-----+-------------------------------+-----------------+------------+ CHAPTER IX. PAGE 165 Inquiry into the Interior Construction of the Earth--_continued_. 166 The earth gasiform at one period. Density including the moon may have been 1/10,000th that of air. Must have been a hollow body. Proofs given. 169 Division of the mass of the earth alone into two parts. 171 Division of the two masses at 817 miles from surface. 172 Reasons why the earth cannot be solid to the centre. 172 Gasiform matter condensing in a cone leaves apex empty. 173 Proportions of the matter in a cone. 174 Calculations of the densities of the outer half of the hollow shell of the earth. Remarks upon the condensation. 175 Calculations of inner half of the hollow shell. 177 Remarks upon position of inner surface of the shell. 179 Calculations of the same. THE INTERIOR OF THE EARTH AND ITS DENSITY--_continued._ When, according to the nebular hypothesis, the ring for the formation of the earth and moon had been thrown off by the nebula, and had broken up and formed itself into one isolated mass--rotating or not on an axis, as the case may have been--it must have been in a gasiform state. What was its density, more or less, may be so far deduced from Table III., where it will be seen that when it had condensed to about one-half of its volume, it must have had a density of only 1/9000th part of our atmosphere, and in which each grain of matter would have for its habitat 16 cubic feet of space, or a cube of 2·52 feet to the side. So that, with an average distance from its neighbours of 2-1/2 feet, a grain of matter could not be looked upon as wedged-in in any way, and would be free to move anywhere. Now, supposing this earth-moon nebula to have been in the form of even an almost shapeless mass, and that it was nearly homogeneous--as it could hardly be otherwise after the tumbling about it had in condensing from a flat ring--its molecules would attract each other in all directions, and as the mass--without having arrived perhaps at the stage of having any well defined centre--would have an exterior as well as an interior, the individual molecules at the exterior would draw those of the interior out towards them, just as much as those at the interior would attract those of the exterior in towards them; but as the number of those at the exterior would--owing to the much greater space there, being able to contain an immensely greater number--be almost infinitely greater than of those nearer to the central part, the latter would be more effectually attracted, or drawn, outwards than the former would be inwards, and there would be none left at the interior after condensation had fairly begun. The mass would speedily become a hollow body, the hollow part gradually increasing in diameter. But let us go deeper into the matter.