CHAPTER V. 



THE BECQUEREL RAJS FROM RADIUM. 



This small amount of radium distributed among the 

 scientific workers in the field has been sufficient for the 

 elucidation of the properties of the Becquerel rays. 



LAW OF ABSORPTION. 



Their surpassing power of penetrating matter generally 

 considered opaque led to their discovery, as we have seen, 

 and it was therefore one of the first properties to be investi- 

 gated. It soon became evident that the power was quite 

 independent of the kind of matter through which they passed. 



It was influenced only 

 by the density of the 

 substance interposed. 

 Aluminum, for example, 

 being light in weight, 

 is to the Becquerel rays 

 what glass is to light 

 comparatively transpar- 

 ent. Lead, on the con- 

 trary, being heavy, 

 comparatively opaque 



Fig. 26. Radiograph showing how the 

 power of the rays to penetrate matter de- 

 pends on the density. The strips A , B 

 and C are platinum, aluminum and paper 

 respectively. It is easy to see that the 



IS 



platinum is penetrated least. 



As a matter of fact, they 

 obey the law of absorp- 

 tion, page 72 (Part III), and in this they resemble the cor- 

 puscles of the cathode rays (Fig. 26). 

 (96) 



