119 
1917-18.] Sound-Waves of the East London Explosion. 
doubtful owing to inconclusive estimates of the time. I am indebted to 
Sir Napier Shaw for two other distant records. At Milford-on-Sea in 
Hampshire (90 miles), a deep boom, apparently a great distance off, was 
heard about 7 p.m. At a place ten miles south of Boulogne (93 miles), one 
steady explosion that slightly shook the windows, and sounded like firing 
out at sea, was heard shortly after 7 p.m. Through the kindness of 
Mr Miller Christy, I have also received another record from the north of 
France, the exact place and time not being given. Two successive reports 
sounding like very distant gun-fire were heard from over the sea. The 
connection of the sounds observed at these places with the East London 
explosion would be interesting if it were established. But it is difficult to 
feel confidence in that connection, all three places being within the range of 
similar sound-waves from other distant sources. 
From the district lying to the north of the outer sound-area I have only 
one record which may refer to the explosion. At North Grimston, near 
Malton (about 180 miles from the source), two heavy bangs in rapid 
succession wrnre heard between 7.10 and 7.15 p.m., and the pheasants in the 
woods called loudly. Owing to the isolation of the place from the rest of 
the sound-area, it is doubtful whether the sound-waves audible there 
originated in East London. 
An observation of some interest was made at Derby, which lies 14 miles 
to the west of the outer sound-area. The sound of the explosion was heard 
in this city by telephone connected at the time with London. 
Nature of the Sound. 
The sound was a deep boom, not much above the lower limit of audibility. 
Several observers remark that it was almost felt rather than heard, and 
this even at places so near the origin as Billericay (18 miles), Chatham 
(22 miles), and Hitchin (34 miles). As sometimes happens with the low 
sound of earthquakes, it was heard by one man who is almost completely 
deaf to ordinary sounds. 
Both sound-areas have frequently been visited by Zeppelins, and the 
sound of their exploding bombs is probably well known to all the 
observers. Their visits have been of some use in providing standards of 
comparison as to nature and intensity, references being frequently made to 
the explosion of bombs at a distance of so many miles. So close was their 
resemblance at some places that special constables turned out and ordered 
lights to be extinguished. Several observers, however — including one who 
has heard more than 500 bombs explode, — detected a difference between 
the two sounds, that of the explosion being longer, heavier (that is„ 
