the Radiations from Radioactive Substances. 15 



This radioactive material is always associated with a positive 

 charge and so can be concentrated on the cathode in a strono- 

 electric field. 



A fuller discussion of the connexion between emanations 

 and excited radioactivity, and the method of transmission of 

 the latter, is reserved for a later communication. 



Some experiments were made which illustrate the quanti- 

 tative connexion between the rate of production of ions on 

 the excited body, and the rate of production of ions by the 

 emanation itself. Fig. 6 shows the general arrangement of 



Fig. 6. 



I *— *-!*- 



the experiment. The radium was placed inside a platinum 

 tube T through which a slow current of air was passed into 

 the testing cylinder C. The platinum tube T was heated by 

 a gas-burner until a large supply of emanation was carried 

 into the testing cylinder with the current of air. The openings 

 of the cylinder were then closed, and by means of the electro- 

 meter, the ionization current was observed between the outer 

 cylinder and the brass rod D fixed centrally along the axis of the 

 cylinder. A strong electric field (P.D. 300 volts) was applied 

 and the excited radioactivity concentrated on the central rod. 

 After several hours' exposure the amount of excited radio- 

 activity on the rod reaches an approximate maximum. The 

 rod was then removed and placed in a testing cylinder of the 

 same dimensions, with the same P.D. between electrodes. 

 The rate of leak was observed with the electrometer. A 

 fresh rod was immediately placed within the emanating 

 cylinder, and the rate of leak observed as soon as possible. 

 This rate of leak is a measure of the number of ions produced 

 by the emanation in the surrounding gas. 



For radium (e) the rate of leak due to the excited radiation 

 was about -J of that due to the emanation. For radium (c) 

 the ratio was as high as | after a long exposure. Since half 

 the energy of the excited radiation in the rod is absorbed in 

 the rod itself, the rate of production of ions due to the excited 



