288 MECHANICAL ELECTRICITY. 



Exp. 40. A brass rod turning instead of a disc, 

 and steel tool, current 5° from the tool towards 

 the brass. 



Magnetism. 



Exp. 41. By filing iron with a steel file, a 

 current of 7^° is produced, from the iron towards 

 the file, and the two metallic bodies become 

 oppositely magnetic, as shown by the following 

 experiments. 



The steel surface becomes positive, and the iron 

 negative, which are electro polar conditions. 



It will be immediately seen, that not only does 

 the friction of a file upon a piece of soft iron induce 

 two oppositely electrical conditions of surface, but 

 that this electrical state is also a truly magnetic 

 condition, and offers an explanation how, or in 

 what manner the various mechanical operations^ 

 screw tapping, drilling, filing, Sfc. evince mag- 

 netic -phenomena. An attempt to establish the 

 opinion of magnetism being a static electro polar 

 condition, was by the author of this paper 

 brought forward, and published in the Report of 

 the British Association, for 1842, page 17. 



