identifying a submerged Telegraph-cable. 441 



from the bank through the guards, and to observe the effects 

 on this instrument, first, when the battery and instrument were 

 joined to the guards of the same cable, and, secondly, when the 

 battery was joined to the guards of one and the instrument to 

 the guards of the other cable. This, however, did not answer. 



My next idea was to join an instrument to the guards, and 

 to observe whether it was sufficiently sensitive to show any 

 sign of the current that would be induced in the guards of the 

 cable when a strong current was sent through the conductor ; 

 and on mentioning this to Mr. J. J. Allen, Assistant Superin- 

 tendent of Indian Government Telegraphs, he suggested that 

 in this case a telephone attached to the guards might be influ- 

 enced. The value of this suggestion was clear to me ; for I 

 have reason to know how exceedingly sensitive an instrument 

 the telephone is, having about a year ago made for Mr. 

 Schwendler the experiment to convey messages from one 

 bank of a river to the other without any conductor between 

 the two banks but the water, which experiment was for a cer- 

 tain distance quite successful. 



I may now be allowed to detail the experiments which I 

 made with the telephone. 



A B is a submerged telegraph-cable about 7300 yards long, 

 and having an absolute translation-resistance of 580 me- 

 gohms; 



is the conductor of copper of 23 ohms resistance ; 



/ CTCT61D the guards, 12 galvanized iron wires each 

 weighing 900 lb. per mile ; 



C D the portion of the cable raised to the repairing-boat ; 



E the signalling battery, joined to the conductor ; 



T the telephone, of 2*5 ohms resistance. 

 Phil. Mag. S. 5. Vol. 9. No. 58. June 1880. 2 I 



