210 Mr. J. South's Aslronomical Observalious. 



tinned visible, notwithstanding its proximity to the planet. 

 Measures of the shadow's distance from the satelHte were 

 procured. At 2'' 22' 10" I distinguished another satellite 

 emerging from the same spot whence the preceding had passed 

 off. My attention was directed to the place some minutes pre- 

 viously, in consequence of a luminous point which far ex- 

 ceeded in splendour the faint light of the planet. As yet only 

 one shadow had been observed, but at 2'' 38' that of the second 

 became visible ; distances of the shadows from their respective 

 satellites were obtained ; distances of the satellites from each 

 other were gotten, and also distances of the shadows from each 

 other. The angles of position of the satellites, and of their 

 shadows, were also ascertained. The interior contact of the 

 first shadow with the limb of the planet, was observed 

 at 3'' 20'; and that of the second at 4* 4' sidereal time. 

 The actual disappearance of the one or the other shadow, 

 owing to the then constant passing of light clouds could not be 

 ascertained. At the commencement of the observations the sun 

 was shining, but the sky, although cloudless, was of a very light 

 blue colour, not at all favourable for sidereal observations. 

 Under more advantageous circumstances in the day-time, I have 

 no doubt measures of the diameters of the shadows might be 

 procured without difficulty. 



%* The five feet Equatorial has a telescope of five feet 

 focal length, and a double object glass of 3|^ inches aperture. 



The Gregorian telescope has a speculum of six inches diameter, 

 and thirty inches focus. 



The measures of the planet's diameters are taken with a wire 

 micrometer made by Mr. Troughton ; its value has been rigor- 

 ously ascertained, and the uniformity of its screw's thread has 

 most satisfactorily stood the severest examinations. 



The declinations of the stars, as also their right ascen- 

 sions, (here given,) will be found suflficiently accurate to identify 

 them, and are for no other purpose introduced. 



Wherever more than one observation of the same phenomenon 

 is given, each may be considered independent of the other ; the 

 same clock is used by each observer, but the moment of obser- 

 vation as estimated by each person is noted upon paper before 

 the least mutual communication is allowed ; so that any coaxing 

 to make observations tally, is absolutely impossible. 



In future communications it is my intention to give all 

 observations in sidereal time, and very much do I wish that 

 other observers would do the same. So Avould the trouble of 

 converting sidereal to mean time, as also the chance of errors in 

 the reduction be entirely precluded ; the considerable in- 

 congruities frequently existing between the sun's observed and 

 computed right ascensions would likewise cease to prejudice 

 the observations. 



