THE THEORY OF THE DYNAMO 



227 



the steel would be in the same direction with the current and produce 

 the field with less expenditure of energy than if it were simply iron. 



There is no difference between a shunt and a series machine. The 

 magnetizing force on the magnet I have set down as proportional to the 

 number of turns multiplied by the current; that is, proportional to the 

 cross-section of the coils multiplied by the current per unit of cross- 

 section, so that the magnetizing action can be the same either from a 

 strong current or a weak current. Therefore, if the exterior dimen- 

 sions of the coils are the same in both cases, the same energy is ex- 

 pended in each in order to produce the same force, so that there is no 



FIG. 8. 



difference between a shunt machine and a series machine as far as the 

 economy of the magnet is concerned. 



I do not wish to take up too much of your time, and will go on to 

 the heating of the armature. Of course the amount of energy expended 

 in the heating of the armature will be dependent on the resistance of 

 the armature. It is well known that the efficiency of the circuit will 

 merely depend upon the relation between the resistance of the arma- 

 ture and the exterior circuit. 



There is one other point in regard to losses ; ' dead wire,' I think, is 

 the technical term for it; I mean that portion of the wire which does 

 not cut the lines of force. In the Gramme pattern the armature is 



