ELECTRICAL MEASUREMENTS 329 



Calculation of Correction Due to Fixed and Hanging Coils 



Self-inductance of fixed coils =f= *0164 henry 

 " " " hanging coil h = -0007 " 



Correction due to fixed coils. From an inspection of the tables it 

 is seen that 



L R+r L R + r 



01 



B,+f~ R" 1.0164 ~~~90T' 



rhere L is the self -inductance of some coil and R -\- r is the corre- 

 sponding resistance. B, is taken as equal to 1 henry 



L 



R + r~ 902 ' 

 But the comparison of L with B^ = 1 is wanted, therefore both numer- 



ator and denominator of ~ ~ are divided by 1-0164 or 



yo 



. L \=B 



R+r 887-45 ' 

 . L_ R + r 



B ~ 887-45 ' 



That is, the self-inductance of -0164 henry of the fixed coils produced a 

 correction of 887-45 902 = 14-55 ohms, which must be applied to 

 the R" circuit if the self-inductance of that circuit is to be considered 

 as 1 henry. 



Correction due to hanging coil. The self-inductance = -0164 henry 

 of the fixed coils gives a correction of * 14-55 ohms, therefore the self- 

 inductance -0007 henry of the hanging coil gives a correction of -62 

 ohms to the R -\- r circuit. Applying these corrections, the results 

 obtained for the several coils under various conditions are given below. 

 The results are given in the following order. 



First. The values are calculated using double leads in the circuits 

 but open resistances as far as possible. 



Second. The variation of the apparent value of the self-inductance 

 of one of the coils with different positions of the coil, resistances, and 

 different kinds of leads. 



Third. Short leads separated about 6 inches and crossed, used with 

 all the coils except B^. 



Fourth. Open leads aad open resistances in the determinations. In 

 the table R" was open resistance plus the resistance of coil B^ and 

 fixed coils of instrument. R + r was made up of the small coil and 

 open resistance plus the amount in the Queen ordinary resistance box. 



