No. XXIII

Continuation of Astronomical Observations, made at Lancaster, Pennsylvania. In a letter from Andrew Ellicott, Esq. to R.

Patterson.

Read Oct. 7th, 1803.

DEAR SIR,

Lancaster O&. 1st, 1803.

I now forward a continuation of my astronomical observations, made at this place: they would have been more numerous had the weather permitted. The season has been remarkably unfavourable for such pursuits.

The results of the observations on the solar eclipse of the 21st of February, the occultations the 30th of March, 27th of May, and 23d of September last, I have not as yet had time to make out:-the duties of my office admitting of but little leisure for scientific enquiries.-But to the observations.

Feb. 21st, 1803. Observations on the beginning of a solar eclipse.

The day was cloudy till about half an hour before the beginning of the eclipse; on which account I had made no preparations to observe it.-A few minutes before the time calculated for the beginning, I directed the telescope to the sun; the lower limb was very tremulous, and indented in many places by a waving, serpentine motion, which will frequently be observed when the sun is near the horizon:-these indents, combined with other causes, produced an uncertainty of a few seconds, (though probably not more than 10 or 12) in the beginning, which I observed at 5h 4′ 57′′ mean time, or 4 50' 57" apparent time.

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, observed at 8h 31′ 13′′ mean time, or 8h 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" 43′ 35′′ mean time, or 10h 33′ 18′′ apparent time:-night remarkably fine:-magnifying power 100.

19th. Immersion of the 3d satellite of Jupiter, observed at 9 18′ 39′′ mean time, or 9 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 this observation with those of the other satellites:-magnifying power 100.

29th. Emersion of the 2d satellite of Jupiter, observed at 7 48′ 16′′ mean time, or 7 43′ 18′′ apparent time:—the planet and satellites well defined, and very steady :-magnifying power 100.

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

The above time of the emersion may possibly be 5 or 6 seconds too late;-not having my attention directed to the precise spot where the moon's limb left the star; but, when I discovered it, the light of the star and the moon's limb appeared 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*.

Lorsque la lune a passé l'opposition, sa partie orientale est éclaireé, sa partie occidentale est obscure; ainsi les immersions se font dans la partie éclaireé, et les émersions se font dans la partie ●bsure; c'est-a-dire, á gauche, dans une lunette astronomique-Je crois que ce sont lá les seules

April 5th. Emersion of the 2d satellite of Jupiter, observed at 10 23′ 29′′ mean time, or 10" 20′ 41′′ apparent time:— night very clear and the belts distinct:-magnifying power

100.

9th. Emersion of the 1st satellite of Jupiter, observed at 9° 9′ 59′′ mean time, or 9h 8' 20" apparent time:-night clear, and belts distinct:-magnifying power 100.

At

22d. Immersion of the 4th satellite of Jupiter, observed at 12h 41 19" mean time, or 12h 42′ 54′′ apparent time. the time this observation was made, the night was very serene and clear:-four belts were distinctly defined on the body of the planet:magnifying power 100.

Emersion of the above satellite was observed at 14h 52' 34" mean time, or 14h 54' 10" apparent time.-The night had become a little hazy, and the belts were scarcely discernable. -The satellite appeared for a few seconds, and then became invisible for more than a minute. From the state of the atmosphere, and the slow manner in which the satellite acquired its light, owing to its oblique way through the shadow of Jupiter, it is my opinion, that at least 2 minutes should be deducted from the observed time of the emersion; which deduction I shall accordingly use in making out the result of the observa

tion.

May 2d. Emersion of the 1st satellite of Jupiter, observed at 9h 21' 34" mean time, or 9h 24′ 46′′ apparent time:night clear, and belts distinct:-magnifying power 100.

9th. Emersion of the 4th satellite of Jupiter, observed at Sh 39′ 28′′ mean time, or Sh 43′ 17′′ apparent time.—The planet and satellites were well defined, and the observation one of the most satisfactory I have made at this place:-magnifying power 100.

Emersion of the 1st satellite of Jupiter, observed at 11h 15′ 46" mean time, or 11h 19' 35" apparent time. This evening I began to pay attention to the decrease of Saturn's ring.

émersions dont on puisse être bien assuré; car quand l' etoile sort de la partie é claireé de la lune, sa lumiere, trop foible par rapport à celle de la lune, ne se distingue pas facilement au premier instant de l'émersion.

Astronomie par la Lande art. 1990.

11th. Saturn's ring well defined; the ansæ are evidently diminishing:-two satellites visible.

14th. Emersion of the 2d satellite of Jupiter, observed at 12h 41′ 54′′ mean time, or 12h 45′ 52" apparent time:-night clear:-magnifying power 100.

16th. Saturn's ring well defined:-the ansæ not perceptibly diminished since the 11th.

27th. Occultation of a star, supposed to be Leonis (a) observed at 8h 17' 53" mean time, or 8h 21' 10" apparent time.

Saturn's ring well defined :-the ansæ decreasing, and appear more luminous towards their extremities than near the body of Jupiter: two satellites very distinct.

June 6th. The night very clear and fine; Saturn's ring was particularly attended to: the ansæ appeared more luminous and sparkling toward their extremities, than near the body of the planet: three satellites were visible.

9th. Saturn's ring yet visible: the anse were distinct during the twilight, but faint afterwards.

13th. Immersion of the 3d satellite of Jupiter, observed at 9h 7′ 56′′ mean time, or 9h 8' 25" apparent time:-the planet and satellites tolerably distinct:-magnifying power 100.

15th. Saturn's ring decreasing: the anse were scarcely descernable after the end of twilight.

17th. Emersion of the 1st satellite of Jupiter, observed at 9h 45′ 43′′ mean time, or 9h 45' 21" apparent time.-The night clear, and the planet and satellites well defined:—magnifying power 100.

Saturn's ring very faint:-the ansæ were invisible after the end of twilight.

18th. Saturn's ring more faint than last evening: the ansæ disappeared before the end of twilight.

21st. Saturn's ring almost invisible:-the anse would frequently disappear for whole minutes, and then become visible for a few minutes more.

22d. The ring of Saturn has almost disappeared: the western ansa only visible, and that for but a few seconds at a time.