ON THE ELECTRIC TELEPHONE. 



W. F. BARRETT, f.r.s.k 

 [Read November 19th, 1877.] 



The following paper does not lay claim to any originality. It 

 is simply a brief description of an instrument which will probably 

 play an important part in the future of the human race ; 

 together with an historical note of what had been accomplished 

 by Reis fifteen years ago. 



The various attempts to communicate audible speech by means 

 of electricity have culminated in the recent discovery by Professor 

 Graham Bell of the articulating telephone. The discovery was 

 not the result of chance but of long and patient endeavour. 

 Every sound of the human voice is communicated from the 

 speaker to the listener by means of aerial vibrations of a definite 

 character. For the same sound the same wave-form is always 

 reproduced. Starting from this fundamental axiom, Professor 

 Bell's first efforts were made with the view of visibly recording 

 speech. A model of the human ear was constructed, to the 

 tympanum of which a delicate style was attached, the movements 

 of which recorded themselves on a moving slip of smoked glass. 

 Thus the vowel sounds and a few simple words were readily 

 recorded by this phonautograph ; which, however, differed but 

 little from similar instruments previously constructed. These 

 experiments revealed to Professor Bell the important point that 

 the transmission of speech by electricity could onlybe accomplished 

 by using what may be termed an undulatory current : that is to 

 say, one that merely varied in strength without the occurrence of 

 any actual interruptions which would give rise to a discontinuous 

 or intermittent current. It is this principle of an unbroken 

 current which distinguishes Bell's telephone from all preceding 

 efforts. The electric currents in this telephone are in simple 

 proportion to the motions of the air produced by the voice, and 

 further the electric waves sent to the distant extremity are (by 

 a receiving arrangement precisely similar to the transmitting 

 instrument), caused to reproduce motions of the air identically 

 the same in character as those that gave birth to the currents. 

 Thus not only is articulation heard perfectly, but moreover, the 



