SECT. X. INVARIABILITY OF ROTATION. (ft 



mountains and continents between the tropics does not 

 impede its velocity, which theory even proves to be the 

 same as if the sea together with the earth formed one 

 solid mass. But although these circumstances be in- 

 sufficient, a variation in the mean temperature would 

 certainly occasion a corresponding change in the velocity 

 of rotation. In the science of dynamics it is a principle 

 in a system of bodies or of particles revolving about a 

 fixed center, that the momentum or sum of the pro- 

 ducts of the mass of each into its angular velocity and 

 distance from the center is a constant quantity, if the 

 system be not deranged by a foreign cause. Now since 

 the number of particles in the system is the same what- 

 ever its temperature may be, when their distances from 

 the center are diminished then- angular velocity must 

 be increased, in order that the preceding quantity may 

 still remain constant. It follows then that as the primi- 

 tive momentum of rotation with which the earth was 

 projected into space must necessarily remain die same, 

 the smallest decrease in heat by contracting the terres- 

 trial spheroid would accelerate its rotation, and conse- 

 quently diminish the length of the day. Notwithstand- 

 ing the constant accession of heat from the sun's rays, 

 geologists have been induced to believe from the fossil 

 remains, that the mean temperature of the globe is de- 

 creasing. 



The high temperature of mines, hot springs, and 

 above all the internal fires which have produced and do 

 still occasion such devastation on our planet, indicate an 

 augmentation of heat toward its center. The increase 

 of density corresponding to the depth and the form of 

 the spheroid being what theory assigns to a fluid mass 

 in rotation, concurs to induce the idea that the tempera- 

 ture of the earth was originally so high as to reduce all 

 the substances of which it is composed to a state of 

 fusion or of vapor, and that in the course of ages it has 

 cooled down to its present state ; that it is still becoming 

 colder, and that it will continue to do so till the whole 

 mass arrives at the temperature of the medium in 

 which it is placed, or rather at a state of equilibrium 

 between this temperature, the cooling power of its own 

 radiation, and the heating effect of the sun's rays. . 



