768 REPORT— 1891. 



with perfect clearness and accuracy. The line has proved to be much better than 

 it ought to have been, and the pxirpose of this paper is to show the reason why. 

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



Miles 



London to St. Margaret's Bay 84-5 



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 : — ■ 



Ohms 



Paris underground 70 



French line 294 



Cable 143 



English line 183 



Total (R) . . . .693 



The capacities are as follows : — 



Microfarads 



Paris underground 0-43 



French line 3-33 



Cable 5-52 



English line 1-32 



Total (K) 10-62 



693 X 10-62 = 7,359 = K E. 



2. Trials of Apparatus. — The preliminary trials were made durinp- 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 ,, (Hunnings). 



D'Arsonval Pencil ,, 



De Jongh .....,, ,, 



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 approxi- 

 mately equal. 



These instruments were therefore selected for the further experiments, which 

 consisted of using local extensions in Paris and London. The wires were in the 

 first instance extended at the Paris end to the Observatory through an exchange 

 at the Avenue des Gobelines. The length of this local line is 7 kms. The wires 

 are gutta-percha covered, placed underground, and not suitable for giving the best 

 results. 



The results were, however, fairly satisfactory. The wires wei'e extended to 

 the Treasury in London by means of the ordinary underground .system. The 

 distance is about two miles, and although the volume of sound and clearness of 

 articulation were perceptibly reduced by these additions to the circuit, conversation 

 was quite practicable. 



Further trials were also made from the Avenue des Gobelines on underground 

 wires of five kilometres long, and also with some renters in Paris with fairly satis- 

 factory results. The selected telephones were equally efficient in all cases, which 



