204 



PROFESSOR E. RUTHERFORD ON THE 



shown that the radium emanation is present in the atmosphere. This, in the course 

 of its disintegration, gives rise to the slowly decaying product, which will be deposited 

 from the air on the surface of all bodies exposed in the open. Such bodies will thus 

 be covered with an invisible film of radioactive matter of very slow rate of change. 

 The results of COOKE* are a strong confirmation of this point of view. By carefully 

 polishing the surface of a brass electroscope, he was able to reduce its rate of discharge 

 to almost one-third of the normal amount. In such a case the radioactive matter 

 was removed from the surface by the process of polishing. The strong radioactivity 

 observed in a room in which radium preparations have once been used, is probably 

 due to the deposit on the walls of the room of this slowly decaying matter from the 

 emanation. 



26. Comparison of the Clianges in tlte Radio-Elfnients. The changes occurring in 

 the three radio-elements and the radiations which accompany them are shown 

 graphically in fig. 15. The radiations from actinium have not yet been sufficiently 



_ 



Radium Emanation Radium A Rad.B Rad.C 



Pad. D 



Rad.E 



o 



Thorium Thorium x Emanation Thorium A Thor. B Thor. C 





O 



Uranium Uranium x Final Product 



Actinium Actinium x Emanation Actin. A Actin. B 

 ? 



Fig. 15. 



Actin.C 



examined to be certain where the y8 or y rays appear in the last change as in the case 

 of thorium. It will be seen that there are, at least, six successive changes in radium. 

 five in thorium, and two in uranium. The first five changes in radium are analogous, 

 in many respects, to the corresponding changes in thorium and actinium. Each of 



'Phil. Mag.,' August, 1903. 



