740 COSMICAL PHYSICS 



combat the difficulty that it demands somewhat more active mole- 

 cular motions for helium than is called for by the mechanical theory 

 of gases, we must yet admit that the objection based upon the low 

 temperature of the highest atmospheric layers is weak. 



Another peculiarity concerning the distribution of gases in the 

 atmosphere is brought out in the observations on polar lights. The 

 principal line in the spectrum of the polar lights is that corresponding 

 to the rare gas, crypton, which is only present in extremely small 

 quantities in the lower regions of our atmosphere. Sir William Ram- 

 say is therefore of the opinion that crypton must be much more 

 generously distributed in the higher layers of the atmosphere than in 

 the lower. Furthermore, tests of air taken at different altitudes, as 

 well as in rising or falling air-currents, indicate that the stirring-up 

 of the air through vertical circulation is sufficient to obliterate the 

 difference in the constitution of the air at different altitudes which 

 would obtain in quiet air owing to the different density of its consti- 

 tuents. Since crypton is heavier than air in the mean, one would ex- 

 pect a tendency whereby this gas would be rarer in the higher layers 

 of the atmosphere than below. The clearing-up of this interesting 

 question is left for thorough spectrum analysis investigations. 



From this short sketch we perceive that meteorology not only 

 stands in the closest connection with other branches of physical 

 science as well as with hydrodynamics, but that it is also connected 

 intimately with questions of chemical, geological, and biological 

 character. The study of the so-called phanologistic phenomena, 

 i. e., the periodically recurring life-processes of the animal and plant 

 world, is also of striking importance in climatological investigations. 

 Furthermore, physical geography and meteorology have much in 

 common. 



