The Groundwork of the Universe, &c. 



51 



" rays " has been trapped and prevented from reaching the 

 electroscope. If a second sheet of paper is added, it is found 

 that the rate of discharge is unaltered, so it appears that the 

 first sheet of paper screened out entirely some constituent parts 

 of the ' rays," and that the part passing the paper ])enetrates a 

 second sheet just as easily as the first. 



Thin lead foil causes stoppage of much of the radiation which 

 passed the paper, but a second thin sheet has no further action. 

 A heavy lead block, however, cuts off all the " rays." Thus there 

 are three constituents : one which passes the paper but not the 

 lead foil, one which is stopped by the heavy lead block after 

 passing through the lead foil, and finally those "rays" which 

 failed to pass through even the paper. 



The component stopped by thin paper is called the Alpha- 

 ray, that stopped by lead foil after passing through the paper, 

 the Beta-ray, whilst the most penetrating component is the 

 Gamma-ray. 



To put the matter in the form of a diagram we have some- 

 thing like Fig. II as a representation of the experimental results. 



TISSUE PAPER. 



LEAD FOIL. 



LEAD BLOCK 



