1824.) 
hy its own pressure into imperceptible 
fissures to a great depth in the interior 
of the earth, and would accumulate in 
the vast cavities it contains. The 
voleanic fires would afterwards gradu- 
ally: revive, and the lava, after having 
obstructed the channels through which 
the water penetrated, would rise to its 
accustomed vent; the diameter of 
which mast continually increase by the 
fusion of its coats. 'These are mere 
conjectures ; but the fact is certain, 
that water dees really existin velcanic 
furnaces. 
It is evident that the science of 
voicanos is as yet involved in much 
uncertainty, Although there are 
strong grounds for the belicf that the 
earth contains substances in a high 
degree combustib!e, we are stil! in 
want of those precise observations 
which might enable us to appreciate 
their agency in volcanic phenomena. 
For this purpose, an accurate know- 
Jedge of the nature of the vapours 
exhaled by.different voleanos is requi- 
site; for the cause which keeps them 
in activity being certainly the same in 
each, the products common to all might 
lead to its discovery. All other pro- 
ducts will be aecicdental; that is to 
Say, they will be the result of the 
action of heat upon the inert bodies in 
the neighbourhood of the volcanic 
furnace. 
‘The great number of burning volca- 
mos spread over the surface of the 
earth, and the still greater number of 
mineral, masses. which bear evident 
marks of their ancient volcanic origin, 
eught to make us regard the ultimate 
or outermost stratum of the earth as a 
erust of scoriz, beneath which exist a 
great many furnaces, some of which 
are extinguished, whiie others are 
rekindled. It is well calculated to 
excite surprise, that the earth, which 
has endured through so many ages, 
should still preserve an intestine force 
sufficient to heave up mountains, 
overturn cities, aud agitate its whole 
mass. 
The greater number of mountains, 
when they arose from the heart of the 
‘earth, must have left these vast 
cavities, which would remain empty 
unless filled by water. I think, how- 
ever, that De Luc, and many other 
geologists, have reasoned very errone- 
eusly on these cavities, which they 
imagine ‘stretching out into long 
galleries, by means of which cuarth- 
Theory of Voicanos, by M. Gay-Lussac. 
499 
quakes are communicated to a dis- 
tance. 
An earthquake, as Dr. Young has 
very justly observed, is analogous to a 
vibration of the air. Itisa very strong 
sonorous undulation, excited in the 
solid mass of the earth by some 
commotion which communicates itself 
with the same rapidity with which 
sound travels. The astonishing consi- 
derations in this great and terrible 
phenomenon are, the immense extent 
to which it is felt, the ravages it pro- 
duces, and the potency of the cause to 
which it must be attributed. But 
sufficient attention has not been paid 
to the ease with which all the particles 
of a solid mass are agitated. The 
shock produced by the head of a pin at 
one end of a long beam causes a yibra- 
tion through all its fibres, and is 
distinctly transmitted to an attentive 
car at the other end. ‘The motion of a 
carriage on the pavement shakes vast 
edifices, and communicates itself 
through considerable masses, as in the 
deep quarries under Paris. Is it 
therefore so astenishing :that a violent 
commotion in the bowels of the earth 
should make it tremble in a radius of 
many hundreds of leagues? In con- 
formity with the law of the transmission 
of motion in elastic bodies, the extreme 
stratum, finding no other strata to 
which to transmit its motion, makes 
an effort to detach itself from the 
agitated mass, in the same manner as 
in a row of billiard-balls, the first of 
which is struck in the direction of 
contact, the last alone detaches itself 
and receives the motion. This is the 
idea I have formed of the effects of 
earthquakes ou the surface of the 
globe; and I should explain their 
great diversity, by also taking into 
eousideration, with M. dé Humboldt, 
the nature of the soil, and the solutions 
of continuity which it may contain. 
In a word, earthquakes are only the 
propagation of a commotion through 
the mass of the earth; and are so far 
from depending on subterranean cavi- 
ties, that their extent would be greater 
in proportion as the earth was more 
homogencous. 
— 
To the Editor of the Monthly Magazine, 
SIR, 
T was very civil of “The Druid in 
London” to point out the play of 
Shakspeare, in which the allusion “I 
had hinted at in my reminiscences of 
84, 
; 
