N ipher—On the Nature of the Electric Discharge. 
two plates where in each gap of Fig. 1, the plates were 
exposed at the opposite terminal. Here we have over 
each film a negative outflow from the pin-head. In the 
negative line the outflow is from the pin-head, which is 
in communication with the machine. In the positive line 
it is an outflow from the grounded pin-head. This out- 
flow is induced by the copper plate below, which is in an 
exhaust condition. Franklin’s fluid has been drawn out 
of it. These discharge lines are also alike in character. 
These results might have been expected, if the ground 
connections in Fig. 1 were broken, and the lines were 
connected to form a circuit between the machine termi- 
nals. This result is similar to that described in the 
former paper? for the Crookes tube. 
It can hardly be claimed that these four photographic 
plates contain in themselves evidence that they are pro- 
duced by au outflow at one terminal of each gap, and by 
an inflow at the other terminals. Such plates have long 
ago been produced at the gap terminals of an electric cir- 
cuit, and they have not suggested such an explanation. 
But when it is known that the so-called positive discharge 
is an inflow of negative electricity, the plates themselves 
seem to be suggestive of such a condition. 
If both terminals in either of the gaps in the discharge 
lines of Fig. 1 be placed on the film of a photographic 
plate, the terminals of the two forms of discharge lines 
will unite with each other as should be expected if one is 
an outflow and the other an inflow. In such an exposure, 
a sheet of glass may be placed between the metal plate 
and the photographic plate. In the exposure of the four 
photographic plates thus far described, the spark gaps 
at the machine were between large knobs. No apprecia- 
ble brush discharges which could affect the film preceded 
the disruptive discharge. 
The exposure table was screened from external sources 
of light due to sparks at the machine. It was also wholly 
surrounded by a metal screen of wire netting, which was 
* These Trans. XIX, 1, p. 7. 
