Mr. W. Spottiswoode on Stratified Discharges. 149 



creased these diagonal lines appear more and more crowded to- 

 gether, until at last they blend into unbroken fiocculent striae. 



This compound nature and mode of formation may be taken 

 as a general characteristic of the fiocculent stria?. In some tubes 

 it is more easily brought out, in others only with greater diffi- 

 culty. 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 fiocculent striae depends, as is easily seen, 

 upon the position at which the elementary striae are replaced. If 

 they are replaced in the positions which their predecessors held, 

 the fiocculent striae will appear straight in the mirror ; if they 

 are replaced successively nearer the positive terminal, the apparent 

 proper motion will be in the normal direction ; if nearer the nega- 

 tive, it will be reversed. 



An ether-tube examined in the same way showed nearly the 

 same features as the last. The elementary striae, however, were 

 not so easily separable ; and the fiocculent striae were formed, as 

 usual, at an earlier stage near the head of the column than near 

 the foot of it. 



In another carbonic-acid tube the proper motion of the fiocculent 

 striae was coincident in direction with that of the elementary ; 

 and the latter were consequently more difficult to disentangle. 

 One point in this tube was particularly noticeable, viz. that as the 

 column of fiocculent striae retreated, so did the negative glow 

 advance. The two remained throughout the entire discharge the 

 same distance apart. 



Fig. 3 represents the discharge in a hydrogen-tube of conical 



Fig. 3. 



form, the diameter of which varied from capillary size to -J inch, 

 the capillary end being at the bottom. The positive terminal is 

 at the top. The principal interest of this tube consists in showing 

 the influence of diameter upon the velocity of proper motion. 

 The wider the tube the freer, it seems, the striae are to move. 

 The same fact may be observed by comparing tubes differing in 

 diameter, but in other respects the same ; but the conical tube 

 brings out the fact in the most striking manner. 



