$S 4 



HISTORY OF SCIENCE. 



As the establishment of a current in the neighbourhood of a parallel 

 closed circuit is equivalent to suddenly bringing a current near that 

 circuit, Faraday tried the effect of moving an already established 

 current up to a closed circuit. Fig. 296 shows the form of the ex- 

 periment. H is a coil of insulated wire connected with the galvano- 

 meter at G through the wires A A; H' is a coil through which the battery 

 current is flowing from the wires P B, B N. When the coil H' is held 

 in the hands, and is being brought near H, a current flows through H 

 and affects the galvanometer. Similarly, while H' is receding from H 

 a current flows, but in a direction opposite to that of the former one. 



FIG. 296. 



The direction of the current in H, on approximation of H', corresponds 

 with that of the induced current on the establishment of the battery. 

 The current on recession corresponds with that which occurs on the 

 cessation of the battery current. 



Soon after this discovery of voltaic induction, coils were made pro- 

 vided with means of rapidly interrupting the primary or battery current, 

 so that the effects of the induced currents should be continuous. 

 Masson, in France, used as an interrupter a toothed metal wheel, with 

 a spring touching each tooth as it passed. This was in 1836, and by 

 1848 several improvements had been introduced into the arrangement 

 by Breguet. A few years afterwards the voltaic-induction machine 

 was perfected by RUHMKORFF, a skilful electrical instrument maker of 

 Paris ; and it has become an instrument of science itself prolific of 

 new discoveries. It is now well known as Ruhmkorff's Coil; and 

 about the coil and its inventor it behoves us to say a few words. M. 

 Ruhmkorff was, as his name suggests, a native of Germany, where he 

 was born in the early part of the present century. He came to Paris 

 to learn the making of philosophical instruments, and afterwards esta- 



