502 Measurement of Mutual Inductance. 



For example, the interrupter was tuned to unison with a 

 standard fork which gave 1 1 9*9^ — - per sec. : with L = 

 0*1000 henry the method gave w-= 120*0 and 119-8— per 

 sec. in two observations. 



Although I have described this method as used for deter- 

 mining the frequency to a first approximation, it can be 

 used, with an accurately known frequency, to determine L 

 and M in terms of P, Q, R, S, and n ; and the use of the 

 vibration galvanometer avoids the difficulty of obtaining 

 a pure sine-curve current. 



6. Results obtained by Modified Carey Foster Method. 



A series (A) of careful tests were made by this method on 

 a standard mutual inductance of nominal value 0*05 henry. 

 This standard consists of a pair of coils of silk-covered wire 

 wound in two deep channels turned on a cylinder of marble, 

 the whole being soaked in hot paraffin wax after winding. It 

 is illustrated in Plate XII. 



It was originally adjusted by Carey Foster's method, using 

 a ballistic galvanometer with an air condenser as standard. 

 A series (B) of tests were made on it, using Carey Foster's 

 Method with a secohmmeter commutator. 



It was also tested (C) by a quite independent method, viz., 

 KirchhofPs Absolute Method with a ballistic galvanometer *. 



In Table II. are shown some of the results of these sets of 

 tests. 



Table II. 



Set, 



A 



B 



C 



i 



Condenser. 



Mica 



Air 



K. 



R. 





Mean 



of set. 



Greatest 

 error from 

 mean of set. 



oopp pop 

 oi en co 6 o\ ob cd B 



OOO*- COffi* 

 O O O — ' OOCOC- 



O OO 05 co co 4- • 



Or 



100-00 



J J 



20 

 50 

 50 



20 



005009 

 0-05008 

 0-05010 



0-05008 

 0-05013 

 0-05013 

 005008 



005019 

 0-05013 

 0-05014 

 005011 

 0-05013 

 005015 

 0-05016 



i 0-05009 

 J 



1 0-05010 



1 



y 0-05014 



I 



1 

 ) 



Parts in 10,000.1 

 2 



6 



10 



Mica 







* Maxwell's Elect. & Mag-, vol.ii. § 759 ; Kirchhoff , Pogg. Ann. lxxvi. 

 April 1849 ; and Glazebrook, Sarganf, & Dodds, Phil. Trans, pp. 223-268 



(1883). 



