Nipher—On the Nature of the Electric Discharge. 17 
This figure also shows fainter images of the glass fibers 
in the position they had been in on a still earlier exposure, 
the hard rubber frame on which the fibers were mounted 
having been turned end for end. In these exposures the 
holder was placed between two plates acting as a con- 
denser, and 100 spark discharges were sent across a 30 
em. spark gap in parallel with the condenser. A shadow 
image of the hard rubber frame is also visible. 
These sources of disturbance having been discovered 
the angle wires were surrounded by black curtains in 
order to protect the photographic plates from the light 
due to the sparks at the machine, and the plates were 
then exposed directly to the wires at the angles. The 
plates were supported on insulating supports at their 
outer lateral edges. Below the plates was a layer of air, 
separating the plate from the sheet of glass serving as a 
table top. It was then found that the films exposed to 
the angles in the positive line were acted upon as quickly 
as those in the negative line. It was finally learned that 
this result was due to negative discharges from the films 
to the positive wire, and that it was not a fogging of the 
film by a discharge from the wire to the film, as was ap- 
parently the case when the film was protected by the hard 
rubber holder. Fig. B of Plate X shows such a result. 
Here the limiting effect of pencil marks on the film is 
shown. Fig. C of Plate X shows a similar limitation of a 
discharge from an angle in the negative line. Here the 
negative leakage is outward from the discharge wire, 
while in Fig. B the flow is inward towards the positive 
discharge wire. In both eases the discharge lines or 
fogged areas on the film begin to form immediately below 
the wire, and elongate outwards, as has been explained. 
It was this experience which led to the results given in 
Plates I, IJ, IV and V, which have been previously ex- 
plained. 
Some work has been done on the momentum effects 
around the angles in the negative line, with plates uncov- 
