THE THEORY OF THE DYNAMO 



but it also applies to the form where we have the armature revolving 

 between two magnets like this (Fig. 2), because we can turn this lower 

 magnet over and bring the two together. The circuits of the lines of 

 force are around in this direction and in this (arrows, Fig. 2). So that 

 there are two circuits of the lines of force instead of one. The energy 

 expended for a given amount of work will be less with this form (Fig. 1) 

 than with this (Fig. 2). That is of very great value to makers of 

 machines. 



The theorem applies to a number of those old machines where there 



FIG. i. 



Fio. 2. 



was a very large number of little magnets revolving around other little 

 magnets. More work is used in sustaining the magnets in that form 

 of machine than in the more modern form where we have only a few 

 circuits. 



I had a number of drawings made of magnets in the Electrical Exhi- 

 bition, and I find very great difference in this respect; more difference 

 where Siemens armatures are used than in any other kind. In dis- 

 cussing these drawings I do not give any names, nor say whether one 

 machine as a whole is better or worse than another. 



First, I will discuss the general forms of the magnet, and then I wish 

 to say something in respect to the form of the pole pieces that inclose 



