[mclennan-treleaven] residual IONISATION IN GASES 



117 



The theory of the Wolff elcetrometer has been given already 

 in the paper by McLennan and McLeod referred to above and it will 

 suffice here to give only the final formula: 



N = 1 • 03 ( AV- AVi) (1) 



for determining the number of ions generated within the air in the 

 electrometer per cubic centimetre per second. In this formula AV 

 is the loss in the voltage per hour of the electrical system with the tube 

 SiSi up and the ions coming to the system from the gas in the whole 

 of the chamber and AVi the loss in voltage per hour with the tube 

 SiSi down and the ions coming to the system from the volume of gas 

 enclosed by the tube, i.e., 31-5 c.c. 



III. 



FIRST INVESTIGATION. 



In the first set of experiments the gases used were air, hydrogen 

 and acetylene. The observations were made in the open at Bowland, 

 Scotland, in a hotel in London, England, on the Atlantic Ocean in 

 S,S, Megantic and in the Convocation Hall of the University of 

 Toronto, the last mentioned building being a new structure and one 

 into which no radium or other radio-active substance had been brought 

 hitherto: 



Table I. 



Ionisation of Gases. 



The readings taken at these various stations in the different 

 gases are recorded in Table I. Those at Bowland with hydrogen, 

 acetylene, and the mixture of methyl iodide and air were taken 

 in a hurry as the time available was short. The acetylene used 

 was taken from a private house supply and was carefully dried 

 before being used, the hydrogen was generated in an improvised 

 piece of apparatus from dilute sulphuric acid acting on granulated 



Sec. Ill, 1915—9 



