Nipher — On the Nature of the Electric Discharge. 71 



Is the positive electrification of a body simply a surface 

 effect 1 



The phenomena described in this and the preceding- 

 paper seem to indicate that the main function of the 

 positive ions, in spark discharge, is to serve as stepping 

 stones of a somewhat unstable character. The anode wire 

 is found to be very effective in converting the air mole- 

 cules into a condition which makes the air a conductor of 

 the discharge. Such an anode wire is absent in the ar- 

 rangement of discharge circuit shown in Plate II of the 

 former paper. (No. 1 of Vol. XIX.) The results in the 

 present paper suggest that there may be a convection dis- 

 charge from the negative glow along that negatively 

 charged wire. This convection discharge is into a Fara- 

 day dark space, with no positive column beyond. In the 

 device of Plate III of the former paper, the positive 

 column is supplied through the agency of the grounded 

 point below the photographic plate. 



In the discharge between the wire and the grounded 

 point below the photographic plate, represented in Plates 

 III and V of the former paper, the photographic plate 

 takes the place of the metal plate in the cases discussed 

 in the present paper. In Plate III, the film is in the 

 negative glow, and facing the cathode. In Plate V it is 

 in the positive or luminous column, and facing the anode. 



In closing, a suggestion which may have practical im- 

 portance may be made. It seems probable that the dan- 

 ger of puncture of X-ray tubes may be materially dimin- 

 ished by grounding the cathode through a wet string 

 resistance. This would result in draining Franklin's 

 fluid through the tube, instead of forcing it through under 

 pressure- 



