398 
Thorium (cont.) 
life of, 333 
total emission of energy from 1 gram 
of, 337 
possible causes of disintegration of, 
338 et seq. 
Thorium X 
methods of separation of, 179 
law of decay of activity of, 182 
law of recovery of activity of, 182 
theory to explain production of, 183 
material nature of, 185 
continuous production of, 186 
explanation of decay of activity of, 
188 et seq. 
effect of conditions on the rate of 
change of, 190 et seq. 
disintegration hypothesis to explain 
production of, 193 et seq. 
minute amount of, produced, 195 
effect of successive separations of, on 
activity of thorium, 296 
theory of decay curve of, 296 et seq. 
Tommasina 
scintillations produced by electrifica- 
tion, 128 
Townsend 
ions by collision, 36, 54 
coefficient of recombination, 38 
diffusion of ions, 49 et seq. 
comparison of charge on ion with that 
on hydrogen atom in electrolysis, 51 
number of molecules per c.c. of gas, 51 
ionization by collision for different 
speeds, 139 
Transmission 
of excited radio-activity of radium 
and thorium, 282 et seq. 
of excited radio-activity of actinium, 
287 ; 
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 radiation from, 90 et seq. 
B rays from, 95 et seq. 
a rays from, 115 et seq. 
y rays from, 142 et seq. 
emission of energy by, 154 
separation of Ur X from, 179 
recovery of activity of, 182 
INDEX 

Uranium (cont.) 
non-separable activity of, 294, 304 
radiations from Ur X, 293 
method of measurement of activity 
of Ur X, 294 
changes in, 294 
conservation of radio-activity of, 308 
et seq. 
résumé of results, 311 et seq. 
theories of radio-activity, 316 et seq. 
discussion of theories of radio- 
activity, 320 et seq. 
source of energy of radiation, 320 et 
seq. 
theory of radio-active change, 322 et 
seq. ‘ 
table of active products, 326 
rate of change of, 332 et seq. 
life of, 333 
radium possible product of, 334 
total emission of energy from 1 gram 
of, 337 : 
possible causes of disintegration of, 
338 et seq. 
Uranium X 
separation of, by Crookes, 178 
separation of, by Becquerel, 179 
decay of activity of, 182 
recovery of activity of, 182 
theory to explain production of, 183 
material nature of, 185 
explanation of decay of activity of, 
188 et seq. 
radiations from, 293 
method of measurement of radiations 
from, 294 
changes in, 294 
Velocity 
of ions in electric field, 39 et seq. 
difference between, of positive and 
negative ions, 42 et seq. 
of 6 particle or electron, 197 et seq., 
110 et seq. 
variation of mass of electron with, 
108 et seq. 
of a particle, 122 et seq. 
of transmission of carriers of excited 
activity, 284 
Villard 
discovery of y rays from radium, 141 
alteration of X ray screen with time, 
168 
activity produced by cathode rays, 372 
Volume 
of radium emanation, calculation of, 
246 
of emanation, determination of, 313 
decrease of, of radium emanation, 
313 
