114 ASTRONOMICAL OBSERVATIONS 



23d. Took the pendulum with the wooden rod from my 

 clock, and substituted a grid-iron one, which I had that day- 

 completed. 



March 1st. Immersion of the 1st satellite of Jupiter, ob- 

 served at 8 h 31' 13" meantime, or 8 h 18' 31" apparent time. 

 The planet tremulous, and the belts indistinct: — magnifying 

 power 100. At 9 o'clock in the evening the thermometer 

 stood at 6°. 



11th. Immersion of the 2d satellite of Jupiter, observed at 

 10 h 43' 35" mean time, or 10 h 33' 18" apparent time: — night 

 remarkably fine: — magnifying power 100. 



19th. Immersion of the 3d satellite of Jupiter, observed at 

 9 h 18' 39" mean time, or 9 k 10' 38" apparent time. — The 

 evening hazy; on which account, I think, that at least 30" 

 ought to be added to the observed time of the immersion; 

 which I shall therefore do in comparing the result of I his 

 observation with those of the other satellites: — magnifying 

 power 100. 



29th. Emersion of the 2d satellite of Jupiter, observed at 

 7 h 48' 16" mean time, or 7" 43' 18" apparent time: — the 

 planet and satellites well delined, and very steady : — magni- 

 fying power 100. 



30th. Observations on the occultation of * n by the moon. 



h I II h / U 



t 



The above time of the emersion may possibly be 5 or 6 

 seconds too late; — not having my attention directed to the pre- 

 cise spot where the moon's limb left the star; but, when I 

 discovered it, the light of the star and the moon's limb appear- 

 ed to be nearly in contact. It is however to be observed, that 

 when the emersions happen on the moon's enlightened limb, 

 the observations may generally be considered doubtful, a few 

 seconds*. 



* Lorsquc la lune a passe 1'opposltion, sa partie orientale est eclairee, sa partie occidentale est 

 obscure ; ainsi les immersions se font dans la partie eclairee, et les emersions se font dans la partie 

 objure ; c' est-a-dire, a gauche, dans une lunette astronomique— Je crois que ce sont la les seules 



