uld here express my debt to them--just a part
of that indebtedness which we all feel to these masters. I wish also
to acknowledge my obligations to Professor Bertram B. Boltwood for his
helpful suggestions in connection with this work.

CONTENTS

CHAPTER I

DISCOVERY OF RADIO-ACTIVITY PAGE

The beginning--Radio-active bodies--An atomic
property--Discovery of new radio-active bodies--Discovery
of Polonium--Discovery of Radium--Other radio-active
bodies found 1

CHAPTER II

PROPERTIES OF THE RADIATIONS

Ionization of Gases--Experimental confirmation--Application
of electric field--Size and nature of ions--Photographing
the track of the ray--Action of radiations on photographic
plates--Discharge of electrified bodies--Scintillations
on phosphorescent bodies--Penetrating power--Magnetic
deflection--Three types of rays--Alpha rays--Beta rays--Gamma
rays--Measurement of radiations--Identifications of the rays 7

CHAPTER III

CHANGES IN RADIO-ACTIVE BODIES

Radio-activity a permanent property--Induced
activity--Discovery of Uranium X--Conclusions drawn--Search
for new radio-active bodies--Methods of investigation--Nature
of the radiations--Life-periods--Equilibrium series 17

CHAPTER IV

NATURE OF THE ALPHA PARTICLE

Disintegrating of the elements--Identification of the
rays--The alpha rays--Alpha rays consist of solid
particles--Electrical charge--Helium formed from alpha
particles--Discovery of Helium--Characteristics of
Helium--Table of constants 25

CHAPTER V

THE STRUCTURE OF THE ATOM

Properties of Radium--Energy evolved by radium--Necessity for
a disintegration theory--Disintegration theory--Constitution
of the atom--Rutherford's atom--Scattering of alpha
particles--Stopping power of substances 32

CHAPTER VI

RADIO-ACTIVITY AND CHEMICAL THEORY

Influence upon chemical theory--The periodic system--Basis
of the periodic system--Influence of positive
nucleus--Determination of the atomic number--Use of X-ray
spectra--Changes caused by ray-emission--Atomic weight
losses--Lead the end product--Changes of position
in the periodic system--Changes from loss of beta
particles--Isotopes--Radio-activity in na