[ 390 ] 



XLVI. On the Determination of the Longitude of Cairo from 

 Greenwich by the Exchange of Telegraph-Signals, By Cap- 

 tain C. Orde Browne, Chief of Egypt Transit-of- Venus 

 Expedition *. 



EGYPT having been chosen by the Astronomer Royal as 

 the position for a group of stations for the observation 

 of the retarded egress of Venus in transit on Dec. 8, 1874, the 

 question arose as to the feasibility of employing the telegraph 

 connexions between England and Egypt to exchange time- 

 signals, in order to determine the longitude from Greenwich. 

 The Astronomer Royal decided to make trial of this method, 

 if a reliable signal could be obtained through the cable of the 

 Eastern Telegraph Company, when such connexions should be 

 made as would bring the English end of the cable into direct 

 circuit with that at Alexandria. 



With a view to ascertaining this, the Astronomer Royal 

 sent me twice to Porthcurnow, in Cornwall, where the cable 

 comes to land, and where the Eastern Telegraph Company 

 have their tenninal station, under the direction of Mr. Edward 

 Bull, to whom the Directors had kindly sent instructions em- 

 powering him to devote the cable to the purposes of the ex- 

 periment for as long a time as might be required. It is not 

 too much to say that to Mr. Bull's services in suggesting expe- 

 dients, and to his determination and perseverance, is to be at- 

 tributed the success in getting the signals through so great a 

 length of line. 



From Porthcurnow there run two cables — one coming to 

 land at Vigo, which is connected by a separate length of cable 

 with Lisbon, the other proceeding direct from Porthcurnow 

 to Lisbon. A single cable runs from Lisbon to Gibraltar, and 

 another from Gibraltar to Malta. From Malta two cables 

 run to Alexandria. 



To connect Porthcurnow directly with Alexandria, then, it 

 is necessary to "join up " the cable-ends at Malta, Gibraltar, 

 and Lisbon, and, if the Vigo cable be used, at Vigo also; and 

 in the experiment that eventually took place this was the line 

 employed. The particulars of the cables thus brought into the 

 circuit are given hereafter. 



On the occasion of the second preliminary experiment, Mr. 

 Ellis, of the Royal Observatory, and Mr. S. Hunter, of the 

 Transit-of- Venus Expedition, who had been appointed by the 

 Astronomer Royal to conduct the work in concert with the 

 officers of the Telegraph Company at Porthcurnow and at 

 Alexandria respectively, came down to Porthcurnow, and 



* Communicated by the Author, 



