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IIIK DIRECT-CURRENT MOTOR 



ril. xil 



magnets, the sum of three turns in parallel ; vertical ordi- 

 nates giving values of the induction factor. 



The second experiment consisted in passing the same 

 current in the armature as in the magnets, running the 

 machine at a fixed speed as a generator, and observing the 

 volts at the brushes. The resistance was taken when the 

 machine was hot, the heat-drop allowed for, and the 

 values of the induction factor deduced and plotted. The 

 following table shows the alteration in the value of the 

 induction factor as actually observed in the speed test, and 

 as calculated from the area of the magnetisation curves. 



In comparing the results of the speed test with those 

 obtained by mechanically integrating the areas, we must 

 remember that the voltmeter placed at the main brushes 

 to read the terminal tension practically integrates the 

 areas of the magnetisation curves lying under all the four 

 poles, taking account of the way in which these curves cut 

 the axis ; whereas in Figs. 67, 68 and 69 we have only 

 two out of four areas, and cannot assume that the other 

 two are the same as those we have determined experi- 

 mentally. 



Let us suppose that the railway motor illustrated in 

 Fig. 66 has to give a total horizontal pull of 500 pounds 



