104 TRANSACTIONS OF THE [dEC. 21, 



Work of motor B per second a maximum for e (E — e) maxi- 

 E 

 mum that is e=:--- 



i 



E^ 



Greatest work of motor B = --rr 



4K 



The practical efficiency of this combination of pump and 

 motor will be diminished because the head E will require a 

 coefficient greater than unity, and the couuterhcad e a coefficient 

 less than unity. 



^ - e(i-x) 



^ ~E(1 + X) 



1 — X 

 The value of ^ must be determined by experiment. 



It will at once be seen that when the motor is acting at its 

 greatest horse-power the theoretical efficiency is 50 per cent, and 



its practical efficiency still less, for we must introduce \-i — ~Y\ ^® 



g 



a factor of tt 



ht 



On the other hand if we increase the counter head e, the efficiency 



of the motor B increases proportionally, but the weight of fluid per 



E— e 

 second — j^- becomes less and less, and the work of the motor 



B per second decreases as p — - decreases. 



But the work of the pump A per second also decreases as 



E(E— e) 



— ^^-:5 — decreases, and the lost work due to resistance to flow 



through pipe and pumps decreases as — j—- decreases. 



It seems hardly necessary to call your attention to a miscon- 

 ception on the part of some, and I should not do so now had it 

 not very recently come to my knowledge that a professor, claim- 

 ing recognition as a high authority in electrical science, is still 

 making the statement that the greatest possible efficiency of an 

 electric motor is 50 per cent. 



With a theoretical efficiency of 50 percent, an electrical motor 

 is doing the largest amount of work in horse-power of which it 

 is capable, but it demands of tlie generating dynamo twice as 

 much power as it gives out. With a greater theoretical efficiency, 

 it does not turn out so much work ])er second, but it makes a de- 

 mand of less than twice its work upon the generating dynamo. 



