1876.] Mr. W. Spottiswoode on Stratified Discharges, 77 



glow retains its unbroken character throughout the entire period o£ the 

 discharge. 



The stratified columns with their intervening rifts are sometimes 

 reproduced towards the close of the discharge ; but this appears to take 

 place only when the battery is in an unusual condition of energy, and 

 disappears when, as in the bichromate battery, polarization of the plates 

 rapidly takes place. On these occasions especially, but also at other 

 times, traces may be seen of the faint lines of light connecting the posi- 

 tive with the negative parts of the discharge mentioned by Wiillner in 

 the paper quoted above. 



Other tubes, when viewed by the eye, show flaky strise more or less 

 difficult to distinguish from one another. Observed in the mirror, they 

 show much the same phenomena as the tube figured above, except that 

 the striae are rather more crowded together and slightly more broken. 

 This is the case especially with ammonia-tubes, in some of which the 

 striae are undistinguishable by the eye, and which accordingly give the 

 impression of an unstratified column of light. 



Fig. 2 represents the appearance in the mirror of another carbonic- 

 acid tube with a current similar to that used in the former case. Viewed 

 by the eye it shows flocculent striae, each having a contour sharply defined 

 towards the negative terminal, loosely defined towards the positive. The 

 following description of the phenomena, taken from my earlier notes, 

 may now be regarded as a description of the apparent proper motion of 

 the flocculent as distinguished from the elementary striae : — " The dis- 

 charge opens with a considerable rush, indicated by the bright line at 

 the commencement. There is no other indication of partial discharges. 

 Proper motion at first towards the negative, afterwards towards the 

 positive terminal. In this, as in other tubes giving striae of this kind, 

 ripples may be observed on the curve of proper motion." 



So far my older notes ; but on closer examination, and when the 

 battery- surf ace exposed is sufficiently reduced, the entire field is seen to 

 be traversed by elementary striae having a normal proper motion. "When 

 the battery-surface is gradually increased, the elementary striae, espe- 

 cially near the head of the column, have their duration shortened so as 

 to leave dark intervals at regular stages in the column. These successive 

 short-lived elementary striae form a series of diagonal lines, each series 

 of which traces a sketch of a flocculent stria. As the surface is still 

 further increased these diagonal lines appear more and more crowded 

 together, until at last they blend into unbroken flocculent striae. 



This compound nature and mode of formation may be taken as a 

 general characteristic of the flocculent striae. In some tubes it is more 

 easily brought out, in others only with greater difficulty. In some it 

 can hardly be verified experimentally without a loss of light so great as 

 to mask the phenomenon. The apparent proper motion of the flocculent 

 striae depends, as is easily seen, upon the position at which the elemen- 



