CH. XVIII.] 



RADIO-ACTIVITY 



177 



becoming conducting, by ionisation from the shock 

 of the flying particles, and as a consequence pre- 

 venting the gold leaves from becoming charged. 



Radio-activity of Ordinary Materials. 



Even in the absence of radium, a charged electro- 

 scope is usually found to leak rather more than any 

 creeping along the supports can account for; this 



FIG. 22. Strutt's mode of demonstrating constant electric production 

 by radium. 



leakage must be due to ionisation of the atmosphere, 

 and a consequent kind of gaseous electrolysis in the 

 air. The ionisation is partly due to stray radiation 

 from outside, but some of it may be due to the 

 radio-activity of materials with which the interior 

 of the electroscope can be lined. Definite experi- 

 ments of this kind have been made by M'Lennan and 

 Burton of Toronto, and by Strutt, also by A. Wood, 

 Rutherford and Cooke. When cylinders of zinc, 

 tin, or lead were used to line the electroscope, a 



L.E. 



M 





