ON ELECTRICAL DISCHARGES THROUGH RAREFIED GASES. 
221 
ceased to need it. In other words, the discharge is like a pair of lazy tongs and not 
like a bullet; and if we remember that we saw reasons for coming to the conclusion 
that the discharge was produced by action at the air-spark terminal and was almost 
independent of the condition of the other terminal, we see a sufficient reason why the 
discharge should be as we have found it to be. As each kind of electricity repels its 
like, there is every reason why the pulse should extend itself throughout the tube, and 
it is not easy to conceive any action that should make it pass through the tube in a 
compact mass like a bullet. This theory would also account for the observed fact that 
the relief-action is more violent near to the air-spark terminal than at a distance from 
it. With the special effect it is not so—indeed, the effect is feebler the nearer we are 
to the air-spark terminal—and this also is, as we have previously remarked, in full 
accordance with the above theory, inasmuch as it is natural that the effect of the 
external pulses should be less marked in proportion as the conflicting action within 
the tube is more powerful and commences more immediately after the special action 
commences. 
To check the correctness of the conclusions arrived at in this section, it may be well 
to contrast the results above described with the analogous results obtained from a coil 
discharge where there is a neutral zone. According to theory, the nature of the relief 
required in such a case is different upon opposite sides of the neutral zone. Hence it 
should be possible to give complete relief to a part of the tube on one side of the 
neutral zone by connecting it with tinfoil placed on the tube at a suitable spot on the 
other side of the neutral zone. This is found to be the case, and further, it is found 
that the two corresponding spots approach and recede from the neutral zone together. 
Moreover, if a long slip of tinfoil be placed on the tube extending from end to end it is 
found that there are relief effects all along it, though of course they are of opposite 
types on opposite sides of the neutral zone, and that a very slight change is caused by 
connecting the strip of tinfoil to earth, showing that the demands of the two portions 
of the tube are well nigh complementary. And further, although the experiment is 
difficult to try in such a way as to leave no doubt as to the result, it has been several 
times observed that the effect of connecting a piece of tinfoil (which is connected to 
earth through a telephone) near one terminal of a tube containing such a discharge 
with a piece near the other is to lessen the sound instead of increasing it, thus showing 
that the electrical wants of the two pieces are opposite in character; and in further 
confirmation of this we may refer to the experiment described on page 212, which in 
a more marked and obvious way exemplifies the fact that the electrical wants of 
pieces of tinfoil on opposite sides of the neutral zone are of opposite signs. 
Concluding remarks. 
Having thus examined the sensitive state of vacuum discharges, and ascertained the 
special cause to which their sensitiveness is due, and also the way in which that cause 
