90 THE DIRECT-CURRENT MOTOR CH. IV 



from the line through one motor, say 100 amperes. 

 From any point I set off distances to represent values of 

 the induction factor. From a set off distances to represent 

 the speeds, on any given tension, for different values of 

 M. Thus if the speed for an induction factor of 4 is 

 represented by af, the speed for M = 8 will be one half of 

 a/, and for M=2 twice af. For convenience, the scale of 

 speeds thus constructed has been continued horizontally, 

 the upper portion of the scale being cut off. 



Suppose that motor A has M= 4 ; join ac ; then ac is 

 a torque curve, since the torques are proportional to the 

 currents. Let the torque load on A be represented by dh ; 

 the current in A is then all amperes. Join fy, this is the 

 speed curve for A, since af is the maximum speed of A. 

 Continue lid to cut fg in e, the speed of A for this load is 

 then given by eh. 



Now in the arrangement that we have described the 

 torque on the two motor shafts must be the same if the 

 diameters of the three bevel wheels are equal. Hence 

 if the resistance of the second motor, B, is the same as 

 that of A, its speed for any load will be found by a similar 

 construction as for .1, taking into account the difference of 

 the induction factors. Suppose that for B we have M=6. 

 Join /;/ ; this will be the speed curve of 7?. Take_//> - equal 

 to lid cutting alt in p, produce rp to cut vy in s. The 

 current in B is ar, and the speed of B is rs. If A and B 

 are rotating in the same direction, the angular speed of the 

 intermediate shaft, t', will be the mean between rs and eh. 

 If . 1 and B rotate in opposite directions the speed of C 

 will be equal to the difference rs and eh. 



By taking different values of M we can find a series ot 

 points giving the speeds of one motor at any fixed load ; 



