548 Royal Society : — 



terminal wires or the charcoal points, the length of the arc being in 

 relation to the number of the elements of the battery. 



With the water-battery I have never been able to obtain the 

 slightest appearance of an arc-discharge ; for whether the terminals 

 of the battery were the plates of my micrometer-electrometer, me- 

 tallic wires, or charcoal, the result was the same ; viz. clearly sepa- 

 rated and distinct sparks, which continued until the water in the 

 cells had nearly evaporated. With four hundred (each cell being 

 insulated) of Grove's nitric-acid battery, similar spark-discharges were 

 obtained between the plates of my micrometer-electrometer, without 

 producing the voltaic arc, although by a momentary completion of 

 the circuit it was obtained with great brilliancy. 



In carbonic-acid vacuum tubes, and particularly in those in which 

 carbon-balls were inserted, the disruptive, as well as the voltaic arc 

 discharge (under the conditions described), was obtained from the 

 nitric-acid battery ; and in both instances the stratified appearance 

 was observed, the difference being, that with the arc-discharge the 

 stratifications were far more vivid and brilliant, and the discharge 

 itself evidently more energetic. With the disruptive discharge, the 

 needle of the galvanometer was but slightly deflected, nor could any 

 apparent chemical action be observed in the battery ; but instantly 

 on the production of the arc-discharge, the needle of the galvano- 

 meter was strongly deflected, and in all the cells of the battery it 

 was evident that intense chemical action had been produced. 



If carbon-balls are attached to the wires of a carbonic-acid vacuum 

 tube, the arc-discharge is obtained from a nitric-acid battery when- 

 ever the potash is heated. This process facilitates the discharge, 

 and assists the disintegration of the carbon particles ; and these in a 

 minute state of division are subsequently found attached to the sides 

 of the glass. It is these particles which produce the arc- discharge, 

 with its intense vivid light so suddenly observed, with far more bril- 

 liant effects than the usual stratified discharge. During its passage 

 the conducting power of the vacuum-tube is found to be greatly 

 enhanced, as shown by the galvanometer, the electroscope, and the 

 intense chemical action in the battery. 



The same explanation that I ventured to offer in the Bakerian 

 Lecture for 1858, as to the cause of the stratified discharge arising 

 from the impulses of a force acting on highly attenuated but resist- 

 ing media, is also applicable to the discharge of the voltaic battery 

 in vacua ; while the fact of this discharge, even its full intensity 

 having been now ascertained to be also stratified, leads me to the 

 conclusion, that the ordinary discharge of the voltaic battery, under 

 every condition, is not continuous, but intermittent — that it consists 

 of a series of pulsations or vibrations of greater or lesser velocity, 

 according to the resistance in the chemical or metallic elements of 

 the battery, or the conducting media through which the discharge 



