Part 106

Per Meridian Mark.

d h ′ ″ 8 ☉ West Limb on Merid. 12 0 36 East Limb on do. 12 2 52 —-—— Centre 12 1 44 Correct Noon per Clock.

Applied to Going of Clock.

Nov. 3d, at Noon ′ ″ } Clock slower than ☉ 4 5.6 } Daily gaining of the Clock ☉ faster than mean time 16 11 } over mean or equal time. —-—— } Clock faster than m. time 12 5.4 }

4th, } Clock slower than ☉ 2 53.2 } ′ ″ ☉ faster than mean time 16 9 } From 3d to 4th 1 10.4 —-—— } Clock faster than m. time 13 15.8 }

7th, } Clock faster than ☉ 0 31 } From 4th mean to 7th } 1 5.1 ☉ faster than mean time 16 00 } at a mean per day } —-—— } Clock faster than m. time 16 31 }

8th, } Clock faster than ☉ 1 44 } ☉ faster than mean time 15 56 } From 7th to 8th 1 9 —-—— } Clock faster than m. time 17 40 } Thus the Clock gains at a mean, per day, 1′ 8″.

Whence, Nov. 2d, at noon, the Clock was 10′ 57″ faster than mean time, gaining 68″ per day; and 4^h 17′ gains 12″, wherefore at the internal contact, the Clock was 11′ 9″ faster than mean time.

Whence the contact was at 4^h 5′ 51″ mean time; or 4^h 21′ 2″ apparent time.

Eclipse of the Sun, January 9th, 1777.

The Gregorian Reflector, with the magnifying power of 95, was made use of for this Observation; which, as well as the Observation of the Transit of Mercury, was made in the College-Library, to which the Telescope belongs.

While Mr. Rittenhouse was endeavouring to adjust the two-f. reflector belonging to the Library of the city of Philadelphia, made by Short, and which had been borrowed on this occasion, I observed with the greatest certainty the first contact of ☾’s limb with the ☉, which was shining very bright, and the telescope in the best order, viz. at 8^h 57′ 27″ per clock.

The same was visible, in about 3″ more, to Mr. Lukens, with the equal altitude instrument, magnifying about 25 times.

Mr. Rittenhouse had not got the other reflector ready to observe the beginning of the eclipse: but the end was observed by both of us to the same instant, viz. at 11^h 48′ 50″ per clock.

The clock, at noon, was 23″ slower than mean time, whence

Beginning of the Eclipse 8^h 49′ 55″ } Apparent End of the same 11 41 15 } time.

N.B. The clock stopped once during the Observation, owing, it was supposed, to the cold weather; but was oiled a little, and set a going again by a stop-watch that beats seconds, and which was set with the clock at the beginning of the eclipse: so that she lost no time. She was examined at noon, and found as above by the meridian mark. But this mark itself, having been lately shaken with the stormy weather, is to be re-examined, and also equal altitudes taken the following days.

The annexed micrometer measures were taken for determining the quantity of the eclipse, chiefly by Mr. Rittenhouse. More would have been taken, but the Sun was hid under clouds for about an hour after the middle of the eclipse, and broke out again a little before the end.

Micrometer Measures.

h ′ ″ inches. tenths. 500ths. 9 15 0 2 2 6 } distances of the cusps. 31 0 3 1 ½ }

10 17 5 1 1 14 } enlightened parts remaining. 22 0 1 1 23 }

11 37 0 1 7 6 } 38 46 1 5 21 } distances of the cusps. 42 26 1 2 18 }

Continuation of the Observations for adjusting the Clock.

Jan. 11th. ☉’s W. limb on Merid. } E. limb on do. } ————— Centre on do.

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Footnote A48:

The calculations are here wanting, in Dr. Smith’s MSS.

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