96 Prof. Rutherford on Excited Radioactivity and 



potential is placed in a closed metal vessel containing a thorium 

 or radium compound the excited radioactivity is confined 

 almost entirely to the negative electrode. If the wire is 

 charged positively, it remains inactive, but the excited radio- 

 activity is produced on the walls of the vessel. 



When no electric field is acting, excited radioactivity is 

 produced on the surfaces of all bodies in the closed vessel, 

 independently of their being good conductors or insulators. 



In previous papers the author has shown that there is a 

 direct connexion between the presence of the radioactive 

 emanation from thorium and radium and the production of 

 excited radioactivity. It will be shown in this paper that the 

 production of excited radioactivity is one of the properties of 

 the emanation from thorium and radium. This excited radia- 

 tion is caused by the deposit on the surface of bodies of 

 radioactive matter, w-hich is transmitted by positively charged 

 carriers travelling through air in an electric field with about 

 the same velocity as the positive ion, produced in air by 

 Rontgen rays. 



§ 2. — Connexion between Excited, Radioactivity and 

 Emanation. 



In a previous paper (Phil. Mag. Jan. 1900) I have showm 

 that thorium compounds continually give off a radioactive 

 emanation. This emanation loses its radiating power rapidly, 

 falling to half value in the course of one minute. Dorn 

 showed later that radium also gave off an emanation, especially 

 w-hen heated. This emanation decayed much more slowly 

 than that from thorium. In some experiments where the 

 radium emanation, mixed with air, was kept in a closed metal 

 vessel, I have found that the activity of the emanation fell to 

 half value after standing several days, but was quite appreci- 

 able after a month's interval. 



These emanations from thorium and radium behave in 

 all respects like radioactive gases or vapours. They diffuse 

 rapidly through gases and through porous substances like 

 paper, but unlike the gaseous ions which they produce in 

 their path, pass through plugs of cotton wool, and bubble 

 through solutions with no appreciable absorption. In a more 

 detailed investigation (Rutherford and Soddy, Phil. Mag. 

 Sept. 1902) it has been shown that the thorium emanation 

 behaves like an inactive gas, and that its activity is not 



Physicists. I have avoided using the latter term, as to my mind, it 

 conveys the idea that the effect is in some way due to an action across 

 the medium : while the experiments in this paper show conclusively that 

 excited radioactivity is transmitted by means of a convection of positively 

 charged carriers. 



