140 Royal Astronomical Society. 



elements is very satisfactory. In the middle of last month the 

 comet became double and presented a most singular appearance, for 

 the nebulosities surrounding the two nuclei scarcely joined each 

 other, and the whole object exactly resembled two comets in very 

 close proximity. This phenomenon was first observed by Professor 

 Challis, with the Northumberland telescope, on Jan. 15. It was, 

 however, seen in America on the 13th. As viewed in Mr. Bishop's 

 refractor on Jan. 24, the comet was much like the dumb-bell nebula 

 in Vulpecula seen under small optical power. The distance between 

 the two comets has been since rapidly increasing, and the deviations 

 of the positions of both comets from those deduced from Santini's 

 Elements are now very great. 



On the 24th of January last, Father De Vico discovered a tele- 

 scopic comet in Eridanus ; this is the third comet detected by our in- 

 defatigable associate. On the subject of comets the Council received 

 a letter from our distinguished Associate Professor Schumacher, 

 dated May 5, requesting that the observations made in England 

 might be immediately forwarded to him, and promising a like return. 

 The Council accordingly directed that all observations which came 

 into their hands should be immediately sent to M. Schumacher; 

 and they hope that those Fellows who observe comets will lose no 

 time in communicating their observations through Mr. Hind, who 

 has undertaken to forward them to Professor Schumacher. 



The return of Mr. Piazzi Smyth to Europe enables the Council 

 to furnish the meeting with a short account of Mr. Maclear's geo- 

 detical operations. 



The anomalies known to exist in Lacaille's southern arc, and 

 which Colonel Everest, when he visited the scene of operation, sus- 

 pected to have arisen from local attraction on the plumb-line, have 

 been the means of leading Mr. Maclear into a very extensive mea- 

 surement of the same kind, of which, in such a report as the present, 

 we can only give a passing notice. When, in 1837, Lacaille's Ob- 

 servatory at his southern end was trigonometrically connected with 

 the Royal Cape Observatory, there was found to be error in the lati- 

 tude of the former, certainly of the kind which the local attractions 

 would cause, but by no means sufficient in amount to explain all the 

 difference between the theoretical and the measured degree. But 

 even this partial explanation was destroyed by Mr. Maclear's subse- 

 quent measures with the zenith sector at both ends of Lacaille's arc, 

 which produced results agreeing (as to the length in the heavens of 

 that arc) almost exactly with that of Lacaille. The discordance 

 being thus thrown upon the trigonometrical part of the operation, 

 Mr. Maclear (1840-41) carefully measured a base of 42,000 feet 

 nearly on the site of Lacaille's and then re-observed all his triangles, 

 feeling confident that the former stations had been recovered in every 

 instance to within a few feet. The length of the degree thus found 

 halved the difference between Lacaille and the modern state of the 

 theory, being about 200 feet less than that of the former, and about 

 as much more than that of the latter. But, the old triangles being 

 but ill-chosen for causing errors of observation to produce their least 



