and Magnetic Permeability. 181 



and 



1A = 311200 

 The resistance of the iron wire to steady currents was meas- 

 ured by means of Wheatstone's Bridge, giving, 



R = 4'3 X 10 9 



Thus Rayleigh's formula, for calculating the permeability, 

 when we know the self-induction of the iron wire to alternat- 

 ing currents, becomes : 



L' = 311200 + t / *-8X10'X 15860 



" 4:7rn ^ 



Discharging the condenser through the larger coil, we had : 



Length of half-oscillation 8*98 cm 



Speed of mirror 3*0 



Distance plate from mirror 300*9 



From this we find the number of complete oscillations per 

 second to be : 



n 633 



Using this value of n, and the calculated value of the self- 

 induction of the coil given above, we find for the capacity of 

 the condenser : 



C 1*848 micro-farads. 



Discharging the condenser through the same coil and the 

 iron wire in series we had : 



Length of half-oscillation 6*91 cm 



Speed of mirror . 2*2 



Distance plate from mirror 300*9 



giving 



n — 605 

 This gives for the combined self-induction of iron wire and 

 copper coil : 



L = 3*745 X 10 7 



Subtracting from this the self-induction of the coil, that of the 

 iron wire becomes : 



L'=3*24 X 10 6 



Substituting this value in Rayleigh's formula we get for the 

 permeability of the iron : 



fi= 327 



Discharging the condenser through the smaller coil alone, 

 we had : 



Length of half-oscillation 7*42 cm 



Speed of mirror _ — 5*6 



Distance plate from mirror 300*9 



