Nipher—On the Nature of the Electric Discharge. 71 
Is the positive electrification of a body simply a surface 
effect? 
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 
IIT 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. 
