242 Natural History of Volcanos and Earthquakes. 



Paris inches of a column of mercury from this formula, we shall 

 have log. e=2.8316686+log. (213+0- — — 



40 

 in which t is the temperature in degrees of Reaumur — — F.* 



It is clear that the elastic force of steam cannot surpass a cer- 

 tain maximum, which it reaches when its density is equal to 

 that of water. This is the case when the elasticity of the vapor 

 6=232952 Paris inches of mercury, or nearly 8320 atmospheres, 

 which supposes a temperature of 2786° F.f 



Thus, if aqueous vapor were to reach its greatest possible elas- 

 ticity, its temperature must exceed that above assumed for the 

 melting point of lava by 504° F. The highest column of lava, 

 which steam at its maximum elasticity is capable of supporting, 

 is, therefore, if we suppose the specific gravity of liquid lava three 

 times as great as that of water, 88747 feet. But a temperature 

 of 2786° F. will, according to the observations at Geneva and in 

 Cornwall, be met with at a depth of 139265 feet, and according 

 to those in the Erzgebirge, at a depth of 155613 feet (about 

 thirty English miles) below the level of the sea near Vesuvius 

 or Etna-X 



Supposing, then, the values found for the maximum elasticity 

 of steam for the corresponding temperature, and for the depth at 

 which that temperature must exist, to be correct, it would not be 

 possible, that a column of lava, of the whole height, from the seat 

 of the volcanos to the surface of the earth, should be raised up. 

 On the other hand, in the same manner as a bubble of air let into 

 a barometer, drives the mercury into the Torricellian vacuum far 

 above the barometric height, aqueous vapor may raise a column 

 of lava of a height equal to its expansive force into the channels 

 opening into the craters. Thus, then, it may happen that aqueous 

 vapor, though far from its maximum elasticity, may yet be able 

 to raise a column of lava equal in height to its elasticity from still 

 greater depths to the surface of the earth. A continual alterna- 

 tion of columns of lava and steam in the channels may be very 

 well conceived, the consequence of which would be an alternate 



* On steam and steam engines in the Abhandlungen der Konigl. technisclien 

 Deputation fur Gevverbe, part i, p. 344. t Ibid. 



X Supposing the mean temperature of this localtiy = 61" F. 



