Dynamo-electric Machines. 289 



Dynamo ivith constant E.M.F. and Velocity. 

 If r=^0, or the main circuit is short-circuited, 



F=-. 

 R 



If r = oo , or the main circuit is not joined up, 



ps ft + p 



If E and v are to be the same in all cases, thoy must be the 

 same in the extreme cases when the main circuit is short- 

 circuited and not joined up. In fact, by (I.), F is constant if 

 x is constant. Whence, equating the above values, 



R R + /> ? 



which is the condition for machines of constant E.M.F. and 

 velocity, under circumstances for which x can be considered 

 constant. 



The same condition can be obtained more generally by 

 making F constant for all values of r. 



P 



If this is true independently of r, the coefficient of r and the 

 constant terms must vanish separately; 



and 



F=* = 



ft n+ P > 



as before. This only holds true so long as x is constant. 



This condition was first given in my letter to the ' Electrician, ' 

 but without having regard to s, or to the variation of x, which 

 is a much more serious thing, or to the stability, which is more 

 serious still. 



In order to take count of these matters, we must prepare 

 the general values of E, C, and p. 



From (I.) we have 



. v 

 n+ -r 



^(M'GnrJ 



