TABLE OF CONTENTS. 



Introduction. xv 



Part 1. Current Conceptions, 



CHAPTER I, THE THREE ENTITIES. 1 



II. COMPOUNDS AND ELEMENTS: MOLE- 

 CULES AND ATOMS. 8 



Part 2. The Periodic Law. 



CHAPTER I. THE MYSTERY OF MATTER. 15 



II. THE ATOMS OF THE ELEMENTS. 17 



III. THE TABLE OF THE LAW. 26 



IV. THE TESTING OF THE LAW. 34 

 V. THE SIGNIFICANCE OF THE LAW 39 



Part 3. Gaseous Ions. 



CHAPTER I. GASES FROM THE STANDPOINT OF 

 PHYSICS : How THEY CONDUCT 

 ELECTRICITY. 45 



II. DISCOVERY OF IONS: A NEW KIND OF 



PARTICLES. 48 



III. DISCOVERY OF CORPUSCLES. 51 



IV. FACTORS OF A CORPUSCLE : AN EX- 



PERIMENT. 54 



V. THE SPEED OF A CORPUSCLE AND How 



IT is ESTIMATED. 59 



VI. THE RELATION OF THE CHARGE ON A 

 CORPUSCLE TO ITS MASS: How IM- 

 PORTANT IT is. 61 



(ix) 



