1834.] 



A short notice of Earthquakes, 



106 



visionary pursuit/* 



French naturalists, have also of late years, by the application of 

 the history of organic remains, to the science of geology, given 

 many enlarged views regarding the former changes of the earth ; 

 comparisons having been made between ancient and modern fossil 

 specimens, and inferences drawn with regard to their habits. 



To proceed however in the more immediate investigation of 

 earthquakes ; formerly peculiar states of the atmosphere were con- 

 sidered productive, and prognostic of these convulsions ; there is 

 generally allowed to be an intimate connexion, but as Mitchell 

 has remarked, it is more probable that the air should be affected 

 by the causes of the earthquakes, than that the earth should be 

 affected in so extraordinary a manner, and to so great a depth by a 

 cause residing in the air." 



It is however the general opinion of all late authorities, that 

 earthquakes, and volcanoes are intimately blended, being the effects 

 of the same agents, although they give rise to different phenomena 

 on the surface of the globe. I shall therefore first give some ac- 

 count of Sir Humphry Davy's theory of volcanic actions ; which is 

 •generally allowed to be the most correct and satisfactory. From ther- 

 mometrical experiments on the temperature of mines, and hot water 

 springs, it has been shewn that the interior of the globe, possesses a 

 high temperature, which in some degree simplifies the problem of 

 volcanic fires. Sir, H Davy says, " that on the hypothesis of a 

 chemical cause for volcanic fires, and reasoning from known facts 

 there appears to be no other adequate source than the oxydation 

 of the metals, which form the basis of the earths and alkalis. He 

 considers, that these from their great affinity to oxygen, could not 

 exist on the surface of the earth, but only in the interior of the 

 globe, and that volcanic fires are occasioned, whenever these are ex- 

 posed in subterranean cavities to the action of air and water/' 

 On examining a stream of lava, issuing from Vesuvius, he ascer- 

 tained that there was no combustion going on at the moment of 

 its exit from the mountain, on lifting up some of it in an iron 

 ladle it did not ignite more vividly, on being exposed to the air, 

 some of it was poured into a glass bottle containing silicious 

 sand at the bottom, a ground stopper was closed at the moment, 

 and the bottle was found to contain when afterwards examined by 

 the test of nitrous gas as large a proportion of oxygen as common 

 air ; when melted nitre was thrown over the lava, it fused from the 

 heat, but there was not the least increase of deflagration, to indicate 



