960 
fighting on shore or at sea, likewise more or less distinct silent 
regions may be indicated. 
2. The two theories proposed for the explanation of silent regions: 
explanation by influence of variations of wind and temperature with 
height (e.g. Moun, RarreicH, FosiwHara), and explanation by the 
change in composition of the atmosphere in very high strata (von 
DEM Borne) give silent regions of a very. different character. The 
meteorological theory leads one to expect i. a. asymmetry with respect 
to the source of sound and difference between two mutually per- 
pendicular directions, and permits all kinds of distances; the physical 
explanation requires complete symmetry with respect to the source 
of sound. It is shown that the latter particularity is also preserved 
for the greater part, if considerable irregularities occur in the distri- 
bution of wind or temperature and that the outer limit of the silent 
region is thereby only slightly changed. 
3. Though for want of observations in most cases the proof 
cannot be given, we must assume that the majority of the well 
described cases of silent regions have been caused by meteorological 
circumstances. 
4+. The meteorological observations in the upper air, made in or 
near our country on the dates treated in this investigation, fail to 
give an explanation of the silent regions observed, though they are 
sufficient to explain the great differences in the first, normal area of 
audibility. 
5. For the physical explanation of these silent regions pleads the 
fact, that the distance from its border to the probable source of sound 
has been always near 160 KM., and that no appreciable deviations 
from the circular form have been found, 
6. The figure, 160 KM., does not agree with the suppositions 
on which von prem Borne has founded his calculations, nor yet 
with other suppositions published hitherto by meteorologists, but 
agrees fairly well with the much smaller percentage of hydrogen in 
the atmosphere according to Craupr, if we assume that up to 10 KM. 
height the composition of the atmosphere does not undergo a per- 
ceptible change. 
7. A percentage of geocoronium as assumed by WeGENER is at 
variance with the results of this investigation. If geocoronium is 
present in the atmosphere, we think that the amount must be much 
smaller than was assumed by WEGENER, 
