328 SCIENCE PROGRESS 



but this must not be taken to mean that the important theoretical portions 

 of the subject are omitted. 



The first five chapters are devoted to the physics of the thermionic tube. 

 The remaining five deal with the various applications of the device, most 

 prominent, of course, being the discussions of the triode as rectifier, amplifier, 

 and alternating current generator. It is a pity that much of this treatment 

 is marred by the author's persistent use of parabolic equations to represent 

 the principal voltage-current characteristic of a tube. Such expressions 

 have no theoretical basis, and should be replaced by those suggested by 

 C. D. Child and I. Langmuir. Anyone attempting to determine the alter- 

 nating current amplitude of a triode generator using the parabolic relation, 

 very soon finds that it does not contain the one term that really matters. 



The treatment of the internal action of a three-electrode tube is based 

 on an application of Maxwell's theory of the shielding action of a grating. 

 Experiment is necessary for cases in which the approximations of Maxwell's 

 analysis are not valid. After reading these chapters one feels grateful for the 

 appreciable inertia of the electron. A triode would function as neither 

 amplifier nor oscillation generator if the electrons followed the lines of electric 

 force. 



Much space is devoted to methods of measuring the amplification factors 

 of thermionic tubes. Such work, of course, is highly important in practice 

 where tubes have to function in parallel or to be interchangeable. But Dr. 

 van der Bijl must have found that his method of determining the amplifica- 

 tion factor described on page 159 is not accurate, the values obtained being 

 determined almost wholly by the sensitivity of the galvanometer used. 



The volume is well printed, and contains many excellent diagrams. To 

 the student of Radiotelegraphy it is sufficient to say that it is uniform with 

 Seelig's translation of Zenneck's Wireless Telegraphy. 



E. V. Appleton. 



nCETEOBOLOGY 



Ou En Est La Meteorologie ? By Alphonse Berget. [Pp. 300.] (Paris: 

 Gauthier-Villars et Cie.) 



This book is one of a series which gives resumes of the most recent advances 

 in various branches of science, and endeavours to indicate also the most 

 important outstanding problems that await solution. This particular 

 volume does not therefore aim at being a text-book of meteorology. 



It is evident that, to M. Berget, meteorology is interesting only in so far 

 as it is applied physics, and for that reason one finds subjects such as the 

 kinetic theory of gases and actinometry expounded at considerable length, 

 while climatological statistics occupy but little space. 



At the outset it is surprising to find a physicist opposed to the use of the 

 absolute scale of temperature in meteorology, and also to the expression of 

 pressure in megadynes per square centimetre instead of in the older units, 

 but, on proceeding further, one is tempted to suspect that the author's evident 

 prejudice against the work of German scientists leads him to dislike any idea 

 that is " outre-Rhin " in origin. Certainly, he loses no opportunity of denoun- 

 cing the " savants d 'outre Rhin," and even Helmholtz does not quite escape 

 his strictures. A spirit of this kind is deplorable in a scientific work. The 

 book certainly deserves to be widely read in this country, as it is quite an 

 education to find how different a view can be held on the Continent as to the 

 exact position of meteorological research, and as to who in recent years has 

 done most to advance it. M. Berget is a great admirer of the American 

 Weather Bureau ; he is an advocate of M. Guilbert's rules for predicting the 

 behaviour of cyclonic depressions, and makes astonishing claims of success 

 for this method ; but for the millennium in forecasting he looks to the har- 

 monic analysis of the curve for barometric pressure on the lines of the work of 



