1877.] R. S. Broiigh— Pro/. Graham Bell's TelcjyJione. 253 



periodic currents being made to operate, a suitable receiver (electro-magne- 

 tic, as in Eeiss's : or electrostatic as in Varley's) in the distant station will 

 there reproduce a note of precisely the same pitch as the note originally 

 sounded in the sending station. 



By this arrangement each contact made in the sending station will 

 transmit a current o£ definite magnitude, depending on the strength of the 

 battery employed. All the current waves thus sent to the hne will be pre- 

 cisely similar, and the only way we can modify them is in regard to the 

 rapidity with which they follow one another. 



Hence the note reproduced in the distant station will represent the 

 original note in pitch only ; the fundamental vibration will be the same, but 

 bereft of all its harmonics. Any characteristic timbre the received note 

 may possess will be entirely due to the nature of the receiving apparatus, 

 and not in any degree to that of the sending apparatus. 



Such, in its main features, was the Telephone of Eeiss — a mere " tone" 

 Telephone, reproducing the pitch, but losing the timbre. It is noteworthy 

 that in such a Telephone, the intensity of the received note is entirely inde- 

 pendent of the intensity of the original note. So long as the original note 

 is strong enough to efficiently work the battery contact, we can, within 

 certain limits, vary the intensity of the received note at pleasure, by vary- 

 ing the strength of the battery employed. 



Now the Telephone before you not only conveys the pitch, but also 

 reproduces the timbre with such exquisite accuracy, that a known voice is 

 at once recognized by the ear. Moreover, it is not only sensible to musical 

 tones, clang-tint and all, but to any noise, so that it is essentially a " sound 

 transmitter." 



To facilitate the comprehension of the construction of the instrument, 

 I have had a large-scale section drawn. JV yS is a hard steel rod, perma- 

 nently magnetized. (See Plate III.) 



A is Si short piece of soft iron, of somewhat smaller diameter than the 

 rod, screwed in to its end AT. A becomes magnetized by induction, so that 

 virtually A S forms a single magnet. 



JS is a circular elastic diaphragm of soft iron about four thousandths 

 of an inch thick. 



G C is Si narrow circular coil, of the thinnest silk-covered copper wire, 

 smTounding the iron core A, 



D JE D is Si light cylindrical wooden case. 



The magnet AT /S' is fixed to the wooden case by means of a screw at ^. 



The diaphragm B is fixed to the wooden case at B B. 



The hollow part of the case surrounding the coil G G acts as a resona- 

 tor. 



This constitutes the whole apparatus. The apparatus in the sending 



