340 Sir W. Snow Harris on a General Law of 



Transactions for 1830, I announced a law of electricity of great 

 generality, viz. that the heating effect of the ordinary electrical 

 discharge transmitted through a metallic wire placed in the cir- 

 cuit is as the square of the accumulation, and is entirely depend- 

 ent on the quantity of electricity discharged, without any regard 

 to the intensity indications of the ordinary electrometers. Con- 

 sequently through whatever interval of air the discharge can 

 pass, as measured by a Lane's electrometer, the heating eftect of 

 the momentary current in the wire will, with a similar circuit, 

 be always the same for the same quantity of electricity, — a de- 

 duction which has since been fully verified by further discoveries 

 in electricity*. M. De la Rive, for exam])le, found the heating 

 efi'ect of the voltaic current, and which he estimated by the 

 beautiful helical thermometer of Brequet, wholly dependent on 

 the quantity of electricity f. Faraday also shows. Experimental 

 Researches (366.), that "if the same quantity of electricity pass 

 through the galvanometer, the deflection of the needle is always 

 the same whatever may be the electrical intensity;" and again 

 (704.), in the case of electro-chemical decomposition, " the force 

 of a given quantity of electricity is always the same, notwith- 

 standing the greatest variations of intensity." Thus the law 

 which I had previously announced has been so far satisfactorily 

 confirmed by the subsequent investigations of two philosophers, 

 whose admirable researches have enriched this branch of 

 physics. 



2. Although my original announcement is thus sanctioned by 

 experimental evidence of the highest authority, yet M. De la 

 Rive, in his valuable work, Traite de I'Eleciricite, recently pub- 

 lished, has quoted largely from certain memoirs of M. leProfesseur 

 Riess of Berlin, who thinks he has shown the fallacy of my an- 

 nouncement, " la faussete de cet enonce." Repeated experiments, 

 he says, "have informed me that the elevation of temperature in 

 a metallic wire by the electrical discharge is proportional to the 

 quantity of electricity accumulated multiplied by its density, or 

 what comes to the same thing, proportional to the square of the 

 quantity divided by the extent of the battery J; " so that his 



Q2 



formula would be T= — , in which T is the elevation of tempe- 

 rature, Q the quantity, and s the extent of the battery. At 

 p. 116, M. Riess attributes my failure in arriving at the same 

 conclusion as himself, to a want of accuracy in my experiments. 



* See also Phil. Trans, for 18.34, p. 225. 

 t Ann. de Chim. et de Phys. vol. lii. p. 177 and 183. 

 X Ann. de Chim. vol. l,\ix. p. 1 13 ; and De la Rive, Traite de V Electricite, 

 vol. ii. ))p. 1.54 and 162. 



