376 O. N. Rood—Nature, etc., of the Discharge of a Leyden Jar. 
The combination of the aureol or violet discharge with the 
multiple sparks, is, I think, to be explained thus: the first 
spark heats and rarefies the air between the electrodes; if then 
the electric current is furnished with sufficient rapidity by the 
coil, the tension of the electricity in the jar may rise sufficiently 
for a discharge through the rarified air before it can cool down, 
and thus produce the violet light. This state of things would 
continue till the electricity began to be furnished more slowly 
by the coil, when it would result that, the air between the elec- 
trodes having time to cool down would no longer permit the 
electricity to pass through it in an unbroken stream, but wou 
ompel it to discharge itself in sparks. According to this idea 
the successive sparks ought to be separated by a gradually 
increasing interval, and this indeed appears to be the case, the rise 
of the separating interval being particularly strongly marked 
toward the close of the total act. Brass balls favor this mixed 
form of discharge, perhaps, by confining the air to a certain 
extent, and thus preventing it from cooling down. Platinum 
points can have no such influence, and with them this pheno- 
menon is rare. With the larger jar it never occurred, as the air 
was always able to cool down before the electric tension had 
sufficient time to rise in its larger surface, so as to warrant a 
discharge. With the small jar and longer striking distances, 
the violet light was not produced for an analogous reason, and 
also perhaps because the air was less confined. 
described in the second part of this paper, this violet light He 
lass, and the use of a lens of vastly larger angular aperture. 
he large number of sparks (15 or 20), given by the small 
ter 
to dispense with arrangements for controling the moment 4 
to 
olv- 
ant 
I will also call the attention to the circumstance that yer 
Le : . : 
