178 Notices respecting New Books. 



written in very simple language and pre-supposing an extremely 

 moderate knowledge on the part of the reader ; and highly advanced 

 treatises, which could be read only by those who had previously 

 undergone a severe training in the higher branches of mathematics, 

 and which were quite beyond the reach of any reader with more 

 modest attainments. Between these two classes of books there was 

 a great gulf fixed, with only very few exceptions. JNo help was 

 offered to the student who, having taken the first steps in the subject, 

 and finding himself unable to attend more classes or seek the 

 guidance of a competent teacher, desired by private study some- 

 what to enlarge the meagre store of knowledge which he already 

 possessed. If he turned to the various books at his disposal, he 

 found that they either did not teach him anything which he did 

 not already know, or else that they gave him a fit of mental 

 indigestion. 



This somewhat discreditable state of affairs has, it is true, been 

 largely remedied nowadays, and the gap which formerly existed is 

 being rapidly filled. It is a most promising sign of the times that 

 our leaders in physical science no longer scorn to produce books of 

 a fairly " elementary " character : it is hardly possible to exaggerate 

 the importance which works of thi> kind have in raising the general 

 level of scientific knowledge, and in stimulating further inquiry. 



It is, therefore, greatly to the credit of the accomplished author 

 of the book before us that as far back as 1877 it had occurred to 

 him that possibly a few people might like to know something about 

 the kinetic theory of gases who did not share the profound know- 

 ledge of the brilliant mathematicians by whose efforts the theory 

 had been largely built up. Accordingly he set to work, and 

 succeeded in producing a book which is now passing through a 

 second edition, and of which the work under review is an English 

 translation by Mr. Baynes. 



Although described as an "elementary Ireatise'' on the subject, 

 the book consists of 352 pages forming the elementary portion, 

 with 120 additional pages of " mathematical appendices," intended 

 for the more advanced reader. This plan of sifting out the 

 mathematics and relegating them to an appendix seems — in the 

 present case, at any rate — to present a distinct advantage: the 

 attention of the reader being thereby directed to the physical 

 aspect of the reasoning, and not being diverted by purely mathe- 

 matical difficulties. In the brief space at our disposal, we can do 

 little more than merely indicate the nature and scope of the con- 

 te)its of the book. It is divided into three parts. Part I. deals 

 with molecular motion and its energy, and is subdivided into five 

 chapters dealing with (1) the foundations of the kinetic theory; (2) 

 the pressure of gases ; (3) Maxwell's Jaw of speed distribution ; (4) 

 ideal and actual gases ; and (5) the relation of molecular to atomic 

 energy. Part II. is concerned with the molecular free paths and 

 the phenomena conditioned by them, and is subdivided into four 

 chapters, dealing with (1) the molecular free paths ; (2) the vis- 



