P Paleologic times, much warmth and little light in, 172. fallacies in geologists’ expositions of, 174-176. climate continuous, 177, 186. seas warm, 177, 178. explained by cloud envelope, 178. corroboration of explanation, 187, 179. excessive rain in, 185, 186. passage into Neologic, essentially astronomic, 185. Pallas, 101. Parabolic speed at orbit, Notes 245. Patroclus, 94. Peirce, 110, 125, 126. Perrine, 15. Perrotin, 116. Perturbations, in motion of planets, heralding a catastrophe, 28, 30. reflected, 63. mass of planet determined by, 68. of asteroids by Jupiter, 98, 99. restrictive action of, 99. the fashioning force of planetary orbits, 99, 100. of rings of Saturn by satellites, 111, 112. of Uranus lead to discovery of Neptune, 121-126. Petersen, Dr., 123. Photometric determinations, 92, 93. background, the fundamental factor in, 92, 93. Piazzi, 96. Pilgrim Star, 5, 6. Planetary astronomy, advance in, 59, 60. Planetology, 203. defined, 173, 174. Planets, 61. knots in spiral nebulæ, 25, 139. developed by agglomeration, 143, 149, 151, 152. Pliny, 5. Plutonic rocks, 160. Pluvial eras, contemporaneous with glacial, 200. Polyp corals, in paleologic times, 186. Pristine motion of planetary particles, retrograde, 144. superfluous energy in, 145. unstable, 145. Ptolemaic system, 58. R Refrigeration, tempered by loss of cloud, 196. Revolutions, of shooting-stars, 39. of asteroids, direct like planets, 100. planetary, in same sense, 129, 130. outermost satellites, retrograde, 132. of satellites explained, 146, 147, Notes 252. Ritchey, 14. Roberts, Dr., 20. Roche, Edouard, 110. Rosse, Lord, 17. Rotation of planets, 131, 132. systematic righting of axes, 132. initially, retrograde, 146. Rotation period, of Venus, spectrographically determined, 83, 85-90. of Mars, spectrographically determined, 88, 89. of Jupiter, spectrographically determined, 89. of Uranus, 116. Royal Observatory, Edinburgh, 7.