718 



INDUSTRIAL APPLICATIONS. 



The condition for the maximum useful work (1256) becomes, 

 in the present case, 



2lR I(2A + BI) 

 ~'~ (A + BI) 2 ' 



BI 



If we replace A + BI by its value 

 the maximum useful value, 





, we have, in the case of 



2R 



8AR\ 



- -) 

 n ] 



As the second member is greater than unity, the external re- 

 sistance should be less than that of the machine ; but it is nearer 

 to equality, the greater the velocity of the machine. 



The relative efficiency for maximum work is 



x 



R+x 



i 



If the magnetic field had its maximum value, <(!) would be equal 



to , and the current produced by the motion of the ring, in an 

 B 



equal resistance R + #, would be 



~ 



On the other hand, the current I 2 capable of giving the field 

 an intensity one half of the maximum, is defined by the condition 



BI 22 B 



from this follows the curious property 



