Symmetry, definition of, 92; figures of, 92 et seq.; plane of, 94; vertical and horizontal, 94; in music, 99 et seq. Sympathetic vibration, 22 et seq., 379. Tailor, nature like a covetous, 9-10. Tangent, the word, 263. Taste, doubtful cultivation of, by the classics, 352-353; of the ancients, 353. Taylor, on the vibration of strings, 249. Teaching, its nature, 366 et seq. Telegraph, the word, 263. Telescope, 262. Telestereoscope, the, 84. Temperament, even, in tuning, 47. Temperature, absolute, 162; differences of, 205; differences of, viewed as level surfaces, 161; heights of, 174; scale of, derived from tensions of gases, 174. Terence, 347. Terms, scientific, 342-343. Thales, 259. Theories, their scope, function, and power, 241-242; must be replaced by direct description, 248. Thermal, energy, 174, 177; capacity, 123, footnote. Thermodynamics, 160 et seq. Thermoelectrometer, Riess's, 133, 169. Thing-in-itself, the, 200. Things, mental symbols for groups of sensations, 200-201. Thomson, James, on the lowering of the freezing-point of water by pressure, 162. Thomson, W., his absolute electrometer, 127, footnote; on thermodynamics, 162; on the conservation of energy, 165; on the mechanical measures of temperature, 174, footnote; on waste of mechanical energy, 175; also 108, 173, footnote. Thought, habitudes of, 199, 224, 227, 232; relationship between language and, 329; incongruence between experience and, 206; luxuriance of a fully developed, 58; transformation in scientific, 214-235. Thoughts, their development and the struggle for existence among them, 63; importance of erroneous, 65; as reproductions of facts, 107. Thread, the individual a, on which pearls are strung, 234-235. Tides, 283. Timbre, 37, 38, 39. Time, 178, 204, 205, footnote. Toepler and Foucault, method of, for detecting optical faults, 313 et seq., 320. Tone-figures, 91. Tones, 22-47, 99 et seq., 212. Torsion, moment of, 132. Torsion-balance, Coulomb's, 109, 168. Torricelli, on virtual velocities, 150; his law of liquid efflux, 150; on the atmosphere, 273. Tourist, journey of, work of the inquirer compared to, 17, 29, 30. Transatlantic cable, 108. Transformation and adaptation in scientific thought, 214-235. Transformation of ideas, 63. Transformative law of the energies, 172. Translation, difficulties of, 354. Tree, conceptual life compared to a, 231. Triangle, mutual dependence of the sides and angles of a, 179. Triple accord, 46. Truth, wooed by the inquirer, 45; difficulty of its acquisition, 46. Tumblers, resounding, 23. Tuning-forks, explanation of their motion, 22 et seq. Tylor, 186. Tympanum, 18. Type, natural laws likened to, 193; words compared to, 191. Ulysses, 347. Understanding, what it means, 211.