I am sorry it is not so. I had much enthusiasm in my youth over this beautiful and orderly arrangement of things: first, the splendid hypothesis, the achievement of a noble mind; then the little model showing the work in its progress; and, finally, the beautifully finished system, the rings all rolled up into planets, traveling unceasingly in paths which eternally marked the size of the central body, or sun, at the time of the separation. But it is now pretty certain that this cannot be the way it all happened. Closer investigation shows that there are mechanical difficulties which were not at first fully recognized. A series of rings could not have been left off by a body so wholly gaseous. The particles composing them would not be sufficiently coherent to permit of separation in any such compact, uniform, and decisive manner. Then, even if such a ring were thrown off, it is not at all certain that it could condense into a planet. Its tendency, indeed, would be to disintegrate rather than to condense. In a body so tenuous the mutual gravitation of its particles would be too feeble to complete the work. Besides, in conflict with the theory is the fact that a few of the satellites of the planets revolve in a direction contrary to that of the planet. And there are other minor, but still important, details in the mechanism of the solar system which cannot be accounted for by the ring theory. And so, while astronomers are still agreed that the whole solar system, which includes the planets, was evolved from a primeval nebula, the theory of leaving off rings which condensed into planets is not found tenable, and the search for some more acceptable theory or some modification of the Laplace theory is now occupying a number of eminent astronomers and philosophers. The result of all this is that no theory of the manner of the evolution of the planets is definitely accepted by the body of astronomers. Much hard labor and ingenious reasoning have been expended in endeavoring to formulate some hypothesis by means of which we may account for observed phenomena. The astronomers with whom these theories have originated are, naturally, more or less ardent in setting them forth. Thus one occasionally sees a decisive and authoritative statement of a theory of the evolution of the planets that seems at first view to account for everything. But no one of these has yet been entirely accepted by astronomers, who are as a class cautious and conservative, and are necessarily critical of any theory, because the value of much of their future work depends upon its accuracy and sufficiency for all details.