DIFFERENT MODES OF GENERATING CURRENTS. 59 



the inducer are favourable to the development of the tension 

 of the induced current in RuhmkorfFs coils, a high speed of 

 rotation, and, therefore, very rapid alternations of magnetiza- 

 tion and demagnetization, are required to produce the maxi- 

 mum effect with magneto-electric machines. It may, there- 

 fore, be said that in general a rapid succession of magnetiza- 

 tions and demagnetizations increases the tension of currents, 

 and allows the magnetic cores to acquire their maximum of 

 magnetization. It will be understood by this that the 

 number of successive inducing effects which a machine will 

 furnish, to be under the best conditions, will depend upon 

 its construction, and that the more readily its magnetic 

 organs are able to undergo magnetization and demagnetiza- 

 tion, the greater should be its speed. 



There are also certain conditions in the relative arrange- 

 ment of the induction organs which are more or less favour- 

 able to a high speed ; for example, in an ordinary magneto- 

 electric machine formed of several induction coils the mean 

 intensity of the sum of all the transmitted currents increases 

 with the velocity of rotation, but in a less ratio than the in- 

 crease of the velocity. This increase depends on two cir- 

 cumstances, that is to say, on the intensity of the current 

 itself, and on the greater or less number of coils connected 

 for tension. The greater the number of coils arranged for 

 tension the less rapidly does the electro-motive force in- 

 crease, and this slowness of increase is the greater as the 

 intensity of the current is greater. 



" It follows from all this," says Le Roux, " that the increments 

 of intensity cost more and more when it is sought to obtain 

 them by increase of velocity ; for, if theoretically each turn con- 

 sumes a quantity of work proportional only to the useful effect 

 it will finally produce, practically such turn causes the loss of a 

 certain quantity of work expended on passive resistance of every 

 kind. Nevertheless, in the calorific applications of electricity, it 

 is of importance to obtain these high intensities, since the useful 

 effect is proportional to their square in a given time ; but in the 



