ON ELECTRICAL DISCHARGES THROUGH RAREFIED GASES. 
185 
becomes flickering and unsteady, and ceases to be, in the proper sense of the term, a 
sensitive discharge. 
It appears, then, that we can pass continuously from the repulsion to the discharge 
form of the relief-effect in any one of three ways : 
(1.) By keeping the relieving system fixed at the same spot on the tube, and 
varying the completeness of relief, the discharge remaining the same ; 
(2.) By keeping the relieving system constant, and varying its position on the tube, 
the discharge remaining the same ; 
(3.) By keeping the relieving system constant and fixed in position, and varying 
the interruptedness of the discharge. 
It is probable that there is a fourth way, viz.: by varying the quantity of the 
discharge, all other things remaining the same. The only phenomenon bearing on 
this point at present observed is that when the condenser is allowed to run down, the 
discharge-effect appears where previously there had only been repulsion. This might 
be supposed to show that decrease of quantity tends to give the discharge-effect, but 
it is probable that the reverse is the case, and that the phenomenon in question is due 
to the increased interruptedness—the greatly longer period of the intermittence of the 
discharge—which accompanies the falling of the tension in the condenser, and which, 
as we have seen, would tend to give the discharge-effect. The importance of slowness 
of intermittence in giving the discharge-effect is shown by the fact that on working the 
coil with a very high-speed break the sensitive discharge thereby produced only gives 
repulsion-effects, while so great is the tendency of the coil discharge when a slower 
break is used to give the discharge-effect, that it will often appear in a luminous 
discharge when the condenser and coil are used under circumstances which, from the 
size of the air-spark, would lead us not to expect it, but will vanish when the coil is 
stopped and the condenser allowed to work alone; thus showing that its appearance 
was due to the pulsations of the coil making themselves felt in the discharge, and by 
their slowness and violence causing the discharge-effect in places where the more rapid 
and equable intermittence of the air-spark woidd not have produced it. No doubt 
some portion of the above effect is due to the greater violence of the coil pulsations, 
but on the whole it tends to support the other experiments which show that the 
discharge-effect is intimately connected with great interruptedness of current. 
It must not be thought that all tubes give both forms of relief-effect. So far as the 
observation of the authors of this paper has extended, all tubes give a repulsion-effect; 
but it is comparatively rare to find tubes which present both the forms. Speaking 
generally, the typical effect, especially with tubes of high resistance, is a repulsion not 
very great in amount. A further discussion of the signification of those forms of relief- 
effect will be necessary when we consider the analogues to them which exist in 
ordinary vacuum discharges. 
In accordance with what has previously been stated, when the air-spark is on the 
positive side, the same effects are obtained by connecting the tinfoil to the negative 
MDCCCLXXIX. 2 B 
