bodies not belonging to our system, exhibiting none of that uniformity which characterises the various bodies constituting the system.
Besides the phenomena above enumerated, there are other traces of uniformity not accounted for by the law of gravitation. It is found that there is a remarkable regularity in the relative distances of the planets. This disposition is known as Bode's law of distances. Mercury being regarded as the point of departure, the distance of any planet from this point is double the distance of the next inferior planet from the same point. For example, the Earth is twice farther from Mercury than Venus is, Venus being the next inferior planet to the Earth.[1] The law of gravitation requires no such regular progression. It would hold equally well though no such regularity could be discovered. There is also something like a trace of law in the disposition of the planets in regard to their magnitude and density—the densest being, generally speaking, nearest the sun, and the largest more remote.
The nebular hypothesis professes to explain, more or less explicitly, the above cases of uniformity, unaccounted for by the theory of gravitation. Laplace supposes that the matter of which the sun and planets are formed, consisted originally of a vast nebula of extreme tenuity. He starts with the hypothesis that
- ↑ The truth of Bode's law was assumed in the calculations which led to the discovery of Neptune, but the distance of this planet is found to be a fact irreconcilable with this law.
