[ 454 '] 



XLVIL On the Measurement of Mutual Inductance by the 

 Aid of a Vibration Galvanometer. By Albert Cami-bell, 

 B.Af (From the National Physical Laboratory.) 



[Plate XII.] 



Contents. 



1. Introductory. 



2. Theory of Modified Carey Foster Method. 



3. Vibration Galvanometer. 



4. Moving Coil Vibration Galvanometer. 



5. Practical Working- of Galvanometer and IIughes-Rayleigh 



Method adapted to Measuring Frequency. 

 0. Results obtained by Carey Foster Method. 



1. Introductory. 



nPHE determination of a self inductance by comparing it 

 A with a condenser by means of Anderson's Method can 

 be made with ease and accuracy, as the two adjustments are 

 independent. The use of a vibration galvanometer in this 

 method as carried out by Rosa and Grover (Bulletin of the 

 Bureau of Standards, vol. i. p. 291, 1905) greatly increases 

 the ease of manipulation and the sensitivity of reading. For 

 several years past we have tested our standards of., mutual 

 inductance against the B.A. Standard Air Condensers (as 

 well as Mica Standards) which have been standardized by 

 Maxwell's Commutator Method. For this purpose I have 

 used Carey Foster's Method f, in which (as in Anderson's 

 Method) the adjustments are easy and the formula simple. 

 The connexions are shown in fig. 1. 



Fio-. ]. 



R is a non-inductive resistance (capable of carrying a fair 

 amount of current); M is ihe mutual inductance to be 



* Communicated bv the Physical Society : read Mav 24, 1907. 

 t PhiL Mag. [5] vol xxiii. p. 121, Feb. 1887. 



