MOLECULAR PHYSICSCHAPTER I. Introduction.The history of the rise of molecular theory has often been written. From Dalton, who first gave to the conceptions of the early atomists a definite meaning and a real experimental basis, through Avogadro and his fertile hypothesis of the molecule, and so on to the kinetic theory of Clausius and Maxwell, the story is told in almost every text-book of Chemistry and Physics, and is familiar as household words to all their readers. Here for a time science seemed to pause in her progress. It seemed as if the memoirs of these brilliant mathematicians were to contain the last word in molecular theory.If this had been so, the following pages would have been superfluous. In the last few years, however, new fields have been opened to the student of molecular phenomena; new methods of approach have been evolved so potent in character that subjects about which we had until then barely sufficient grounds for speculation are now laid open to direct expeTable of Contents PACE; Chapter I-Introduction i Historical survey The old and the new physics The molecular, theory of matter Molecular magnitudes; Chapter II-The Physics of the Electron 10 The discharge of electricity through gases Cathode rays Measurement of the ratio of the mass to the charge for the cathode rays Measurement of the charge on an electron Photography of the tracks of ionizing particles; Chapter III-The Positive Particle 34 The a-particles from radio-'active substances Counting the a-particles The charge on an a-particle Production of helium from a-rays; Chapter IV-The New Method of Analysis 42 Positive particles in the discharge tube Sir JJ Thomson's' experiments Measurement of the velocity and mass of the positive particles Positive ray analysis The new gases Application of the method to the study of chemical decomposition Electrical methods of measurement; Chapter V-The Nature and Si