152 Whitehead and Hill — Measurement of Self- Inductance, 



Cc i F <t, 



c B t-r 



as possible and in the more accurate work the resistances of the 

 several arms of the network were measured after adjustments 

 on a Nalder standard "Post Office" box. All resistances are 

 in International ohms. 



Methods Used. 

 I. 

 Method 25. — The first method tried was that designated in 

 Professor Rowland's article as number 25. It is an absolute 

 method intended for the measurement of either self-induction 

 or capacity, the value of 



which depends upon the 

 square of the current 

 frequency. It was given 

 a thorough test by Dr. 

 T. D. Penniman,* except 

 in so far as his method 

 of measuring the fre- 

 quency was rough com- 

 pared with that used in 

 this investigation, and he 

 ascribes the lack of uni- 

 formity of his results 

 chiefly to a want of 

 knowledge of the current period. It was therefore thought 

 well to give the method a hasty trial in regard to the meas- 

 urement of self-induction. In this method the hanging coil is 

 shunted off the fixed coils circuit and the deflection with a 

 non-inductive resistance in circuit with the hanging coil is 



made the same as that of an 

 inductive resistance in cir- 

 cuit with the hanging coil. 

 The method and connec- 

 tions are shown in figs. 2 

 and 3 ; F and II represent 

 the fixed and hanging coils 

 of the electrodynamometer ; 

 R, R 7 and r, the total resist- 

 ances of the three branches ;, 

 L is the self-inductance of 

 the coil to be measured, W 

 is a reversing commutator. 

 The formula for the method 

 as deduced by Dr. Penniman is, 



^ 2 L 2 = (R-R) (R+r) 

 where p is equal to 2tt multiplied by the current frequency. 



* This Journal, viii, p. 35, 1899. 



