1862.] 337 



18. From the first appearance of the luminous discharge in No. 315, 

 until when thirteen or fourteen bright disks or separate striae were 

 observed, the discharge was not resolvable by a vibrating or a rotating 

 mirror ; with the full power of the battery, the disk nearest the 

 negative was truncated and impinged on the glow which surrounds 

 that ball (fig. 13): this truncated disk was also distinguishable by 

 its pale green colour ; those in its nearest contiguity had more or less 

 a reddish tinge ; the round negative glow was brilliant and of a bluish- 

 white colour ; minute bright scintillations emanated from the negative 

 ball, while distinct luminous flash discharges took place through 

 the strise. On examining these intermittent discharges by two 

 revolving mirrors, kindly lent me by Professor Wheatstone, they 

 appeared stratified ; but whether this did not arise from the passing 

 of these discharges through the bright and dark portions of the 

 continuous discharge, might have been considered doubtful, had I 

 not in another tube observed a similar stratified discharge under 

 more favourable circumstances. This tube, No. 324, is of the same 

 form and dimensions as 3 1 5 ; on heating it with a spirit-lamp when 

 it was in the circuit of the battery, the luminous discharge showed 

 four clearly defined separated striae, which remained fixed and steady 

 in their relative positions ; in this state momentary stratified dis- 

 charges were observed at intervals of from five to ten seconds, these 

 striae assuming a conical form, as in Plate II. fig. 14. 



I have observed somewhat similar intermittent discharges with the 

 nitric-acid battery, possibly under more favourable conditions ; and 

 with a more extended series than I then used*, the true nature of 

 this discharge may be ascertained. 



19. The discharge from an electrical machine when passing through 

 air in the dark, presents the well-known form of a brush at the 

 end of the wire attached to the prime conductor, and of a star at the 

 point of another wire attached to the rubber, or in connexion with 

 the earth. I have shown f that if this discharge is allowed to pass 

 through a vacuum-tube, stratifications will be obtained similar to 

 those from an induction coil, and that the discharge of a Leyden jar, 

 if passed through a wet string and a vacuum tube, is stratified ; these 



* Proc. Roy. Soc. March 1860. f Phil. Trans. 1858, p. 6, sect. 21. 



\ Phil. Trans. 1858, p. 15, sect. 53. 



2 B 2 



