VOL. LXXVII.] PHILOSOPHICAL TRANSACTIONS. 215 



been noticed the 18th ; but, whether owing to my great attention to the former 

 satellite, or to the closeness of this latter, which was nearly hidden in the rays 

 of the planet, I could not be well assured of its motion. The first moment that 

 offered for continuing these observations was on Feb. the Qth, when I saw my 

 first discovered satellite nearly in the place where I expected to find it. I per- 

 ceived also, that the next supposed satellite was not in the situation where I had 

 left it on the 7th, and could now distinguish very plainly that it had advanced in 

 its orbit, since that day, in the same direction with the other satellite, but at a 

 quicker rate. Hence it is evident, that it moves in a more contracted orbit; and 

 I shall therefore call it in future the first satellite, though last discovered, or 

 rather last ascertained ; since I do not doubt but that I saw them both, for the 

 first time, on the same day, Jan. 11th, 1787. 



I now directed all my attention to the first satellite, and had an opportunity to 

 see it for about 34- hours; during which time, as far as one might judge, it pre- 

 served its course. The interval which the cloudy weather had afforded was how- 

 ever rather too short for seeing its motion sufficiently, so that I deferred a final 

 judgment till the 10th; and, in order to put my theory of these 2 satellites to a 

 trial, I made a sketch on paper, to point out before-hand their situation with 

 respect to the planet, and its parallel of declination. The long expected evening 

 came on, and, notwithstanding the most unfavourable appearance of dark wea- 

 ther, it cleared up at last. And the heavens now displayed the original of my 

 drawing, by showing, in the situa,tion I had delineated them, the Georgian pla- 

 net attended by 2 satellites. For upwards of 5 hours I saw them go on together, 

 each pursuing its own track; and I left them situated, about 2 o'clock in the 

 morning on February the 1 1 th, as represented in a figure then drawn of their 

 appearance. 



I have not seen them long enough to assign their periodical times with great 

 accuracy; but suppose that the first performs a synodical revolution in about 84- 

 day s, and the 2d in nearly 13-l days. Their orbits make a considerable angle 

 with the ecliptic; but to assign the real quantity of this inclination, with many 

 other particulars, will require a great deal of attention, and much contrivance: 

 for, as estimations by the eye cannot but be extremely fallacious, I do not expect 

 to give a good account of their orbits till I can bring some of my micrometers to 

 bear on them ; which, these last nights, I have in vain attempted, their light 

 being so feeble as not to suffer the least illumination, and that of the planet not 

 being strong enough to render the small silk-worm's threads of my delicate micro- 

 meters visible. I have however several resources in view, and do not despair of 

 succeeding pretty well in the end. 



