ON ELECTRICAL DISCHARGES THROUGH RAREFIED GASES. 
223 
therefore, of either of these important features alike leads us to the conclusion that 
the essentials of the discharge of electricity through rarefied gases are the same whether 
the discharge be interrupted, uninterrupted, or wholly discontinuous, and perhaps 
alternate, as in the case last mentioned. 
Now the simplest, and indeed the only obvious explanation of this result is, that the 
character which was found to be fundamental in sensitive discharges, viz.: disruptive¬ 
ness, is common to both kinds of discharge; and that the difference between the two 
kinds is to be sought in the scale on which that character is displayed.* In both dis¬ 
charges each terminal pours forth its electricity to satisfy its own needs, and only in a 
very secondary degree to satisfy the needs of the opposite terminal. The one terminal 
does not feel the electric state of the other directly, as would be the case were they 
metallically connected, but pours forth its electricity in the shape of free electricity, 
and leaves it to wander at its own will in that shape. If these matters could be 
demonstrated conclusively-—in other words, if it could be shown that all disruptive 
discharges are discontinuous, and that the appearance of continuity is, in the case of 
the ordinary discharge, solely due to the extreme rapidity with which consecutive 
pulses follow each other, and the correlative fact that each individual pulse is of 
extreme minuteness, a great step would be gained in our knowledge of the nature of 
electric discharges ; and though this is not to be hoped for at present, we trust that 
the results recorded in this paper add considerably to the evidence in favour of them, 
and we shall now proceed to indicate the considerations which have led us to this 
conclusion. 
In the first place it is undeniable that all the phenomena of vacuum discharges, and 
especially the terminal phenomena, may be presented by discontinuous discharges, 
each individual member of which is wholly independent of those before or after it, so 
that we may say that they may be produced by single instantaneous discharges. And if 
the circumstances be such as to produce considerable regularity in the successive 
discharges, we shall have all the characteristic phenomena of the steady uninterrupted 
discharge presented by them. Hence the idea of continuity of discharge is not 
necessary to account for these effects. Nay, further, we can show that a continuous 
displacement of electricity from the surface of a body will fail to produce these effects 
when a more rapid displacement (of an equal amount) will produce them. In the 
experiment given on page 170 it is found that, if the wire to the outside of the tube 
comes from the positive terminal of the machine, the appearance within the tube is of 
a negative terminal and vice versd. Now, as the action must necessarily be alternate 
within the tube, there must be as great a discharge of positive electricity during the 
one part of the process as there is of negative during the other. The only difference 
is that the one occupies only the time required for a spark to pass between the 
* To tliis we must add the restriction that, in the case of the ordinary discharge, the discontinuous 
pulses in which the electricity leaves the terminals must be very minute, a condition which is almost a 
corollary from the greater rapidity of intermittence in that discharge. 
