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 effect of successive precipitations on, 358 recovery curve after large number of precipitations, 359 products of, 363 non-separable activity of, 363 radiations from active products of, 363 division of activity amongst active products of, 363 rate of emission of energy by, 432 theories of radio-activity of, 438 discussion of theories of radio-activity, 441 et seq.  source of energy of radiations, 442 et seq.   theory of radio-active change, 444 et seq.   table of radio-active products of, 449   rate of change of, 458   life of, 458   conservation of radio-activity of, 469   total emission of energy from 1 gram of, 475   possible causes of disintegration of, 486 et seq.

Thorium A period and properties of, 352 et seq.   absence of rays in, 352   effect of temperature on, 354  Thorium B   period and properties of, 352 et seq.   effect of temperature on, 354   radiations from, 363  Thorium X   methods of separation of, 220   law of decay of activity of, 221   law of recovery of activity of, 221   theory to explain production of, 224   material nature of, 226   continuous production of, 227   explanation of decay of activity of, 229   effect of conditions on the rate of change of, 233   disintegration hypothesis to explain production of, 234   minute amount of, produced, 237   effect of successive separations of, on activity of thorium, 358 et seq.   analysis of decay and recovery curves of, 358   radiations from, 363  Tommasina   scintillations produced by electrification, 160  Townsend   ions by collision, 39, 57   coefficient of recombination, 41   diffusion of ions, 51 et seq.   comparison of charge on ion with that on hydrogen atom in electrolysis, 53   number of molecules per c.c. of gas, 54   ionization by collision for different speeds, 171  Transformations, successive   theory of, 325 et seq.   nomenclature of, 328   activity due to, 337   detection of a rayless change in, 341   in uranium, 346 et seq.   in thorium, 351 et seq.   in actinium, 364 et seq.   in radium, 371 et seq.   list of, 449   origin of radium in, 459   helium, a result of, 476 et seq.   possible cause of, 486 et seq.   application of, to evolution of matter, 497 et seq.

Transmission of excited radio-activity of radium and thorium, 318 et seq. of excited radio-activity of actinium, 323

Travers and Ramsay amount of helium in fergusonite, 486

Troost rays from hexagonal blende, 4

Uranium discovery of radio-activity of, 5 persistence of radiations of, 6 discharging power of rays, 7 absence of reflection, refraction and polarization, 7 examination of uranium minerals, 11 et seq. relative activity of compounds of uranium, 12 nature of radiations from, 109 β rays from, 114 α rays from, 141 γ rays from, 180 separation of Ur X from, 219 recovery of activity of, 219 changes in, 346 et seq. non-separable activity of, 347 radiations from Ur X, 347 et seq. method of measurement of activity of Ur X, 347 emission of energy by, 418 theories of radio-activity of, 437 et seq. discussion of theories of radio-activity, 441 et seq.