The telescopic observations of Herschel I. satisfied him that there are very many double stars--double not merely because they are accidentally in the same line of view, but because they are connected physically, revolving round each other. These observations were continued and greatly extended by Herschel II. The elements of the elliptic orbit of the double star zeta of the Great Bear were determined by Savary, its period being fifty-eight and one-quarter years; those of another, sigma Coronae, were determined by Hind, its period being more than seven hundred and thirty-six years. The orbital movement of these double suns in ellipses compels us to admit that the law of gravitation holds good far beyond the boundaries of the solar system; indeed, as far as the telescope can reach, it demonstrates the reign of law. D'Alembert, in the Introduction to the Encyclopaedia, says: "The universe is but a single fact; it is only one great truth." Shall we, then, conclude that the solar and the starry systems have been called into existence by God, and that he has then imposed upon them by his arbitrary will laws under the control of which it was his pleasure that their movements should be made? Or are there reasons for believing that these several systems came into existence not by such an arbitrary fiat, but through the operation of law? The following are some peculiarities displayed by the solar system as enumerated by Laplace. All the planets and their satellites move in ellipses of such small eccentricity that they are nearly circles. All the planets move in the same direction and nearly in the same plane. The movements of the satellites are in the same direction as those of the planets. The movements of rotation of the sun, of the planets, and the satellites, are in the same direction as their orbital motions, and in planes little different. It is impossible that so many coincidences could be the result of chance! Is it not plain that there must have been a common tie among all these bodies, that they are only parts of what must once have been a single mass? But if we admit that the substance of which the solar system consists once existed in a nebulous condition, and was in rotation, all the above peculiarities follow as necessary mechanical consequences. Nay, more, the formation of planets, the formation of satellites and of asteroids, is accounted for. We see why the outer planets and satellites are larger than the interior ones; why the larger planets rotate rapidly, and the small ones slowly; why of the satellites the outer planets have more, the inner fewer. We are furnished with indications of the time of revolution of the planets in their orbits, and of the satellites in theirs; we perceive the mode of formation of Saturn's rings. We find an explanation of the physical condition of the sun, and the transitions of condition through which the earth and moon have passed, as indicated by their geology.