224 Prof. Rutherford on D3p2nien.ee of the Current through 

 Since A 2 is very small compared with ad y 



or 





and i x __ 9V 2 



Kx 32rf* 



Similarly, if the plate is charged negatively and i 2 is the 

 corresponding current, 



h , 9V 2 

 K 2 327rrf 8# 

 Therefore *i _ Ki , 



i 2 K 2 ? 



or the currents are directly proportional to the velocities of 

 the ions. 



If the condition of very intense ionization at the surface is 

 fulfilled, so that the potential-gradient is very small near the 

 surface, the following results must hold : — 



(1) Currents in the two directions vary directly as the 

 velocities of the ions. 



(2) Current varies as the square of the P,D. 



(3) Current varies inversely as the cube of the distance 

 between the plates. 



(4) There is a limiting current for a given P.D. which 

 depends only on the distance apart of the plates and the 

 velocity of the ions, and is independent of the ionization at 

 the surface, provided it exceeds a certain value. 



These results must hold, whether the ionization is produced 

 by the agency of flames, glowing bodies, Rontgen-rays, ultra- 

 violet light, or any other means of producing intense ionization 

 near the surface of an electrode. 



When this investigation had been completed and was ready 

 f >r publication, a paper by C. D. Child appeared in the 

 4 Physical Review 9 for March. In the paper Child fully 

 develops this same equation in order to utilize it for the 

 purpose of measuring the velocity of ions drawn from flame- 

 gases. 



I had also independently concluded an experimental inves- 

 tigation in order to verify the theory, where strong surface- 

 ionization was produced at the surface of a plate heated by 

 the electric current. These results, which amply confirm the 

 theory, will be published shortly. 



Child's results show clearly that, using a flame as a source 



