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Scientific Proceedings, Roifal Dublin Society. 



to uranium and one to ionium. The weight of this particle of pitchblende is 

 about -roth of a gramme. If all its rays escaped freely at its surface, some 

 9,600 a rays would leave it per second, and the number of ions created in 

 the air per second would be about 960 millions. The diagram shows the 

 successive shells, as they could be formed in air, to natural scale. 



RADIUM c. 



We shall now pursue the study of radiant matter within the confines of 

 another branch of science — that which deals with the nature, origin, and 

 structure of tlie rocks. We gain this much by the transfer, that the invisible 

 effects we have just been endeavouring to picture to ourselves, as taking place 



