On the Luminous Discharge of Voltaic Batteries, 545 



plate, evidently three negative envelopes on a great scale. When 

 the plate was positive, the effect was comparatively feeble." The 

 preceding is an extract from notes made by the Rev. Dr. T. R. Ro- 

 binson, when he first witnessed the experiments in my laboratory, 

 on the 5th of August, 1859. With the same vacuum I have 

 always obtained similar results. 



In 187 and 196 (fig, 1) with carbon-balls in the tubes, the discharge 

 of the nitric-acid battery elicits intense heat, and probably changes 

 the condition of the vacuum. On the 5th of August, 1859, "the 

 discharge in 187 presented a stream of light of intolerable brightness 

 [I again quote from Dr. Robinson's notes], in which, through the 

 plate of green glass, with which he observed the phenomena, strata 

 could be observed. This soon changed to a sphere of light on the 

 positive ball, which became red-hot, the negative being surrounded 

 by magnificent envelopes, whilst with the horseshoe magnet the 

 positive light was drawn out into strata. The needle of a galvano- 

 meter in circuit was violently deflected, and the polarity reversed, 

 settling at a deflection of 45°. On heating the potassa, the dis- 

 charge again bursts into a sun-like flame, subsequently subsiding 

 into three or four large strata, of a cloud-like shape, but intensely 

 bright." 



On a subsequent occasion I found that the discharge did not pass 

 for about a minute after the circuit was completed, when a fine glow 

 appeared on the negative ball, fig. 1 A. Around the positive ball 



Kg. 1 A. 



there was a trifling glow, in a few seconds a momentary brilliant 

 flash, and the discharge ceased. The potash was then again heated ; 

 the large negative glow reappeared, followed almost instantly by a 

 remarkably brilliant stratified discharge, with intense chemical action 

 in the battery, denoted by the evolution of nitrous fumes ; at this 

 moment I separated the discs of the micrometer-electrometer, and thus 

 broke the circuit. 



I now arranged the apparatus by attaching gold-leaf electroscopes 

 to both terminals, and introduced the galvanometer, so as to enable 

 me to examine more carefully the action that would take place when 

 the potassa was heated. On heating the potassa, the fine negative 

 glow (fig. 1 A) was again developed ; the leaves of the electroscope 

 did not close ; but as the negative glow increased, the needle of the 

 galvanometer was suddenly deflected, immediately (although the glow 

 continued) returning to zero ; as more heat was applied a small globe 



