336 
MRS. H. AYRTON ON THE MECHANISM OF THE ELECTRIC ARC. 
far as it goes, confirms the conclusions to which I have been led by a theoretical 
consideration of the conditions. Since, therefore, all the principal phenomena of the 
arc but one, # with cored and with solid carbons alike, may be readily accounted for 
Length of Arc. 
Fig. 18. Suggested curves connecting 8V/8A with the length of the arc for a constant direct current 
without recourse to any such unusual attributes as a negative resistance, or even a 
large back E.M.F., it seems superfluous to imagine their existence without stronger 
proof of it than has yet been obtained. 
* The one exception is the fall of potential of some 8 to 11 volts at the junction of the negative carbon 
with the arc. This may be a true back E.M.F. 
