714 INDUSTRIAL APPLICATIONS. 



For a constant velocity, the sine of the angle of lead is then pro- 

 portional to the intensity of the current, and for the same current 

 this angle diminishes as the velocity increases. 

 As a function of the external circuit, we have 



P p + wr' 

 tan0 = 



27T R 4- #!+.*' 



and, for an infinite velocity, 



r ' 



tan0 = . 

 p\ 



1269. DYNAMOS. This is the name usually given in practice to 

 magneto-electrical machines, like those of Gramme, in which the 

 current itself is used either wholly or in part to excite the inductors. 

 The current of the inductors being I, the function <(!) which, with 

 M. Marcel Deprez, we may call characteristic function^ is at first null, 

 for 1 = 0, to almost the remanent magnetisation; it then increases 

 with the intensity, and tends in general towards a maximum with 

 the magnetisation of the armatures. 



For a machine in full work, the energy absorbed by each turn 

 of the ring, W 1 = !<(!), only depends on the strength of the current. 



The same work W : would be effected by a force applied at the end 



W 



of a lever equal to unity, the numerical value of which was - ; this 



W 



quotient - - is the motor couple of the machine. W x is again the 



27T 



numerical value of the force which should be applied at the 

 end of a radius of length , corresponding to a circumference 



27T 



equal to unity, in order to obtain the same work; this is what 

 has led M. Marcel Deprez* to call this quantity the static effort 

 of the machine. 



In the expression 



MARCEL DEPREZ. Comptes rendus, Vol. xcv., p. 778. 1882. 



