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THE LONDON PARIS TELEPHONE.[1]

[Footnote 1:  Paper read before the British Association.—­Elec.  Engineer.]

By W.H.  Preece, F.R.S.

1.  I have already on two occasions, at Newcastle and at Leeds, brought this subject before Section G, and have given the details of the length and construction of the proposed circuit.

I have now to report not only that the line has been constructed and opened to the public, but that its success, telephonic and commercial, has exceeded the most sanguine anticipations.  Speech has been maintained with perfect clearness and accuracy.  The line has proved to be much better than it ought to have been, and the purpose of this paper is to show the reason why.

The lengths of the different sections of the circuit are as follows: 

London to St. Margaret’s Bay 84.5 miles. 
St. Margaret’s Bay to Sangatte (cable). 23.0 "
Sangatte to Paris. 199.0 "
Paris underground. 4.8 "
-----
Total. 311.3 "

The resistances are as follows: 

Paris underground. 70 ohms. 
French line. 294 "
Cable. 143 "
English line. 183 "
—–­
Total (R) 693 "

The capacities are as follows: 

Paris underground. 0.43 microfarads. 
French line. 3.33 "
Cable. 5.52 "
English line. 1.32 "
——­
Total (K). 10.62 "

693 x 10.62 = 7,359 = K R

a product which indicates that speech should be very good.

2. Trials of Apparatus.—­The preliminary trials were made during the month of March between the chief telegraph offices of the two capitals, and the following microphone transmitters were compared: 

    Ader.  Pencil form. 
    Berliner.  Granular form. 
    D’Arsonval.  Pencil "
    DeJongh. " "
    Gower Bell. " "
    Post office switch instrument.  Granules and lamp filaments. 
    Roulez.  Lamp filaments. 
    Turnbull.  Pencil form. 
    Western Electric.  Granular.

The receivers consisted of the latest form of double-pole Bell telephones with some Ader and D’Arsonval receivers for comparison.  After repeated trials it was finally decided that the Ader, D’Arsonval, Gower-Bell (with double-pole receivers instead of tubes), Roulez, and Western Electric were the best, and were approximately equal.