488 SCIENCE PROGRESS 



matter in a simple way before his readers, having been reminded of the 

 great Euler, who wrote a famous algebra addressed to his manservant. He 

 rightly thinks that there is advantage in explaining a complicated, if not 

 difficult, matter to untrained minds. He thinks that the subject-matter of 

 the book shows that the algebra of symmetric functions and an important 

 part of combinatory analysis are beautifully adapted to one another. But 

 perhaps the most difficult kind of writing is that which aims at putting 

 things as simply as possible ; and the author's task has therefore not been 

 as easy as the reader, who is gratified with his exposition, may think. That 

 he has succeeded in his task will be admitted by all. The book contains six 

 chapters : the first on the Elementary Theory of Symmetric Functions ; the 

 second Opening the Theory of Distribution ; and the remaining chapters 

 on further details of Distribution, 



PHYSICS 



Matter and Motion. By J. Clerk Maxwell. Reprinted with Notes and 

 Appendices by Sir Joseph Larmor, and with a new photograph of the 

 Author. [Pp. XV + 163.] (London: Society for Promoting Christian 

 Knowledge; New York : The Macmillan Co., 1920. Price 55. net.) 



In reintroducing this classical essay on the principles of dynamics, the editor 

 remarks justly that " as a reasoned conspectus of Newtonian dynamics, 

 generalising gradually from simple particles of matter to physical systems 

 which are beyond complete analyses, drawn up by one of the masters of the 

 science, with many interesting side-lights, it must retain its power of sug- 

 gestion, even though parts of the vector exposition now seem somewhat 

 abstract." The conspectus has been made more complete by the addition 

 of the chapter from Maxwell's treatise on Electricity and Magnetism " On the 

 Equations of Motion of a Connected System," and further by the editor's 

 appendix on the Principle of Least Action, 



Reissued during the stir produced by the confirmation of Einstein's 

 Relativity Theory, interest naturally focuses on those sections which relate 

 to the relativity of our knowledge of space and time. One cannot help feeling 

 that Maxwell, like most men of his day, had not resolved for himself the 

 contradiction between two lines of thought. He is careful to urge (§ 35) 

 that acceleration is relative and cannot be interpreted absolutely. On the 

 other hand, he describes in detail the ideal experiment of Newton's bucket, 

 and the practical one of Foucault's pendulum, as means of determining the 

 absolute rotation of the earth. While the human mind confessed itself unable 

 to conceive of permanent standards of direction, it appeared that Nature 

 did select from all the variety of conceivable standards one which fitted 

 best to the course of its happenings. 



At first sight, the new theory of Relativity, which is the subject of the 

 editor's first appendix, succeeds in resolving the paradox. But it may yet 

 be that the last word has not been said. In Einstein's theory, for example, 

 the specification of the field of gravitation is dependent upon the arbitrary 

 choice of the system of measurement. The mathematical quantities involved 

 serve, in fact, to define the relation of the system of measurement to the 

 sequence of natural phenomena. From this point of view the new law of 

 gravitation appears as a limitation upon the system of measurement which 

 the observer may use. The law in one form consists in identifying the 

 so-called " curvature of space-time " with the presence of matter. This is 

 only saying that some systems of measuring space and time fit on to our 

 observations of matter better than others. Or if we adopt the equivalent 

 form of the law as contained in the principle of least action, we have to 

 admit that in the long-run we have to choose our system of measuring so 

 as to make the action a minimum. 



