And now let us see how this hypothesis tallies with the facts. One inference from it must be, that large masses will progress towards final consolidation more slowly than small masses. Though a large concentrating spheroid will, from its superior aggregative force, generate heat more rapidly than a small one; yet, having, relatively to its surface, a much greater quantity of heat to get rid of, it will be longer than a small one in going through the changes we have described. Consequently, at a time when the smaller members of our Solar System have arrived at so advanced a stage of aggregation as almost to have obliterated their central cavities, and so reached high specific gravities; the larger members will still be at that stage in which the central cavities bear great ratios to the surrounding shells, and will therefore have low specific gravities. This contrast is just what we find. The small planets Mercury, Venus, the Earth, and Mars, differing from each other comparatively little in density as in size, are about four times as dense as Jupiter and Uranus, and seven times as dense as Saturn and Neptune--planets exceeding them in size as oranges exceed peas; and they are four times as dense as the Sun, which in mass is nearly 5,000,000 times greater than the smallest of them. The obvious objection that this hypothesis does not explain the minor differences, serves but to introduce a further confirmation. It may be urged that Jupiter is of greater specific gravity than Saturn, though, considering his superior mass, his specific gravity should be less; and that still more anomalous is the case of the Sun, which, though containing a thousand times the matter that Jupiter does, is nearly of the same specific gravity. The solution of these difficulties lies in the modifying effects of centrifugal force. Had the various masses to be compared been all along in a state of rest, then the larger should have been uniformly the less dense. But during the concentrating process they have been rotating with various velocities. The consequent centrifugal force has in each case been in antagonism with gravitation; and, according to its amount, has hindered the concentration to a greater or less degree. The efficient aggregative force has in each case been the excess of the centripetal tendency over the centrifugal. Whence we may infer that wherever this excess has been the least, the consolidation must have been the most hindered, and the specific gravity will be the smallest. This, too, we find to be the fact. Saturn, at whose equator the centrifugal force is even now almost one-sixth of gravity, and who, by his numerous satellites, shows us how strong an antagonist to concentration it was in earlier stages of his evolution, is little more than half as dense as Jupiter, whose concentration has been hindered by a centrifugal force bearing a much smaller ratio to the centripetal.