THE 



POPULAR SCIENCE 



MONTHLY. 



MAY. 1905. 



PRESENT PROBLEMS IN RADIOACTIVITY.* 



By Professor K. RUTHERFORD, 



MCGILL UNIVERSITY. 



SINCE the initial discovery by Becquerel of the spontaneous emis- 

 sion of new types of radiation from uranium, our knowledge of 

 the phenomena exhibited by uranium and the other radioactive bodies 

 has grown with great and ever increasing rapidity, and a very large 

 mass of experimental facts has now been accumulated. It would be 

 impossible within the limits of this article to review even briefly the 

 more important experimental facts connected with the subject and, 

 in addition, such a review is rendered unnecessary by the recent 

 publication of several treatises f in which the main facts of radio- 

 activity have been dealt with in a fairly complete manner. 



In the present article an attempt will be made to discuss the 

 more important problems that have arisen during the development of 

 the subject and to indicate what, in the opinion of the writer, are the 

 subjects which will call for further investigation in the immediate 

 future. 



Nature of the Radiations. 



The characteristic radiations from the radioactive bodies are very 

 complex, and a large amount of investigation has been necessary to 



* Address given to the International Congress of Arts and Science, St. 

 Louis, 1904. 



t Mme. Curie, ' These presentee a la Faculte des Sciences,' Paris, 1903. 

 H. Becquerel, ' Recherches sur une propriete nouvelle de la mati&re,' Typographic 

 de Firmin Didot et Cie,' Paris, 1903. E. Rutherford, 'Radioactivity,' Cam- 

 bridge University Press, 1904. F. Soddy, ' Radioactivity,' Electrician Co., 

 London, 1904. 



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