252 E. S. Brongh— Pro/. Graham BelVs Teleplione. [Dec. 



be come to which will result in the long-desired improvement being car- 

 ried out. 



The Chair was then taken by the President, the Hon. Sir E. C. Batlet, 

 K. C. S. I. 



Mr. R. S. Beough read the following note on Professor Graham 

 Bell's Telephone- 

 Pro/! Oraham BelVs TelepJio^ie. 



With the aid of the report of the admirable description of Prof. Bell's 

 Telephone, given by Mr. W. H. Preece before the meeting of the British 

 Association at Plymouth, and of the excellent papers recently published on 

 the same subject in " Nature," the " Engineer," and " Engineering," we 

 have been enabled to make up a few for experimental purposes in the Tele- 

 graph Workshops at Alipore ; and, as I have no doubt many Members of 

 the Society are anxious to make themselves practically acquainted with 

 these most ingenious instruments, I have ventured, at the instance of the 

 Honorary General Secretary, to place a pair before you this evening. 



Before proceeding to illustrate practically the working of the Tele- 

 phones, it will perhaps be generally acceptable if I give a brief preliminary 

 explanation of their principle and construction. 



I will follow Mr. Preece in recalling to mind the fact that the charac- 

 ter of a musical note, that is of a sensible periodic sound, is determined by 

 its condition with respect to three qualities, namely, 'pitch, timlre, and in- 



The pitch, increasing as the period of the note diminishes, will vary 

 directly as the number of vibrations per unit of time. 



The timhre, as Helmholtz has shewn, depends on the harmonics of the 

 fundamental simple vibration, which are present. 



. While the intensity increases and diminishes with the amplitude of the 

 vibrations. 



Theoretically speaking, the transmission of different notes, in so far as 

 regards only their different pitches, by means of electricity is a compara- 

 tively simple thing. We have only to arrange so that when we sound the 

 note to be transmitted at, what in Telegraph parlance I shall call, the 

 *' sending station," its vibrations shall be communicated to a moveable con- 

 ductor, which shall make and break contact between a battery and the line 

 with the precise frequency of the vibrations it takes up. Thus for each 

 contact made, a current will be sent to the line ; and a series of periodic 

 currents will be received at the distant station, the length of whose period 

 will depend on the pitch of the note sounded at the sending station. These 



