12 



THE DIRECT-CURRENT MOTOR 



CH. I 



In Fig. G magnetisation curves are given for a high 

 tension arc light dynamo. This machine has a ring 

 armature with 80 sections and 47 turns per section, mak- 

 ing A = 3,76Q. The areas of the curves for 3, 6, and 

 9 amperes in the magnets are as 100, 159, and 178. 

 The corresponding values of N as obtained by a method to 

 be presently described are 1-05x10, T68 x 10 6 , and 

 1-89 xlO 6 . ' 



MAGNETISATION CURVES 

 FOR ARC LIGHT DYNAMO. 



Let us suppose that the armature is turned through an 



QCA 



angle equal degrees. Each conductor will then sweep 



through the space that lies between it and the next 

 conductor. The number of lines of force occupying this 

 space is represented by the area of the strip of the curve 

 between the two conductors ; hence each conductor will 

 cut a number of lines of force represented by the area of 

 the strip next to it. Let dn be the area of any such strip, 

 and dl the time occupied in turning the armature through 



