DISTRIBUTION OF ENERGY. 733 



the electromotive force of the machine by automatic means, by 

 displacing the brushes, or acting on the supply of steam. 



1279. The properties of characteristics have furnished M. Marcel 

 Deprez* with two ingenious mechanical solutions for machines of 

 constant velocity. 



If all the parts utilised are arranged in series, and the inductors 

 are shunted, the compensation may be very near when we utilise the 

 characteristic curve in the part in which it is nearly parallel to the 

 right line L 



Draw through the point D (Fig. 263) a right line DN parallel 

 to the former. If we increase the resistance x that is to say, the 

 useful work starting from zero the external current, which is ex- 



C> Tf 



pressed by i=nb , varies as the ratio . 



y DC y 



The ratio is at first equal to when the resistance is null; 



MP 



it then increases to a maximum for the resistance x = CP l ' > it 



then diminishes and acquires its original value N'Q for a resistance 

 which will be given by the abscissa of the point where the right 

 line CN cuts L. 



As long as the resistance x is less than CP, the machine has 

 the curious property that with a constant velocity the external 

 work increases with the resistance, so that the introduction of a 

 new apparatus into the circuit increases the work of each of the 

 preceding ones. It will thus be understood that within certain 

 limits it is possible to obtain a satisfactory regulation. 



The second solution holds for the case in which the apparatus 

 are shunted. Let : 



e be the difference of potential of the poles A and B which 



is to be kept constant, 

 x the interposed resistance, 

 R the resistance of the machine, 



we have 



E-e 



R 



* MARCEL DEPREZ. Comptes rendus, Vol. xcin., pp. 892, 950. 1881. 



