Some of the other relations of the bodies are not less remarkable. The primary planets shew a progressive increase of bulk and diminution of density, from the one nearest to the sun to that which is most distant. With respect to density alone, we find, taking water as a measure and counting it as one, that Saturn is 13/32, or less than half; Jupiter, 1 1/24; Mars, 3 2/7; Earth, 4 1/2; Venus, 5 11/15; Mercury 9 9/10, or about the weight of lead. Then the distances are curiously relative. It has been found that if we place the following line of numbers,— 0 3 6 12 24 48 96 192, and add 4 to each, we shall have a series denoting the respective distances of the planets from the sun. It will stand thus— 4 7 10 16 28 52 100 196 Merc. Venus. Earth. Mars. Jupiter. Saturn. Uranus. It will be observed that the first row of figures goes on from the second on the left hand in a succession of duplications, or multiplications by 2. Surely there is here a most surprising proof of the unity which I am claiming for the solar system. It was remarked when this curious relation was first detected, that there was a want of a planet corresponding to 28; the difficulty was afterwards considered as in a great measure overcome, by the discovery of four small planets revolving at nearly one mean distance from the sun, between Mars and Jupiter. The distances bear an equally interesting mathematical relation to the times of the revolutions round the sun. It has been found that, with respect to any two planets, the squares of the times of revolution are to each other in the same proportion as the cubes of their mean distances,—a most surprising result, for the discovery of which the world was indebted to the illustrious Kepler. Sir John Herschel truly observes—“When we contemplate the constituents of the planetary system from the point of view which this relation affords us, it is no longer mere analogy which strikes us, no longer a general resemblance among them, as individuals independent of each other, and circulating about the sun, each according to its own peculiar nature, and connected with it by its own peculiar tie. The resemblance is now perceived to be a true _family likeness_; they are bound up in one chain—interwoven in one web of mutual relation and harmonious agreement, subjected to one pervading influence which extends from the centre to the farthest limits of that great system, of which all of them, the Earth included, must henceforth be regarded as members.” {12} Connecting what has been observed of the series of nebulous stars with this wonderful relationship seen to exist among the constituents of our system, and further taking advantage of the light afforded by the ascertained laws of matter, modern astronomers have suggested the following hypothesis of the formation of that system.