the Interior qftJie Earth. 285 



volcanoes of the interior of France, viz. (in 1806) those of the 

 volcano of Murol in Auvergne, and (in 1809) those of the vol- 

 cano of Cherchemiis, near Issarles at Mezin. I found the vo- 

 lume of the matters of each eruption much inferior to that of a 

 cubic kilometre *. From these data, and others of a similar kind, 

 which I have collected in various parts, I consider myself war- 

 ranted to assume the volume of a cubic kilometre, as the ex- 

 treme term of the product of eruptions considered in a general 

 sense. Now, such a mass is almost nothing compared with tho 

 bulk of the globe. Spread over its surface, it would form a 

 layer not more than one five-hundredth part of a millimetre in 

 thickness -f-. In exact terms, if we suppose the crust of the earth 

 to have a mean thickness of twenty leagues of 5000 metres, a con- 

 traction capable of shortening the mean radius of the central 

 mass Txgjth of a millimetre, would be sufficient to produce the 

 matter of an eruption. 



Proceeding on these data, if we suppose that contraction alone 

 produces the phenomenon, and that over the whole earth there 

 take place five eruptions annually, we find that the difference 

 between the contraction of the consolidated crust and that of the 

 internal mass^ only shortens the radius of that mass one millime- 

 tre in a century. If there be only two eruptions yearly, it takes 

 two centuries and a-half to produce the same shortening. We 

 see, that, in all cases, an excessively small action is sufficient to 

 produce the phenomena. 



It will be remarked, that this action, if it be real, is necessa- 

 rily in connection with the total contraction which the globe ex- 

 periences from the effect of secular cooling. It furnishes a 

 basis for calculating the very slight influence which this total 

 contraction exercises in accelerating the velocity of rotation. 



Nothing less than the enormous power, which I have pointed 

 out, could suffice to raise the lavas. In the particular case in 

 which they would come exactly from a depth of twenty leagues 

 it is easy to prove, from their mean specific gravity, that they 

 would be pressed by a force equivalent to that of about 28,000 

 atmospheres. It is, besides, well known, that they flow almost 

 always after the eruption of the gaseous matters, which may very 

 easily be conceived, according to my theory. 



• The Kilometre is 39371,00000 cubic English inches. 

 t The Millimetre is .03937 English cubic inches. 



