Oxford Clarendon Press, 1915. — 524 p.
The electrical properties of gases have formed the subjects of many theoretical and experimental researches since Röntgen and Becquerel discovered the rays which render the gases conductors of electricity. These discoveries provided a means of studying the conductivity obtained with small electric forces, and the researches have led to satisfactory theories of many of the phenomena connected with electric discharges. The nature of the rays has also been studied and the remarkable physical properties of the various types of rays have been clearly defined. At the same time new investigations were made of the cathode rays which give rise to Röntgen rays when they collide with solid objects and thus form a connecting link between the currents in gases and the penetrating rays emitted by radio-active substances. Wiehert, in 1897, made the important discovery that the charged particles which compose the cathode rays move with a velocity about one-tenth of the velocity of light, and that the mass associated with the atomic charge was about one two-thousandth part of the mass of an atom of hydrogen. The essential difference between the electrons and the positive ions was thus ascertained. These fundamental discoveries having attracted the attention of many physicists, numerous researches were made which have added to our knowledge of molecular physics, and during the course of the experimental work several books have been written giving accounts of the progress that has been made from time to time. The best-known treatises are those by Sir J.J. Thomson and the collection of original researches, "Ions, Electrons, and Corpuscules", published by H. Abraham and P. Langevin. These branches of electrical science have increased so much in recent years that it has become impossible to give a complete description of the principal researches in one or two ordinary volumes. About three years ago, on the suggestion of Professor Marx, several physicists co-operated in bringing out a treatise in six volumes dealing with the electrical properties of gases and the subject of radiation in general. This volume contains my contribution to the treatise and is limited to a description of the conductivity obtained in gases at ordinary temperatures and at pressures ranging from atmospheric pressure to pressures of the order of one millimetre in which the discharges may be explained by the theory of ionization by collision. I have also given a brief description of the principal experiments on cathode rays and positive rays obtained in high vacua, as the results are of importance in connection with the general theory of electrical conductivity. I have been unable to find space to give complete accounts of many interesting investigations, and students who wish for further information are recommended to consult the original memoirs to which I have referred. While I have been engaged in this work I have received many valuable suggestions from Mr. F. B, Pidduck, and my best thanks are due to him for his assistance and also for having corrected the proofs.
