July 14, 1905.] 



SCIENCE. 



47 



ence. Abstruse ideas are left out just so far 

 as possible, and the work, although not phrased 

 in popular language, as we understand the 

 term to-day, is nevertheless very clearly and 

 readably written. Mr. Strutt has evidently 

 the faculty of presenting scientific facts in a 

 very pleasing and attractive and convincing 

 form. In short, he shows the stamp of the 

 teacher. 



Notwithstanding all the evident care of 

 preparation in the work, Mr. Strutt has once 

 or twice allowed himself to become careless in 

 the use of terms. For example, on page 66, 

 when treating the selfelectrification of radium, 

 he uses the term ' perpetual motion,' stating 

 that the above phenomena more clearly ap- 

 proach it than any other action we are ac- 

 quainted with. It seems to me that the term 

 is very wrongly applied, because perpetual mo- 

 tion means the performance of work without 

 the expenditure of energy ; and there certainly 

 is energy expended in the above phenomena. 

 Later on in the book (page 16Y) he states 

 that ' Nothing that we can do to any portion 

 of matter will in the smallest degree affect its 

 weight,' etc. This is rather too loose a state- 

 ment to let pass without comment. 



Chapter I. discusses some general state- 

 ments about the discharge of electricity 

 through gases, a subject that Dr. J. J. Thom- 

 son has so thoroughly investigated. The dis- 

 cussion of the cathode and Koentgen rays con- 

 tains descriptions of the various phenomena 

 connected with them. 



Chapter II, deals with the discovery of 

 radioactivity, the first portion treating of the 

 signal work of Becquerel, who discovered the 

 rays which bear his name, namely, those rays 

 which are given off by some salts, and which 

 have photographic properties, but which differ 

 from Eoentgen rays and also from ordinary 

 light. 



The discussion of the various phenomena 

 relative to uranium prepares the reader for 

 the story of the discovery of radium. Mr. 

 Strutt explains in an interesting and instruct- 

 ive manner the chemical procedure gone 

 through to make it possible to obtain radium 

 from pitchblende, a mineral in which was 

 discovered by Madame Curie a radioactivity 



far in excess of what was expected. This fact 

 led Madame Curie to conclude that there 

 resided in the mineral some other more active 

 constituent than uranium. 



In Chapter III. we have the properties and 

 nature of the radiations described together 

 with the fluorescent, chemical and physiolog- 

 ical effects. This is followed by a rather 

 complete discussion of the alpha rays, beta 

 rays and gamma rays, with several diagrams 

 illustrating experiments carried out to deter- 

 mine the deflection of the alpha rays and beta 

 rays. The experiments with gamma rays have 

 so far been negative. 



At considerable length in one of the chap- 

 ters is described the subject of radioactvity in 

 the earth and its atmosphere, a branch of the 

 work to which Mr, Strutt has contributed 

 rather extensively. Other chapters treat of 

 absorption and ionization; changes occurring 

 in radioactive bodies; the products of radio- 

 active change. 



The last chapter gives a short account of 

 the electrical theory of matter, to which Pro- 

 fessor J. J. Thomson has given much thought. 

 This chapter is very suggestive and supplies 

 food for contemplation. 



At the end of the book there are three ap- 

 pendices, the first of which contains a number 

 of experiments which any one may perform 

 with a bit of radium, A sufficient Amount of 

 radium necessary for these experiments would 

 cost in the neighborhood of twenty-five dollars. 

 With this appendix are given two plates. 



The other two appendices treat respectively 

 of the mathematical theory of the deflection 

 of the beta rays ; a short account of the ex- 

 traction of radium from large quantities of 

 pitchblende. 



The book is non-mathematical throughout, 

 except for the appendix mentioned, and shows 

 a keen insight into the subject dealt with. 

 This, however, is to be exi^ected from a man 

 who has done so much work in the realm of 

 radioactivity. On the whole, the book is to 

 be commended to those who are of a scientific 

 turn of mind, and who wish to understand 

 clearly the principal phenomena of radio- 

 activity. G. B. Obear. 



Peovidence, May 24, 1905. 



