l88 ON PROFESSOR BELl's ARTICULATING TELEPHONE. 



It cannot be too distinctly stated that there is no mechanical 

 conveyance of sound vibrations. The sound is converted into 

 electricity/, which travels along the wire and is reconverted into 

 sound at the other end. Conversation has been carried on 

 between stations more than 200 miles apart on land, and also 

 through 60 miles of submarine cable, with instruments constructed 

 exactly like those described above, which I now show you. The 

 currents so produced are very feeble ; Mr. Gavey, of the Bristol 

 Post Office, tells me that he attempted to measure the strength of 

 a telephone current, and estimates it at less than the one ten- 

 millionth part of that produced by a pint Daniell's cell. 



It is necessary that all extraneous noise should be carefully 

 excluded, while conversation is being carried on by the telephone. 

 It will then be found that speech is reproduced with perfect 

 distinctness, and that different voices may be readily recognised 

 through it. Singing, and instrumental musical tones may often 

 be heard when articulate speech is inaudible^ or at least 

 indistinguishable. 



One great objection to the use of the Telephone over busy 

 lines arises from this fact ; — a wire conveying a very feeble current, 

 or none, placed near a wire over which a strong current is 

 passing, is liable to be acted upon by the stronger current, through 

 what is called Induced Electricity- Hence, a telephone wire near 

 others conveying battery currents, draws induced currents into itself, 

 and these, entering the receiving telephone, are there converted into 

 sounds which are very like the pattering of hail against a window, 

 and are quite enough to overpower the human voice. Hence 

 though telephones can easily be used over single wires, conversation 

 is much interfered with if the wire at any point in the circuit is 

 near wires used for ordinary telegraphic purposes. Through the 

 kindness of Mr. Sampson, (Postmaster of Bristol,) and of the 

 Netham Chemical Co., I was enabled to verify this for myself on 

 the private wire between our General Post Office, and the Netham 

 Works. 



