328 Scientific Intelligence. 



of gases and on the handling of the same contains much new 

 matter, especially with reference to the liquefaction of hydrogen 

 and the fractional distillation of gas mixtures at low temperatures. 

 All the very recent determinations of the physical constants of 

 the rare gases of the argon group, as well as the new methods 

 used in their measurement, are included. An entire new chapter 

 has been added by the translator on the specific and latent heats 

 of gases, which contains much valuable information both as to 

 methods and results. These constitute the main additions. 



As a whole, this German edition can be said to add to the 

 value of a work already indispensable to the worker in gas analy- 

 sis or low temperature research. l. p. w. 



12. The Dynamical Theory of Gases ; by J. H. Jeans. Pp. 

 viii, 352. Cambridge, 1904. (University Press.) — In the first five 

 chapters of this book is given the theory of the distribution of 

 velocities and of the partition of energy in conservative systems. 

 Two methods of deriving the law of distribution of velocities are 

 given : the classical method of Maxwell and Boltzmann, and a 

 method devised by the author which is not unlike that of Gibbs 

 (Elementary Principles in Statistical Mechanics). Then follow 

 two chapters developing the physical properties of gases as pre- 

 dicated by this theory and the comparisons with experiment. The 

 unsatisfactory result of this comparison, especially in the case of 

 the ratio of the specific heats, is due to the fact that the theory 

 assumes that molecules form conservative systems. This leads to 

 the theory of a non-conservative gas which is treated in the next 

 three chapters. Here for the first time in the book is introduced 

 an hypothesis as to the structure of the molecule. The assump- 

 tion is made (supported by the evidence of spectroscopy) that the 

 ultimate components of the gas possess a number of isochronous 

 free vibrations. With the aid of this assumption the complete 

 theory is worked out, and the agreement with experiment is 

 shown to be of a very satisfactory nature. Next come six chap- 

 ters on the various free path phenomena. The book concludes 

 with applications of the theory to planetary atmospheres, molec- 

 ular aggregation and dissociation, and the calculation of the size 

 of molecules. In the appendices are given tables to aid in the 

 evaluation of the exponential integrals of common occurrence in 

 the kinetic theory. 



Altogether this is the most satisfactory treatise on the subject 

 that the writer knows. It is particularly excellent in its treat- 

 ment of the historic difficulties connected with the question of the 

 partition of energy. The treatment of the non-conservative gas 

 is very original and suggestive. The orderly perspicuous devel- 

 opment, the excellent historical perspective, the clear separation 

 of assumption and fact, and the unusual attention paid to the 

 quantitative numerical side of the subject, all contribute to make 

 this one of the notable books of the year. l. p. w. 



