290 MECHANICAL ELECTRICITY 



being sufficiently powerful to induce magnetic 

 polarity in any considerable mass of metal.* 



Exp. Another file was neutral, rattier attrac- 

 tive. The repulsive end of a piece of magnetic 

 iron wire was employed. After filing briskly 

 around the surface of its extremity, the file 

 repelled, and the wire attracted the north-pole. 



Exp. Took the opposite extremities of the 

 file and wire, the wire repelled, the file attracted, 

 but on rubbing them together, an instant change 

 took place. The file repelled, and the wire 

 attracted the needle. 



Repeated with the same results. These opera- 

 tions were performed when the metals pointed 

 southward. It was discovered, however, that an 

 opposite result took place when the filing was 

 performed towards the north. The file then 

 attracted and the wire repelled the north-pole ; 

 but the evinced trifling difference of affinity be- 

 tween iron and steel, as shown in (15) may tend 



* The finer the materials employed the more highly de- 

 veloped were the magnetic effects, and on this account iron 

 wirt was used. 



