Inquiry into the interior construction of the Earth--_continued_ 184 Density of 8·8 times that of water still too high for the possible compression of the component matter of the earth as known to us 185 Reasons for this conclusion drawn from crushing strains of materials 186 A limit to density shown thereby 187 The greatest density need not exceed 6·24 of water 188 Gases shut up in the hollow centre. Their weight must so far diminish the conceded maximum of 6·24 189 Density of inner half of earth at 3000 miles diameter. Greatest density may be less than 5·833 of water 190 Supposed pressure of inclosed gases very moderate 191 Meaning of heat limit to density. Temperature of interior half of shell and inclosed gases must be equal 193 State of the hollow interior 194 Results of the whole inquiry 195 CHAPTER XI. The Earth. The idea entertained by some celebrated men, and others 197 Difficulties of forming a sphere out of a lens-shaped nebula 199 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 200 What is gained by its being a hollow shell 201 Geological theories of the interior discussed. Volcanoes and earthquakes in relation to the interior 202 Liquid matter on the interior surface of the shell, and gases in the hollow, better means for eruptions than magma layers 206 Focal depths of earthquakes within reach of water, but not of lavas 207 Minute vesicles in granite filled with gases, oxygen and hydrogen, but not water 209 The Moon. A small edition of the earth 211 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 212 Form and dimensions during rotation. Altered form after it stopped 213 Agreeing very closely with Hansen's "curious theory" 214 CHAPTER XII.