957 
on October 8th were extraordinarily favourable for a wide propa- 
gation of sound in the area which surrounded the source of sound, 
but that rays, starting with large elevation were not disturbed at 
all in the lower strata, so that a return to the earth was made 
possible only in connection with the change in composition of the 
higher strata of the atmosphere. 
October 17%. This time, too, almost no curvature is to be expected 
for steep rays in the lower 10 KM.; the increase of wind from 
NE. +5 M. to S. 10 M. per second in the Ci does not neutralize 
the curvature from the surface, caused by the normal decrease of 
temperature. Also the inversions are of little importance, at least in 
our country and at Lindenberg. The temperature does not at all 
rise to the surface temperature. 
In consequence, little is heard in this country of the war-noises 
in Flanders, in Zealand-Flanders nothing at all. The naval battle on 
the North Sea is likewise not heard at Helder and further in the 
province of North-Holland ; the motion of the Ci. from the South, indeed, 
was not apt to cause a downward curvature of rays from a Westerly 
direction. For the undoubtedly heard sounds in Friesland and Gro- 
ningen, therefore, no other explanation remains than the refraction 
by the higher strata of the atmosphere. 
October 18%, Cirrus-observations have not come to our know- 
ledge; the weather conditions of the previous day and the fact, that 
the high pressure was increasing, allow us however to assume, 
that no very great velocities occurred in higher strata. Hence there 
was only an increase of the NE. wind up to the A.Cu level at 
+ 3000 M., an increase decidedly unfavourable for the refraction of 
the sound towards the earth in the troposphere, but of little influence 
on the curvature of the sound rays in the higher atmosphere. The 
ESE-wind, observed with probably very high A.Cu, has no influence 
on the propagation of the sound in a NE.-ly direction, as was 
observed on this day. Inversions will have been of little impor- 
tance in our neighbourhood. 
That the NE-wind, increasing upwards, was unfavourable for the 
propagation near the surface appears clearly enough from the scarcity of 
observations in Zealand, which contrast remarkably with the numerous 
reports, even of heavy sounds, beyond 160 KM. 
For the first time here an indication appears of the limit of in- 
creased audibility at about 200 KM. from the place, where the 
English naval guns were in action. If these guns were indeed the 
most audible at this distance, we should have to assume, that the very 
steep sound rays, wanted for the minimum distance with these guns, 
