Perspective, 76 et seq.; contraction of, 74 et seq.; distortion of, 77. Pessimism and optimism, 234. Pharaohs, 85. Phenomenology, a universal physical, 250. Philistine, modes of thought of, 223. Philology, comparison in, 239. Philosopher, an ancient, on the moral and physical sciences, 89. Philosophy, its character at all times, 186; mechanical, 155 et seq., 188, 207, 259 et seq. Phonetic alphabets, their economy, 192. Photography, by the electric spark, 318 et seq. Photography of projectiles, 309-337. Photography, stupendous advances of, 74. Physical, concepts, fetishism in our, 187; ideas and principles, their nature, 204; inquiry, the economical nature of, 186; research, object of 207, 209. Physical phenomena, as mechanical phenomena, 182; relations between, 205. Physico-mechanical view of the world, 155, 187, 188, 207 et seq. Physics, compared to a well-kept household, 197; economical experience, 197; the principles of, descriptive, 199; the methods of, 209; its method characterised, 211; comparison in, 239; the facts of, qualitatively homogeneous, 255; how it began, 37; helped by psychology, 104; study of its own character, 189; the goal of, 207, 209. Physiological psychology, its methods, 211 et seq. Physiology, its scope, 212. Piano, its mirrored counterpart, 100 et seq.; used to illustrate the facts of sympathetic vibration, 25 et seq. Piano-player, a speaker compared to, 192. Picture, physical, a, 110. Pike, learns by experience, 267. Pillars of Corti, 19. Places, heavy bodies seek their, 224 et seq. Planetary system, origin of, illustrated, 5. Plasticity of organic nature, 216. Plateau, his law of free liquid equilibrium, 9; his method of getting rid of the effects of gravity, 4. Plates of oil, thin, 6. Plato, 347, 371. Plautus, 347. Playfair, 138. Pleasant effects, cause of, 94 et seq. Pliny, 349. Poetry and science, 30, 31, 351. Poinsot, on the foundations of mechanics, 152 et seq. Polarisation, 91; abstractly described by Newton, 242. Politics, Chinese speak with unwillingness of, 374. Pollak, 299. Polyp plant, humanity likened to a, 235. Pompeii, 234; art in, 80. Popper J., 172, 216. Potential, social, 15; electrical, 121 et seq.; measurement of, 126; fall of, 177; swarm of notions in the idea of, 197; its wide scope, 250. Pottery, invention of, 263. Prediction, 221 et seq. Prejudice, the function, power, and dangers of, 232-233. Preparatory schools, the defects of the German, 346-347; what they should teach, 364 et seq. Pressure of a stone or of a magnet, will compared to, 14; also 157. Primitive acts of knowledge the foundation of scientific thought, 190. Problem, nature of a, 223. Problems which are wrongly formulated, 308. Process, Carnot's, 161 et seq.