Readers not acquainted with this phenomenon may be referred to an
interesting correspondence in the pages of _Nature_ (Oct. 1895, and
_Seq._), opened by Professor G.H. Darwin--
"In the delta of the Ganges," he says, "dull sounds, more or less
resembling distant artillery, are often heard. These are called
Barisal guns, but I do not know the meaning of the term."
The same sounds have been recorded by M. Rutot of the Geological
Survey along the Belgian coast, and are alleged to be pretty common in
the North of France. M. van der Broeck, Conservator of the Museum of
Natural History of Belgium, says--
"I have constantly noticed these sounds in the plain of Limburg since
1880;--more than ten of my personal acquaintances have observed the
fact. The detonations are dull and distant, and are repeated a dozen
times or more at irregular intervals. They are usually heard in the
daytime, when the sky is clear, and especially towards evening after a
very hot day. The noise does not at all resemble artillery, blasting
in mines, or the growling of distant thunder."
M. van der Broeck elsewhere refers to "similar noises heard on
Dartmoor, and in some parts of Scotland." Readers of Blackmore's story
of "Lorna Doone" will remember, among other valuable observations of
out-door life, his accounts of "the hollow moaning sound" during the
intense cold of the winter, of which he gives so graphic an account.
It was "ever present in the air, morning, noon, and night time, and
especially at night, whether any wind was stirring or whether it were
a perfect calm" (Chap. xlvi.).
Another correspondent in _Nature_ refers to remarkable noises among
the hills of Cheshire: "When the wind is easterly, and nearly calm on
the flats, a hollow moaning sound is heard, popularly termed the
Soughing of the Wind, which Sir Walter Scott, in his glossary to 'Guy
Mannering,' interprets as a hollow blast or whisper."
Another writer quotes experiences in East Anglia, tending to show that
such sounds may be reports arising from the process of "faulting"
going on, on a small scale, at a great depth, and not of sufficient
intensity to produce a perceptible vibration at the earth's surface.
It would seem that in districts such as Comrie in Perthshire, East
Hadden in Connecticut, Pignerol in Piedmont, Meleda in the Adriatic,
&c., sounds without shocks are common during intervals, which may last
for several years. Remarkable sounds, not apparently accounted for,
are reported to proceed from Lough Neagh in Ireland.
See _Nature_, Oct. 1895, and following numbers; articles by M. van der
Broeck in _Ciel et Terre_ (Belgium), Dec. 1, 1895, and following
numbers, also _Geol. Mag._, vol. ix. 1892, pp. 208-18.