127 
1917-18.] Sound-Waves of the East London Explosion. 
Peterborough), Kimbolton (near Huntingdon), Bottisham (near Cambridge), 
Fornham St Martins (near Bury St Edmunds), and Little Bardfield (near 
Braintree). It is important to notice that nine of these places (namely, 
Thrapston, Biggleswade, Dunton, Chatteris, Groby, Uppingham, Stamford, 
Holme, and Kimbolton) are in the narrow and lofty portion at the west end 
of the silent zone. 
Air-Waves beyond the Sound- Areas . — Windows were shaken at three 
places outside the inner sound-area, namely, Frith Hill near Godalming 
(36 miles) violently, Cowley St John near Oxford (56 J miles) twice, and 
Eynsham near Oxford (64 miles). Pheasants were alarmed in the usual 
way at Swyncombe near Henley-on-Thames (45 miles), Bradfield (51 miles), 
West Woodhay near Newbury (63 miles); and there is no reason, I think, 
for doubting that they were also disturbed at Nursling near Southampton 
(77 miles) and Alderbury near Salisbury (84 miles). Beyond the northern 
boundary of the outer area, pheasants are said to have screamed shortly 
after 7 p.m. at Bishop Burton near Beverley (about 165 miles), North 
Grimston near Malton (about 180 miles), and Thirsk (about 200 miles). I 
know of no reason for rejecting these records except the great distances 
to which the air-waves must have travelled. 
Paths of the Sound-Waves and Inaudible Air- Waves. 
Direction of the Wind . — I am indebted to Sir Napier Shaw for kindly 
giving me the following information : — 
“ The wind at Kew Observatory at 7 p.m. was blowing from the N.E. at 
4'6 metres per second. 
“ The pressure distribution had been changing very slowly during the 
preceding twenty-four hours. An anticyclone centred over Sweden and a 
cyclone over Corsica dominated the map, so that over S.E. England the 
general flow of air within a few thousand feet of the surface must have 
been from the East. The surface winds tending outwards from the high- 
pressure region had a northerly component. The weather having been 
consistently overcast, there were no pilot-balloon ascents reaching a greater 
height than two or three thousand feet on the 18th, 19th, or 20th, so that 
the available records only refer to the Easterly current. 
“The telegraphic reports show that the sky was overcast at 18h. (6 p.m.) 
over the whole of England, the only exception being Dungeness, where ‘ Sky 
three-quarters covered ’ was telegraphed. The direction of motion of the 
upper clouds could not be observed at 18h. or 21h. at most telegraphic 
stations, but the following entries occur : — 
