1876.] Mr. W, Spottiswoode on Stratified Discliarges. 81 



The following are some of the general conclusions to which the fore- 

 going experiments seem to lead : — 



I. The thin flake-like stria?, when sharp and distinct in their appear- 

 ance, either are short-lived or have very slow proper motion, or both/ 



II. The apparent irregularity in the distribution of such strise, during 

 even a single discharge of the coil, is due, not to any actual irregularity 

 in their arrangement, but to their unequal duration and to the various 

 periods at which they are renewed. These striae are, in fact, arranged at 

 regular intervals throughout the entire column. The fluttering appear- 

 ance usually noticeable is occasioned by slight variations in position of 

 the elementary striae at successive discharges of the coil. With a view 

 to divesting the coil-discharge of this irregular character, as well as for 

 other purposes, I devised two different forms of contact-breakers (one of 

 which is described in the Eoyal Society's 'Proceedings,' vol.xxiii. p.4oo); 

 but I postpone a description of the second, as well as of the experiments 

 arising from its use, to another occasion. 



III. The proper motion of the elementary striae is that \vhich apper- 

 tains to them during a single discharge of the coil. This appears to be 

 generally directed from the positive towards the negative terminal. Its 

 velocity varies generally within very narrow limits. It is greater the 

 greater the number of coils employed, or the greater the electromotive 

 force of the current. In some tubes it may be seen to diminish towards 

 the close of the discharge ; and even in rare instances alternately to 

 increase and to diminish during a single discharge. 



lY. Mocculent striae, such as are usually seen in carbonic-acid tubes, 

 are a compound phenomenon. They are due to a succession of short- 

 lived elementary striae, which are regularly renewed. The positions at 

 which they are renewed determine the apparent proper motion of the 

 elementary striae. If they are constantly renewed at the same positions 

 in the tube, the flocculent striae will appear to have no proper motion 

 and to remain steady. If they are renewed at positions nearer and 

 nearer to the positive terminal, the proper motion will be the same as 

 that of the elementary striae ; if they are renewed at positions further 

 and farther from the positive terminal, the proper motion T\ill be 

 reversed. 



y . The velocity of proper motion varies, other circumstances being the 

 same,*W'ith the diameter of the tube. This was notably exemplified in 

 the conical tube. In tubes constructed for spectrum-analysis the capil- 

 lary part shows very slight, while the more open parts often show consi- 

 derable proper motion. 



YI. Speaking generally, the discharge lasts longer in narrow than in 

 wide tubes. In spectrum-tubes the capillary part gives in the mirror an 

 image extending far beyond that due to the wider parts. 



YII. The coil-discharge appears, in the earlier part of its dev elopment 

 at least, to be subject to great fluctuations in extent. In all cases there 



YOL. XXY. a 



