INDEXED. 



THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SEME 



JULY 1902. 



s- 



I. Comparison of the Radiations from Radioactive Substance s 

 By E. Rutherford, M.A., D.Sc, Macdonald Professor of 

 Physics, and Miss H. T. Brooks, M.A.,McGill University, 

 Montreal *. 



ALL the radioactive substances possess in common the 

 power of acting on a photographic plate and of ionizino- 

 the gas in their immediate neighbourhood. The intensity of 

 the radiations may be compared by means of the photographic 

 or electrical action ; and in the case of the strongly radio- 

 active substances by the power of lighting up a fluorescent 

 screen. Such comparisons, however, do not throw any light 

 on the question whether the radiations are of the same or of 

 different kinds. It is well known that such different types 

 of radiation as the short waves of ultra-violet light, Rontgen 

 and cathode rays all possess the property of producing ions 

 throughout the volume of the gas, lighting up a fluorescent 

 screen and acting on a photographic plate. None of the 

 radiations from the various radioactive substances show any 

 trace of regular reflexion, refraction, or polarization t. 



There are two general methods of differentiating to some 

 extent between the various types of radiations. 



( D By observing whether the rays are appreciably deviated 

 by a magnetic field. 



(2) By comparing the relative absorption of the rays by 

 solids and gases. 



* Communicated by the Authors. 



t A very complete and admirable account of radioactive substances by 

 Henri Becquerel and P. & Mme Curie is given in vol. iii. of the Reports 

 ■of the Congres International de Physique held at Paris, 1900. 



Phil Mag. S. 6. Vol. 4. No. 19. July 1902. B 



