194 S. Newcomb on the apparent inequalities, ete. 
heve, been pointed out by geologists. But the effect of this 
cause could scarcely be sensible. But, if we admit that the 
arrangement of the fluid. 
I conclude, from this discussion, that we have reason to sus- . 
pect that the motion of rotation of the crust of the earth is 
subject to inequalities of an irregular charaoter, which, in the 
present state of science, can be detected only by observations of 
the moon, ‘This suspicion can be neither confirmed nor remov- 
ed until we have more positive knowledge than we now have of 
the possible inequalities which may be produced in the mean 
motion of the moon by the action of gravitation. 
The operation of calculating these inequalities, though com- 
licated and difficult, is certainly within the powers of analysis. 
so, well; the length of the day is not variable, and the future 
positions of the moon can be safely predicted. If not, it will 
follow either that the motion of the moon is affected by other 
causes than the gravitation of the known bodies of the solar 
