﻿776 Repulsive Effect upon Poles of Electric Arc. 



As 



we have 



0<a<l, 



i<§; ....... (9'> 



and putting v = 400 cm./sec, I = 8 amp.= 0*8 E.M.U., 

 P == 1*43 dyne (Table II.), the ratio e/fi for the positive 

 particles issuing from the anode results : 



-<225E.M.U. 



I£ onlv a half of the observed P is due to recoil, — ^ 500. 



ft — 



The value e/ft being 9580 for hydrogen atoms, becomes 



9 = 740 for carbon atoms if carrying one elementary 



charge. Then the range 255 (or 500) does not conflict with 

 the values theoretically admissible. 



It may be observed that the meaning of values e/jjL less 

 than the theoretical is that carbon particles on starting from 

 the crater are not fully disintegrated and ionized. 



Holding a different point of view, Prof. Tyndall lias also 

 reached the conclusion (loc. cit.) that the observed pressure P 

 can be best accounted for as a recoi] by departure and by 

 impact of carbon ions. The electrons, probably, contribute 

 very little to the mechanical pressure P. 



Summary. 



The experiments of Duffield, Burnham, and Davis with 

 carbon-carbon arc are generally in a good agreement with 

 mine. The main results are : 



1. In the electric arc there is a repulsive effect upon the 

 poles, increasing with the current. The range of P is less 

 than 10 dyne with currents up to 20 amp. P does not vary 

 much with the arc-length L, except when L = -^-0, when P 

 becomes evidently greater. 



2. The carbon quality has a great influence on P. It seems 

 that metallic salts cause an increase in the pressure on the 

 cathode and diminish that on the anode (S.). 



3. With uncored carbons the repulsion on the cathode 

 appears smaller than that on the anode. On the contrary, 

 the specific pressure p per unit crater surface is greater on 



