LONGITUDE, AND OBSERVATIONS OF THE TRANSIT. 365 



SUMMARY OF LONGITUDE OF POINT VENUS. 



!i m s 



By the Meridional Transits of the Moon 4. 13. 42-11 



By the Zenith Distances 4. 13.43-05 



By the Occupations of Stars 4. 13. 42-52 



The preliminary longitude of Point Venus, Rodriguez, obtained by Lord 

 Lindsay, by the transportation of 42 chronometers between that station and 

 his observatory at Belmont, Mauritius, is 



4 h . i3 m . 43" -o. 



In this determination the longitude of SUEZ and ADEN were determined by 

 telegraph signals (that of Suez being given in Part II., Section 3), and the 

 chronometers were transported from Suez to Mauritius before the transit of 

 Venus, and from Mauritius to Aden after the transit. These long sea voyages 

 are fatal to the accurate measurement of Meridian distances by chronometers ; 

 it is nevertheless highly satisfactory to find such close agreements as the 

 above. 



The final longitude of Point Venus may be assumed to be 



4 h . i3 m . 42 8 '5 i s 'o. 



In computing the final Equations derived from the observations of the 

 Ingress and Egress of Venus, 1874, December 8, the Longitude of the Head 

 Station at Point Venus was assumed to be 4 h . 13 m . 43 s 0. Hence the error 

 of the Greenwich Sidereal Time is 8 t = + s "5. 



G. L. T. 



OBSERVATIONS OF THE TRANSIT AT POINT VENUS. 



NEATE'S OBSERVATIONS OF INGRESS. 



The instrument used by Lieutenant Neate was an Equatoreal, with object 

 glass of 6 inches aperture, driven by clock-work, constructed for the expe- 

 dition by Messrs. Troughton and Simms. It was fitted with double-image 

 micrometer and solar diagonal reflector, as represented in Plate III. The 

 equatoreal mounting was supported by an iron pillar, which at Rodriguez 

 stood upon a foundation of brickwork laid on the rock. It was protected by 

 a portable wooden observatory, constructed at Greenwich. A sidereal clock 



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