ON ELECTRICAL DISCHARGES THROUGH RAREFIED GASES. 
199 
IX .—On the nature of strice , and the artificial production of striation in the luminous 
( sensitive) discharge. 
We have seen that positive and negative pulses on the outside of the tube, 
co-periodic with the discharges that pass through it, cause the interior of the tube 
within the tinfoil to assume the character of positive and negative terminals respec¬ 
tively. The negative terminals so formed possess all the characteristics usually 
appertaining to terminals of such shape, but otherwise they do not give us any 
suggestions specially valuable for our present inquiry. With the positive terminals, 
however, the case is far different, as we shall proceed to show, taking as an example 
the special effect when the air-spark is in the positive circuit. 
We have seen that the positive discharge due to a ring of tinfoil forms a hollow 
cone with a sharply-defined luminous outer surface. This cone, if the nearest negative 
terminal is the negative terminal of the tube, passes into a column of diffused 
luminosity similar in all respects to the ordinary luminous column which starts from 
the positive terminal of a tube. But if there is another similar ring of tinfoil also 
connected with the positive terminal between the former ring and the negative 
terminal, the luminous column that starts from ring No. I is stopped by ring No. 2, 
and from this latter ring there starts a second hollow luminous cone which stretches 
away in its turn towards the negative terminal in a diffused luminous column as before 
described. If these rings be placed at the proper distance from one another, and the 
size and exhaustion of the tube be suitable, the short luminous column between the 
rings will dwindle down to a hollow cone with blunt rounded head, this head being 
greatly superior in brightness to any other part of the cone and stretching to a point 
close up to or even a little within the next ring, so that it is in the middle of the space 
enclosed by the hazy blue inside surface of the hollow cone that starts from that ring. 
And by using additional rings this can be made to repeat itself until the whole 
luminous column is segmented into these hollow luminous cones or shells with bright 
rounded heads. 
The theory which the authors of this paper desire to put forward is, that each of 
these luminous cones or shells is a perfect stria both in function and structure. The 
resemblance in appearance is most striking. In the luminous shells which we have 
just described there is the same convex bright outline pointing towards the negative 
terminal, and the same hazy blue ill-defined hollow surface turned towards the shell 
immediately behind or on the side towards the positive terminal of the tube, and there 
are the same dark intervals dividing consecutive shells as divide consecutive striae. In 
fact, this segmented discharge presents to us all the familiar phenomena of striated 
discharges in which the striae have rounded or conical forms. Moreover, the conical is 
not the only type of striae which can be successfully produced in this manner. It is 
equally possible to form flat or annular striae by proper adjustments of the air-spark 
interval, as explained in page 192. And as these are precisely the forms which natural 
