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LH. On the Galvanometer Resistance to be employed in testing 

 with Wheatstone's Diagram. By Louis Schwendler, Elec- 

 trician to Siemens Brothers, Woolwich*. 



IT has been proved elsewhere that, in measuring resistances 

 with Wheatstone's diagram, the highest degree of sensi- 

 tiveness is attained when the four branch resistances are equal ; 

 but no investigation exists at present, to my knowledge, for de- 

 termining the equally important question, 



Which relative galvanometer resistance raises the magnetic mo- 

 ment of the galvanometer to a maximum when the other branches 

 of the diagram are given. 



It has been further proved that, in order to raise the magnetic 

 moment of the galvanometer in simple circuit to a maximum, 

 the resistance of the galvanometer must be equal to the external 

 resistance. 



For analogous reasons, it may be inferred that there must be 

 a similar law in measuring resistances with Wheatstone's dia- 

 gram ; and the only question is, Which in this case is the ex- 

 ternal resistance ? 



An inquiry into this question is the purpose of the present 

 paper. 



In fig. 1 let a, b c, and d represent the resistances of the four 

 branches, / that in battery branch, and g the unknown resistance 

 of the galvanometer. Now, if we call A, B, C, D, F, and G re- 



Fig. 1. 



-I 



1 



spectively the current in each of the six different branches, and 

 E the electromotive force, we have, according to the two laws of 



Communicated by the Author. 



