117 
1917-18.] Sound-Waves of the East London Explosion. 
The inner sonnd-area is of unusual form. It is distorted in two 
directions so that the area is slightly crescent-shaped. To the east-south- 
east it extends as far as Canterbury (48 miles); but, in this direction, 
observations are rare and the form of the boundary is in consequence 
uncertain. Towards the north-east and south the area is singularly 
restricted, the distance of the boundary from the source being 20 miles in 
the former direction and 19 in the latter. In contrast, the extension 
of the north-westerly branch of the area is all the more remarkable. It 
runs up, through Hertfordshire and Bedfordshire, into Northamptonshire, 
ending in the neighbourhood of Ecton and Wellingborough at 664 miles 
from the source of sound. From north-west to south-east the length of the 
inner area is 111 miles, its greatest width is 49 miles, and the area covered 
by it is 3390 square miles. 
The outer sound-area is of greater extent. Its length from near 
Nottingham to the east coast of Norfolk is 131 miles, its greatest width is 
44 miles, and the area included 5000 square miles. It is probable that the 
portion of this area which extends into the sea beyond the coast of Norfolk 
is not of great size, and that the angle subtended by the area at the source 
is about 90°. The axis of the area is directed E. 24° S. The most distant 
places at which the sound was heard are Bestwood (near Nottingham) 
and Stow (near Lincoln), which are respectively 117 and 128 miles from 
the source of sound. The least radial distance of the outer boundary is 
107 miles. 
The width of the silent zone varies from 28 miles at its western end, to 
43 miles near the centre and 48 miles at the eastern end. The distance 
from the source of the outer margin of the silent zone varies from 65 to 95 
miles, the average distance being 75 miles. 
Isacoustic Lines. 
It is evident from the records that the sound varied very greatly in 
strength, especially in the inner area. To determine the rate of variation, 
I drew up the following rough scale of sound-intensity, some of the principal 
terms employed in the descriptions being added : — 
A. Very loud sound . — A terrific bombardment, a terrible explosion, 
louder than any bomb or crash of thunder. 
B. Moderately loud sound . — A heavy boom, a loud report, heavy gun- 
fire, a very loud or heavy clap of thunder. 
C. Faint sound . — Distant guns booming, the distant roll of thunder, 
the dull boom of a distant explosion, a heavy gust of wind, the roar 
of a furnace. 
