49 ᾿ΒΕΒΡΟΕΒ1---1850. 
except that the earthquake sound is less sonorous. It has been compared 
with distant thunder and with distant guns, but it is more rumbling in its 
nature; in short, it admits of no exact comparison. I have noted that when 
the shocks occur during a heavy gale, this dull rumbling sound is not per- 
ceptible: it is overcome by the nearer noise of the wind.” 
The allusion to the steam ship chimney here relates to a peculiar and 
most powerful sound, a true musical tone, which is produced occasionally 
when there are powerful blazing fires under the boilers, with a strong draft, 
and the furnace-doors are partially shut, in which case the funnel acts as a 
great organ pipe, to which the furnace-doors play the parts of reeds, and 
the draft of the fire that of bellows. The note here is about the lowest that 
the organ is capable of sustaining. 
I have myself met a gentleman who had for a long time resided in the 
convulsed districts of South America, and whose occupation as a mining 
engineer gave him large opportunities of observation, and who compared the 
noise most usual to that of steam blowing off into cold water: a low irre- 
gular rumble, accompanied with still more irregular, sharp detonations, such 
as we may hear frequently in travelling by railway, when steam is blown 
from the engine boiler into the tender to heat the cold water therein ; the note 
however being in the case of earthquakes far graver than in this instance. 
In the Caraccas earthquake (April 1812), the explosions of the voleano 
of the island of St. Vincent were heard at the Rio Apura, like the discharge 
of the heaviest artillery; the distance in a straight line being 210 nautical 
leagues, of 20 to a degree, a distance as great as from Mount Vesuvius to 
Paris. (Humboldt’s Per. Nar., vol. iv. p. 27.) 
Yet the “ Bramidos,” however awful and loud, may be derived from a very 
slight original stroke or grinding together of rock surfaces, the volume of 
sound being multiplied by the vast surface of the earth from which at nearly 
the same instant it is transmitted to the air and thence to the hearer. Thus, 
for example, the large blocks of stone on the Breakwater of Plymouth, or 
on the piers of Kingstown Harbour, Ireland, are some of them so circum- 
stanced, as to oscillate slightly like logan-stones, and to strike together under 
water by the motion of the waves, with, however, a force and range of mo- 
tion so slight, that, when left dry at low water, and moved thus by hand, the 
blow is quite inaudible at a few feet distance ; nevertheless, when so moved 
by the swell under water, the noise and crash sound quite formidable, and 
would at first lead the hearer to suppose the whole structure was washing 
away from beneath him, when thus heard on a calm clear day with a swelling 
sea. 
There is a deep mountain tarn in Ireland, Lough Bray, one boundary of 
which is a steep mural precipice under water; when a stone of a few pounds 
weight is dropped gently from a boat at this side of the lake, the crash of 
its descent under water, as it falls over the face of the precipitous rocks which 
emerge from the dark waters, conveys a most awful impression. So also the 
ticking of a watch, inaudible even to the holder when held in the hand, 
becomes distinctly heard across a large room when laid on a table. The 
signals in use by a blow given to the side of a diving-bell, and clearly trans- 
mitted through some fathoms of water, are also in point. 
The intensity of the sound heard at a given station will depend in some 
degree upon the same circumstance that will determine its time of occurrence 
with relation to the shock, and it will also much depend upon the sonoricity 
of the media (formations) through which it passes to be heard. Thus, what- 
ever may be the original impulse producing the noise, whether fracturing of 
