Nipher — Physics During the Last Century. 119 



original position. On breaking connection of A side with the 

 battery, again a disturbance of the needle." 



Later he varied the experiment and writes : — 



** In place of the indicating helix, our galvanometer was 

 used, and then a sudden jerk was perceived when battery 

 communication was made and broken, but it was so slight as 

 to be scarcely visible. It was one way when made and the 

 other way when broken, and the needle took up its natural 

 position at intermediate times." 



The device which Faraday describes was a transformer. 

 The impulses which he saw in the needle were due to induced 

 currents. He immediately proceeded to produce induced cur- 

 rents by the motion of a closed conductor, in a magnetic 

 field. That was the first dynamo, and was constructed during 

 the same month. If any person had asked of Faraday that 

 exasperating question, what is the practical value of your dis- 

 covery ; how are induced currents available for money-getting? 

 he would have been unable to make any satisfactory reply. 

 The effects which he observed, were utterly insignificant. Who 

 would then have imagined that these feeble impulses would 

 some day transmit articulate speech? Who could have 

 imagined the ponderous machinery now employed in pumping 

 induced currents through massive conductors, to light large 

 cities, and to move heavy cars loaded down with passengers? 

 Even fifteen years ago the man who would have predicted that 

 this city would contain the railway system which it now has, 

 would have been considered a lunatic by every street railway 

 man. It would have been suflScient answer to such folly, that 

 there was no traffic to sustain such an enormous outlay of 

 capital with the necessary running expense. It would have 

 been called the idle fancy of a useless brain. 



It became apparent in 1873 that the dynamo was reversible. 

 The same machine might be mechanically driven and used as 

 a generator, and it might be electrically driven in the reverse 

 direction and develop power as a mechanical motor. This 

 result had indeed been foreshadowed by Pacinotti in a re- 

 markable paper in 1864. But his machine remained forgotten 

 in the museum of the University of Pisa until the Gramme 

 machine appeared in 1871. Pacinotti pointed out clearly 



