Chemistry and Physics. 457 



be detected by the motion of small masses of discrete cloud mate- 

 rial, the behavior of numerous floating: seeds, or small floating 

 feathers. 



It is the author's conclusion that since the most attentive 

 observation has failed to suggest a solution of the problem, 

 the only hopeful method of attack is by way of direct experi- 

 mental investigation. A list of twelve articles detailing the 

 author's observations is appended to the communication. — Proc. 

 Caml. Phil. Soc. 20, 227, 1920. f. e. b. 



7. Elementary Calculus; by William F. Osgood. Pp. ix, 

 224. New York, 1921 (The Macmillan Co.).— A new text on 

 Elementary Differential Calculus which aspires to attention in 

 this well-occupied field should present some special claim to recog- 

 nition.' The author's aim to present the subject with emphasis on 

 the ideas and methods of the calculus and their use in solving 

 problems in physics and geometry, is well maintained. The 

 tendency of the student to regard differentiation as a mechanical 

 process whereby an answer is to be obtained is strongly depre- 

 cated and the illustrative examples are so selected that they 

 should seem to him as of interest and value. 



More than usual pains has been taken to make the logic rigor- 

 ous, which will doubtless appeal to the mathematicians. On the 

 other hand the illustrations used are so concrete and physical 

 that they afford the very kind of mathematical training which 

 the physics teacher desires his students to have had. 



Of the eight chapters, one describes the character of the simple 

 functions, and five are devoted to the manner and result of their 

 differentiation. Chapter II discusses the application of deriva- 

 tions to curves, to maxima and minima, to velocity and to rates. 

 Chapter VII is the most unusual in a book of this scope. In it 

 is presented a valuable discussion of the methods of graphical 

 solution and approximation for numerical equations which do not 

 come under the standard rules of algebra and trigonometry. 



It is a book which merits the attention of teachers of Freshman 

 courses in colleges and technical schools. f. e. b. 



8. Space, Time and GravitaMon; by A. S. Eddington. Pp. 

 vii, 218. Cambridge, 1920 (Cambridge University Press). — 

 The author is one of the most prominent of the English pro- 

 tagonists of the relativity theory. The purpose of the book 

 is to expound the theory and its implications without the 

 use of much technical mathematics, but with strong empha- 

 sis upon the rightness of the author's view. The polemical 

 character of the book is evident in the introductory chapter which 

 is cast into the form of a dialogue between a physicist, a mathe- 

 matician, and a relativist, in which the physicist becomes some- 

 what involved in a metaphysical fog. 



The first three chapters are devoted to the Fitz-Gerald con- 

 traction and the geometry of the space-time manifold. The next 

 three chapters show how on the equivalence theory all the forces 



