ged conductors by
ionized gas.

Sec. 2. The Condensation of water-vapour by Ions:
Vapour will not condense without nucleus--Wilson's
experiments on electrical condensation--Wilson and
Thomson's counting experiment--Twenty million ions
per c.cm. of gas--Estimate of charge borne by ion--
Speed of charges--Zeleny's and Langevin's
experiments--Negative ions 1/1000 of size of
atoms--Natural unit of electricity or electrons.

Sec. 3. How Ions are Produced: Various causes
of ionization--Moreau's experiments with alkaline
salts--Barus and Bloch on ionization by phosphorus
vapours--Ionization always result of shock.

Sec. 4. Electrons in Metals: Movement of
electrons in metals foreshadowed by Weber--Giese's,
Riecke's, Drude's, and J.J. Thomson's researches--Path
of ions in metals and conduction of heat--Theory of
Lorentz--Hesehus' explanation of electrification by
contact--Emission of electrons by charged body--
Thomson's measurement of positive ions.

CHAPTER IX

CATHODE RAYS AND RADIOACTIVE BODIES

Sec. 1. The Cathode Rays: History of discovery--Crookes'
theory--Lenard rays--Perrin's proof of negative
charge--Cathode rays give rise to X-rays--The canal
rays--Villard's researches and magneto-cathode rays--
Ionoplasty--Thomson's measurements of speed of rays--
All atoms can be dissociated.

Sec. 2. Radioactive Substances: Uranic rays of Niepce
de St Victor and Becquerel--General radioactivity of
matter--Le Bon's and Rutherford's comparison of uranic
with X rays--Pierre and Mme. Curie's discovery of
polonium and radium--Their characteristics--Debierne
discovers actinium.

Sec. 3. Radiations and Emanations of Radioactive
Bodies: Giesel's, Becquerel's, and Rutherford's
Researches--Alpha, beta, and gamma rays--Sagnac's
secondary rays--Crookes' spinthariscope--The emanation
--Ramsay and Soddy's researches upon it--Transformations
of radioactive bodies--Their order.

Sec. 4. Disaggregation of Matter and Atomic Energy:
Actual transformations of matter in radioactive bodies
--Helium or lead final product--Ultimate disappearance
of radium from earth--Energy liberated by radium:
its amount and source--Suggested models of radioactive
atoms--Generalization from radioactive phenomena
-Le Bon's theories--Ballistic hypothesis generally
admitted--Does energy come from without--Sagnac's
experiments--Elster and Geitel's _contra_.

CHAPTER X

THE ETHER AND MATTER

Sec. 1. The Relations between the Ether and Matter: