564 MESSRS. W. SPOTTISWOODE AND J. FLETCHER MOULTON 
Page. 
Section XXVII.— General conclusions as to the electric discharge.—II. In vacuum discharges the 
durational character of the negative cos compared with the positive discharge increases with the 
degree of exhaustion and becomes very marled in extremely high exhausts. 
Contrast between positive and negative intermittence. 642 
Experiments with, the standard-tube and a supplemental ring .. 643 
Contrast between positive and negative intermittence in high vacua . 644 
Section XXVIII. —General conclusions as to the electric discharge .— III. On the positive column. 
Experiments with unipolar discharge of variable length. 646 
The range of visible action of the disconnected terminal. 646 
Luminosity indicates the presence of free positive electricity, and a local demand for negative . 646 
Action of an external wire connected with the positive (air-spark) terminal explained. 648 
Section XXIX.— General conclusions as to the electric discharge. — IV. Molecular streams. 
Comparison of molecular streams with discharge of lamp-black from negative terminal . 649 
Neither standard-tube nor telephone indicate any special electrical action at phosphorescent 
localities ..... . . 650 
The discharge proper appears to be independent, both in velocity and in direction, of molecular 
streams. 651 
The streams are probably connected with the starting of the discharge, but not with its ulterior 
course. 651 
Index to the references to the figures in the text. 652 
Introduction. 
In our previous paper we examined the essential conditions for the existence of 
sensitiveness in vacuum discharges, and found that sensitive discharges are produced 
by a rapid succession of discharges of free electricity from one or both of the terminals 
of the tube, each individual discharge being so small in quantity as to be instan¬ 
taneous.* The effects which are produced by the approach of a conductor to a tube 
containing a sensitive discharge were shown to be due to the fact that these individual 
or component discharges are composed of free electricity, either of a positive or of a 
negative kind, and that this free electricity during its passage through the tube 
exercises its ordinary static induction through the space around it; and this, com¬ 
bined with the sudden and instantaneous character of the component discharge itself 
and the consequent suddenness with which the free electricity appears in any part of 
the tube, produces impulsive electric action on the sides of the tube and in the space 
outside it, leading to instantaneous rearrangement of the electricity within the con¬ 
ductor and consequently to discharges from the side of the tube in its immediate 
neighbourhood, to which these effects are immediately due. 
While subsequent researches have confirmed us in our opinion as to the correctness 
of these conclusions, they have also brought home to us more fully the exact bearing 
which the examination of the sensitive discharge has upon the general theory of 
* It will be understood that the term “instantaneous” is not used in its strict sense of occupying 
absolutely no time, but in the sense of occupying so short a time that it may be neglected in comparison 
with the whole period between two discharges. 
