72 TIII-: i>i!;i:<T-rri:i;KNT MOTOR en. iv 



parallel to the same line. The magnets should be shunt 

 wound and separately excited, and provided with rheostats 

 so that the induction factor of each dynamo can be ad- 

 justed to any desired value and kept constant. The 

 connections will be made so that the dynamos tend to turn 

 in the same direction when both are acting as motors. 



We have further to suppose that by means of a 

 pulley fitted on to one of the dynamo shafts and con- 

 nected by a belt to a third dynamo, or by simply coupling 

 a third dynamo direct on to the shaft line, we can produce 

 a load of any required amount or of any required sign ; in 

 other words, we suppose that we can vary the mechanical 

 torque on the shaft, making it either positive so that the 

 dynamos have to act as motors, or negative so that they 

 act as generators. Any arrangement will act provided 

 the motion can be assisted or retarded at will. 



The two dynamos may be distinguished by the letters 

 A and B. Suppose that dynamo A has an induction 

 factor of 6 and a resistance of 1'2 ohms, and that dynamo 

 B has an induction factor of 4 and a resistance of 1 - 09 

 ohms. Let the tension of the line be 1 20 volts. 



Set off aft in Fig. 18 equal to 100 amperes, the maxi- 

 mum current in A. Set off ad equal to 110 amperes, the 

 maximum current in B. Let af represent 1,200 r.p.m., 

 the speed of A when its induced tension is equal to the 

 tension of the line. Let ag represent 1,800 r.p.m., the 

 speed of B when its induced tension is equal to the ten- 

 sion of the line. Join fb and gd. These will be the speed 

 curves of the two dynamos on a base of current in the 

 armature. 



Since the dynamos are mechanically coupled, we can 

 at once find from the diagram the current that each is 



