935 
Geophysics. — “The propagation of sound in the atmosphere”. 
By Dr. B. van EvERDINGEN. (Communicated by Dr. J. P. van 
DER STOK). 
(Communicated in the meeting of October 30, 1915). 
§ 1. In various investigations on the propagation of heavy sounds 
over great distances, especially in the case of volcanic eruptions and 
explosions, deviations have been found, partly regular, partly irregular. 
The source of sound is always surrounded by an area of regular 
or irregular shape, where the sound is heard everywhere; but the 
source is far from being always situated symmetrically within this 
area, and the dimensions of the latter are not even in the first place 
determined by the intensity of the sound. In many cases a second 
area of audibility occurs, separated from the first by a region where 
no sound at all is heard. Sometimes this second area partly surrounds 
the first, sometimes it only consists of isolated spots — only this 
can be said generally, that the smallest distance from the source of 
sound for this second area as a rule is much more than 100 KM. 
and that the intensity of sound at this smallest distance is by no 
means smaller than at the outer border of the first area of audibility, 
which is much nearer to the source of sound. 
To illustrate this we have collected on plate I. some of the cases 
that have been investigated most carefully. 
1. (Fig. 1). Dynamite explosion (15000 KG.) at Förde in West- 
falen, December 14th 1903. Investigated by Dr. G. voy DEM Borne’). 
The small erosses indicate, in this and all following figures, the 
places where sound was heard, the cireles those where nothing 
was heard. 
With one singie exception the places where the explosion was 
heard are enclosed by two border-lines: the first line small, 20 to 
50 KM. round Förde, but displaced towards NW., the second one 
large, with an inner border at about 110 KM., and reaching outwards 
to about 180 KM., within a sector of 90° opening E. of Förde. 
2. (Fig. 2). Dynamite explosion (25000) KG.) near the Jungfrau 
railway on November 15, 1908. Investigated by Dr. A. DE QUERVAIN ®). 
Again with one exception the region of audibility may be divided 
into two parts: The first, which extends from the ‘“Kigerwand”, 
where the explosion occurred, some 30 KM. towards NE. and NW., 
whereas at a distance of 60 tot 70 KM. sound was heard at isolated 
mountain summits; the second much larger, within a sector with 
1) Die Erdbebenwarte 4, p. 1—4, 1904. 
2) Annalen der Schweizerischen Meteorologischen Zentralanstalt, J 908, 
