1-22 Prof. E. Rutherford and Mr. S. J. Allen : Excited 





Observations made in a similar way, to determine the velocity 

 of the negative ion, were not very definite on account of 

 variations during an experiment. The results showed that 



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the velocity of the two ions was about the same, but it was not 

 possible to decide whether the negative ions move slightly 

 faster than the positive, as is the case for ions produced by 

 Rontgen and Becquerel rays in air. 



The results obtained for the velocity of the ions are only 

 approximate in character, but they point to the conclusion 

 that the ions produced spontaneously in the atmosphere travel 

 at about the same rate in the electric field as the ions produced 

 in air by Rontgen and Becquerel rays. In a recent determi- 

 nation Zeleny * has shown that the sum of the velocities of 

 the positive and negative ions, produced by Rontgen rays in 

 dry air, is about 3*2 cms. per sec. 



Variation of the Number of Ions in the Air. 



By noting the maximum current between the gauzes, an 

 estimate can be made of the number of ions per unit volume 

 present in the air drawn through. 



If A is the area of the cross-section of the cylinder, u the 

 mean velocity of the current of air, N the number of ions 

 per unit volume, the maximum current i observed by the 

 electrometer is given by i = A.u.'N,e 

 where e is the charge on an ion. 



* Phil. Trans. Koy. Soc. 1900. 



