Coulomb, his electrical researches, 108, 109, 113; his notion of quantity of electricity, 173; his torsion-balance, 168. Crew, Prof. Henry, 317, footnote. Criticism, Socrates the father of scientific, 1, 16. _Critique of Pure Reason_, Kant's, 188. Crucible, derivation of the word, 49, footnote. Crustacea, auditory filaments of, 29, 272, 302. Cube of oil, 5. Culture, ancient and modern, 344. Currents, chemical, 118; electrical, 118; galvanic, 132; measurement of electrical, 135-136; of heat, 244, 249-250; strength of, 250. Curtius, 356. Curved lines, their asymmetry, 98. Curves, how their laws are investigated, 206. Cycles, reversible, Clausius on, 176. Cyclical processes, closed, 175. Cyclops, 67. Cyclostat, 298. Cylinder, of oil, 6; mass of gas enclosed in a, 179. D'Alembert, on the causes of harmony, 34; his principle, 142, 149, 154; also 234, 279. Danish schools, 338, footnote. Darwin, his study of organic nature, 215 et seq.; his methods of research, 216. Deaf and dumb, not subject to giddiness, 299. Deaf person, with a piano, analyses sounds, 27. Death and life, 186. Definition, compendious, 197. Deiters, 19. Delage, 298, 301, 302. Democritus, his mechanical conception of the world, 155, 187. Demonstration, character of, 362. Deportment of the energies, conformity in the, 171-175. Derivation, laws only methods of, 256. Descent, Galileo's laws of, 193; generally, 143 et seq., 204, 215. Description, 108, 191, 236, 237; a condition of scientific knowledge, 193; direct and indirect, 240; in physics, 197, 199. Descriptive sciences, their resemblance to the abstract, 248. Determinants, 195. Diderot, 234. Dielectric constant, the, 117. Difference-engine, the, 196. Differential coefficients, their relation to symmetry, 98. Differential laws, 204. Differential method, for detecting optical imperfections, 317. Diffraction, 91, 194. Diffusion, Fick's theory of, 249. Discharge of Leyden jars, 114 et seq. Discoveries, the gist of, 270, 375. Discovery and invention, distinction between, 269. Dissonance, explanation of, 42; definition of, 33, 44. See _Consonance_. Distances, estimation of, by the eye, 68 et seq. Dogs, like tuning-forks, 23; their mentality, 190. Domenech, Abbé, 92. Dramatic element in science, 243. Drop of water, on a greased plate, 8; on the end of a stick, 8; in free descent, 8. Dubois, 218. Dubois-Reymond, 370, footnote. Dufay, 271. Dynamics, foundations of, 153 et seq. Ear, researches in the theory of, 17 et seq.; diagram of, 18; its analysis of sounds, 20 et seq.; a puzzle-lock, 28; reflected in a mirror, 93; no symmetry in its sensation, 103. Earth, its oblateness not due to its original fluid condition, 2; rotation of, 204; internal disturbances of, 285.