Carhart — Direct and Counter Electromotive Forces. 97 



ciency, is then the angle between the asymptotes, or 45°, and 

 the tangent of 45° is nnity. The limits of the efficiency corres- 

 pond to the points where the curve touches the asymptotes. 



It is also evident that near the point where B is a minimum 

 E, increases most rapidly. That is, near the point where the 

 efficiency is one-half it has its greatest increments. Beyond 

 an electrical efficiency of about 75 per cent, the direct and 

 counter electromotive forces increase in nearly' the same ratio, 

 and the efficiency therefore increases very slowly. 































'■:■; 

























H 



2 





























/ 



£ / 























L 



K 





























W 



































B/ 



























U 



/w 











? 







































































s 



S f 



























s 



T 

























Jr s 



s 





























, ' 











__^"*" 







C 











fs 



^~-- 



--- 



--- 



• t~ 





3 







p 



9 





R 









1 



j 



2 







3 







A 







s 







6 



b 





E 



4S 



30 



20 



10 







E and E / denote direct and counter electromotive forces ; C current and R 

 resistance in circuit connecting generator and motor ; W the total electrical en- 

 ergy contributed by the generator, and W, the electrical energy absorbed by the 

 motor in unit time ; e the eccentricity ; A and B the semi-axes ; m and n the 

 coordinates of the focus of the hyperbola ; a the angle between the axis of X and 

 the axis of the conic section. 



The diagram shows, further, that E, and C pass through cor- 

 responding series of values, but in the inverse order. The 

 current is proportional to E— E„ the resistance being constant; 

 and since the intercepts of a secant between an hyperbola and 



Am. Jour. Sci.— Third Series, Vol. XXXI, No. 182.— Feb., 1886. 



1 



