Kinsley — Discussion of Series Dynamo- Electric Machines. 125 



The resistance determined by the fall 



of potential method was r = 3.38 



In the twelve cases observed. 

 The resistance computed from the line 



with the machine in operation was r = 3.135 

 The resistance gotten by fall of 



potential method was r = 3.15 



The difference is accounted for by a better brush contact 

 while the machine is running. 



20 



Fig. 11 



40 



60 



Series Motor Test. Effect of Varying the Speed 

 when the Resistance is Constant. 



The fact that the lines are always straight shows that with 

 widely varying speeds * the fall of potential through the ma- 

 chine remains a constant. 



* S. P. Thomson, " Dynamo-Electric Machinery," p. 89, indorses the 

 theory of " an apparent increase of resistance proportional to the speed," 

 which was " first pointed out by Cabanellas in Comptes Eendus, Jan., 1882." 

 In the above careful tests no evidence of a change of resistance can be 

 found. 



