40 
Interior Condition of the Earth. — Le Conte. 
last we will call the " suh-crust liquid layer." This view 
would give substantial solidity and rigidity to the earth taken 
as a whole and would therefore satisfy the physicists, and at 
the same time would account for all the phenomena spoken of 
above and therefore satisfy the geologists. The object of this 
note is to show in a simple way, which I have long used in my 
class lectures, that such a constitution is in full accord with 
known physical laws. 
If in fig. 1, 5S be the sur- 
face of the earth and aha, 
portion of the radius ; and if 
taking these as coordinate 
axes, we measure depths 
on a h and corresponding 
temperatures on s s; then 
a' uniform rate of increase 
would be correctly repre-! 
sented by the straight line 
c d and at the depth of twen- 
ty-five miles, a?, the heat-or- 
dinate of 2,500^ 
lid be 
Fig. 1. ss=Surface of earth, ab^partof 
radius, c ff=line of uniform increase of 
temperature c e=line of actual increase, /jr 
=line of fusion. 
reached. And if this temper- 
ature be taken as the fusing 
point of rocks it would seem, 
and has been concluded, that all below is liquid. 
But there are many general reasons for thinking that the 
interior temperature does not increase uniformly for all depths, 
but at a continually decreasing rate ' and therefore that the 
line correctly representing the increase, is not a straight, but a 
curved line like c e. The assumed fusing temperature of 
2,500° would therefore not be reached at 25 miles but much 
lower down, say at x ' perhaps 40 miles. Here then at last we 
would have fusion if the fusing point at that depth were 2,500°. 
But not so ; for the fusing point of all bodies, except a few like 
ice which contract in the act of fusion, is raised by pressure 
and in proportion to pressure. In the figure the line f g rep- 
resents this increase of fusing point with depth. Hopkins^ 
has made many experiments on the more fusible solids — such 
as sulphur, wax, stearine, &c., to determine the rate of eleva- 
iGeoI. Mag. vol. 7, p. 99, 1880. 
■^ British Assc. Report 1854. 
