(1909) exists consists of a faint nebulous star of less than the ninth magnitude. The wonderful transformations just described had been forecast in advance of the discovery of the nebulous spiral encircling the star by the spectroscopic study of the latter. At first there was no suggestion of a nebular constitution, but within a month or two characteristic nebular lines began to appear, and in less than six months the whole spectrum had been transformed to the nebular type. In the mean time the shifting of the spectral lines indicated a complication of rapid motions in several directions simultaneously. These motions were estimated to amount to from one hundred to five hundred miles per second. The human mind is so constituted that it feels forced to seek an explanation of so marvelous a phenomenon as this, even in the absence of the data needed for a sound conclusion. The most natural hypothesis, perhaps, is that of a collision. Such a catastrophe could certainly happen. It has been shown, for instance, that in infinity of time the earth is sure to be hit by a comet; in the same way it may be asserted that, if no time limit is fixed, the sun is certain to run against some obstacle in space, either another star, or a dense meteor swarm, or one of the dark bodies which there is every reason to believe abound around us. The consequences of such a collision are easy to foretell, provided that we know the masses and the velocities of the colliding bodies. In a preceding chapter we have discussed the motions of the sun and stars, and have seen that they are so swift that an encounter between any two of them could not but be disastrous. But this is not all; for as soon as two stars approached within a few million miles their speed would be enormously increased by their reciprocal attractions and, if their motion was directed radially with respect to their centers, they would come together with a crash that would reduce them both to nebulous clouds. It is true that the chances of such a “head-on” collision are relatively very small; two stars approaching each other would most probably fall into closed orbits around their common center of gravity. If there were a collision it would most likely be a grazing one instead of a direct front-to-front encounter. But even a close approach, without any actual collision, would probably prove disastrous, owing to the tidal influence of each of the bodies on the other. Suns, in consequence of their enormous masses and dimensions and the peculiarities of their constitution, are exceedingly dangerous to one another at close quarters. Propinquity awakes in them a mutually destructive tendency. Consisting of matter in the gaseous, or perhaps, in some cases, liquid, state, their tidal pull upon each other if brought close together might burst them asunder, and the photospheric envelope being destroyed the internal incandescent mass would gush out, bringing fiery death to any planets that were revolving near. Without