Chemistry and Physics. 473 



tangent at its extremity is equal to tan -1 n. It is also proved 

 that no other surface can satisfy the requirements of the prob- 

 lem.— Verh. d. Deutsch. Phys. Gesell, 13/16, 103, 1918. 



H. S. U. 



9. Aviation; by Benjamin M. Carmina. Pp. ix, 172, with 

 92 figures. New York, 1919 (The Macmillan Co.).— "In the 

 compilation of this book, the guiding principle has been to use 

 matter of actual theorico-practical value to the aviation students 

 to enable them to work knowingly." The successive chapters 

 are devoted respectively to the following topics: theory of 

 flight, aeroplane construction, rigging, propellers, maintenance, 

 and flight hints. The explanations and "theory" are clearly 

 presented and they seem to be as thorough and reliable as is 

 possible under the two restricting conditions consistently ful- 

 filled by the text-proper, namely (a) the hypothesis that the 

 student has had no previous acquaintance with the subject, and 

 (b) the complete absence of even the most elementary mathe- 

 matics. The line diagrams are numerous and they illustrate 

 the text admirably. 



The appendix deals with aerodynamical formulae and calcu- 

 lations. Nearly all of the typographical and notational errors 

 are confined to this section. The sentence immediately follow- 

 ing the second formula on page 135 is especially confusing. 

 A very useful glossary of definitions of technical terms, 

 arranged alphabetically, precedes the index. In conclusion, the 

 writer of this brief notice desires to commend the scientific 

 spirit of the text in general, and to endorse the quotation (p. 

 157) : "The metric system removes the confusion arising out 

 of the excessive diversity of weights and measures prevailing in 

 the world, by substituting in place of the arbitrary and incon- 

 sistent systems actually in use, a single one constructed on 

 scientific principles and resting on a natural and invariable 

 standard." h. s. u. 



10. Molecular Physics, Second Edition; by James Arnold 

 Crowther. Pp. viii, 190. Philadelphia, 1919 (P. Blakiston's 

 Son & Co.). — A careful comparison of the latest edition with 

 the first (see 39, 314, 1915) shows that the revision has been 

 thoroughly done and that the scope of the text has been mate- 

 rially extended. The number of chapters has been increased 

 from nine to ten, the titles of the sixth and seventh now being 

 respectively "The Structure of the Atom" and "The Electron 

 Theory of Valency." All of the typographical errors which we 

 detected in the first edition have been corrected in the second, 

 and a subject index has been added. On the whole, the author's 

 desire "to present a coherent and intelligible account of the 

 present state and most recent advances in the electron theory of 

 matter ' ' seems to be fully realized in the present edition. 



h. s. u. 



