THE THEORY OF THE DYNAMO 



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of force pass up through here (abed) and then out and around through 

 here (e e), &c., to complete the circuit. As I saw the machine in the 

 exhibition these outside pieces (ee) were closer to the poles of the 

 magnets than I have drawn them. If they are put too near, some lines 

 of force, instead of passing across the field of force, where the wires 

 revolve, as they ought to do, pass off at these openings, the circuits 

 going around in this way (arrows f f). In this case there is a loss due 

 to leakage of the lines of force, and we shall therefore have to expend 



FIG. 5. 



FIG. 6. 



more energy in keeping up the magnet. There is energy expended in 

 keeping up the field outside as well as in keeping up the field through 

 the armature. It is important that this point should be considered. 

 These questions, ' How many lines of force go across this opening and 

 are effective in producing the current, and how many escape off without 

 passing through the opening and are lost?' are just as important as 

 the question of the leakage of the current in the wire. There are 

 defects in many of these machines in that respect. In this form of 

 machine (Fig. 1), where there is a simple circuit, this magnet has to be 



