522 Astronomical Society. 



of these lists contains the computed differences of longitude between 

 Edinburgh and Greenwich, and the other between Edinburgh and 

 Cambridge; each contains 36 combined results, some of which 

 differ by a much greater quantity than the probable error above 

 assumed. The mean of all the results, as deduced by Professor 

 Henderson, likewise shows the degree of approximation which the 

 method may be considered as capable of giving, in the most favour- 

 able cases. Each of the lists referred to consists of a mean of the 

 differences of the observed intervals at the two places on the several 

 days stated, so that each series of results contains about 100 corre- 

 sponding intervals ; and, consequently, the final difference of lon- 

 gitude, deduced from each list, is the mean result of 36 mean quan- 

 tities, deduced from about 100 corresponding intervals, observed at 

 both stations. In fact, there are 136 corresponding transits made 

 at Edinburgh and Greenwich, and 133 at Edinburgh and Cambridge ; 

 and from all these the difference of longitude between Greenwich 

 and Cambridge comes out = 13"^ 5»-5 — 12™ 44^-4, or 2P-1. But 

 the difference of the longitude of the two places, ascertained by 

 other means, and, doubtless, with scrupulous exactitude, is 23*"54 ; 

 so that the final result of the moon-culminating observations is wide 

 of the truth l)y more than 2 seconds of time. 



The author concludes by observing, that the results here referred 

 to, instead of tending to depreciate the method, may be considered, 

 on the contrary, as affording proof of its excellence ; for, in respect 

 of distant meridians, an error of 2 seconds is undeserving of notice. 

 It is however evident, that, considering the inferiority of instruments, 

 and other sources of error incident to a temporary station, a tolera- 

 ble degree of accuracy can only be expected from an extensive series 

 of corresponding observations. 



On the Position of Lacaille's Stations at the Cape of Good Hope. 

 By Thomas Maclear, Esq. M.A. F.R.S., Astronomer Royal at the 

 Cape. Communicated by Captain Beaufort, R.N. F.R.S. This 

 paper was in part read. 



April 12. — The reading of Mr, Macleai''s paper, on the Position 

 of Lacaille's Stations at the Cape, was resumed, and concluded. 



The astronomical celebrity of the Abbe de Lacaille's visit to the 

 Cape of Good Hope in the last century, together with the remark- 

 able results deduced from his arc of the meridian, naturally prompted 

 Mr. Maclear to become acquainted with his stations, and to connect 

 the southern, which was his observatory, with the present Royal 

 Observatory. In undertaking this task, he soon found that tlie lapse 

 of eighty-five years had obliterated all local evidence of the French 

 astronomer's operations ; and the fact that he was there at all was 

 only kept alive by the inquiries of Captain Everest in 1821. Having 

 carefully perused the various Memoirs of Lacaille relative to his 

 Cape operations, as well as his printed Journal, Mr. Maclear applied 

 to his Excellency Sir Benjamin D'Urban, the governor of the colony, 

 for leave to inspect the oflicial documents. This was readily granted ; 

 but although several letters and notices interesting to the astronomer 

 were brought to light, nothing was discovered tending to promote 



