ELEMENTARY THEORY OF ELECTROMAGNETISM. 6l 



in Fig 48, and to calculate this flux let us consider an element of 

 this plane Ax centimeters wide and 161,000 centimeters long 

 ( = .one mile) , the distance of the element from the axes of the 



I I 



1 - f D-x 



fe. *..^... 



Fig. 48. 



wires being x and D x centimeters respectively. The 

 magnetic field intensity at the element Ax due to the wire W 

 is: 



x 



and the magnetic field intensity at the element Ax due to the 

 wire W" is: 



according to Art. 19. The total magnetic field intensity at the 

 element is H' + H", and the flux across the element is 

 (H r + H") multiplied by the area of the element, namely 

 161,000 Ax square centimeters. Therefore: 



(Ax Ax 

 ~x~ + ~D 



Integrating this expression from x = R to x = D R, we get: 



= 644,000 J log e 



J (5) 



Therefore, since - = L according to Art. 31, we have: 



J~\ _ D 



L = 644,000 log e (6) 



PERTY OF ELECTRICAL LABORATORY, 



r^GUtTV OP *PJ*Cl6D SCIENCE. 





