ON ELECTRICAL DISCHARGES THROUGH RAREFIED GASES. 
201 
that which passes into the tube moves synchronously from the interior of the tube at 
each ring of tinfoil, forms the bright shell or stria, and passes on to the next shell or 
stria; thus supplying the place of the positive pulse that the ring of tinfoil there has 
just sent on. The last shell passes its discharge to the negative terminal, and the 
first shell receives a discharge from the positive terminal. In this way a discharge 
passes through the tube identical in quantity and character to that which passes into 
it from the positive terminal. 
If, then, we are right in supposing that the series of artificially produced hollow 
shells are analogous in their structures and functions to strise, it is not difficult to 
deduce, from the explanation above given, the modus operandi of an ordinary striated 
discharge. The passage of each of the intermittent pulses from the bright surface 
of a stria towards the hollow surface of the next may well be supposed by its 
inductive action to drive from the next stria a similar pulse, which in its turn drives 
one from the next stria, and so on. Thus the processes in the naturally and artificially 
striated columns are precisely similar, save that in the case of the latter the 
pulses from the several strise are excited by induction from without the tube, 
while in the case of the former the induction is that of the discharge itself in its 
passage from stria to stria. The passage of the discharge is due in both cases to an 
action consisting of an independent discharge from one stria to the next ; and the 
idea of this action can perhaps be best illustrated by that of a line of boys crossing a 
brook on stepping stones, each boy stepping on to the stone which the boy in front of 
him has left. 
The truth of the foregoing theory is confirmed by the fact that it is not only by 
means of the positive special effect that we obtain formations analogous to striae, but 
we can also obtain them by means of the other special and relief-effects when the 
electrical actions are of such a kind as would lead us to expect them according to 
the theory here put forward. Take, for example, the positive relief-effect. When 
the pulses passing through the tube are positive and a finger is placed on the tube, 
the positive relief-effect so caused consists, under certain relations of quantity and 
tension in the discharge (and notably when the discharge is due to the action of a 
small, coil, as described on page 210, the negative terminal of the tube being put to 
earth), of a faint haze beneath the finger, and a large dark space extending right across 
the tube, and stretching for some distance from the spot on which the finger rests 
along the tube towards the positive end (Plate 18, fig. 16).'* The termination of the 
positive luminous column at the place where it abuts on this dark space, is bright 
with a sharply-defined rounded outline, like the bright head of a stria, excepting that 
instead of pointing centrally along the tube it is slightly tin-own upwards so as to 
point to the spot where the finger is placed. Here, again; we have a case in which 
* If the positive terminal be put to earth, the strise will be immediately beneath the fingers as in 
Plate 18, fig. 16 a, as should be the case. 
MDCCCLXXTX. 
