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LECTURES TO SCIENCE TEACHERS. 



it, and are fully occupied in tuning your instrument, for 

 the note to fade away and die out. We may partially get 

 over this difficulty by bowing them with a double-bass 

 bow, but the highest tuning-forks are difficult to bow, and 

 the best plan, which has been carried to a great pitch of 



. 4. Tuning-fork on box. 



accuracy by Helmhpltz, is to excite them by electricity. An 

 intermittent current is made to pass through one prong of 

 the fork by means of a stile and mercury cup, enabling the 

 prong to close the circuit. An electro-magnet pulls by its 



