CAMBRIDGE UNIVERSITY PRESS WAREHOUSE, C. F. CLAY, MANAGER. London: FETTER LANE, E.C. ALSO London: H. K. LEWIS, 136, GOWER STREET, W.C. Leipzig: F. A. BROCKHAUS. New York: G. P. PUTNAM'S SONS. Bombay and Calcutta: MACMILLAN AND CO., LTD. [All Rights reserved] THROUGH GASES BY J. J. THOMSON, D.Sc., LL.D., PH.D., F.R.S. FELLOW OF TRINITY COLLEGE, CAMBRIDGE CAVENDISH PROFESSOR OF EXPERIMENTAL PHYSICS, CAMBRIDGE SECOND EDITION 12555 CAMBRIDGE: AT THE UNIVERSITY PRESS 1906 I HAVE endeavoured in this work to develope the view that the conduction of electricity through gases is due to the presence in the gas of small particles charged with electricity, called ions, which under the influence of electric forces move from one part of the gas to another. My object has been to show how the various phenomena exhibited when electricity passes through gases can be coordinated by this conception. rather than to attempt to give a complete account of the very numerous investigations which have been made on the electrical properties of gases; I have therefore confined myself for the most part to those phenomena which furnish results sufficiently precise to serve as a test of the truth of this theory. The book contains the subject-matter of lectures given at the Cavendish Laboratory where a good deal of attention has been paid to the subject and where a considerable number of physicists are working at it. The study of the electrical properties of gases seems to offer the most promising field for investigating the Nature of Electricity and the Constitution of Matter, for thanks to the Kinetic Theory of Gases our conceptions of the processes other than electrical which occur in gases are much more vivid and definite than they are for liquids or solids; in consequence of this the subject has advanced very rapidly and I think it may now fairly be claimed that our knowledge of and insight into the processes going on when electricity passes through a gas is greater than it is in the case either of solids or liquids. The possession of a charge by the ions increases so much the ease with which they can be |