946 
with his suppositions. Though the order of magnitude for the 
distances at which the ray returns to the earth remains the same, 
all distances, and with them the radius of the silent region, become 
sensibly smaller. 
We give here only the results near this point: 
Height H, where the Return to the 
at. ray becomes horizontal. earth at distance D. 
a. 30°56’ 75 KM. 114 KM. 
24°27’ 80 103 
20553 85 109 
19°12’ 90 131 
Hence at all events we find a value for the limit of tbe silent 
region, far from those encountered in reality. 
In the first place, we had to consider further the suppositions 
on the composition of the atmosphere made by other writers. 
Dh. Whauner’s') hypothesis about the occurrence of geocoronium 
in the atmosphere. 
WerGeNeR takes at the surface the lower percentage of hydrogen 
0.0033 °/, according to RarreiH, but does not allow for the mixing 
by convection currents. As VON DEM Borne practically did not do 
that either, or at least only very partially, WeGENER’s percentage 
of hydrogen remains much lower. 
0 20 40 60 80 100 KM. 
Hydrogen 0.0038 0.0 il 12 55 67 
Geocoronium = — — — 5 19 29 
Partially the low percentage of hydrogen is balanced by the 
hypothetical geocoronium, as this would be .5 times lighter than 
bydrogen. On the whole, therefore, the course of the rays is only 
slightly changed, as the course depends on the rapid decrease of 
the molecular weight between 60 and 80 KM. 
The limit of the silent region is indicated by the following sets 
of values: 
a EIS D. 
16°43’ 105 148 
20°26’ 95 118 
31°44’ 82.7 121 
42°32’ (7.2 151 
If these data are combined in a graphic (fig. 8), we find as limit 
of the silent region 114 KM. for an initial angle of 25° of the 
sound ray. 
1) A. WEGENER, Beiträge zur Geophysik, 11, p. 104, 1912. 
