Whitehead and Hill — Measurement of Self -Inductance. 161 



success. The present writers set up the method and compared 

 coil P with the ^-microfarad condenser. The method is very 

 sensitive. With r — 3070 ohms and R = 485 ohms, a change 

 of two ohms in r caused a change of l mm in the deflection of 



the electrodynamometer. Determinations of the ratio ^ were 



not made for the reason that if we wish accurate results it is 

 necessary to measure the absorption resistance of the condenser. 



This should be done at each determination of ^, as the absorp- 



tion has been found to vary greatly both with the temperature 

 and the frequency. 



The diagrams and formulae for Methods 4 and 5 are given : 

 also the values of the resistances of the arms which seemed to 

 give the most sensitive arrangement. As before, coil P, was 

 compared with the ^-microfarad condenser. 



Method Jf.— See tig. 10. 



L _ -jR'(r + R,)+R'(R' + R,)} {R'(R' + R,) + R'(R, + R'H 



C R'R" 



As adjusted, 



R /; = 88-54 ohms 

 R' = 1021-8 ohms 

 R* = 99-5 " 

 r = 492-0 " 

 R = 317-5 " * 



With C = -086 ampere, 



a change of 4*4 ohms in 



r is barely detectable and 



a change of ten ohms in 



R' produces only 2 mm deflection as measured on the scale of 



the electrodynamometer. 



Method 5. — See fig. 11. 



L _ [R; (R' + R , )+R, ( R y + R ')] [R'( R' + R,)+r(R' + R')] 



C ~ (R' + R').(ii' + R,) 



As adjusted, 



R /y = 100 ohms n 



R" = 88-5 " 



= 1041-5 " 



^ 317-5 " 



= 1678-4 " 



r 



This method is some- 

 what more sensitive 

 than Method 4, how- 

 ever, it is not possible 

 to adjust closer than 

 one part in five hundred. 



