Bell's Telephonic Researches 



circuit by operators, each manipulating a differ- 

 ent key of the instrument. These messages would 

 be read bv operators stationed at the distant 

 piano, each receiving operator listening for sig- 

 nals for a certain definite pitch, and ignoring all 

 others. In this way could be accomplished the 

 simultaneous transmission of a number of tele- 

 graphic messages along a single wire, the number 

 being limited only by the delicacy of the listener's 

 ear. The idea of increasing the carrying power 



Fig. i 



of a telegraph wire in this way took complete 

 possession of my mind, and it was this practical 

 end that I had in view when I commenced my 

 researches in electric telephony. 



In the progress of science it is universally found 

 that complexity leads to simplicity, and in nar- 

 rating the history of scientific research it is often 

 advisable to begin at the end. 



In glancing back over my own researches, I 

 find it necessary to designate, by distinct names, 

 a variety of electrical currents by means of which 

 sounds can be produced, and I shall direct your 

 attention to several distinct species of what may 

 61 



