Observations with the Melbourne Great Telescope. 65 



be in a position for minimum deviation. The pivot at h is 

 removable, so that the right-angled arm A R, can be fixed 

 at^/ c b, &c., as one or more prisms are required, the other 

 prisms of course being removed. 



Art, XXI. — Some Notes of Observation with the Melbourne 

 Great Telescope. By Fame Macgeorge, Esq. 



[Eead 12th March, 1871.] 



Mr. Le Sueur's last recorded observations were on the 9th 

 May, 1870, and from that time until the 1st August, 1870, 

 when the Great Telescope was entrusted to me, there appears 

 to have been a period of almost uninterrupted bad weather, 

 during which Speculum A was repolished by Mr. Le Sueur. 

 With that speculum, whose performance has been pei'fectly 

 satisfactory, the observations from which I now make a 

 few extracts have been made. 



A Comet (2 of 1870 ?) of which the elements are supplied 

 in the A stronor)iische Nachrichten of June 1870, appearing 

 to be tolerably favorably situated after perihelion for 

 observation from the Melbourne Observatory, Mr. Le Sueur 

 having computed its place from the elements furnished 

 by that journal, turned the Great Telescope upon it at 7 p.m. 

 13th August, 1870. It was then in the constellation 

 Centaurus in about RA lOh. 45 m. S.P.D. 38° 29', but from 

 the want of a convenient star of reference no differential 

 place could be obtained on that evening. It corresponded 

 with the usual description of telescopic comets, being nearly 

 round, tailless, condensed towards an ill-defined nucleus of a 

 few seconds diameter nearly central, and thinning away 

 outwards until lost against the sky, the approximate total 

 diameter being about 8' 0". The Spectroscope showed the 

 usual cometic lines, one faint band reading 26-9-3 of the 

 Grubb Spectroscope about midway between the F and the 6 

 groups which with same adjustment read 25-7-3 and 27-5-5 

 respectively. At each side of this, faint glimpses of still 

 fainter bands once or twice appeared, but both Mr. Le Sueur 

 and myself failed, after long watching, to obtain a reading of 

 either, and on subsequent occasions the object had become so 

 faint that no spectrum whatever could be obtained, 

 appreciable to the eye. The central line appeared, however, 

 to fall approximately into the position of the brightest of 

 the Nitj'ogen lines. 



F 



