OP AN ELECTRIC DISCHARGE. 



17 



spark springs over. An exterior mechanical action takes place 

 here, which, as so much work consumed, must be deducted from 

 the total action, in order to obtain that portion which is changed 

 into heat within the system of bodies under consideration. 



With respect to the magnitude of the work here expended, 

 and its influence on the development of heat, I am enabled 

 to adduce an experimental corroboration of the theory. It is, 

 in the first place, clear that the consumption of work must 

 depend on the resistance presented to the passage of tTie electri- 

 city by the non-conducting layer, and hence that it will be more 

 considerable when the ends of the connecting wires are separated 

 by a non-conducting solid body than when merely air intervenes 

 between them. From this it follows, that in the first case an 

 air-thermometer placed in some other portion of the circuit must 

 be less warmed than in the latter case; this indeed has been 

 established by a series of experiments carried out by Riess. 



At the place of interruption were placed either two small 

 discs, or two small balls, or two points opposite to each other, 

 at a distance of 0*2 of a line apart in each case. Between these 

 the bodies mentioned in the first column of the following table 

 were introduced one after the other; and the quantities of heat 

 developed under precisely the same conditions are contained in 

 the following columns. Where Riess has given several numbers 

 I have given the mean : — 



Body introduced. 



Layer of air 



A card 



Two cards with tinfoil between them 



Two cards 



A plate of mica 



Heat developed in Air-thermometer on 

 the passage of the spark. 



Between the 

 discs. 



15-9 



n-7 



9-7 

 8-0 

 6-8 



Between the 

 balls. 



15-4 



12-0 



9-3 



8-8 



4-7 



Between the 

 points. 



151 

 11-6 



10-4 



4-8 



The influence of the solidity of the bodies penetrated by the 

 spark is very plainly visible here*; and it is at the same time 



* Only in the case where two cards with tinfoil between them were applied 

 do we find an exception, inasmuch as those three bodies exercised a less influ- 

 ence than the two cards alone. According to this we must assume that the 

 plate of tinfoil, although it also was penetrated, caused, not an increased con- 



SCIEN. MEM.— i^a^ Phil, Vol. I. Part I. C 



