ONDUCTION OF ELECTEICITY THROUGH GASES J BY J. J. THOMSON, D.Sc., LL.D., PH.D., F.R.S. FELLOW OF TRINITY COLLEGE, CAMBRIDGE CAVENDISH PROFESSOR OF EXPERIMENTAL PHYSICS, CAMBRIDGE CAMBRIDGE : AT THE UNIVERSITY PRESS. 1903 Oc 711 ' T4- Cambridge : PRINTED BY J. AND C. F. CLAY, AT THE UNIVERSITY PRESS. I Si if PREFACE. T 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 cla: ned 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 liquid. The possession of a charge by the ions increases so much the ease with which they can be traced and their properties studied that as the reader will see we know far more about the ion than we do about the uncharged molecule. vi PREFACE. L With the discovery and study of Cathode rays, Rb'ntgen rays and Radio-activity a new era has begun in Physics, in which the electrical -properties of gases have played and will play a most important part ; the bearing of these discoveries on the problems of the Constitution of Matter and the Nature of Electricity is in most intimate connection with the view we take of the processes which go on when electricity passes through a gas. I have endeavoured to show that the view taken in this volume is supported by a large amount of direct evidence and that it affords a direct and simple 'explanation of the electrical properties of gases. The pressure of my other duties has caused this book to be a considerable time in passing through the press, and some important investigations have been published since the sheets relating to the subjects investigated were struck off. I have given a short account of these in a few Supplementary Notes. My thanks are due to Mr C. T, R. Wilson, F.R.S., for the 'assistance he has given me by reading the proofs and I am indebted to Mr Hayles of the Cavendish Laboratory for the preparation of the diagrams. J. J. THOMSON. CAVENDISH LABORATORY, CAMBRIDGE. August, 1903. TABLE OF CONTENTS. CHAP. PAOB I. Electrical Conductivity of Gases in a normal state . C 1 II. Properties of a Gas when in the conducting state . . 8 III. Mathematical Theory of the Conduction of Electricity through a Gas containing Ions . 64 IV. Effect produced by a Magnetic Field on the Motion of the Ions . . . . . . .';*. . 79 V. Determination of the Ratio of the Charge to the Mass of an Ion 91 VI. Determination of the Charge carried by the Negative Ion . 121 VII. On some Physical Properties of Gaseous Ions . . . 133 VIII. lonisation by Incandescent Solids ,\ T^V. . 155 IX. lonisation in Gases from Flames . -^^\ \, . . . 193 X. lonisation by Light. Photo-Electric Effects . . .211 XL lonisation by Rontgen Rays. . . . \. . . 244 XII. Becquerel Rays . \ . * .,.'.''. \ . . 274 l/XIIL Spark^Discharge c^/ \ . .'. . ,, . . . 346 XIV. The_Electric Arc . . * ,, \ . . 416 v XV. Discjarge through Gases at Low Pressures . ^ . ' . . 432 XVI. Theory of the Discharge through Vacuum Tubes . . .479 XVII. Qailiode Rays '. . 493 XVIII. Rontgen Rays . 523 XIX. Properties of Moving Electrified Bodies 530 SUPPLEMENTARY NOTES .545 INDEX 555 [...]... plates being exposed to the action of One substance Rontgen rays or the radiation from a radioactive of quadrants of of the plates is connected with one of the pairs an electrometer, the other pair of quadrants being put to earth terminals of a is connected with one of the The other plate A B PROPERTIES OF A GAS 12 [11 battery of several storage cells, the other terminal of the battery being connected... centimetre D the coefficient of diffusion of the positive ions of the gas, the gas, the number of negative ions per cubic centithrough metre, then we see that in consequence of diffusion the rate m of increase in the is equal to D d?n : -^ number of positive ions per cubic centimetre assuming that the surfaces of equal density of the ions are planes at right angles to the axis of x Thus taking recombination... have described show that the rate of leak of electricity through gas in a normal state is influenced by a great variety of circumstances, such as the pressure of the gas, the volume of gas in the electric field, and the amount of dust or fog held in suspension by it; all these effects receive a ready explanation on the view to which we are led by the study of the by gases whose conductivity has been... scale was a measure of the rate of leak through the gas The following results were obtained by both Geitel and Wilson the rate of escape of electricity in a closed vessel is much smaller than in the open and the larger the vessel the greater is the rate of leak The rate of leak does not increase in proportion to the difference of potential between the gold leaves and the walls of the vessel the rate... pairs of quadrants of the electrometer are connected together, then the con; nection between the quadrants is broken and as a current of and B, the electricity is passing across the air space between B gets charged up and the needle of the electrometer is plate A deflected ; the rate of deflection of the electrometer measures the current passing through the gas By making a series of observations of this... cases in which foreign matter present in gases is not removed by such treatment, and the case of the discharge of negative elec- from the gas settling : thus down of : from a point (vide infra) shows that under certain conditions the admixture of a very small amount of foreign matter to tricity a gas produces a great diminution in the rate of escape of electricity through * it ft Wilson, Proc Roy Soc Ixix... coefficients of diffusion of the ions in air, oxygen, hydrogen and carbonic acid gas have been determined by Town19 send* by a different method; ionised air being sucked through very narrow tubes and the loss of ions suffered in passing through a known length of tubing determined method axis of is which is The theory of the ionised gas is sent through a metal tube the taken as the axis of z, the gas... alone The of following tables give the velocities of the coefficients Townsend diffusion on the C.G.s system of units as deduced by from his observations TABLE Gas I COEFFICIENTS OF DIFFUSION IN DRY GASES PROPERTIES OF A GAS 28 TABLE II Gas [19 COEFFICIENTS OF DIFFUSION IN MOIST GASES WHEN 19] IN THE CONDUCTING STATE 29 The results given in Tables I and II show that the excess of the velocity of diffusion... feet of solid rock Wilson* has recently investigated the greatest rates of leak through different gases and has obtained the following results through many Relative rate of leak Gas Relative rate of leak Specific gravity 1-00 -184 1-69 2-64 air Ho C0 2 S0 2 CHC1 3 I'OO 2'7 1-10 1-21 1-09 4-7 made the very interesting observation that the rate of leak in a closed vessel increases, after the refilling of. .. sides of the vessel receiving a charge which they which the electricity escaped the rate if this were the method the conduction is ; of leak by would not increase with the * size of the vessel Elster and Geitel, Physikalische Zeitschr ii p 560, 1901 CHAPTER PROPERTIES OF A GAS 7 THE WHEN IN II THE CONDUCTING STATE electrical conductivity of gases in the so small that as we have seen the proof normal . ONDUCTION OF ELECTEICITY THROUGH GASES J BY J. J. THOMSON, D.Sc., LL.D., PH.D., F.R.S. FELLOW OF TRINITY COLLEGE, CAMBRIDGE CAVENDISH PROFESSOR OF EXPERIMENTAL PHYSICS, CAMBRIDGE CAMBRIDGE : AT THE UNIVERSITY PRESS. 1903 Oc 711 ' T4- Cambridge : PRINTED BY J. AND C. F. CLAY, AT THE UNIVERSITY PRESS. I Si if PREFACE. T 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. 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. the distance between the plates has been verified by measurements of the saturation currents through gases exposed to Rontgeri rays*. 14. Even when there is no current of electricity passing through the gas and removing some or all of the ions, the number of ions present in