of Small Resistances. 



37 



coil, but it would have been equally convenient for the lower 

 ones also. 



Jfatfhiessen and Hockin's Metliod, — The connexions are 

 shown in fig. 5. By altering the resistances Ei and Rg a 



Fig. 5. 



balance Avas obtained with the galvanometer circuit connect- 

 ing T with each of the potential points of A and B in 



Bi 



succession. Let a, l>, c, d be the respective values of ^ ^ 



for the four positions ; then ^ "*" ' 



b — a 

 d^r 



Although great care was taken to build up Ri and Rg from 

 standard resistances, the method was found to be 7nuch less 

 accurate than any of the four preceding ones. For example, 

 the ratio of coil Y to coil Z was given as 10*0032 by one set 

 of readings, and as 10*0057 by another. An examination of 

 the formula shows that the degree of accuracy of the result 

 may be much lower than that of the separate observations of 

 a, b, Cy and d. 



In Table I. are given the collected results, the numbers 

 being the observed resistances of the coils X, Y, and Z 

 reduced to 17° C. 



Table I. 



X. 



^^t^«d- Microhms. 



Y. 



Microhms. 



Z. 



Microhms. 



(I"* Potentiometer 100007 



lOOOl-Sj 

 10001-22 

 10001-23 



999-947 

 999-972 

 999-93^ 



(2) Thomson Bridge 100005 -g 



(3) Two-step ' lOOOOo'^ 



(4) Differential Galvanometer ; 100007 -^ 



