EARTHQUAKES. 
543 
If tlie commonly received theory of the cause of earth¬ 
quakes is true—that, namely, which ascribes them to the elas¬ 
tic force of gases accumulated or generated in subterranean 
reservoirs—it is evident that open channels of communication 
between such reservoirs and the atmosphere might serve as a 
harmless discharge of gases that would otherwise acquire de¬ 
structive energy. The doubt is whether artificial excavations 
can be carried deep enough to reach the laboratory where the 
elastic fluids are distilled. There are, in many places, small 
natural crevices through which such fluids escape, and the 
source of them sometimes lies at so moderate a depth that they 
pervade the superficial soil and, as it were, transpire from it, 
over a considerable area. When the borer of an ordinary ar¬ 
tesian well strikes into a cavity in the earth, imprisoned air 
often rushes out with great violence, and this has been still 
more frequently observed in sinking mineral-oil wells. In 
this latter case, the discharge of a vehement current of inflam¬ 
mable fluid sometimes continues for hours and even longer 
periods. These facts seem to render it not wholly improbable 
that the popular belief of the efficacy of deep wells in miti¬ 
gating the violence of earthquakes is well founded. 
In general, light, wooden buildings are less injured by 
earthquakes than more solid structures of stone or brick, and 
it is commonly supposed that the power put forth by the earth 
wave is too great to be resisted by any amount of weight or 
solidity of mass that man can pile up upon the surface. Bat 
the fact that in countries subject to earthquakes many very large 
and strongly constructed palaces, temples, and other monu¬ 
ments have stood for centuries, comparatively uninjured, sug¬ 
gests a doubt whether this opinion is sound. The earthquake 
of the first of November, 1755, which was felt over a twelfth 
part of the earth’s surface, was probably the most violent of 
which we have any clear and distinct account, and it seems to 
have exerted its most destructive force at Lisbon. It has often 
been noticed as a remarkable fact, that the mint, a building 
of great solidity, was almost wholly unaffected by the shock 
which shattered every house and church in the city, and it? 
