that the same process of concentration which has gone on in the case of our solar nebula has been going on in the case of other nebulae. The history of the sun is but a type of the history of stars in general. And when we consider that all other visible stars and nebulae are cooling and contracting bodies, like our sun, to what other conclusion could we very well come? When we look at Sirius, for instance, we do not see him surrounded by planets, for at such a distance no planet could be visible, even Sirius himself, though fourteen times larger than our sun, appearing only as a "twinkling little star." But a comparative survey of the heavens assures us that Sirius can hardly have arrived at his present stage of concentration without detaching, planet-forming rings, for there is no reason for supposing that mechanical laws out there are at all different from what they are in our own system. And the same kind of inference must apply to all the matured stars which we see in the heavens. When we duly take all these things into the account, the case of our solar system will appear as only one of a thousand cases of evolution and dissolution with which the heavens furnish us. Other stars, like our sun, have undoubtedly started as vaporous masses, and have thrown off planets in contracting. The inference may seem a bold one, but it after all involves no other assumption than that of the continuity of natural phenomena. It is not likely, therefore, that the solar system will forever be left to itself. Stars which strongly gravitate toward each other, while moving through a perennially resisting medium, must in time be drawn together. The collision of our extinct sun with one of the Pleiades, after this manner, would very likely suffice to generate even a grander nebula than the one with which we started. Possibly the entire galactic system may, in an inconceivably remote future, remodel itself in this way; and possibly the nebula from which our own group of planets has been formed may have owed its origin to the disintegration of systems which had accomplished their career in the depths of the bygone eternity.