TRANSFORMERS. 739 



of the battery; the total current is always in the same direction, 

 or alternately in opposite directions, according as E' is greater 

 or less than AR. In these conditions the machine would have 

 no application; it can only produce a useful result if at each 

 semi-period the direction of one of the electromotive forces is 

 reversed. 



This reversal is produced spontaneously when the external 

 electromotive force is a polarization, like that of voltameter or an 

 electric arc. 



If the electromotive force is always less than its maximum value, 

 the current is still sinusoidal, and the useful work. is zero. When 

 it is possible that the electromotive force of the machine may be- 

 come greater than the maximum polarization, the current presents 

 two very distinct characters. As long as the polarization is not 

 overcome, if c is the capacity of the electrodes, the differential 

 equation is first 



We should then take equation (6) during the fraction of the period 

 for which the maximum E' of polarization is attained. The ex- 

 pression for the current is then very complicated, since the con- 

 ditions are different for two portions of the same period, and the 

 exponentials do not neutralize each other. 



1284. ON TRANSFORMERS. M. Jablochkoff* has had the idea 

 of interposing in the circuit of an alternate-current machine a series 

 of shunt condensers, so as to distribute the energy of the current 

 on different parallel circuits, in the ratio of their resistance and 

 the capacity of the corresponding condenser. He then applied 

 the same arrangement to the secondary currents of an induction 

 coil worked by an alternating primary current. If the same primary 

 current supplies several coils arranged in series, the induced current 

 of each takes its energy in an indirect form from the principal 

 circuit ; in this way a method of distributing energy is effected 

 comparable with the use of shunt wires for continuous circuits. 

 This is the principle of the method used for several years and 

 known as transformers. 



Let us suppose that a circuit containing a sinusoidal electro- 

 motive force E sin w/ acts on an adjacent closed circuit, assuming 

 that there are no electromagnets, or at any rate that the mag- 

 netisation of iron is proportional to the magnetising force. 



BBB 2 



