THE ARMATURE REACTIONS OF ALTERNATORS 237 



authors in the matter of dynamo-machine construction has made me 

 read their communications with great interest, and as I have observed 

 that in certain cases my own view has not been well understood, I 

 consider it desirable to present certain supplementary considerations 

 to make this theory still more simple and to complete it finally. At the 

 outset it should be pointed out that my diagram should not be con- 

 sidered as belonging to the category of E.M.F. but rather to that 

 of ampere-turn diagrams. The two classes are often equivalent, because 

 if one commences with E.M.F.'s one proceeds with fluxes, and ends 

 necessarily with ampere-turns. But I desire to reduce to a minimum 

 the complication of considerations relative to the saturation of field- 

 magnets, of which I fear the difficulties have been needlessly exaggerated. 

 In what follows I will refer first, very briefly, to the essential 

 points of my method of 1899, and I will show in what points it has 

 been improved, or is susceptible of improvement. 



PART I. DIAGRAM OF OPERATION. 



Principles of the Theory of Two Reactions. I have long been sur- 

 prised that polyphase alternators and direct-current machines have 

 not been treated from the point of view of reaction, since these 

 phenomena are fundamentally of absolutely the same order, since 

 the dephasing alternating current produces effects of the same order 

 as the displacing of the brushes in a direct-current dynamo. It is 

 known that in the latter case the displacement causes a direct magnetic 

 reaction to be developed, whilst in the neutral position there is only 

 a transverse reaction. By similar reasoning as to the automatic 

 dephasing of alternating currents and of the property which polyphase 

 currents possess of being decomposable into active and reactive com- 

 ponents, I have been led to the following proposition: 



When an alternator supplies a current dephased by an angle <[> with 

 respect to the internal induced E.M.F., the armature reaction may be 

 considered as the resultant of a direct reaction produced by the reactive 

 current sin $ and a transverse reaction due to the active current I cos <p. 



In addition to the above, the stray magnetic fields must be taken 

 into account. These are proportionate to the currents and in phase 

 with them. We will consider them later on. 



The second fundamental proposition of this theory is the follow- 

 ing: 



The two reactions (direct and transverse} and the stray flux take 



