226 ON FARADAY'S LINES OF FORCE. 



n ' 



The equivalent currents are $1, and /, -g> , and their duration is r. 



/i 71 



When the communication with the source of the current is cut off, there 

 will be a change of R, This will produce a change in the value of r, so that 

 if R be suddenly increased, the strength of the secondary current will be increased, 

 and its duration diminished. This is the case in the ordinary coil-machines. The 

 quantity N depends on the form of the machine, and may be determined by 

 experiment for a machine of any shape. 



XII. Spherical shell revolving in magnetic field. 



Let us next take the case of a revolving shell of conducting matter under 

 the influence of a uniform field of magnetic force. The phenomena are explained 

 by Faraday in his Experimental Researches, Series n., and references are there 

 given to previous experiments. 



Let the axis of z be the axis of revolution, and let the angular velocity 

 be a*. Let the magnetism of the field be represented in quantity by /, inclined 

 at an angle to the direction of z, in the plane of zx. 



Let R be the radius of the spherical shell, and T the thickness. Let the 

 quantities a,, /J e , y,.be the electro- tonic functions at any point of space; a,, 6,, c,, 

 a,, ft, y, symbols of magnetic quantity and intensity; a,, b,, c,, a,, &, y, of 

 electric quantity and intensity. Let p t be the electric tension at any point, 



< 2); 



