388 
Dorn (cont.) 
loss of weight of radium, 336 
Durack 
ionization by collision of electrons of 
great velocity, 139 
Dust 
effect of, in recombination of ions, 39 
effect of, on distribution of excited 
activity, 260 
Earth 
amount of radium in, 344 
age of, 344 
excited activity deposited on, 354 
activity concentrated on peaks of, 354 
emanation from, 363 
very penetrating radiation from, 366 
Ebert 
condensation of emanation from the 
earth, 359 
Ebert and Ewers 
emanation from the earth, 358 
Electric field 
deflection of 8 rays by, 106 
deflection of a rays by, 121 
movement in, of carriers of excited 
activity, 282 et seq. 
action on, of carriers of excited ac- 
tivity from “‘ emanating substance,” 
287 R 
Electrolysis 
separation of radio-tellurium by, 21 
of solutions of emanation X, 276 
of thorium solutions, 277 
of radium solutions, 276 
Electrometer 
description of, 74 et seq. 
use of, in measurements, 74 
construction of, 76 et seq. 
Dolezalek, 78 
adjustment and screening of, 79 
special key for, 81 
application of, to measurements of 
radio-activity, 81 et seq. 
Measurement of current by, 84 
capacity of, 85 
use with quartz piezo-électrique, 87 
Electron 
definition of, 53 
identity of 8 rays with electrons, 102 
et seq., 107 
variation of apparent mass of electron 
with velocity, 108 et seq. 
evidence that mass of electron is 
electro-magnetic, 112 
diameter of, 112 
production of, under different condi- 
tions, 347 
Electroscope 
description of, used by Curie, 70 
INDEX 

Electroscope (cont.) 
construction of, for accurate measure- 
ments, 71 
use of, in measurements of minute 
currents, 71 
of C. T. R. Wilson, 73 
use of, in measuring conductivity of 
air in closed vessels, 373 et seq. 
use of, for determining radio-activity 
of ordinary matter, 378, 380 
Elster and Geitel 
radio-active lead, 25 
effect of magnetic field on conductivity 
produced in air by radium rays, 95 
scintillations produced by active sub- 
stances, 127 - 
action of radium rays on spark, 171 
photo-electric action of body, coloured 
by radium rays, 174 
radio-active matter in earth, 345 
discovery of excited activity in atmo- 
sphere, 351 
emanations from the earth, 357 
radio-activity of air in caves, 362 
radio-activity of the earth, 362 
radio-activity of natural carbonic acid, 
364 
variation of radio-activity in atmo- 
sphere with meteorological condi- 
tions, 364 et seq. 
effect of temperature and pressure on 
atmospheric radio-activity, 365 
Emanation 
rate of heat emission by, 158 
variation of heat emission with time, 
160 
of thorium, discovery and properties, 
197 
methods of measurement of, 199 
decay of activity of, 200 
effect of thickness of layer, on 
amount of, 202 
increase of, with time, to a maxi- 
mum, 204 
of radium, 205 
decay of activity of, 206 
of actinium, properties of, 208 
of radium, phosphorescence produced 
by, 209 et seq. 
rate of emission of, 213 
effect of conditions, on rate of emis- 
sion of, 214 
regeneration of emanating power, 215 
continuous rate of production of, 216 
et seq. 
source of thorium emanation, 220 
source of radium emanation, 222 
radiations from, 222 
effect of pressure on production of, 224 
chemical nature of, 225 
