ON ELECTRICAL DISCHARGES THROUGH RAREFIED GASES. 
171 
that it simply produces intermittence in the discharge through the tube without 
interfering with it in any other way. 
Another method of producing a sensitive discharge is by the use of a very rapidly 
vibrating break, such as that described in a paper “ On Stratified Discharges ” * 
* The following is an extract from the paper in question:— 
“ In the stratified discharges through rarefied gases produced by an induction-coil workiug with an ordinary 
contact-breaker, the striae are often unsteady in position and apparently irregular in their distribution. 
Observations made with a revolving mirror led me to conclude that an irregular distribution of striae does 
not properly appertain to stratification, but that its appearance is due to certain peculiarities in the current 
largely dependent upon instrumental causes. 
“ Having reason to think that the defects in question were mainly due to irregularity in the ordinary 
contact-breaker, I constructed one with a steel rod as vibrator, having a small independent electro-magnet 
for maintaining its action. The natural vibrations of the rods which were tried varied from 320 to 768 per 
second; while under the action of the battery-current and electro-magnet they varied from 700 to 2500, or 
thereabouts, per second. The amplitudes of the vibrations were exceedingly small, in fact not exceeding 
•01 of an inch; and it is to this fact, coupled with the extreme rapidity and consequent decision of make 
and break, that I mainly attribute the steadiness of the results. 
“ With a contact-breaker of this kind in good action several phenomena were noticeable ; but first and 
foremost was the fact that, in a large number of tubes (especially hydrocarbons) the striae, instead of 
being sharp and flaky in form, irregular in distribution, and fluttering in position, were soft and rounded 
in outline, equidistant in their intervals, and steady in proportion to the regularity of the contact-breaker. 
These results are, I think, attributable more to the regularity than to the rapidity of the vibrations. And 
this view is supported by the fact that, although the contact-breaker may change its note (as occasionally 
happens), and in so doing may cause a temporary disturbance in the stratification, yet the new note may 
produce as steady a set of strife as the first: and not only so, but frequently there is heard, simultaneously 
with a pure note from the vibrator, a strident sound, indicating that contacts of two separate periods are 
being made; and yet, when the strident sound is regular, the striae are steady. On the other hand, to any 
sudden alteration in the action of the brake (generally implied by an alteration in the sound) there always 
corresponds an alteration in the striae. 
“ It is difficult to describe the extreme delicacy in action of this kind of contact-breaker, or ‘high break,’ 
as it may be called. The turning through 2° or 3° of a screw, whose complete revolution raises or lowers 
the platinum pin through '025 of an inch, is sufficient to produce or to annihilate the entire phenomenon. 
A similar turn in a screw forming one foot of the pedestal of the brake is enough to adjust or regulate the 
striae; and a slight pressure of the finger on the centre of the mahogany stand, apparently rigid, or even 
on the table on which the contact-breaker stands, will often control their movements. 
“ The discharges described above are usually (although not always) those produced by breaking contact; 
but it often happens, and that most frequently when the strident noise is heard, that the current produced 
by making contact is strong enough to cause a visible discharge. This happens with the ordinary as with 
the high break ; but in the latter case the double current presents the very remarkable peculiarity that 
the striae of one current are so arranged as to fit exactly into the intervals of the other; and, further, that 
any disturbance affecting the column of striae due to one current affects similarly, with reference to 
absolute space, that due to the other, so that the double column moves, if at all, as a solid or elastic mass. 
And this fact is the more remarkable if we consider, as is easily observed in a revolving mirror, that these 
currents are alternate, not only in direction, but also in time, and that no one of them is produced until 
after the complete extinction of its predecessor. And it is also worthy of note that this association of 
strise is not destroyed even when the two currents are separated more or less towards opposite sides of the 
tgbe by the presence of a magnetic pole. There seems, however, to be a tendency in that case for the 
z 2 
