THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



JUNE 1847. 



LIX. On the Use of a double Circuit in the measurement of 



Electrical Forces. By Isaac B. Cooke, Esq.^ 



[With a Plate.] 



A CCORDING to the theory of Ohm, the electric force 

 ■^^ circulating through each part of a galvanic circuit is 

 equal to the quotient of the sum. of the affinities in action 

 divided by the sum of the resistances to be overcome. Thus 



*~R + r' 

 where F represents the force, A the sum of the affinities 

 generating the current, R the resistance of the electromotor 

 and the wires attached, and r the resistance of the wire of a 

 galvanometer included in the circuit. 



If a secondary wire, whose resistance is represented by w, 

 have its ends attached to the two points of connexion between 

 the wires of the electromotor and those of the galvanometer, 

 so as to form with the galvanometer-helix a divided course for 

 the circulation of the current, the equation for the force be- 

 comes 



R + L' 

 where 



r + xv 



The magnitude of that part of the current passing through 

 the galvanometer wire is expressed by 



r- J" II. 

 ^^-R + L*r' 



• Communicated hy the Autlior, 

 Phil. Map.. S. 3. Vol. 30, No. 203. June 1847. 2 D 



