TRANSFORMERS. 741 



This fraction increases with w; the maximum, which corresponds 

 to infinite velocity of the electromotor, is 



R L' 2 



In the transformers of MM. Gaulard and Gibbs,* the two 

 wires, primary and secondary, are wound together on a cylindrical 

 core formed of a bundle of iron wires. The transformers of 

 MM. Zipernowski, Deri and Blathy,f on the contrary, consist of 

 a ring of iron wires on which the two circuits are coiled together 

 as in the windings of a Gramme machine. 



1285. The coefficient of self-induction of the primary circuit 

 contains a term relative to the machine itself; we shall assume 

 that it is very small compared with that which arises from the 

 portion of the circuit comprised in the transformer. If the in- 

 ducing and the induced circuit have the different numbers of turns 

 N and N', and the mean diameter is almost the same, we have 

 sensibly 



and may then write 



Let us consider the resistance R' of the secondary circuit as 

 formed of two parts, the one b' comprising the transformer and the 

 connections, and the other x which corresponds to the useful 

 work U; we have 



TT A' 2 A 2 M 2 o> 2 

 U = # =x 



2 2 J< 



* L. GAULARD and J. D. GIBBS. La Lumiere Ehctrique, Vol. vui., p. 189. 

 1883. 



f G. FERRARIS. La Lumiere Electrique, Vol. xvn., p. 145. 1885. 



