286 TRANSIT OF VENUS, 1874. EGYPT. 



the Eastern Telegraph Company's submarine cable, gave differences as 

 follows : 



Difference in receiving signals. 

 E - H. 



At Koyal Observatory, Greenwich, by use of Varley's artificial cable 



1874, August i3 and i5 (direct comparison) o'oo 



, , 1 5 and 1 8 (compared through B) +0*14 



At Porthcurno, on the Eastern Telegraph Company's submarine cable 



1874, August 3o (compared through B) o'oo 



, , 3o (direct comparison) o'iz 



No comparisons of the method of observing the first start of the beam 

 were made, as the use of this method was not proposed until the Egyptian 

 Expedition was about to leave England. 



Now, as regards the actual corrections to be applied 



Mr. Criswick observed transits at Greenwich (or the transits of other 

 observers were reduced to his method), and exchanged signals on the English 

 land line with Mr. Ellis at Porthcumo. 



Mr. Ellis at Porthcurno exchanged signals on the English land line with 

 Mr. Criswick at Greenwich, and on the submarine line with Mr. Hunter at 

 Alexandria. 



Mr. Hunter at Alexandria exchanged signals on the Egyptian land line 

 with Captain Browne at Mokattam, and on the submarine line with Mr. Ellis 

 at Porthcurno.* 



Captain Browne observed transits at Mokattam, and exchanged signals on 

 the Egyptian land line with Mr. Hunter at Alexandria. 



The manner of giving signals was similar both in the land and cable work. 

 The personal equations of E and H thus disappear in the deduced longitude, 

 and C and B may be supposed to have been in direct connexion. By what 

 has preceded it will be seen that B makes contact in giving signals O s> 033 

 earlier than C, the effect of which is to increase the east longitude of 

 Mokattam by the half of this quantity, because each operator gave signals 

 in one half only of the whole number of groups. Or the apparent longitude 

 requires a correction of O s> 016. 



As regards the receipt of signals, it is to be remarked that E and H both 

 used, on the one hand a land line, and on the other hand a submarine line. 



* Mr. Hunter also observed transits at Alexandria for determination of the longitude of 

 Alexandria, but this does not come into consideration here. 



