the Electrical Conduction produced by it. 



145 



Di stance of 



Uranium cylinder 



from L. 



T. 



Kate of leak in 



scale-divisions 



per minute. 



Calculated 

 rates of leak. 



d 



d+25 cm. 

 cZ+50 „ 

 d+100 „ 

 d+200 „ 



t 



t-\-\ sec. 

 *+2 „ 

 *+4 „ 

 '+8 „ 



*159 

 111 



* 87 

 62 

 39 



*159 

 112 



* 87 

 60 

 37 



In the third column are given the observed rates of leak, and 

 in the fourth column the calculated values. 



The values were calculated on the assumption that the rate 

 of recombination of the ions was proportional to the square 

 of the number present, i. e. that 



dn 

 dt 



— an' 



where n is the number of ions present and a is a constant. 

 The two numbers with the asterisk were used to determine 

 the constants of the equation. The agreement of the other 

 numbers is closer than would be expected, for in practice the 

 velocity of the blast is not constant over the cross-section, 

 and there is also a slight loss of conductivity of the gas due 

 to the diffusion of the ions to the side of the long tube. 



It will be observed that the rate of recombination is very 

 slow when a small number of ions are present in the gas, and 

 that the air preserves one quarter of its conducting power 

 after an interval of 8 seconds. 



§ 14. Velocity of the Ions. 



The method* adopted to determine the velocity of the 

 ions in Eontgen conduction cannot be employed for uranium 

 conduction. It is not practicable to measure the rate of re- 

 combination of the ions between the plates on account of the 

 very small after-conductivity in such a case ; and, moreover, 

 the inequality of the ionization between the two plates greatly 

 disturbs the electric field between the plates. 



A comparison of the velocities, under similar conditions, of 

 the ions in Eontgen and uranium conduction can, however, 



Phil. Mag. S. 



* Phil. Mag. Nov. 1897. 



5. Vol. 47. No. 284. Jan. 



1899. 



L 



