Chemistry and Physics. 89 



From a consideration of observations upon the appearance of 

 twilight the height of the upper limit of the atmospheric layer 

 reflecting light is placed at about 74 km. After this " end of 

 twilight " there is, however, a very pale, bluish light, the obser- 

 vation of which led See to estimate the height of the correspond- 

 ing reflecting layers at 214 km. Wegener believes it probable 

 that this altitude corresponds to the boundary between the 

 spheres of hydrogen and the hypothetical lighter gas, which he 

 calls "geocoronium." 



Since observations show that small meteors begin to glow at a 

 height of about 150 km. and go out at about 80 km., it appears 

 that their play is entirely within the hydrogen atmosphere, if the 

 conclusions here advocated are true. In that case their luminos- 

 ity is due to their collision with hydrogen, and their disappear- 

 ance is probably caused by volatilization. Larger meteors often 

 show a great increase in brilliancy at a certain point in their 

 course, thus indicating a sudden change in the atmosphere, and 

 they have been observed to explode at heights varying from 3*7 

 to 46-7 km. 



It is important in this connection that Pickering found several 

 hydrogen lines in the spectrum of the luminous trail of a meteor, 

 although Blajko in two cases observed very bright lines at 393 

 and 389, which Wegener takes to be identical with the nitrogen 

 line 391, which is very prominent in northern light spectrum, and 

 hence he believes that these meteors had penetrated to the nitro- 

 gen atmosphere. 



The amount of oxygen in the air has been found to vary but 

 little, or not at all, from the surface of the earth to an altitude of 

 15^ km. This is attributed to vertical mixing, but an analysis of 

 air from a height of 8 km. by E. Erdmann showed per liter a 

 total of 37 - 7 C0 of helium, neon and hydrogen, the lightest con- 

 stituents of the air, while air at the surface of the earth contains 

 26*2 CC of these gases. Similar results were obtained by Hugo 

 Erdmann by the comparison of air from the surface with that 

 from an altitude of 4 to 4£ km., so that it appears that in spite of 

 vertical mixing, a concentration of the lighter constituents with 

 the altitude is indicated. 



Several arguments, based upon the appearance and spectra of 

 the aurora borealis, are brought forward in favor of the layer 

 theory of the atmosphere, but they will not be noticed in detail 

 here. It should be mentioned, however, that Scheiner has 

 expressed the opinion that the northern light lines indicate the 

 presence of an unknown, very light gas, and the author takes 

 occasion to identify this with Mendeleeff's speculative element 

 with the atomic weight / 0*4, and with his own hypothetical 

 "geocoronium," which he believes to form a stratum above the 

 hydrogen stratum. 



The following tables give the results of the author's calcula- 

 tions where the hypothetical geocoronium is taken into account : 



