645 
ON THE SENSITIVE STATE OF VACUUM DISCHARGES. 
in the positive than in the negative intermittence—for we know that this, like all 
the other phenomena of intermittence, depends on sudden changes of tension and not 
on the absolute tension at any moment. And if the impulsive change of tension is 
less violent with the negative than with the positive intermittence, it would seem to be 
a necessary conclusion that it is due to the more durational character of the former 
discharge. 
There is a cognate class of experiments which, when taken in connexion with those 
we have just described, adds very great force to the conclusions we propose to draw 
from them. If we try the special effects we shall find the characteristics reversed. 
While the positive intermittence which gave such very violent relief-action only gives 
very slight action at the tinfoil, the negative intermittence causes the most violent 
disturbances there. Just as previously in the case of the positive-relief, so now with 
the negative special; the sparks stream between the wire and the tinfoil if they are 
made to approach one another, while if contact is made the electricity streams from 
all the edges of the tinfoil in the most violent manner. This must, we think, be 
because the negative pulses that arrive at the terminal can only get relief there slowly 
by pouring into the tube. They therefore press with all their force at the tinfoil 
seeking and finding like relief, through the inductive discharges to which they give 
rise. And it is a considerable time before the rise of tension in the tube, rapid 
though it be, is capable of balancing this pressure of the negative from without in its 
endeavours to get relief either by entering the tube or otherwise.* 
We shall not dwell further on these experiments. It is difficult, we think, to 
accoimt for the phenomena they present in any other way than by accepting the truth 
of the theory that is given at the head of this section, viz.: that the contrast between 
the two types of discharge, as far as the time required for their emission is concerned, 
becomes greater as the degree of exhaustion increases. 
XXVIII. General conclusions as to the electric discharge. 
III. On the positive column. 
We purpose in the present section calling attention to some experiments which 
throw light upon the function of the positive column, and give us a clue to the action 
which is going on where it appears, and of which it is doubtless the result. A portion 
of the experimental evidence relating to this has been already given in Section XXIII., 
and has to some extent been interpreted there. We shall now give further evidence 
in favour of the views there advanced. 
* Lest it should be thought that these phenomena were due simply to the high resistance of the tube, 
we took a tube whose vacuum was so low (we estimated it at about 2 inches of mercury) that the resist¬ 
ance was even greater than in the high tension tubes. No perceptible difference was found between the 
sensations caused by discharges of positive and negative intermittence, nor in the sparking distance 
between the earth wire and the tinfoil. 
4 O 
MDCCCLXXX. 
