[2] “Laplace has given us proof that the period of the earth’s axial rotation has not changed 1-100 of a second of time in two thousand years.” Warren. “Recreations in Astronomy,” p. 145. [3] Ball. “In Starry Realms,” p. 31. CHAPTER II. DENSITY AND GRAVITATION. 1st. _Density._ The sun’s density is one-fourth that of earth, while Mercury’s is one-fifth greater than earth’s, showing that Mercury’s substance must be more than five times denser than the sun’s, whereas it is not 36,000,000 miles distant from it; so near, in fact, and so recently thrown off from the sun as to be thought that human beings could not live upon it. Why is it that this dense substance did not, while a portion of the sun, sink to its centre? It might be said that on cooling, after being thrown from the sun, the body became more and more dense, the same as is said of earth. But if so why is it that Neptune, seventy-five times farther from the sun, has a density only one-fifth that of earth, and Uranus but a little more; while Jupiter’s density is less than the sun’s, and Saturn’s not even one-seventh that of earth? All of these planets lie in an immensely cold and far away region and were thrown off by the sun, if at all, many years before Mercury, and, according to the supposed theory, should be cold bodies. Some think, with apparent show of reason, that before planet-making began the heavier materials of the general mass had gravitated toward the centre, while the lighter substances remained near the surface. “If so,” to quote the words of Prof. Winchell, “the first planets separated would contain more of the substances which, at temperatures familiar to us, make gases and water. Similarly, the later planets disengaged would acquire a large proportion of the substances which form solid rocks. In the case of the earth we may suppose that the greater part was rock-making material, since the earth’s specific gravity is so high; but watery stuff in sufficient amount to provide for oceans and rains, went off with the rock-material, and with these, the lighter stuff for an atmosphere. But in the case of Venus, most of the stuff was rock-material, if not the whole of it; while with Mercury it seems probable that little water-stuff was included. In the opposite direction, Saturn, Uranus, and Neptune must have received a large excess of water and atmospheric stuff. It is rational to suppose that their oceans have always covered the whole land, as ours does more than half. In fact, these bodies must be composed chiefly of water and atmosphere; as their specific gravities are low as water and cork.”[4] Now if this is a good explanation what shall we say of the sun from which these planets were separated? If it grew more and more solid as it contracted until Mercury, nearly ten times denser than Saturn, was thrown off, why is not the sun denser than Mercury? whereas we find it with but one-fourth the density of earth.