948 
e. Without geocoronium, but with a hydrogen percentage as assumed 
by WeGENER, and moreover mixing up to 10 KM. 
At greater heights the percentage of hydrogen then becomes : 
0 20 40 60 80 100 120 KM. 
d. 0.01 0.14 2.6 304 68.7 70.5 67.0 
é. 0.00383 0.014 0.25 5.2 42.3. “91:0 » 98.2 
These assumptions are the most diverging as to the quantity of 
hydrogen, a thing which becomes especially important at 60 KM. 
The course of the rays is then characterised by the following figures : 
« Hi: DA 
d. olen 15) 124 
8 81.7 106 
20°38’ 85 102 
US 90 119 
e. 38°48" 90) 160 
BOZO: 95 133 
Doce! 100 126 
Dil 105 131 
Minimum distance for d += 102 e + 126. 
We see how the decrease of the quantity of hydrogen leads to 
shifting the limit of the silent region farther off. Therefore the 
question arises: Is there a reason to assume a still smaller quantity 
of hydrogen ? 
This really appears to be the case. The determination by CLAUDE *), 
in which very large quantities of air were liquefied, led to the result, 
that the volume percentage of hydrogen in the atmosphere at the 
surface would be only 0.0001, against 0.0005 Helium. For the three 
rare gases Neon, Helium and Hydrogen together 0.0021 was found. 
The most recent determination of these constituents was made by 
ERDMANN ®) in samples of air, collected at various heights in the 
atmosphere at the time of the nearest approach to the earth of the 
tail of HauLey’s comet on 18/19 May 1910. The quantity of air in 
these determinations was never more than 650 em°. Per liter of air 
26 to 57 mm’. of the gases mentioned was found ; only for the 
height of 4500 to 8000 M. it was possible to ascertain the presence 
of hydrogen by means of the spectroscope, most clearly in the latter 
case. Hence at the surface the percentage of hydrogen is far below 0.0026. 
From the increasing proportion of rare gases with greater height 
1) G. CLAUDE, C.R. 148 p. 1454, 1909. 
2) ERDMANN, Ergebn. d. Arb. d. K P. Aeron. Obs. Lindenberg, 6. p. 227, 1911. 
