THE EEVOLUTIONS OF THE CRUST OF THE EARTH. 287 



the generating body, that is to say, that it could give birth to other 

 bodies, still less important, viz, to satellites. 



As to the movement of the secondary bodies, this was regulated by 

 the rotation of the principal body. When the mass of the ring com- 

 menced to condense, two movements were produced, through its con- 

 nection with the center of gravity of the solar system. The parts 

 nearest to the sun were removed (by the condensation) farther away, 

 that is, nearer to the planetary center, and as their velocity, on account 

 of their inertia, remained the same, and as, besides, this velocity was less 

 than that of the center of gravity of the planet, they had a tendency 

 to fall behind. The parts farthest from the sun, on the contrary, 

 approached nearer to it, and their angular velocity, being originally 

 greater, they had a tendency to advance beyond the center of gravity 

 of the planet. These two contrary motions made the secondary body 

 turn around the principal body in the direction in which the latter 

 revolved around the sun. 



The ring which must have formed our earth was remarkable neither 

 in position nor size; but as it is the only one of which we know, although 

 very imperfectly, the different phases of planetary development, it must 

 especially attract our attention. 



We have already shown how every ring must finally break and con- 

 glomerate its substance into a single spheroid, in which are manifested 

 the same luminous and calorific phenomena as in the sun, although 

 with less intensity, as these must be in proportion to the mass. The 

 earth, by the contraction of its gaseous globe, acquired a movement of 

 rotation, increasing in rapidity as the volume became less. At the dis- 

 tance of sixty terrestrial radii a ring was detached which afterward gave 

 birth to the moon. The globe diminished more and more in volume 

 until the cooling became so considerable that the liquids formed in the 

 photosphere were precipitated in the order of their density. A thick 

 atmosphere enveloped this incandescent nucleus. 



The increase in temperature of the earth toward its center, its density 

 too slight, {5Ai according to Reich,) for the enormous pressure of its 

 entire mass, the nature of the ancient eruptive rocks and the flattening 

 of the globe prove that the earth has passed through a liquid and in- 

 candescent condition, and notwithstanding its present coolness, its cen- 

 tral heat is still great. It is true that Herbert Spencer demonstrated* 

 that it was not necessary for the earth to be in a soft state to be flat- 

 tened. As the intensity of the centrifugal force increases in cubic propor- 

 tion to the dimension of the mass, while under the same conditions the re- 

 sistance increases as the square, it follows that if the mass continues to 

 augment, there will come a time when -the centrifugal force will be 

 greater than the limits of the resistance and cohesion, and in consequence 

 all the mass will yield to a certain degree: 



The most resistant substance known to us, having a hundred millionth 



* Philos. Mascaz., 1847, p. 194. 



