The ether. Its nature considered. Behaves like a gas 226 Can be pumped out of a receive 227 Light and heat do not pass through a tube _in vacuo_. Laboratory experiments examined 228 Light and darkness in a partial vacuum, though high 229 Electricity not a carrying agent 230 Why there are light and dark strata in a high vacuum 232 The real carrying agent through a high vacuum is the residue of ether left in it. Digression to consider the aurora 233 How air may be carried to extraordinary heights. Zones of air carried up are made luminous by electricity 234 Comparison of this method with experiments quoted 236 Experiment suggested to prove whether light passes freely through a vacuum tube 237 The ether does not pervade all bodies freely 238 It must be renounced altogether or acknowledged to be a material body, subject to expansion, condensation, heating or cooling 239 How light and heat pass through glass 239 Temperature of the ether variable. Zodiacal light, cause of 240 CHAPTER XIV. The ether considered and its nature explained. Further proofs given by Dr. Crookes's work, of its material substance 244 Highest vacuum yet produced. Absorbents cannot absorb the ether 246 Dr. Crookes's definition of a gas. Not satisfactory. Why 247 A fluid required to pump matter out of a vessel 248 Gas as described by Dr. Crookes would not suit 249 The ether the only elastic fluid we have. The only real gas, if it is a gas 250 A possible measure of the density of the ether 250 Causes of dark and light zones in high vacua 251 The real conductor of light in a high vacuum 252 How a vacuum tube glows, when electricity passes through it 254 Conclusions arrived at through foregoing discussions 255 Some exhibitions of light explained 256 Gases can be put in motion, but cannot move even themselves 257 The ether shown to be attraction. And primitive matter also 258 All chemical elements evolved from it. Its nature stated 259 Action at a distance explained by the ether and attraction being one and the same 259 CHAPTER XV.