62 Mr. W. Spottiswoode on Stratified Discharges. [Jan. 31, 



In particular, with the nitrogen tube above mentioned, and other 

 similar tubes, the direction of the flow reversed itself as the charge in 

 the condenser became more exhausted. This was apparently due rather 

 to a diminution in strength of current, or quantity of electricity pass- 

 ing through the tube, than to fall in tension, inasmuch as any particular 

 phase could be maintained by gradually diminishing the resistance in 

 the circuit as the tension declined. The penultimate phase was a for- 

 ward flow from the positive terminal, the ultimate a fixed condition of 

 striae. When sufficient resistance was interposed in the circuit, these 

 striae showed a faint indication of fissure into pairs of laminae, and 

 even actually broke into pairs by forward jerks. Yery shortly after 

 this the column became blurred, and the discharge then finally ceased. 

 It should be further mentioned that by a suitable increase or diminu- 

 tion of resistance in the circuit the flow could be reversed again and 

 again at pleasure. 



It has frequently been noticed that in some tubes the column of 

 striae shows a tendency to mobility, while in others it is comparatively 

 fixed ; in one case it appears to be in a position of unstable, in the other 

 in a condition of stable, equilibrium. The former may generally be 

 exemplified in hydrogen and nitrogen vacua, the latter in carbonic 

 acid, hydrochloric acid, and other vacua. Experiments which I have 

 recently made with another, in some respects yet more powerful, 

 method, tend to bring out the connexion between these two classes, 

 but I reserve an account of them for a future occasion. 



Pursuing this subject further, I repeated the same experiments with 

 an 18-inch, instead of a 4-inch coil, using as a battery either six large 

 bichromate of potash cells, or, with still better effect, a large Gramme's 

 machine, worked by steam. The results were in every way satisfac- 

 tory. Tubes in which with the 4-inch coil the striae were at best only 

 imperfectly developed, or in which it was impossible to maintain the 

 discharge for any appreciable time, were illuminated successfully in 

 both respects ; and in many cases the supply of electricity from the coil 

 to the condenser could be so regulated as to maintain special phases for 

 an indefinite time. The change of tint from pale salmon colour to 

 violet-gray in (impure ?) carbonic acid vacua, due to increased tension, 

 as observed by Mr. De la Rue with his great battery, were here dis- 

 played with great brilliancy. 



The advantage of the 18-inch over the 4-inch coil consisted not so 

 much in the tension as in the quantity of electricity given off to the 

 condenser at each secondary discharge ; and it seems probable that a 

 coil specially constructed with very thick primary and secondary, and 

 capable of giving sparks from J to \ inch in length, would be the most 

 suitable instrument for the purpose. It would, of course, be necessary 

 that the condenser should have sufficient capacity to act as a fly-wheel 

 during the intermittence of the supply from the coil. 



