180 Trowbridge and Adams — Circular Magnetization 

 In these coils : 



For the larger coil : 



For the smaller coil 



D 0-3969 cm 

 d 0*1241 cm 



a 43-5558 

 R 2-1292 



n 144- 

 L 3-421 XlO 7 



a 40-2016 

 R 1-4194 



n 64- 



L 7-125X10 6 



The iron wire was in the form of a rectangle, 200 feet long 

 and 60 feet wide, the diameter of the wire being 0-105 inches. 

 B-ayleigh's formula for self-induction with alternating cur- 

 rents is : 



L' = I ( A + a/h*L_ 



where 



I length of wire. 



R resistance for steady currents. 



n number of alternations per second. 



//, permeability. 



A is a constant, depending upon the geometric form of the 

 circuit, and can be calculated from the self-induction of the 

 circuit with steady currents. For steady currents, Rayleigh's 

 formula becomes : 



-«(A + t) 



Using Maxwell's formula for the self-induction of two parallel 

 wires, and applying it to this case, we get for the self-induc- 

 tion of the iron wire to steady currents : 



Here 



Hence 



b c 



L = 4c log h 4b log 1- /i(b + c) 



a a 



c length of rectangle. 



b width " 



a radius of wire. 



/ length of wire. 



L= 311200 4- 15860yu,/2 



