Occultation of a fixed Star ly Jupiter. 143 



Large pieces of fresh made charcoal should be attached to a 

 weight, and let down through the oil into the water by means of 

 a cord. The charring of the cask long since recommended, ought 

 to be attended to. After the charcoal has remained for some 

 time in the water, it ought to be drawn up by the cord, and re- 

 cently prepared pieces should be attached to the weight, and let 

 down. This could be repeated daily, and the water could be drawn 

 from a cock at the lower part of the cask. In this manner char- 

 coal could be put in or removed without exposing the surface of 

 the water to the atmosphere. 



I remain your most obedient humble servant, 



Joseph MacSweeny. 



XXV. Occultation of a fixed Star ly Jupiter. 



To Mr. Tilloch. 

 ^ Aug. 24, 1819. 



Sir, — \Jn viewing Jupiter, on the 8th instant, about 9 o'clock 

 in the evening through a small reflecting telescope, I observe'd 

 a bright star, apparently about the 7th magnitude, nearly in con- 

 junction with him, in a line with his satellites, but on the oppo- 

 site or western side ; all the satelhtes being at that time on the 

 eastern side of Jupiter. It was at about the same distance from 

 Jupiter's body as the fourth satellite, and of about the same 

 brightness. Having no convenient instrument at hand for mea- 

 suring the distance, I can only speak from estimation. On the 

 following evening, I could not discover the star ; it being either 

 eclipsed by Jupiter's body, or else rendered invisible, through the 

 smoky atmosphere of this place, by the superior brilliancy of Ju- 

 piter.' On the following evening (the 10th), it was nearly in con- 

 junction with the 4th satellite, and might readily have been mis- 

 taken for one of Jupiter's satellites by a casual observer ; as the 

 2d satellite was then eclipsed. On endeavouring to identify this 

 star, which is situated near 9 Capricorni, and wliich exceeds in 

 brilliancy many in its immediate vicinity, I was surprised to find 

 that it is not inserted in any catalogue. I have examined in 

 vain the large and small catalogues of Bode, the catalogues of 

 Piazzi, Bessel, Cagnoli, Zach, and the Hisloire Celeste of La- 

 lande. But in none of them (although many smaller stars are 

 noted) is there the least mention of it. Indeed I was much sur- 

 prised to find, in the course of this inquiry, how much remained 

 to be done towards forming a complete catalogue of all the stars: 

 but, such an undertaking would be so laborious, that 1 fear, 

 without the aid of private application, and a more general com- 

 munication amongst observers, the task will never be fully accom- 

 plished. 



