Whitehead and Hill — Measurement of Self -Inductance. 159 



look for the value of L to be affected in the same way by a 

 slight heating of one or more of the resistances, j The formula 

 for Method 14, neglecting hanging coil correction is 



jwja* 



R'RJ [r(K + R, + R, + R') + (R' + R )(R' + R,)] ) 

 R(r + R y +R) ' ( 



The method was set up and some determinations made of the 

 inductance of coil C. The method proved much less sensitive 

 than Method 14, under comparable conditions only about one- 

 half. By sensitive is meant the degree of accuracy to which it 

 is possible to change the resistances, in securing adjustment. 



It is to be noted that the formula as given neglects the self- 

 inductance of the fixed and hanging coils of the electrodynamo- 

 meter. The exact formula is not difficult to work out, but the 

 method is hardly sensitive enough to justify the trouble. 



A few measurements of the inductance of coil C were made 

 with some care. The values obtained were low compared with 

 those previously obtained, as will be seen from the following 

 example. 



R /y = 1201-'7 ohms 



R" = 1560-6 ohms 



r=309-91 ohms 



R = 99-89 " 



R'= 133-33 " 

 L = 1-1483 henry s 



n— 69-153 " 



IV. 



Methods i, #, 3, etc. — Attention was not turned to the first six 

 methods given in Professor Rowland's paper, which are for the 

 comparison of self-inductance with capacity. They are all zero 

 deflection methods depending on a ninety degree phase differ- 

 ence. As will be seen from the formulae, the value of — is 



independent of the frequency. Two of these methods have 

 already been used. 

 Method 6 was 

 studied by Mr. 

 Penniman but did 

 not yield favorable 

 results. Method 3 

 was employed b y 

 Mr. Potts in the 

 course of some 

 work on electric ab- 

 sorption, and was 

 found very satisfactory. The diagrams and formulae for 

 the methods are as follows. The method of deducing the 

 formulae is the same as that followed in the preceding cases. 



