Manchester Memoirs, Vol. xlviii. (1904), No. 8. 5 



■experimental means employed in the detection of the new 

 invisible radiations. The last, which expresses the 

 intensity of the rays directly in terms of an easily 

 measured electrical quantity, has been developed by 

 Rutherford into an extremely accurate and convenient 

 method for the qualitative and quantitative study of the 

 property of radio-activity. 



It is a matter of remark how nearly the corpuscular 

 forms of radiation resemble the undulatory variety, as 

 ■exampled by the X ray. It furnishes a remarkable vindi- 

 cation of the insight of Newton into natural phenomena, 

 that, when the process he imagined light to be was dis- 

 covered three centuries after, it should have been first 

 taken for a different variety of light vibration. The 

 •a rays of the corpuscular class can only be differentiated 

 from the X rays of the wave class by the application of 

 the most powerful agencies and by the aid of the most 

 refined measurements the present century can command. 



Two years after the original discovery of radio-activity 

 in uranium, it was shown that the element thorium 

 possessed the same property to about the same degree. 

 In the same year Mme. Curie satisfied herself that these 

 two of all the known elements possessed the property, 

 but was led to suspect the existence of a new and 

 powerful radio-active element in the mineral pitchblende. 

 The latter often contains 80 per cent, of uranium oxide, 

 but it is several times more radio-active than either 

 uranium or thorium oxide in the pure state. After many 

 years' work in conjunction with M. Curie and M. Bemont, 

 in which the radio-activity furnished the necessary means of 

 tracing the new element, a minute amount of the latter in 

 the form of chloride was separated from pitchblende in the 

 pure state, and given the name radium. The proportion in 



