354 Sir W. Suow Harris on a General Law of 



only when wc employ large quantities of electricity and circuits 

 of considerable extent, that we may neglect the battery resistance 

 as being extremely small. It was not until I employed circuits 

 of 300 to 900 feet long (10), and a considerable electrical accu- 

 mulation, that I found the numbers representing the heating 

 effect on the thermo-elcctrometer in the simple inverse ratio of 

 the length of the circuit, or nearly so. This source of resistance 

 to discharge, therefore, is an clement of much importance. It 

 appears however to have escaped M. Riess's attention altogether. 



When we take into account these several sources of disturb- 

 ance, we can scarcely hope to find the heating effect of a given 

 quantity of electricity always reciprocally proportional to the 

 number of jars, or what M. Riess calls the "extent of the bat- 

 tery," although the results may approach that ratio. 



In some instances, if the quantity of electricity be small and 

 the jars of the battery of great capacity, having for example from 

 4 to 6 square feet of coated glass each, then the comparative 

 resistance introduced into the circuit of discharge by the addition 

 of other similar jars, becomes of much greater importance ; if, 

 however, we increase the quantity of electricity, the comparative 

 influence of this resistance will be diminished. I found, in accu- 

 mulating a large quantity of electricity upon jars of great capa- 

 city, that the effect was not greatly different while the accumu- 

 lations were effected upon one jar or two ; but this result did not 

 obtain with a small charge. 



22. The announcement, which I first made in 1830, of the 

 law of electrical discharge, the subject of this paper, must be 

 understood rather in relation to the indications of the ordinary 

 statical electrometers attached to the battery, than in respect of 

 any hypothetical condition of the discharge itself as to "tension" 

 or " density," as announced by M. le Professeur Riess. All I pre- 

 tend to state is, that the heating effect is altogether independent 

 of the extent of surface upon which the electricity is expanded, 

 and of all electrometric indications, all other things being fhc 

 same. 



23. With respect to my experiments, they are certainly not 

 open to the criticism with which M. Riess, quoted by M. De la 

 Rive, has regarded them. They were made with great care, and 

 no expense was spared in the construction of the electrical appa- 

 ratus. The electrical machine employed was a most perfect 

 instrument. It had a plate of glass 3 feet in diameter, and 

 was well adjusted in all its parts ; the cushions were insulated 

 on each side of the plate, and were joined by an efficient nega- 

 tive conductor. The action of this instrument, when in working 

 condition, was perfectly regular and efficient, and ])roduced a 

 precisely equal quantity of electricity at each turn of the plate. 



