[23] Since writing this chapter I have seen a paper by Luigi d'Auria dealing mathematically with 'Stellar Motion, etc.,' and am pleased to see that, from quite different considerations, he has found it necessary to place the solar system at a distance from the centre not very much more remote than the position I have given it. He says: 'We have good reasons to suppose that the solar system is rather near the centre of the Milky Way, and as this centre would, according to our hypothesis, coincide with the centre of the Universe, the distance of 159 light years assumed is not too great, nor can it be very much smaller.'--_Journal of the Franklin Institute_, March 1903. INDEX Adrianus Tollius on stone axes, 203. Air criminally poisoned by us, 260. Albedo explained, 162. Algol and its companion, 39; change of colour of, 41. Allen, Prof. F.J., on living matter, 193; on importance of nitrogen, 195; on physical conditions essential for life, 196. Alpha Centauri, nearest star, 74. Ammonia, importance of, to life, 195. Anaximander's cosmic theory, 2. Angles of a minute and second, 80. Arcturus, rapid motion of, 172. Argument of book, summary of, 310. Astronomers, the first, 2. Astronomy, the new, 24. Astrophysics, a new science, 32. Atmosphere, qualities requisite for life, 210; requisite composition of, 212; aqueous vapour in, 214; and life, 243; effects of density of, 245; a complex structure, 259; its vital importance to us, 260. Ball, Sir R., on dark stars, 143; _Time and Tide_, 233. Barnham, S.W., on double stars, 123. Blue of sky due to dust, 251. Boeddicker's map of Milky Way, 164. Brewster, Sir D., against Whewell, 15. Campbell, Prof., on spectroscopic binaries, 125; on uncertainty of sun's motions, 179; on number of binary systems, 286. Carbon compounds, vast numbers of, 194. Carbonic acid gas essential for life, 196. Central position of sun, importance of, 305. Chaldeans the first astronomers, 2. Chalmers Dr., on plurality of worlds, 13. Chamberlin, T.C., origin of nebulæ, 120; on stellar disruption, 186. Chromosphere, the sun's, 107. Clerke, Miss A.M., on limits of star system, 138; on Milky Way, 158, 160; on solar cluster, 165; on uncertainty of the sun's motion, 177. Climate, persistence of mild, 222. Clouds, importance of, to life, 248. Clusters in relation to Galaxy, 67. Comte, on impossibility of real knowledge of the stars, 25. Conclusions of the book, 317; bearing of, on science and on religion, 319. Corona of sun, 108. Criticisms of article in _Fortnightly Review_, 168, 180. Darwin, Prof. G., on meteoritic hypothesis, 133; on origin of moon, 233; on instability of annular systems, 295. Day and night, uses of, 215.