40 L.Semann on Geological Phenomena in the Solar System. | 
much less than the pores produced by the shrinking of the 
rocks. i 
If, now, we attempt a similar calculation for the atmosphere, 
we find that in supposing a height of eight kilometers, the total 
volume of the air which surrounds our globe, brought to the 
density which it has at the surface, would be about four mil- 
lions of cubic myriameters, the volume of the earth being equal - 
to 1083 millions, or 270 times that of the air, so that a contrac 
tion of the primitive volume producing a vacuum of four thou — 
sandths (3) would be more than sufficient to absorb the whole — 
of the atmosphere. (In calculating the volume of the atmosphere — 
we have multiplied the surface of the globe in square myriame — 
ters, by 0°8, which gives a sufficiently accurate result, the more 
so that the density of the air in the interior of the earth will be 
everywhere greater than at the surface.) 
+ now remains to be seen whether the assumption of 4 
shrinking of four thousandths can be justified by analogies. 
the want of direct determinations of the porosity of crystalline ; 
rocks, upon which subject Iam not aware of any published ex- — 
riments, the observations upon the fusion of rocks, and the - 
eterminations of their densities in the crystalline and vitreous — 
states admit of an indirect application to the question before us. — 
The experiments of Charles Ste. Claire Deville in the Comptes — 
Rendus for 1845, and of Delesse in the Bulletin for 1847, agree s0 
closely in this matter that we give them the preference over 
those of Bischoff, published in 1842. Deville and Delesse found — 
that the fusion of rocks yields glasses whose density is generally — 
inferior to that of the rock in the crystalline state. -This diminu- 
tion for granite is equal to from nine to eleven hundreths, andit | 
is evident that such a glass passing to a crystalline state and re 
taining its volume must present vacant spaces in direct propor- — 
tion to the augmentation of density, that is to say, equal to about — 
one-tenth of its volume. If we take the mean ae ges granite 
space than our calculation requires. _ 
_ The vitreous state of a body is nothing more than a fixing of 
its me in i positions oa se to them in the liqui 
state, and probably represents the liquid in its greatest de - 
of density. The ae pedilinition of barley sugar, of wrought che | 
