The wonderfully complex laws of revolution here described, however, are not to be understood as obtaining in our system alone. They _everywhere_ prevail where Attraction prevails. They control _the Universe_. Every shining speck in the firmament is, no doubt, a luminous sun, resembling our own, at least in its general features, and having in attendance upon it a greater or less number of planets, greater or less, whose still lingering luminosity is not sufficient to render them visible to us at so vast a distance, but which, nevertheless, revolve, moon-attended, about their starry centres, in obedience to the principles just detailed—in obedience to the three omniprevalent laws of revolution—the three immortal laws _guessed_ by the imaginative Kepler, and but subsequently demonstrated and accounted for by the patient and mathematical Newton. Among a tribe of philosophers who pride themselves excessively upon matter-of-fact, it is far too fashionable to sneer at all speculation under the comprehensive _sobriquet_, “guess-work.” The point to be considered is, _who_ guesses. In guessing with Plato, we spend our time to better purpose, now and then, than in hearkening to a demonstration by Alcmæon. In many works on Astronomy I find it distinctly stated that the laws of Kepler are _the basis_ of the great principle, Gravitation. This idea must have arisen from the fact that the suggestion of these laws by Kepler, and his proving them _à posteriori_ to have an actual existence, led Newton to account for them by the hypothesis of Gravitation, and, finally, to demonstrate them _à priori_, as necessary consequences of the hypothetical principle. Thus so far from the laws of Kepler being the basis of Gravity, Gravity is the basis of these laws—as it is, indeed, of all the laws of the material Universe which are not referable to Repulsion alone.