OF AN ELECTRIC DISCHARGE. 31 



ducing a bad conductor at one of these connexions, the heating 

 of any portion of the principal arc is diminished in almost the 

 same degree as if the said bad conductor had been introduced 

 into the principal arc itself. 



Dove seems to have otherwise explained the circumstance, 

 that with four batteries, four connecting wires being present, the 

 heat generated in each is greater than in the single connecting 

 wire of a single battery. After having remarked that with four 

 batteries he obtained a length of spark sixteen times as great as 

 w^th one, but that when two interruptions existed at the same 

 time in two of the connecting wires the sum of the lengths of 

 the sparks obtained was less than the length obtained with one 

 interruption in a single wire, he proceeds*, " While the heat 

 generated in a combined battery in each of the four connecting 

 wires is fourfold, the sixteen-fold length of stroke refers to the 

 total combination as to an entire connecting wire.'^ In this 

 case he seems to lay down the principle, that in the four wires 

 together the heat generated will be sixteen-fold. Still plainer, 

 although without definite numbers, this opinion is expressed at 

 another place, where the point under consideration is that the 

 length of wire melted by a cascade battery increases with the 

 increase of the elements discharged. He says thereto " Now 

 as the same increase takes place in the intervening wires, when 

 the number of the combined batteries is gradually increased, 

 with four batteries we can melt four lengths of wire at the same 

 time, every one of which is greater than that which can be 

 melted by a single battery." 



Quite apart from the question whether Dove, in expressing 

 himself thus, really entertained the above opinion, as this may 

 readily be the conclusion arrived at by the reader of his paper, 

 and as, if the opinion were -well-founded, it would contradict our 

 theory, I think it incumbent on me to say a few words in con- 

 nexion with the subject. 



The total heat generated cannot be greater than the increase 

 of the potential due to the discharge, and this is, as already 

 mentioned, about four times instead of sixteen times as great 

 with four batteries as with one. Now if an electric air-thermo- 

 meter, the wire of which has a great reduced length, be succes- 



• Pogg. Ann. vol. Ixxii. p. 415. f Pogg. Ann. vol. Ixxii. p. 412. 



