NIAGARA IN HARNESS 



is supplied unchanged ; but for more distant consump- 

 tion it is raised to ten thousand volts; and that por- 

 tion which is sent away to the factories of Buffalo and 

 other equally distant places is raised to twenty-two 

 thousand volts. 



The transformation from a relatively low voltage 

 to the high one is effected by means of what is called a 

 step-up transformer. This is an apparatus which brings 

 into play a principle of electric induction not very dif- 

 ferent from that which was responsible for the genera- 

 tion of the current of electricity in the dynamo. The 

 principle is that evidenced in the familiar laboratory 

 apparatus known as the Ruhmkorff coil. The trans- 

 former consists essentially of a primary coil of relatively 

 large wire, surrounded by, but insulated from, a second- 

 ary coil of relatively fine wire. When the interrupted 

 current is sent through the primary coil of such an ap- 

 paratus, an induced counter-current is generated in the 

 secondary coil. Of course there is no gain in the actual 

 quantity of electricity, but the voltage of the current 

 generated in the finer wire is greatly increased. For 

 example, as we have seen, the current that came from 

 the dynamo at twenty-two hundred volts is raised to 

 ten thousand or twenty-two thousand volts. These 

 proportions may be varied indefinitely by varying the 

 relative sizes and lengths of the primary and secondary 

 coils. 



How shall we picture to ourselves the actual change 

 in the current represented by this difference in voltage ? 

 We might prove, readily enough, that the difference is a 

 real one, since a wire carrying a current of low voltage 



