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_..