64 ASTRONOMICAL OBSERVATIONS 



17th, About 9 h 14' 9" mean time, or 8' 1 59' 47" apparent 

 time, tlie 1st satellite of Jupiter disappeared behind the body 

 of the planet: Jupiter being too near the opposition for the 

 eclipse to be visible. — Observations of this kind cannot be made 

 with great accuracy. 



March 10th, Emersion of the 2d satellite of Jupiter, obser- 

 ved at 12'' 2G' 10"mean time, or 12 h 15' 41" apparent time : 

 — night remarkably fine, magnifying power of the telescope 

 100. 



]6th, Immersion of the 4th satellite of Jupiter, observed at 

 12' 50' 1" meantime, or 12 1 ' 41' 13" apparent time : — the 

 night clear, but the moon was so near to the planet that her 

 superior light rendered the satellites less distinct; on which ac- 

 count I suspect that at least 10" ought to be added to the time 

 of the immersion, and which I have used in deducing the 

 longitude from this observation: magnifying power 100. 



21st, Emersion of the 1st satellite of Jupiter, observed at 

 8 h 2' 53" mean time, or 7 1 ' 55' 32" apparent time: — the night 

 fine, — magnifying power of the telescope 100. 



28th, Emersion of the 2d satellite of Jupiter, observed at 

 6 h 57' 57" mean time, or 6 h 52' 45" apparent time. 



Emersion of the 1st satellite of Jupiter, observed at 9 h 57' 21" 

 mean time, or 9 h 52' 12 v/ apparent time: — night remarkably 

 line: magnifying power 100. 



April 4th, Emersion of the 2d satellite of Jupiter, observed 

 at 9 h 34' 5 7" mean time, or 9' 1 31' 5 6" apparent time. 



Emersion of the 1st satellite of Jupiter observed at 1 l h 5 l' 36" 

 mean time, or ll" 48' 36" apparent time. — Night uncom- 

 monly clear: magnifying power 100. 



20th, Emersion of the 1st satellite of Jupiter, observed at 

 10 h 9' 28" mean time, or 10' 10' 40" apparent time : — night 

 a little hazy, belts badly defined, magnifying power 100. 



May 6th, Emersion of the 1st satellite of Jupiter, observed 

 at 8 h 27' 56" mean time, or 8 h 31' 33" apparent time:- — very 



(Mem de Berlin 1748/., 103.) M, de l'lsle l'attribuoit a la diffra&ion ou a l'infleflion des rayons qui 

 rasent les bords de la lune (Mem, pour servir a l'hist. de l'astron 1738, p. 249.) l_e phenomene, ob- 

 serve par Grimaldi et par Newton (Opt. parte 3d ) servoit sur-tout a M de l'lsle pour e\pliquer les 

 anneaux que Ton voit autour du soleil dans les eclipses totales ; pour moi, je pense que e'est un: 

 simple illusion optique occasionee par l'irradiation ou le debordement de lumiere. 



Astron. par La Lande Tom. 2d. art. 1991. 



