THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



FEBRUARY 1881. 



XII. On the Measuring of Electrical Conductivities. 

 By G. Ki'rchhoff*. 



¥7^ OR the comparison of the resistances of short wires Sir 

 J- W. Thomsonf has given a method founded on an arrange- 

 ment which is a modification of the Wheatstone bridge. 

 Another method which may serve for the same purpose is in 

 many respects more convenient, and, as it appears, not inferior 

 in accuracy ; it is based on the employment of a differential 

 galvanometer, the windings of which can be set so that a cur- 

 rent flowing successively through them produces no deflection 

 of the needle. If a circuit be formed out of the two resist- 

 ances to be compared, and a battery, and the two wires of the 

 differential galvanometer be inserted as secondary closings to 

 them, and if the resistance of one of these wires be varied till 

 deflection of the needle vanishes, then the ratio of the resist- 

 ances to be compared will be equal to the ratio of the resist- 

 ances of the galvanometer-wires, provided that the above- 

 indicated setting has been given to the windings. If now 

 such resistances be added to the galvanometer-wires that de- 

 flection of the needle again vanishes, the ratio of the added 

 resistances will also be equal to the ratio of those to be com- 

 pared %. 



* Translated from the Monatsbericht der koniglich preussischen Akademie 

 der Wissenschaften zu Berlin, July 1880, pp. G01-613. 

 t Phii. Mag-. [4] xxiv. p. 149 (1862). 

 t Tait (Trans. R. Soc. Edinb. vol. xxviii. 1877-78, p. 737) has com- 



Phil. Mag. S. 5. Vol. 11. No. Q6. Feb. 1881. G 



