[ 506 ] 



LVI. Adjustment of the Kelvin Bridge. 

 By Rollo Appleyard*. 



IN a recent paper by Mr. J. H. Reevesf an alternative 

 method of adjusting the ratios of the resistances in the 

 Kelvin bridge was described ; the following remarks may be 

 regarded as a note upon that paper. 



The measurement of a resistance by the arrangement 

 adopted by Mr. Reeves involves two operations. It may be 

 shown, however, that for certain purposes the two adjust- 

 ments can be combined mechanically, and balance effected 

 bv a single test. 

 y 8 Kg. 1. 



Consider the conductors R, r, a, b, x, and y in fig. 1. It 

 is required to compare R with r. In the accepted form of 

 the Kelvin bridge a, b, x, and y have fixed values, such that 

 ay = bx, and balance is obtained by the one operation of 

 varying R or r. Mr. Reeves prefers to keep R and r fixed ; 

 and, consequently, he has first to find provisional values of a, 

 b, x, and y such that ay £= bx ; and then to balance again, 

 using these values, to find R : r ; with the plug, this time, 

 inserted at P. 



Fk. 2. 



ccj 



— : ii — ■ 



But fig. 1 suggests that a + b, and x+y, or convenient 

 parts of them, may each be formed into a slide-wire, and 

 that these two slide-wires may be placed parallel to one 



* Communicated by the Physical Society : read April 24, 1896. 

 t Supra, p. 414. 



