Page:Radio-activity.djvu/588

  adjustment and screening of, 95
  special key for, 97
  application of, to measurements of radio-activity, 97 et seq.
  measurement of current by, 100
  capacity of, 101
  use with steady deflection, 103
  use with quartz piezo-électrique, 105

Electron
  definition of, 56
  production of, under different conditions, 76 et seq.
  identity of β rays with electrons, 120 et seq.
  variation of apparent mass of electron with velocity, 127 et seq.
  evidence that mass of electron is electro-magnetic, 129 et seq.
  diameter of, 131

Electroscope
  description of, used by Curie, 85
  construction of, for accurate measurements, 86
  use of, in measurements of minute currents, 86
  of C. T. R. Wilson, 89
  use of, in measuring conductivity of air in closed vessels, 531 et seq.
  use of, for determining radio-activity of ordinary matter, 537

Elster and Geitel
  radio-active lead, 27
  effect of magnetic field on conductivity produced in air by β rays, 113
  scintillations produced by active substances, 158
  action of radium rays on spark, 208
  photo-electric action of body, coloured by radium rays, 214
  radio-active matter in earth, 494
  discovery of excited activity in atmosphere, 501
  emanations from the earth, 507
  radio-activity of air in caves, 507
  radio-activity of the soil, 515
  radio-activity of fango, 516
  variation of radio-activity in atmosphere with meteorological conditions, 517
  effect of temperature and pressure on atmospheric radio-activity, 518

Emanation
  of thorium, discovery and properties of, 238
  methods of measurement of, 240
  decay of activity of, 241
  effect of thickness of layer on amount of, 243
  increase of, with time to a maximum, 245
  of radium, 246
  decay of activity of, 247
  of actinium, properties of, 249
  of radium, phosphorescence produced by, 251
  rate of emission of, 254
  effect of conditions on rate of emission of, 255
  regeneration of emanating power, 256
  continuous rate of production of, 257
  source of thorium emanation, 261
  source of radium and actinium emanation, 263
  radiations from, 263
  effect of pressure on production of, 265
  chemical nature of, 267
  experiments to illustrate gaseous nature of, 268
  rate of diffusion of radium emanation, 269
  rate of diffusion of thorium emanation, 275
  diffusion of, into liquids, 276
  condensation of, 277
  temperature of condensation of, 280
  volume of, from one gram of radium and thorium, 288
  measurement of volume of, from radium, 289
  diminution of volume of, 290
  spectrum of emanation, 292
  connection between emanation and excited activity, 298
  effect of removal of, on activity of radium, 371 et seq.
  fraction of activity of radium due to, 374
  effect of rate of escape of, on activity of radium, 374
  heat emission of, 420, 431
  variation of heat emission with time, 421 et seq.
  enormous emission of energy from emanation, 431
  radio-activity of atmosphere due to emanations, 504
  sucked up from the earth, 507
  in caves, 507 et seq.
  rate of decay of activity of, from the earth, 508
  condensation of, from the atmosphere, 510
  in well water and springs, 510 et seq.
  from "fango," 516
  effect of meteorological conditions on amount of, in atmosphere, 517 et seq.