Chemistry and Physics. 369 



in a narrow tube than in a wide one. This difference in yield 

 must be connected with the current density rather than with the 

 potential gradients, since the difference between the latter in nar- 

 row and wide tubes is insufficient to plausibly account for it. 



3. As the length of the positive column traversed by the gas 

 is increased the yield of active nitrogen reaches a limit. This is 

 due to the destructive action of the discharge which, above a 

 certain concentration, nullities the active modification as fast as 

 it is generated. 



4. It has been shown in previous papers that a trace of oxygen 

 (or almost any other admixture) greatly increases the yield of 

 active nitrogen. The amount of oxygen required to bring about 

 this result considerably increases the fall of potential at the 

 cathode, but it does not measurably influence the gradient in the 

 positive column. 



5. Active nitrogen can be produced by the spark at atmos- 

 pheric pressure, but the phenomena are much less brilliant than 

 at low pressures. The destructive influence of the surrounding 

 gas on the active modification is responsible for this difference. 



6. The particles scattered from a copper cathode when the 

 uncondensed discharge passes can be made to emit the line 

 spectrum of the metal in a stream of active nitrogen. — Proc. 

 Roy. Soc, vol. xcii (A), p. 438, July, 191G. n. s. u. 



7. The Emission of Electricity from Hot Bodies ; by O. W. 

 Richardson. Pp. vii, 304, with 35 figures. London, 1916 

 (Longmans, Green and Co.). — This book is the seventh of the 

 series of "Monographs on Physics" edited by J. J. Thomson 

 and Frank Ilorton. A fair idea of the field covered in the text 

 may be derived from the titles of the chapters, which are : 

 "I. Mainly Considerations of a General Character. II. Theory 

 of the Emission of Electrons from Hot Bodies. III. Tempera- 

 ture Variation of Electron Emission. IV. The Effect of Gases 

 on the Emission of Electrons. V. Energetics of Electron Emis- 

 sion. VI. The Emission of Positive Ions by Hot Metals. VII. 

 The Effect of Gases on the Liberation of Positive Ions by Hot 

 Metals. VIII. The Emission of Ions by Heated Salts, and IX. 

 Ionization and Chemical Action." 



Due to the non-existence of a satisfactory and comprehensive 

 theory of conduction for conductors of the metallic type, Richard- 

 son has treated the subject of the second chapter in as general a 

 manner as possible, thereby reducing the part played by special 

 theories to a minimum. The last chapter includes a brief account 

 of the results of some experiments recently made by the author 

 with regard to electrons liberated by chemical action. The purely 

 technical side of the general subject has been wisely omitted 

 from the text, but the titles of the most important books and 

 papers relating to this phase are given in the preface. Numerous 

 bibliographical foot-notes facilitate supplementary reading, and 

 the volume closes with both name and subject indices. The high 

 standard set by the preceding numbers of the " Monographs" is 

 fully maintained in the present volume, so that this publication 

 will be found very valuable by students of advanced physics. 



h. s. IT. 



