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pole-pieces radial, as in the author's 

 machine. The author assumed a con- 

 stant coefficient of self-induction in the 

 armature. In the machine which had 

 originated the unwarrantable assumption 

 of the curve of sines the self-induction 

 was nearly constant. It was a Siemens 

 machine used by Mr. 'Joubert. There 

 was very little iron near the armature, 

 and the coefficient of self-induction was 

 sensibly constant. In the modern ma- 

 chine there was not a constant coefficient 

 of self induction in the armature. This 

 would, he was afraid, detract from the 

 usefulness of Mr. Atkinson's ingenious 

 application of the integraph. The sim- 

 plest way of calculating these things was 

 not to take the coefficients of self-induc- 

 tion, but to find out how many lines of 

 force were cutting the circuit at any 

 time, by plotting the field-magnets out, 

 and working through a graphic method. 

 It was a long and tedious process, but it 

 could be done, and done with the same 

 accuracy as, for example, Professor 

 Forbes' dynamo leakage calculations. In 



