356 LECTURES TO SCIENCE TEACHERS. 



sends off can be transmitted through the line of wire to the 

 distant receiving instrument. There are the four notes of the 

 chord, and you can distinctly hear the pitch of each particular 

 note sent from one end by means of a key, repeated at the 

 other end of the wire. This is a very remarkable transfor- 

 mation of energy. What we have done before is compara- 

 tively easy to understand. We have sent the actual vibra- 

 tions of a sounding body through thin pieces of wood ; but 

 in this instrument we have transformed vibrational energy 

 into another form of molecular force, electricity, one which 

 we consider to be probably vibratory, though the point is 

 still sub judice ; then we transmit the force along a metal wire 

 miles away, and at the further end we are able to re-analyse 

 it back into sound vibrations once more. It is likely to prove 

 of very great value practically. For instance, certain receiving 

 instruments will only respond to their own forks, and in 

 telegraphing you will easily understand how it would keep 

 perfect secrecy. In military service it would be possible 

 to have a telegraph set up like this, so that you, carrying 

 the right receiving instrument, would not be liable to what 

 was often done in the American War, namely, to have a 

 wire " tapped " and the messages carried off by the enemy. 



