PIERRE SIMON LAPLACE 143 



formed of vapours, and of which we have suggested the formation, 

 we shall see to arise in the centre of each of them, a nucleus in- 

 creasing continually, by the condensation of the atmosphere which 

 environs it. In this state, the planet resembles the Sun in the 

 nebulous state, in which we have first supposed it to be ; the cooling 

 should therefore produce at the different limits of its atmosphere, 

 phenomena similar to those which have been described, namely, rings 

 and satellites circulating about its centre in the direction of its motion 

 of rotation, and revolving in the same direction on their axes. The 

 regular distribution of the mass of rings of Saturn about its centre 

 and in the plane of its equator, results naturally from this hypothesis, 

 and, without it, is inexplicable. Those rings appear to me to be 

 existing proofs of the primitive extension of the atmosphere of 

 Saturn, and of its successive condensations. Thus, the singular phe- 

 nomena of the small eccentricities of the orbits of the planets and 

 satellites, of the small inclination of these orbits to the solar equator, 

 and of the identity in the direction of the motions of rotation and 

 revolution of all those bodies with that of the rotation of the Sun, 

 follow the hypothesis which has been suggested, and render it ex- 

 tremely probable. If the solar system was formed with perfect 

 regularity, the orbits of the bodies which compose it would be circles, 

 of which the planes, as well as those of the various equators and 

 rings, would coincide with the plane of the solar equator. But we 

 may suppose that the innumerable varieties which must necessarily 

 exist in the temperature and density of different parts of these great 

 masses, ought to produce the eccentricities of their orbits, and the 

 deviations of their motions, from the plane of this equator. 



In the preceding hypothesis, the comets do not belong to the solar 

 system. If they be considered, as we have done, as small nebulae, 

 wandering from one solar system to another, and formed by the 

 condensation of the nebulous matter, which is diffused so pro- 

 fusely throughout the universe, we may conceive that when they 

 arrive in that part of space where the attraction of the Sun pre- 

 dominates, it should force them to describe elliptic or hyperbolic orbits. 

 But as their velocities are equally possible in every direction, they 

 must move indifferently in all directions, and at every possible in- 

 clination to the elliptic ; which is conformable to observation. Thus 

 the condensation of the nebulous matter, which explains the motions 



