478 



Dr. H. A. Wilson on the 



It will be seen that in every case the current falls off 

 slowly with increasing distance between the electrodes. 



The fall of potential between the electrodes was examined 

 by means of a third electrode, consisting of a fine horizontal 

 wire which was put in between the disk electrodes and could 

 be moved along from one to the other. Its potential was 

 measured by means of a Kelvin's multicellular electrostatic 

 voltmeter. 



Fig. 2 shows the variation of the potential along the flame 

 obtained as just described. The distance between the disks 

 was 17*7 cms. and the P.D. used 550 volts. It will be 

 seen that there is a sudden fall of potential near each electrode 

 and a uniform gradient in the space between the electrodes. 



600 

 Volts. 











Fig". 



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Let W]_ = number of positive ions present per c.c. 

 n 2 = „ negative ,, „ ,, 



h 1 z= velocity of positive ions due to one volt per cm. 

 k 2 — „ negative „ „ „ „ 



X = electric intensity in volts per cm. 

 e = charge on one ion. 

 i = current density. 

 Then we have the well-known equation 



i = X<?(y( / " 1 ?i 1 + Jc 2 n 2 ) . 

 Where X is uniform n 1 = n 2 , so that i = Hen(k 1 + k 2 ). 

 According to this equation we should expect the current 

 through the flame to be proportional to the potential gradient 

 existing between the electrodes. To test this, two small 

 electrodes were put in the flame 0"5 cm. apart, and the P.D. 

 between them was measured by means of a quadrant electro- 

 meter. It was found that the P.D. between them was very 



