interacting movements in space, we could never reach the inside limits of such a sphere of control, because the piling up of orb behind orb adds but an infinitesimal fraction to the force of gravity, for as the orbs themselves multiply in distance progressively by hundreds, their relative attractions inversely diminish by ten thousands. No possible increase of suns directly in mass could compensate for such an inverse ratio of squares, even if all intergalactic space were peopled with suns, instead of being, in fact, like a vast ocean, with a few small clusters of islands scattered here and there throughout its illimitable extent. Of these vast realms of space, Professor Ball asks, "Is our sidereal system to be regarded as an oceanic island in space, or is it in such connection with the systems in other parts of space as might lead us to infer that the various systems had a common character? The evidence seems to show that the stars in our system are probably not permanently associated together, but that in the course of time some stars enter our system and other stars leave it, in such manner as to suggest that the bodies visible to us are fairly typical of the general contents of the universe. The strongest evidence that can be presented on this subject is met with in the peculiar circumstances of one particular star. The star in question is known as No. 1830 of Groombridge's catalogue. It is a small star, not to be seen without the aid of a telescope.... We shall probably be quite correct in assuming that the distance is not less than two hundred billions of miles.... The velocity is no less than two hundred miles per second.... The star sweeps along through our system with this stupendous velocity.... The velocity being over twenty-five miles a second, the attraction can never overcome the velocity, so that the star seems destined to escape." Of the star Alcyone he says, "Doubtless that star is thousands of billions of miles from the earth; doubtless the light from it requires thousands of years--and some astronomers have said millions of years--to span the abyss which intervenes between our globe and those distant regions." And yet these stars, these galaxies, and even all the nebulæ we see or ever shall see, are merely in the vestibule of space; we have scarcely even yet lifted the outer curtain at the entrance of those vast realms. That the popular, but pseudo-scientific, idea of a series of ever-widening concentric orbits, increasing at every new expansion by an inconceivable ratio, is incredible we can well understand, and it is a satisfaction to know that such a wild hypothesis finds no warrant in the dicta or the demonstrations of science. And it is in the failure of gravity to control over the intervening space which lies between those vastly distant centers that we may hope to find the inklings of a more far-reaching law, by which nebulæ like that of Orion crystallize out