27<) Till- AllKI'icd II ( rinln(//sf. Novcnilicr, IS'U 
'I'he outliiu' lu'iv »>iven is of the iKirest chariicter. and for illiis- 
Iratioiis, dt'tails. jjroofs, and ((nantitativc calcnlations 1 refrr 
those who want to know more to tlie work itself, as also for those 
portions which deal Avith other theories, and are of a destructive 
ratlier than constructive nature. 
CoNiniioN oKiiiK ivMrrns In-ikkioh. 
Thr Kiliili il Soliil Sphmild. 
The latest niatlienuitical investiijations go to prove that the 
earth, taken as a whole, is solid, having a rigidity between that of 
glass and steel. The facts of physical geology are in accord with 
tliis view: for if the interior be wholly Huid, as some few contend, 
or if the nucleus be solid and the exterior shell solid with a zone 
of molten matter between, as others assume, the explanations of 
the physical conformation of the surface, its mountains and 
ocean-basins, become cpiestions of flotation onh'. 
The crust of the earth would lie like a sheet of ice. This fact 
seems to me never to have been fully reali/,e<1 by those theorists 
who favor either of these views. 
Till' Xllch itx (if tlic Kd rtll l>i)ss(ssis II liiijli Trill inrilt II rr. 
There is such a general consensus of opinion that the earth at 
a flepth of from 25 to oO miles below the surface is at a tempera- 
ture e(|ual to that of molten rock at the surface that it is unnec- 
essary for me to go over the arguments in favor of this widely 
prevalent view. If we assume that it is so. a very little calcula- 
tion will show that matter at the di'pth of say :>0 miles is subject 
U) an enormous pressure, to which we can find no parallel 1)V ex- 
perimental methods at the surface. Thirty miles = 158.-100 feet; 
so that if we estimate that a column of the crust of the earth one 
inch S(iuare has a mean weight per foot of 1 . .") pounds, the pres- 
sure at the depth of ;>(> miles will 1»e in round nnnilx-rs not less 
than .1(1(1 tons \)vv square inch, or 14,4(t(t tons per s([nare foot. 
It has been proved liy the ex})eriments of the late Mr. Hopkins 
that there is in certain solids a relation between the melting- 
point and the pressure; so that, if the rock at tlu' (U'pth of ;50 
miles is at a temperature sufficient to melt it under ordinary pri's- 
sures at the surface, the additional pressure of 1(1(1 tons per 
scjuare inch may solidify it liy raising its melting-point, or at 
least render it plastic. It' the pressni'c increase more rapidly 
