Longitude of the Melbourne Observatory. 79 



Art. VIII. — Notes on the Longitude of the Melbourne 

 Observatory. 



By E. J. White, Esq. 



[Read before the Royal Society of Victoria, 25th September, 1876.] 



The Melbourne Observatory having been selected by the 

 American and German parties charged with the observation 

 of the last transit of Venus in these parts of the world 

 as a principal station of reference for the determination of 

 the longitudes of their stations, it becomes a matter of some 

 importance to investigate the authority on which the lon- 

 gitude of the Melbourne Observatory itself depends. 



The longitude of Melbourne Observatory was originally 

 determined from that of Williamstown by means of trian- 

 gulation. The longitude of Williamstown Observatory was 

 found by means of moon culminations observed in the years 

 1860, 1861, and 1862 ; of these 142 were compared with 

 corresponding observations at Greenwich and the Cape of 

 Good Hope, from which 9h. *39m. 38*8s. was computed and 

 adopted as the longitude east of Greenwich ; the triangu- 

 lation showed that the Melbourne Observatory was 16"00s. 

 to the east of Williamstown, so that 9h. 39m. 54-8s. was 

 adopted for the former. In the year 1874 we were requested 

 by the German Commissioners entrusted with the manage- 

 ment of the transit of Venus expeditions to observe all the 

 moon culminations that were visible in Melbourne during 

 the months of October, November, and December, in 1874, 

 and January of the next year. This was done, and we 

 succeeded in observing 29 culminations of the first limb, 

 and 20 of the second limb. On finally reducing these 

 observations lately, it became a matter of interest to see 

 how this independent determination of our longitude would 

 agree with the one derived from Williamstown. Sir 

 George Airy, the Astronomer Royal, having recently obli- 

 gingly furnished us with the observations of the moon 

 taken during the same period at Greenwich, it became 

 possible to easily determine this agreement without directly 

 computing the longitude. This was done in the following 

 manner : — The Greenwich list contains the Nautical Almanac 

 errors of the moon's right ascension, as found from actual 

 observation at Greenwich ; the errors of the Nautical Alma- 

 nac were also computed from the Melbourne observations, 

 using our adopted longitude ; if, now, the Melbourne errors 

 for the same dates come out the same as the Greenwich 



