no means as an established fact in astronomical science. And, as a hypothesis, it labors under this peculiar difficulty, that it evidently never can be verified. It must ever remain a _mere_ guess, directly opposed by an obvious induction from those nebulae which are resolvable into perfect stars. The fact, that one or two bright points, assumed to be centres of aggregation, are seen in some of these nebulae, is of no importance. If a bright star be seen from this earth in the same line of vision with the nebula, it will be projected on the ground of that nebula, and will appear as a part of it, though it may be many millions of miles on this side, and have no more connection with it than the planet Jupiter would have, if it should happen to be in conjunction with the nebula, and thus appear for a short time to be projected upon its disc. There is one consideration of some weight, though we have never seen it adverted to, which tends directly to confute the nebular hypothesis. That faint radiance called the zodiacal light, which is seen to stream up in the form of a cone from our sun, is assumed by our author to be a residuum of the nebulous matter belonging to our system, which has not yet been drawn into the sun, though it is on its way thither. Others have supposed, with far more probability, that it is the sun's atmosphere, and therefore its present shape and size will never change,--as they never have changed, during the period in which they have been observed by man. But no matter; we are now reasoning upon our author's hypothesis. If the zodiacal light be composed of primitive nebulous matter, it must now be comparatively thick and dense, since the process of aggregation has been going on for countless ages, and, in our system, is considered as nearly completed; just as when a sediment is forming in a tumbler full of turbid water, after the upper portion of the fluid has become entirely clear, there will be a stratum of water next to the sediment more turbid than the whole was before the deposition began. Yet this light is very faint, when seen only from the distance of our earth; and at the boundaries of our system, from the orbit of Uranus, for instance, we cannot believe that it is visible at all. Is it likely, then, that a portion of this nebulous matter, in which the process of deposition has hardly begun, and which is seen from a distance so vast, that in comparison with it the whole diameter of our solar system is but a point, would be visible from this earth? In the case of the other nebulae, a multitude of perfectly formed suns, uniting their respective beams, are seen only as a faint, whitish speck on the blue arch. And yet we are required to believe, that the luminous matter which will ultimately form but one sun, or perhaps two, while still thinly diffused over an immense tract of space, the process of aggregation having hardly commenced, is yet visible to our eyes at this vast distance.