REVIEWS 705 



remained a purely empirical one until Boltzmann showed its significance from the 

 standpoint of the classical statistical mechanics. But this was only a partial success, 

 for the " law " was, after all, not generally valid. It was not until Einstein took the 

 bold step of discarding the principle of equipartition of energy (as Planck had 

 already done in the case of radiation) and applied Planck's quantum theory to the 

 energy content of solids that the property of specific heat became one of the first 

 importance for the theory of the solid state. It is now well established, both 

 experimentally and theoretically, that the " law " of Dulong and Petit is not really 

 a law at all in the sense that the " constant " involved in it is a function of the 

 temperature. Einstein's work was, however, itself incomplete, and Nernst gives a 

 very clear account of the extension of Einstein's theory undertaken by Lindemann 

 and himself and later the more important contribution made by Debye. 



Perhaps the most suggestive part of the book is to be found in the three con- 

 cluding sections as pointing the way to further investigation of many widely varying 

 phenomena, such as the molecular weight of solid compounds, the behaviour of 

 substances at very low temperatures in respect of specific heat, thermal expansion, 

 compressibility, conduction of heat and electricity, magnetic susceptibility, thermo 

 e.m.f. and the Thomson effect. The relation of the quantum theory to the electron 

 theory is indeed one of the most vital of all, and already since the delivery of these 

 lectures a very considerable amount of work has been done in this direction (cf. 

 Lindemann, Phil. Mag. January 191 5). It is a remarkable fact that in spite of the 

 amazing rapidity with which the quantum theory has entered into the fundamental 

 problems of physics and chemistry we are still absolutely in the dark as regards a 

 clear physical conception of the quantum itself. This very fact, however, should 



prove the great incentive for further research. 



W. C. McC. Lewis. 



A Textbook of Inorganic Chemistry. In nine volumes. Edited by J. Newton 

 Friend, D.Sc, Ph.D. Volume I. Part I. : An Introduction to Modern 

 Inorganic Chemistry, by J. Newton Friend, H. F. V. Little, and 

 W. E. S. TURNER; Part II. : The Inert Gases, by H. V. A. BRISCOE. 

 [Pp xv + 385, with frontispiece, plate and 88 other illustrations. Crown 

 8vo ] (London : Charles Griffin & Co., Ltd. Price of Vol. I. \os. 6d. net.) 



The volume before us is the first of a series of nine, which is intended evidently to 

 form the standard work in English upon inorganic chemistry. It is, of course, not 

 the first which deserves the title, but it so very clearly marks the fundamental 

 change which has been made in the last twenty years in regard to method of 

 treatment and point of view, that its appearance is significant. This is the 

 conclusion come to on inspection of the first volume ; it remains to be seen, of 

 course, whether the later volumes will pursue the same ideal. It is rather a 

 remarkable fact that British scientists have never taken at all kindly to the 

 preparation of treatises on the grand scale. Such work seems in the past to have 

 appealed more particularly to the Teutonic mind, though the utility of a consider- 

 able amount of such work has been rendered of somewhat doubtful value through 

 the absence of the one essential factor, the exercise of the critical faculty. A 

 merely massive compendium which includes, or strives to include, everything that 

 has been published on a particular subject, is rather a burden than an assistance 

 to the development of a science. The present volume is fairly complete as regards 

 facts, and a particular point has been made in the matter of literature references. 

 Above all, it does appear to have been written with a real appreciation of proportion 

 and critical selection. It must have been obvious to the compilers that their chief 



