all the above bodies, and likewise of the sun, in the same direction as their orbitual motion, and in planes but little inclined to one another; fourthly, the small eccentricity of the orbits of the planets and satellites. Now the theory of gravitation throws no light whatever on this extraordinary amount of uniformity. Consistently with the law of gravitation, there might be a wide diversity, instead of such a marked uniformity. There is no reason, as far as the mechanical action of gravity is concerned, why the planets should not move in opposite directions, and why their orbits should not have every possible degree of inclination to one another. It is utterly impossible, Laplace argued, to ascribe this amount of uniformity to chance, and therefore the human mind is irresistibly impelled to seek some key to it. He was further stimulated to seek a common explanation, from the circumstance that a like uniformity is not to be found in the motions of the comets. These bodies are regarded as not belonging to our system. It is indeed ascertained, that a few revolve regularly in elliptic orbits round the sun; but these few, out of the thousands that undoubtedly exist, are regarded as children of adoption, and not of birth.[1] Here then we have the case of
- ↑ Laplace indeed points out a uniformity in the case of the comets, viz., the great eccentricity of their orbits; but this is employed as a confirmation of the nebular hypothesis. He holds that the motions of the less eccentric were destroyed by the resistance of the nebulous matter in the process of condensation, and that only the more eccentric were spared such a fate.
