1884.] On the Evidence that the Earth's Interior is Solid. 769 
into which it would gradually pass.. It is not probable that the 
crust would break up and begin to sink, because even if its sur- 
_ face grew cold it would always have this hot, solid base, lighter 
_ than the underlying viscous liquid, which, owing to the increasing 
specific gravity as the interior was approached, would probably 
be more dense than any of the overlying cold crust. 
Even if the crust should become heavier, break up and begin 
to sink, this sinking would be very slow on account of the vis- 
cosity of the liquid and its constantly increasing density, while 
the heat imparted to the sinking crust would tend to bring it to 
_ about the same specific gravity as the liquid, as the sinking mass 
_ feared its melting point. But above and beyond all, it would 
_ n reach a point at which the liquid, being of different compo- 
_ Sition, had a higher specific gravity than the crust, and no farther 
_ Sinking could take place. We should thus expect to have formed 
_ the earth’s surface a crust which never would sink, or if it 
_ Sank at all, would for only a comparatively short distance, giving 
nse at that point to a solid crust floating upon a denser hetero- 
_ Seneous liquid. While willing to admit that the crust when cold 
_ Would be heavier than the liquid out of which it was formed, it 
is denied that the exterior would cool to such an extent as to be 
heavier until solidification had taken place to sufficient depth to 
reader the contraction of the exterior portion of but little effect ; 
q that is the increased density of the liquid immediately beneath 
the hot lighter interior portion of the crust would more than 
_ ‘Sunterbalance the increased density of the cold exterior portion 
: of that crust. 
_ _ >i William Thomson's idea of a crust on solidification sinking 
+ center of the earth and building up a honey-combed mass, 
x omy applicable to a homogeneous liquid globe of but slight 
K ty, whose material contracts in passing from the liquid to 
ME Solid state. 
shar a condition of the earth as the writer supposes, a grad- 
ty rom the cooled surface crust towards the hotter inte- 
„n Portions of that crust, thence into the plastic and viscous 
TS AP Satin RT a a tly 
away of the nucleus from the rigid crust, but the entire 
Would contract as a whole, causing a linear shortening of 
“st through compression. This would occasion a crush- 
together of this crust, causing it to be depressed in some 
