346 Address of Sir Wm. Thomson at the Glasgow Meeting, 
theory. From this it follows that precession and nutations of 
the solid crust, with the practically perfect flexibility which it 
would have even though it were 100 kilometers thick and as 
stiff as steel, would be sensibly the same as if the whole earth 
from surface to center were solid and perfectly stiff. Hence pre- 
cession and nutations yield nothing to be said against such hy- 
potheses as that of Darwin,* that the earth as a whole takes 
relatively to land. i 
The state of the case is shortly this:—The hypothesis of a 
perfectly rigid crust containing liquid violates physics by as- 
suming preternaturally rigid matter and violates dynamical as- 
tronomy in the solar semi-annual and lunar fortnightly nute 
tions ; fiat tidal theory has nothing to say against it. On the 
other hand the tides decide against any crust flexible enough to 
perform the nutations correctly with a liquid interior, or a8 
flexible as the crust must be unless of preternaturally rigid 
matter, 
relative densities of rock, solid and melted, at or about = 
temperature of liquifaction, it is, I think, quite certain that “bl 
lid rock is denser than hot melted rock: and no possible 
degree of rigidity in the crust could prevent it from bre . 
ieces and sinking wholly below the liquid lava. Somet 
ike this may have gone on and probably did go on for shoe 
* “ Observations on the Parallel Roads of Glen Roy and other P — < 
ber in Scotland, with an attempt to prove that they are of Marine Origin. 
actions of the Royal Society for Feb., 1839, p. 81. 
