O. N. Rood on the Electric Spark. 363 
sitive plate was developed with pyrogallic acid as usual, when it 
was found that pictures of the path of the spark had been tr 
This path was very often not continuous from one electrode to 
the other, sometimes there were two or even three breaks in it, 
while it often happened that the discharge from the positive was 
not in line with that from the negative electrode. See figures 2 
and 3, which are enlarged $ 
and 5 diameters. 
With a microscope magni- a etl 
fying 20 diameters I have 
err 
tions in the electric spark when dis- 3. 
charged freely in the air. OO 
. _ We are therefore led to conclude 
that it is probable that the photographic figures are traced mainly 
y the luminous particles just before their departure for the op- 
posite electrode, and if any effect is to be ascribed to luminous 
particles coming from the opposite electrode, it is only that of a 
diffused and faint blackening of the plate. Luminous material 
particles are here spoken of because it is held, (as Pliicker very 
properly insists,)' that electric light existent by itself is a fiction. 
In all his experiments with the Leyden jar, Feddersen found 
that the discharge proceeded simultaneously at each electrode, 
positive electricity starting from the positive and traveling to- 
ward the negative electrode, while at the same exact instant of 
time negative electricity started for the positive electrode. This 
1s also known to hold good with voltaic electricity, and there 
Seems to be no reason why it should not also be true with the 
induction coil, so as to render applicable to the induction spark 
the results obtained with the Leyden jar or electric machine. 
The following set of experiments on the induction spark was 
undertaken at the suggestion of Dr. W. Gibbs 
o 
__ his was in order to make a comparison of the figures obtained 
with those previously secured in using frictional electricity. 
The plates were sensitized as described in my first communica- 
_ two insulated metallic points were fastened at varying distances 
 Pogg, Ann., Bd. exiii, 274. 
