712 INDUSTRIAL APPLICATIONS. 



and the ring is turned through the angle of two successive coils, 



27T 



= ft, the effect is the same as if a single coil had turned, for each 

 4w 



half of the ring, through the angle TT the induced discharge corre- 

 sponds to the flow of force pf(x). 



4th. If the brushes make an angle ft with the transverse plane, 

 a rotation ft corresponds to the flow of force p\_f(n) 2/(ft)~\- ^ e 

 have thus the series of determinations 



A O =/(T), 



AX =/(*)- 2/08), 



consequently 



These successive values of the function, from f(ft) to /(w/3), 

 determine sufficiently all intermediate values. 



1268. PARTICULAR CASE. The ring is usually a kind of hollow 

 cylinder, formed of iron wires, or by a thin strip coiled as a spiral, 

 the successive layers of which are insulated. The induced currents 

 are thus avoided which tend to form in the meridian section, and 

 which, by heating the metal, would cause a considerable loss of 

 energy. 



If the original field is uniform, and of the intensity F, the ring 

 becomes magnetised almost like an unlimited cylinder (388) that 

 is to say, uniformly and the intensity of magnetisation is 



or sensibly 



If a is the radius of the cylinder, its potential at the distance r 

 from the axis, at an external point, the abscissa of which is x, is 

 expressed by (359) 



_ a 



T _ *r = JT _ -v 



