140 Mr. Satyendra Ray on the 



laws of induction. Assuming the plane of the electric 

 circuit to pass through the axis of the flywheel, every tube 

 of induction that enters the circuit through the cast iron 

 between X and Y, where the brushes make contact, goes out 

 of it between the same two points from the rest of the circuit. 

 Also from symmetry of the magnetic field about the axis of 

 the flywheel the number of tabes of induction moving across 

 XY in the cast iron is exactly equal to the number of the 

 tubes of induction moving across the rest of the circuit at 

 right angles to the plane of the circuit. The tubes sweep 

 longitudinally across the plane of the electric circuit, and 

 the E.M.F. between X and Y in the cast iron is equal to the 

 E.M.F. between Y and X in the rest of the circuit and the 

 direction is continuous. 



In the analogue we get closed tubes of electric induction, 

 and it is easier to calculate the induced E.M.F. in the cir- 

 cuit, in a form analogous to the expression kiri for the 

 magnetomotive force round a magnetic circuit threaded by 

 an electric current, by regarding the rotating flywheel 

 carrying a negative magnetic charge as constituting a 

 "magnetic current " threading the electric circuit. 



Assuming a magnetic charge in motion to constitute a 

 " magnetic current element " obeying Laplace's rule, the 

 electric intensity at any point of a circular coil of radius a 

 and of resistance R, due to a magnetic pole m moving along 

 the axis of the coil, can be put in the form 



-r^ 7 ds 1 . ' * 



b = k . m . -j- . — .sin U, 



at r 



■r being the distance of m from coil, 6 the angle between r 

 and the axis of the coil. We have, therefore, from definition: 



Induced E.M.F. 



; o ds 1 . 



= k .lira.m . 77.-5. sine' 



dt r 2, 



7 . sin 6 d6 



— k . 'lira . m .— - . — , 

 a dt 



iind Induced Current 



7 27T//1 . * d0 

 = k.^ .smd. Jt ; 



C idt = k.^. C sin 0d0, 



_ j -linn 



