174 
MESSRS. W. SPOTTISWOODE AND J. FLETCHER MOULTON 
tively slow break is used. Some observations were published (“ On Stratified Dis¬ 
charges, II.,” Proceedings of the Poyal Society, May 18, 1876) by one of the authors of 
this paper, relative to the appearance of the coil discharge when viewed in a large 
revolving mirror moving through one revolution between each contact made by the 
break,The rapidity with which the contacts followed each other was necessarily 
slow in comparison with the rapidity of intennittence of which we have been speaking; 
but, what is of more importance, the duration of the discharges, consequent upon the 
nature of the contacts, was far greater. Moreover, it was found that each discharge 
was of a very complicated character. The discharge opened with a sudden rush, 
* The break here used was a mercurial one, the plunger of which worked on a cam attached to 
the axle of the mirror, so that the action of the contact-breaker was regulated by the motion of the 
mirror, and the image was always formed in the same position in the field of view. An opaque screen 
with a slit in it was usually placed on the tube so as to 
face the mirror. In order to convey a clearer idea of the 
phenomena alluded to in the text than could otherwise be 
obtained without reference to the paper itself, one of the 
diagrams is reproduced. This represents the appearance (in the 
mirror) of a carbonic acid tube with the slit attached. This 
tube, viewed by the eye, shows flake-like fluttering striae, with 
a slight tendency to flocculency near the head of the column. 
The commencement of the discharge is at the right hand, and 
the negative terminal at the top. The drawing fairly repre¬ 
sents the appearance of the upper part or head of the column 
of striae during one complete coil-discharge. When the battery- 
surface exposed is small, the whole consists of, first, three or 
four columns of striee of decreasing length, and afterwards of 
an almost unbroken field of striae. Each of the initial columns 
is perfectly stratified; and the same disposition of striae prevails 
throughout the entire discharge. The striee which fill the main 
part of the field present a proper motion nearly uniform, but 
slightly diminishing towards the end. These striee are for the 
most part unbroken, but are occasionally interrupted at ap¬ 
parently irregular intervals. When the battery-surface is 
increased, the elementary striee are more broken, and near the 
head of the column the interruptions occur as in the figure. 
The separation of the earlier part of the discharge into striated 
columns divided by intervening rifts does not, excepting in the 
case of the first, extend far towards the positive terminal. Nevertheless, even as far as the positive 
terminal itself, there seems at times to be a fuller development of discharge than is subsequently 
maintained. 
The first rift in the discharge, following the first outburst, is sometimes distinguishable even as far as 
the positive terminal; and perhaps in those cases indicates a real cessation of the discharge. This is 
corroborated by the fact that a similar interruption is then perceptible in the glow surrounding the 
negative terminal; but after this the negative glow retains its unbroken character throughout the entire 
discharge. 
