408 J. R. Mayer on Celestial Dynamics. 
gone ages. 
While we are surrounded on every side by the monuments 
of violent volcanic convulsions, we possess no record of the ve- 
locity of the axial rotation of our planet in antediluvian times. 
It is of the greatest importance that we should have an exact 
knowledge of a change in this velocity, or in the length of the 
day during historic times. The investigation of this subject by 
the great Laplace forms a bright monument in the department 
earth’s rotation to the mean time of the moon’s revolution deter- 
com- 
of a day therefore may be considered to have been constant 
during historic times. 
This result, as important as it was convenient for astronomy, 
was nevertheless of a nature to create some difficulties for the 
physicist. With apparently good reason it was concluded that, 
if the velocity of rotation had remained constant, the volume of 
ears 
to the extent of ;1,th of a second, or ,!.th part of a day, 
, 43,000,000 
that during this long space of time the radius of the earth on 
iG6i in volume, as a result of the cooling-process, 
