 why clouds are more abundant at certain levels and less abundant 

 at others. 



We recently have learned how the velocity of the wind generally 

 increases with altitude, and why it so increases. At last, and that 

 quite recently, we have found a logical and experimentally supported 

 theory of the electrification that gives the lightning flash, and with 

 it we have acquired a clearer understanding of the mechanism of 

 the thunderstorm. 



These are only some of the comparatively recent discoveries in 

 connection with the phenomena of the atmosphere, and opportunity 

 lies near and inviting for many more. 



The genesis of the ordinary cyclonic storm still needs much study 

 and discussion. The relation of topography, nature of the surface, 

 sunshine, etc., to air movements, both horizontal and vertical, need 

 to be intensively studied because of their importance to the art of 

 aviation, especially aviation as a means of commercial travel and 

 as a sport. Through this investigation we may reasonably hope to 

 acquire the art of soaring, and thereby realize the gentlest of all 

 modes of travel. 



The immediate problems of the atmosphere calling for solution 



are numerous, but I shall mention only one more. On the whole the 



earth is negatively charged. What then is the origin of this negative 



charge and how is it perpetually maintained ? 



War Department. 



Office of the Chief Signal Officer, 

 Washington, April, 1917. 



