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MESSRS. W. SPOTTISWOODE AND J. FLETCHER MOULTON 
of these represents the actual means by which the electricity is propagated through 
the tube must be decided by other evidence. All that is claimed as following from 
these experiments is that the charge passes (disruptively) from the air-spark terminal 
m the shape of what we know as free electricity, and in such shape passes through 
the tube until it arrives at the other terminal and becomes neutralized by the opposite 
electricity that is awaiting it there. And this is shown conclusively by the identity of 
the relief-effect throughout the whole of the tube.* 
The cogency of these arguments will become more evident if we consider certain 
results obtained with an' arrangement which rendered the conditions of the two 
terminals of the tube electrically symmetrical instead of permitting them to be in so 
radically different electric conditions as is the case where an air-spark is used. 
If we take a coil giving rapid discharges of small quantity, we shall obtain a 
sensitive discharge. If the tube be symmetrical in figure, and the terminals as nearly 
alike as possible, then, on examination, we shall find that the sensitiveness is very 
slight in the centre of the tube and that it increases towards the ends. This is in 
marked contrast to the ordinary sensitive discharge hitherto described, which shows a 
sensitiveness gradually decreasing through the whole length of the tube as we pass 
from the air-spark terminal; and, moreover, the character of the relief-effects differs in 
the two portions of the tube. In the portion towards the positive terminal the effects 
are similar to those presented by a tube having an air-spark in the positive, while in 
the portion towards the negative terminal the effects are similar to those in a tube 
having an air-spark in the negative. The part of the tube near the centre, which 
shows little or no sign of sensitiveness, will be called the neutral zone. 
Nor is this the only peculiarity presented by this form of sensitive discharge. If 
we place a piece of tinfoil on the tube near to one of the terminals and coimect it with 
the nearer terminal we get a marked effect, wholly different from the to-earth or 
relief-effect. If, on the other hand, we connect it with the more distant terminal we 
get an effect which, though stronger and more marked in character, is decidedly of the 
type of the to-earth-effect. These peculiarities are in no way caused by the double 
current, as they are well marked when the break-current alone passes. 
These phenomena are easily explained by the supposition that owing to the 
* These conclusions, coupled with the experiments with the Leyden jar described in the last section, 
have a curious bearing on the question of the rival theories of electricity. So far as the authors of the 
present paper are aware, no attempt has ever been made to determine the sign of the electricity in the 
disruptive discharge. Hitherto if a Leyden jar charged with positive electricity was allowed to discharge 
itself into a neighbouring conductor, it was uncertain whether positive electricity passed from the jar to 
the conductor or negative electricity passed from the conductor to the jar, or whether both operations 
took place. The present experiments indicate a possible method of ascertaining in which of these ways 
the discharge actually takes place—at all events, when the disruptive discharge takes place in the modified 
form of a discharge through a vacuum tube. It would, however, be premature to assume that any such 
considerations as these would decide the vexed questions involved in the present electric theories until the 
matter has been much more thoroughly examined into than has as yet been the case. 
