(5) That the region of greatest density, and the position of the interior surface of the shell, may be expressed with very approximate accuracy as follows:--The former must be at 0·7939 of the mean radius of the earth, and the latter at 0·5479 of the same; both counted from the centre. (6) That if the earth is a hollow sphere, the same must be the case with all the major planets and their satellites, the sun, and all the suns, or stars, that are seen in the heavens; and that their interior proportions and form must be in much the same ratios to their radii as those we have found for the earth. CHAPTER XI. PAGE 197 The Earth. The idea entertained by some celebrated men, and others. 199 Difficulties of forming a sphere out of a lens-shaped nebula. 200 Various studies of the earth's interior made for special purposes. Difficulty some people find in conceiving how the average density of little over 5·66 can be possible, the earth being a hollow sphere. 201 What is gained by its being a hollow shell. 202 Geological theories of the interior discussed. Volcanoes and earthquakes in relation to the interior. 206 Liquid matter on the interior surface of the shell, and gases in the hollow, better means for eruptions than magma layers. 207 Focal depths of earthquakes within reach of water, but not of lavas. 209 Minute vesicles in granite filled with gases, oxygen and hydrogen, but not water. 211 The Moon. A small edition of the earth. 212 Rotation stopped. Convulsions and cataclysms caused thereby. Air, water, vapour driven off thereby to far off hemisphere. Liquid matter in hollow interior would gravitate to the inside of the nearest hemisphere. 213 Form and dimensions during rotation. Altered form after it stopped. 214 Agreeing very closely with Hansen's "curious theory." CONSEQUENCES OF THE EARTH AND MOON BEING HOLLOW BODIES. _The Earth._--The idea that bodies such as those of the solar system, even of the whole universe, have their greatest density where the greatest mass is and are hollow spheres, is so natural and logical, more especially if it is supposed that they have all been formed out of some kind of nebulæ, that it seems strange it has never been brought forward prominently before. We say prominently because we know that the earth has been considered to be a hollow sphere by very eminent men, such as Kepler, Halley, Sir John Leslie, and by others of less name long after them. In support of this last remark, we shall make a few extracts--with comment on them--from an article on the "Interior of the Earth" in "Chambers's Journal" for February 1882, which have some interest in connection with our work.