954 
an opening of 90° towards NE., the inner border being formed by 
a circle with a radius of about 140 KM., the outer border lying at 
about 180 KM. not counting isolated spots at 200 and 220 KM. 
Hence in both cases the two areas of audibility are separated by 
an interspace, which Vor bEM Borre baptized “Zone des Schweigens” 
and which we shall call the “silent region”. 
3. Three eruptions of the voleano Asama in Japan, investigated 
by S. Fusiwwara '). 
a. December 7 1900. (Fig. 3). Heavy eruption, in which the 
sound and air-wave broke woodwork and windowpanes at a distance 
of more than 10 K.M. With the exception of one report, all places 
where the sound was heard are enclosed within a single line, starting 
from a place at the coast South of the voleano, passing by the vol- 
cano at a small distance Westward, curving round towards a place 
on the coast NE. of the voleano and, of course, following the coast 
thence. Within this area there lies a smaller one on the south 
coast where nothing was heard. 
Remarkable is the propagation of sound in almost exclusively 
easterly directions, coinciding with the direction in which the ashes 
fell. The extreme distance is about 300 KM. 
b. (Fig. 4). December 25 1910. Moderate eruption. The sound was 
heard eastward up to a distance of JOO KM., and moreover at two 
isolated spots at 130 and 210 KM. distance. To the west there is 
searcely other than abnormal audibility, which starts at 90 KM. 
and goes on up to 150 KM. 
c. (Fig. 5). April 4 1911. Also a moderate eruption. First region 
of audibility small, nowhere surpassing the 50 KM. limit; second 
region larger and at 120—210 KM. mostly in westerly directions. 
The density of the reports is especially Jarge at 140—150 KM. in W. 
In all, silent regions occur in 9 of the 18 cases which were 
investigated by FusiwHara, at least if we decide to use that name 
for every region of silence which is bounded inside and outside by 
regions of audibility. The distances vary between 90 and 220 KM. 
usnally between 120 and 200 KM. 
4. A case of gunpowder and dynamite explosion at Kobe on 
April 3'¢ 1910, described by the same investigator (Fig. 6). The 
region of audibility is single and much more regularly shaped than 
is the case in most of the volcanic eruptions, but still far from 
symmetrical round the source of sound. The “silent region” indicated 
in the chart is somewhat dubious, being supported by only one 
observation. 
7) Bulletin Central Meteorological Observatory Japan, Il, 1. 1912. 
