By the duration between the beginning and end of the eclipse, at Kinderhook we find the sum of the horiz. semid. reduced to the time of the conjunc. 32′ 08′′ 39 If we suppose that the true duration was greater than what was observed, by 4", which appears very probable, we shall have. By the observation at Natchez, supposing the beginning 4 ́ ́ before it was perceived by Mr. Dunbar. 32 09 17 32 09 00 Sum of the horiz. semidiam. in conjunction by a mean of the observations 32 09 08 Comparing these sums and differences of semidiameters with the tables we find the correction of the semidiameter of the . -1′′ 93 -1 87 The occultation of Spica Virginis, May 24th, 1801, was observed in all Europe, the observations most to be confided in and the most proper to determine the diameter of the moon. are the following. Im. Mean time. 8 49 16 2 Royal observatory in the island of Leon. Difference of meridians. Difference of latitudes in conjunction by the observations in the island of Leon. Correction of the semidiameters of the by the observations of M. Mechain, combined with the difference of latitudes observed in the island of Leon. By the observations in the Military School. 9 28 37 0 00 34 10 7 9 29 01 9 I have also calculated the annular eclipse, April 1st, 1764, by the new tables, and have deduced Semidiameter corresponding to the constant lunar parallax of the tables. Constant semidiameter of the Correction. 15' 33" 69 1 70 15 31 99 31 03 98 From this statement, it will appear, that the semidiameter of the moon, ascertained in the occultations, may vary 2" on account of the irregularities of the disk of the moon; it may be further remarked, that the periodical variations of the parallax of the moon, by the new tables, are those which Mayer found by his theory, and which differ from the coefficients determined by Laplace. According to the calculations of Mr. Burckhardt, the sum of the periodical differences of the two authors above mentioned, may, under very extraordinary circumstances, amount to 7".In this case the uncertainty of the semidiameter of the moon would be 1′′ 9. In the explanation of these tables, it is maintained that M. Burg has diminished the diameter of the moon by 2", but it is easy to see that the diameter of the moon by these tables, is the same as has been determined by M. De Lalande. For the proportion of the horizontal equatorial parallax of the moon, and the horizontal diameter of the moon according to Burg, is 60: 32′ 45′′ 1. According to De Lalande, the proportion between the horizontal parallax at Paris and the horizontal diameter of the moon, 60 32′ 46" 6, vide the tables of the third edition of his astronomy, printed in 1797, page 77. According to Burg, the constant equatorial parallax. =57′ 01′′0 =56 58 3 And although the constant parallax of De Lalande referred to the equator differs nearly 4", nevertheless, the constant semidiameters are the same. From the above data, the horizontal diameter of the moon corresponding to the constant parallax for Paris, will be, which proves that the results are sensibly the same. No. XLVIII. Observations on the Eclipse of 16 June, 1806, made by Simeon De Witt Esq. of Albany, State of New-York, addressed to Benjamin Rush M. D. to be by him communicated to the American Philosophical Society. Read May 1807. Albany, April 25th, 1807. DEAR SIR, WITH this I send you for the American Philosophical Society, a painting, intended to represent the central eclipse of the sun on the 16th of last June. It is executed by Mr. Ezra Ames, an eminent portrait painter of this place, and gives, I believe, as true a representation of that grand and beautiful phenomenon, as can be artificially expressed. The edge of the moon was strongly illuminated, and had the brilliancy of polished silver. No common colours could express this; I therefore directed it to be attempted as you will see, by a raised silvered rim, which in a proper light, produces tolerably well, the intended effect*. As no verbal description can give any thing like a true idea of this sublime spectacle, with which man is so rarely gratified, I thought this painting would not be an unwelcome present to the Society, or an improper article to be preserved among its collection of subjects for philosophical speculation. But, in order to have a proper conception of what is intended to be represented, you must transfer your ideas to the heavens, and imagine, at the departure of the last ray of the sun, in its retreat behind the moon, an awful gloom immediately diffused over the face of nature; and round a dark circle, near the zenith, an immense radiated glory, like a new creation, in a moment bursting on the sight, and for several minutes fixing the gaze of man in silent amazement. * This painting is deposited in the Hall of the Society, and strongly resembles the drawing made by Mr. Ferrer, 15 miles below Albany, which is represented in Pl. VI. Fig. 1. The luminous circle on the edge of the moon, as well as the rays which were darted from her, were remarkably pale, and had that bluish tint, which distinguishes the colour of quicksilver from a dead white. I attempted to make observations on the different stages of the eclipse, but for the want of a meridian, and glasses of sufficient powers, I am sorry I could not make them with the accuracy I wished. I however send them as they are,-they may possibly. be of some use among the collections from other quarters. I have also taken some pains to ascertain the extent of the moon's shadow, in a northerly and southerly direction. The best information I have obtained is from Judge Thorn of the County of Washington, who assures me that the northern edge of the shadow passed nearly along the south bounds of Campbell's patent in the town of Granville, which on my map of the State, lies in latitude 43° 22′ and longitude 0° 45′ east of the meridian of New-York; and from Johannes Miller Esq. of the county of Orange, who determined the southern edge of the shadow in the town of Montgomery, to have crossed the road leading from Ward's bridge to Goshen, three miles and five chains, counted from the bridge. This will be in latitude of about 41° 30′ and longitude 0° 14' west from the meridian of New-York. The middle of a straight line between those two points, falls on Hudson's river, in latitude 42° 26′ which is near the village of New-Baltimore, at which place, therefore, the centre of the shadow must have passed, that is about fifteen miles below this city. The following observations on the eclipse of the sun, June 16th, 1806, were made in the city of Albany, in latitude 42° 38′ 42′′, longitude 73° 47′ west from Greenwich. The latitude has been ascertained by a series of observations on stars near the zenith, chiefly a Lyra and Capella, with a sector made for me by the late David Rittenhouse. The longitude I computed by taking 75° 09′ for Philadelphia, and deducting 1° 22′ for the difference between Philadelphia and Albany. This difference is deduced from surveys connecting the two places. I regulated my clock by observations of equal altitudes of the sun, taken with one of Ramsden's best brass sextants, furnish 30. ed with a small telescope. Four of these observations were made on the 14th, one on the 16th, and three on the 17th. In observing the eclipse, I used the achromatic telescope of my sector already mentioned, its magnifying power is about The commencement of total obscuration is mostly to be depended on. Before the re-appearance of the sun, I lost it out of the field of the telescope, and I unfortunately omitted to remove the dark glass; I therefore noted the end of total obscuration, only by the naked eye, and of course cannot so much depend on it. It is probably taken some seconds too late. The arrival and departure of the penumbra, were taken tolerably accurate. The air was uncommonly serene, and afforded the finest opportunity for observations. I intended to have forwarded this last fall, as soon as I could get the painting done, but the navigation of our river being obstructed earlier than usual, my intentions were defeated. I am, with great regard Your obedient humble Servant, Doctor Benjamin Rush. The following errata have been found in the communications of J. J. De Ferrer in this Volume. Page 163, line 31. Cayo Sta. Maria. Lat. for 23° 12′ 00′′ read 22° 39′ 24′′ = 164, last line, for Teneriffe, read In the Azores. E+1. tang. Xa=15,8072 read E'+1' tang. ' 232, line 32. for apparent elongation at the ingress 934" 416 read 934" 437 |