610 EARTHQUAKES. 



•nral ravines and caves, but quarries, wells, and other human ex- 

 cavations, which break the continuity of the terrestrial strata 

 and facilitate the escape of elastic vapors, have a sensible influ- 

 ence in diminishing the violence and preventing the propagation 

 of the earth-waves. In all countries subject to earthquakes this 

 opinion is still maintained, and it is asserted that, both in ancient 

 and in modem times, buildings protected by deep wells under or 

 near them have suffered less from earthquakes than those the 

 architects of which have neglected this precaution.* 



If the commonly received theory of the cause of earthquakes 

 is true — ^that, namely, which ascribes them to the elastic 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 destructive 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 artesian well strikes into a cavity in the 

 earth, imprisoned air often rushes out with great violence, and 

 this has been stiU more frequently observed in sinking mineral- 

 oil wells. In this latter case, the discharge of a vehement cur- 

 rent of inflammable fluid sometimes continues for hours and even 

 longer periods. These facts seem to render it not whoUy improb- 

 able that the popular belief of the efficacy of deep weUs in miti- 

 gating the violence of earthquakes is well founded. 



In general, light, wooden buildiugs are less injured by earth- 

 quakes 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 upon the surface. But the fact that 

 in countries subject to earthquakes many very large and strongly 

 constructed palaces, temples and other monuments have stood 

 for centuries, comparatively uninjured, suggests a doubt whether 



* Laitogrebb, QescMchte der Vulkane, ii., pp. 19, 20. 



