566 
MESSRS. W. SPOTTISWOODE AND J. FLETCHER MOULTON 
local tension at the terminal and pass through the tube in the shape of free electricity 
until they meet with and are neutralised by discharges of an opposite kind, which 
usually happens at the opposite terminal of the tube. This passage through the tube 
is not instantaneous, though it is extremely rapid ; and the portion of the tube in 
advance of the discharge is in a state of electric emptiness (or approximately so) while 
that behind the discharge is filled with the free electricity of the discharge—the dis¬ 
charge spreading out like a pair of lazy tongs and not passing through the tubes in a 
compact form like a bullet. 
The question of the nature and formation of striee will not here be again discussed; 
for, in addition to the fact that the explanations given in the previous paper exhaust 
the subject so far as the authors are at present able to deal with it, the high vacua 
with which we shall chiefly have to do are not suited to the production of striated 
discharges. The ideas of positive luminosity and negative dark space will, however, be 
just as important in this investigation as in the former one, for they are the funda¬ 
mental elements of all vacuum discharges. 
It will be observed that we adhere throughout to the language of the two-fluid 
theory of electricity. This is done because it not only suffices for our purposes, but 
is the one that is most naturally suggested by the phenomena. But it must be borne 
in mind that this is by choice, and for the purposes of clearness and convenience only, 
and not as expressing any scientific conclusion as to the theory which ought to be 
preferred. We are not yet sufficiently advanced to be able with any profit to 
consider the merits of the rival theories. 
XIV. —On the effect of intermittent inductive action of an impulsive type upon 
continuous vacuum discharges. 
The discharges treated of in our former paper were discontinuous ; and the influences 
whereby the “special” and “relief” effects were produced were more or less directly 
the outcome of the intermittence of the discharges themselves. In the present section 
we shall deal with phenomena produced in a different manner. The discharges 
operated on will be in themselves continuous (using that term in the same sense as in 
our former paper, i.e., as equivalent to non-sensitive), and the effects will be produced 
by electrical influences being brought to bear upon them which are due to the 
intermittence of a wholly distinct electrical system. 
The arrangement ordinarily used by the authors for the purpose of examining the 
phenomena described in this section consists of two large Holtz machines, in one of 
which there are twelve revolving plates of ebonite, and twelve fixed plates of glass, 
and in the other there are six such plates (Plate 25, fig. 1). The discharge from the 
larger machine is made to pass through a tube of moderate vacuum, say about 
2 millims. pressure, care being taken that no air spark is interposed at any place in 
the circuit, so that the discharge is neither intermittent nor sensitive. A narrow slip 
