648 
MESSRS. W. SPOTTISWOODE AND J. FLETCHER MOULTON 
Another proof that the positive column marks an intense local demand for negative 
electricity is the attendant phosphorescence. We have already remarked upon this 
in Section XXI11. It assimilates the positive column to a line of centres of positive 
discharge. 
This seems to throw much light upon the meaning of the blank-space surrounding 
centres of negative discharge. It marks the area through which the centre of negative 
discharge is capable of exerting such an influence" as to prevent that intensity of 
demand for negative electricity arising or continuing, which is the condition of the 
existence of positive luminosity in that particular gaseous medium. We are not as 
yet able to define what is the nature of this influence, or how it is exercised, but there 
seems to us to be clear evidence of its existence. In this way we can understand the 
existence of the blank spaces between strise. They show the space which is, as it were, 
protected from intense need of negative electricity by the influence of the gaseous 
negative terminal composed of the hollow hazy surface of the next stria.t 
We have said that the positive column is like a line of centres of positive discharge, 
and it is attended by phosphorescence in high vacua, just as such a line of centres would 
be, supposing them to lie close along the surface of the tube. But the positive lumi¬ 
nosity can be attracted to the side of the tube by a wire connected with the positive 
terminal and passing along near the surface of the tube—the air-spark being, of course, 
in the positive. The true significance of this phenomenon is worthy of remark now 
that we know the exact meaning of the thin pencil-like column of positive luminosity. 
The course of reasoning given in Section XXIII. has shown that there is a continual 
discharge of negative electricity directed towards this positive luminosity from the 
surrounding portion of the tube, and that it is thus the locus of the centres of excita¬ 
tion throughout the tube. The presence of the wire parallel to and near the tube has, 
we see, the property of fixing this locus of centres of excitation on the side of the tube 
nearest to itself. Now we know that all that it can do is to excite by induction 
testablj the presence of a negative discharge from the angle of the wire. In other words, the presence of 
the positive luminosity at the angle had caused there so strong a local demand for negative electricity 
that it caused a discharge to take place from the angle; the remainder of the wire (although subjected to 
the general demand for negative electricity) that must exist throughout the tube only serving as a reser¬ 
voir from which the discharge was drawn. [July, 1880.] 
* It may be objected that inasmuch as the breadth of the blank-space ordinarily increases with the 
degree of exhaust, this hypothesis would make the extent of the negative influence greater in tubes of 
high exhaust than in other tubes : a result which seems startling in view of the enormously greater diffi¬ 
culty that electricity finds in passing through the former. But it must be remembered that it is much 
more difficult to produce luminosity in such tubes, and it may well be that this more than counteracts the 
other effect, and enables the influence of the negative terminal in preventing the formation of luminosity 
to extend through a greater range than in low vacua where a much less intense need suffices to cause it. 
t It will be understood that this is not intended to be a further explanation of the genesis or structure 
of strise and the blank spaces between them. It leaves the matter where it was left by our previous 
paper. It is only intended as an illustration of the application of the present theory of the blank-space to 
a particular and well-known case of its occurrence. 
