78 THE IiIKKCT-rn.'UK.vr MOTOR ell IV 



bearings, hysteresis, &c. If, then, the torque supplied to 

 sucli an arrangement proves by measurement to be greater 

 than that required to make up the difference between the 

 assisting torque of the current in 13 and the resisting 

 torque of that in .1, the amount by which it is greater 

 represents the torque lost in friction, &c.. in the combina- 

 tion. This will be considered further when we come to 

 discuss the application of these principles to the testing of 

 dynamos. 



When the resistances and induction factors of two 

 dynamos are given, and also the tension of the line, we see 

 that there is a definite speed at which they must run in 

 order that the current generated by the one shall be equal 

 to that received by the other ; so that our arrangements 

 for the experiment must admit of the machines being run 

 at the required speed. When this is done the current 

 from the line will be nothing, and will remain nothing as 

 .long as the speed remains constant. If the speed be 

 increased some current will pass into the line, while 

 if the speed be decreased current will be received from the 

 line. 



Let us now suppose that the torque supplied from the 

 external source be removed altogether, and that the torque 

 lost in friction is nothing. We shall find that a current 

 will pass from the line in amount equal to the intercept 

 in-, where the current axis is cut by the curve of combined 

 torque. At the same time the speed will fall off, the new 

 speed being found by the vertical ordinate of the combined 

 speed curve drawn through the point r. 



Since no torque is supplied from outside, the 

 assisting torque of tt must equal the resisting torque of A, 

 hence the currents in the two dynamos must be related to 



