es, change in position of element by loss of, 47

Chalcolite, natural and artificial, 4

Constants, table of, 31

Curie unit, 22

Disintegration of the element, 25

Disintegration series, 24

Disintegration theory, 35

Electroscope, 12

Equilibrium series, 22

Helium, characteristics of, 30
discovery of, 29

Ionium, discovery of, 6

Ionization, application of electric field to, 10
experimental confirmation, 9

Ionization of gases, 7
theory of, 8

Ions, size and nature of, 10

Isotopes, 47

Lead, atomic weight varies with source, 45
radio-active, 6
the end product, 45

Life-periods of radio-active bodies, 21

Periodic system, 41
basis of, 42

Polonium, discovery of, 4

Positive nucleus, influence of, 43

Potassium, radio-activity of, 3

Radiations, action on phosphorescent bodies, 13
action on photographic plates, 11
discharge electrified bodies, 12
magnetic deflection of, 14
measurements of, 15
penetrating power of, 13, 15

Radio-active bodies, elemental nature of, 20
examination of, 20
life periods of, 21

Radio-activity, an atomic property, 3
cosmical, 51
influence on chemical theory, 41
products in atmosphere, 51
products in earth's crust, 50
products in soil waters, 50

Radium, action on organic matter, etc., 33
amount in pitchblende, 5
discovery of, 5
emanation, 22
energy evolved by, 34
properties of, 5, 32

Rays, alpha, 15, 16, 26
beta, 15, 16
gamma, 15, 16
identification of, 16, 25
magnetic deflection of, 14
photographing track of, 10
types of, 14

Rubidium, radio-activity of, 3

Spinthariscope, 13

Stopping power of substances, 39

Thorium X, discovery of, 18, 21

Uranium atom, disintegration of, 36

Uranium minerals, radio-activity of, 3

Uranium X, discovery of, 17, 21, 23

X-ray spectra, 44

Zinc sulphide screen, 13

TRANSCRIBER'S NOTES

1. Passages in italics are surrounded by _underscores_.

2. Images have been moved from the middle of a paragraph to the
closest paragraph break.

3. The original text includes certain Greek alphabets. For this text
version [alpha], [beta], [gamma] indicate first three letters of Greek
alphabet respectively.

4. In this version, the number following carat character ^ is to be
interpreted a