720 



SCIENCE. 



[N. S. Vol. XX. No. 517. 



state of our experimental knowledge of the 

 subject. 



The first chapter is a description of Mme. 

 Curie's now well-known researches upon uran- 

 ium and thorium compounds — researches 

 which led (1) to the discovery of radium, 

 polonium and actinium; and (2) to the an- 

 nouncement that radioactivity, whatever its 

 nature, was an atomic property. This last 

 announcement was based at first upon perhaps 

 rather meager evidence, but it has since met 

 with fuller and fuller confirmation. Never- 

 theless it still needs more complete*investiga- 

 tion. 



In the second chapter is found a descrip- 

 tion (which Madame Curie is of all persons 

 most competent to give), of the methods which 

 have been used in the separation from pitch- 

 blende of radium, polonium and actinium. 

 The chapter concludes with an account of 

 what is perhaps the most important work 

 which has come from the hands of Madame 

 Curie, viz., the determination of the atomic 

 weight of radium. Any one who is familiar 

 with the details of this work will be little in- 

 clined to credit the correctness of determina- 

 tions which lead to values other than 225. 



The third chapter deals with the nature of 

 the radiations from radioactive substances — a 

 subject in which Rutherford's experiments 

 first brought order out of confusion, but to 

 which the contributions of the Curies have 

 been of but little less importance. The proof 

 that the Beta rays impart negative charges to 

 conductors upon which they fall, and the in- 

 verse proof that the body from which these 

 rays emerge is left with a positive charge, 

 were first made by Mme. Curie. Again, the 

 study of the penetrating power of the Alpha 

 rays of poloni^im, in which the important dis- 

 covery was made that the fraction of the rays 

 absorbed by various media increases with the 

 thickness of the medium already traversed, 

 was made first by the Curies. It is very diffi- 

 cult at present to reconcile this discovery with 

 Becquerel's conclusion that the magnetic 

 deviability of the Alpha rays diminishes with 

 an increasing distance frona the source. The 

 third chapter contains also the important work 

 in which M. Curie demonstrated the ionizing 



action of radiura rays upon liquid dielectrics, 

 and showed that this action is wholly inde- 

 pendent of temperature. The chapter con- 

 cludes with a description of the heating and 

 luminous effects produced by radioactive sub- 

 stances — subjects in which the greater part of 

 the knowledge which we now possess has come 

 from the Curies. 



The last chapter, upon induced radioactivity, 

 is perhaps the least satisfactory of any in the 

 book to the student who is not already thor- 

 oughly familiar with Rutherford's work on 

 radioactive change, and on the nature of ex- 

 cited radioactivity ; for he will be likely to find 

 himself confused by a mass of disconnected 

 facts. Madame Curie is evidently not yet 

 completely converted to the disintegration 

 theory of radioactive processes. She therefore 

 adopts the conservative method of confining 

 herself in the main to a presentation of the 

 existing state of our experimental knowledge, 

 leaving to the last three pages of the book the 

 discussion of the various hypotheses which have 

 been advanced to account for the emission of 

 energy exhibited in radioactivity. Here she 

 presents briefly the four following hypotheses, 

 (1) Atomic disintegration of the radioactive 

 substances; (2) transformation of gravita- 

 tional energy; (3) absorption of some unknown 

 form of ether energy; (4) atomic disintegra- 

 tion of other substances induced by the pres- 

 ence of a radioactive substance. Although 

 she inclines less markedly than most of us 

 toward the first, a leaning in that direction is 

 nevertheless observable. 



R. A. MlLLIKAN. 



UNrvERsiTy OF Chicago, 

 October 19, 1904. 



International Catalogue of Scientific Litera- 

 ture. First Annual Issue — L — General 

 Biology. London, Harrison & Sons. 1903. 

 Pp. xiv -1-144. 



This branch of the ' International Cata- 

 logue of Scientific Literature ' is stated to 

 include the following: "(1) Literature dealing 

 with methods of work and investigation com- 

 mon to all branches of biologic science; (2) 

 Literature dealing with the morphology, de- 

 velopment or physiology of living organisms 



