110 Prof. Rutherford on Excited Radioactivity and 



previously shown that the amount of excited activity in the 

 central rod, when diffusion alone is acting, is '14 of the total; 

 for in cases where the carrier is only able to travel over a 

 small fraction of the distance between the electrodes during 

 a half alternation, only a small amount of the excited radio- 

 activity on the central rod is due to the deposit of positively 

 charged carriers by the electric field. The greater proportion 

 is due to the diffusion of carriers to the electrode and to the 

 carriers which are deposited when the central rod is the 

 anode. The amount of this latter is, as we have shown, 

 about five per cent, of the total. It is difficult to make more 

 than a rough estimate of the amount of excited activity on 

 the electrode in the various cases. For these reasons the 

 corrected values of p in the table for the frequencies of 34 

 and 47 per second are probably not more than about one- 

 third of the observed value '16. 



In the above table a rough correction is made for some of 

 the values of p and the resulting velocity calculated. 



It will be seen that the values of the velocity of the carrier 

 lie between 1*0 and I'D cm. per sec. for a potential-gradient 

 of 1 volt per cm. This is about the same range of values as 

 that obtained for the carrier of thorium excited radioctivity. 



From the nature of the results it is not possible to definitely 

 decide whether the carriers of thorium and radium excited 

 activity travel at exactly the same speed. The results, how- 

 ever, indicate that the carriers in the two cases are not very 

 different in speed, and that consequently they do not differ 

 much in size. 



We may conclude from these experiments that the greater 

 part of the excited radioactivity from both thorium and 

 radium compounds is due to the deposit of positively charged 

 carriers, produced from the emanations on the cathode, and 

 that these carriers travel at about the same rate as the positive 

 ion produced in the air by Rontgen rays. 



When no electric field is acting excited radioactivity is 

 transferred by the diffusion of these carriers to the surface of 

 all bodies immersed in the emanation. 



§ 9. Origin of the Carriers. 



Before discussing the question of the method of production 

 of these positive carriers which cause excited activity, a brief 

 resume is necessary of the physical properties of the ema- 

 nations from thorium and radium. In the first place the 

 emanations behave in al] respects like radioactive gases of 

 high molecular weight. They do not carry with them any 



