iSDgal Jn^titutinn of ffireat ISritain. 



WEEKLY EVENING MEETING, 



Friday, March 15, 1861. 



Sir Henry Holland, Bart. M.D. F.R.S. in the Chair. 



Latimer Clark, Esq. 

 On Electrical Quantity and Intensity, 



The modifications of the strength of the electric current in dynamic 

 electricity, and in the amount of charge in static electricity, are at 

 present usually defined by the terms Quantity and Intensity. The 

 speaker pointed out that the expression intensity, as ordinarily under- 

 stood, really involved two perfectly distinct qualities, and dwelt on the 

 advantage which would accrue to electrical science by the habitual 

 separation of the complex idea of intensity into its two component 

 parts, viz. that of tension, as propounded by Ohm in his celebrated 

 mathematical investigation of the galvanic circuit ; and that oi quantity, 

 as developed by Faraday in those valuable researches in which he 

 established the definite quantitative character of electro-chemical 

 decomposition and the action of electricity on the galvanometer. The 

 term " tension," as here used, is intended to convey the same idea as 

 the expression electromotive force, or as the term " electric potential," 

 employed by Green and other mathematicians, and is entirely dis- 

 sociated from the idea of quantity ; both terms are equally applicable 

 to electricity at rest or in motion. 



The quantity of electricity, both in its static condition and in its 

 motion through conductors, usually varies directly as the tension, and 

 hence their joint effects have been ordinarily confounded together and 

 attributed to one cause under the name of intensity ; but since the 

 tension and quantity do not, under all circumstances, vary in the same 

 ratio, there exists an absolute necessity for their clear separation 

 before any numerical reasoning can be founded on them. Cases of 

 the independent variation of tension and quantity were shown, and it 

 was pointed out that all the most striking properties of electricity, such 

 as the decomposition of water and salts, the combustion of metals, the 

 deflection of the galvanometer, the attraction of the electro-magnet, 

 and the physiological effects of the current were really dependent, as 

 regards their magnitude and energy, solely on the quantity of elec- 

 VoL. IIL (No. 34.) 2 A 



