for the year 1877. xxv 



apparatus at the two stations can be secured, a thing not 

 very difficult to accomplish. From the skill required to 

 work the ordinary duplex system successfully, it is still 

 doubtful whether it will come into general use, and the 

 complications of the ordinary multiple system will, I 

 imagine, keep it rather in the category of telegraphic curi- 

 osities, which are already numerous, than permit of its 

 practical application to commercial telegraphy. 



These remarks, however, do not apply with so much force 

 to the last achievement in Telegraphic Electricity, the 

 Harmonic Telegraph or Telephone ; and as the discoveries in 

 this direction bear signs of promise, a few words on the 

 subject may not be out of place here. It has long been 

 known that the number of electric impulses that can be 

 sent along a conductor in a given time under proper condi- 

 tions appear to be, comparatively speaking, almost unlimited; 

 at all events, as numerous as are necessary to produce almost 

 every sound audible to the human ear. It has been shown, 

 for instance, that if the electric contacts, and hence impulses, 

 are given by the vibrations of tuning forks or musical reeds 

 at the sending station of a telegTaph line^ tuning forks or 

 reeds of a similar pitch can be set in action at the distant 

 station, and that a full series of musical notes can thus be 

 transmitted from one station to another. Some electricians 

 have lately put this into practice, notably Mr. Eeiss, of 

 Friedrichsdorf, in Germany ; Mr. Elisha Gray, of Chicago ; 

 Professor Bell, of Boston ; and M. Paul la Cour, of Copen^ 

 hagen. To make what I have to say clear,, I must call your 

 memory to the fact that musical notes or sounds to which 

 the human ear is sensible consist of vibrations varying 

 from eight up to about 86,000 per second ; if they 

 are below eight they simply constitute a number of 

 separate noises, bat if more than eight they form a tone ; 

 beyond 36,000 per second they become insensible to 



