ir2ti ] 



JjIX. On the Method of Transmission of the Excited Activity 

 of Radium to the Cathode. By Walter Makower, B.A., 

 jB.Sc; John Harlina Research Fellow in the University of 

 Manchester* . 



1. Introduction. 



IT has Ijeen shown by Rutherford f that when a negatively 

 charged rod is exposed to the emanation from thorium 

 in a closed vessel, the quantity of excited activity deposited 

 upon the rod in a given time is independent of the pressure 

 of the gas with which the emanation is mixed as long as this 

 pressure exceeds a certain value, but that below this limit 

 the quantity of excited activity deposited on the negative 

 electrode diminishes, at first slowly, and then more rapidly, 

 as the pressure of the gas is reduced. 



This phenomenon gives reason to suppose that at the 

 moment of its formation the excited activity is uncharged, 

 and that it is only by some subsequent secondary action upon 

 the gas in which it is produced that it acquires the positive 

 charge in virtue of which it is carried to the negative elec- 

 trode. It was with a view to investigating the nature of 

 this secondary action that the present experiments were 

 undertaken. 



No experiments regarding this point seem as yet to have 

 been carried out with radium emanation ; for this reason, 

 and on account of the rapid rate of decay of thorium emana- 

 tion and the consequent inconvenience of working with this 

 substance, radium emanation was employed in the present 

 research. 



The variation with pressure of the amount of excited 

 activity deposited in a given time on a negatively charged 

 rod when exposed to a constant quantity of emanation was 

 carefully investigated, and it was found that at low pressure 

 the excited activity deposited on the rod depended, not only 

 on the pressure of the gas, but also on the distance between 

 the positive and negative electrodes. 



As the result of some preliminary experiments it was ehown 

 that the activity acquired by the rod was independent of the 

 difference of potential between the electrodes over a con- 

 siderable range. In these experiments a potential- difference 

 of about 60 volts was used throughout. 



* Communicated bv tlie Physical Society, 

 t Phil. Mag. [5] yol.'.xlix. (1900). 



