An Account of an Occultation of the Star χ Tauri by the Moon, Observed at Leicester: By the Rev. Mr. Ludlam, in a Letter to the Rev. Mr. Maskelyne, Astronomer Royal

XXIX. An Account of an Occultation of the Star ξ Tauri by the Moon, observed at Leicester: By the Rev. Mr. Ludlam, in a Letter to the Rev. Mr. Maskelyne, Astronomer Royal. Reverend Sir, Here send you an account of the occultation of the star ξ Tauri by the moon, as we saw it at Leicester April 28, 1770. The necessary observations for examining the clock, are subjoined, which I think should always be done by those who have not fixed observatories; or where their instruments are not well adjusted at first, and frequently examined afterwards. Without being thus particular, no one can judge what degree of credit may be afforded to such observations; and it has, besides, this advantage, that if a mistake should be made in the calculations grounded on them, any person versed in Astronomy can rectify it. I beg the favour of you to communicate this to the Royal Society; and am, With the greatest respect, Their and your most humble servant, Leicester, April 29, 1770. W. Ludlam. The immersion was noted at $1x^h\ 41^m\ 7^s$ by the clock. I think it might be two seconds sooner, because the clock being of necessity at a distance from the telescope, the instant of the immersion was signified by striking upon a bell. The emersion was about $x^h\ 31'$ but with some uncertainty, the star being hid by a cloud at its first coming out. By the observed transits of the sun and stars, the clock lost three seconds between the $25^{th}$ and $28^{th}$. On the $25^{th}$, by corresponding altitudes, the clock was $1'\ 46''$, 8 too slow; whence on the $28^{th}$ it was $1'\ 49''$, 8 too slow. This confirms the observation made by corresponding altitudes on the $28^{th}$, by which it was $1'\ 50''$ too slow at noon: the clock was then losing at the rate of four seconds a day; whence, on the $28^{th}$ at $1x^h$, it was $1'\ 51''$, 5 slower than mean time. The equation of time on the $28^{th}$ at $1x^h$ was $2'\ 47''$, 5, whence the immersion was at $1x^h\ 45'\ 44''$ apparent time. The Telescope made use of was one of Dollonds, with a triple object glass of $33\frac{1}{3}$ inches focal distance, and which magnifies 52 times. Transits | Day of the month | Transits | Time by the clock | Paillage over | Object | |------------------|----------|-------------------|---------------|--------| | | First wire | Meridian | Third wire | | | 1770 | M s | H m s | M s | | | April | 24 | 53 54 | xxii 54 42 | 55 27 1/2 | Sun | | | | 56 6 | 56 53 1/2 | 57 58 | | | | 26 | 7 36 | x 8 21 | 9 52 | γ Virginis | | | 27 | 11 8 | ix 11 55 | 12 41 | β Leonis | | | | 3 39 | x 4 25 | 5 93 | γ Virginis | | | | 17 28 | 18 24 | 19 9 | δ Virginis | | | | 46 35 | 47 21 | 48 61/2 | Spica V | | | | 53 24 | xxiii 54 11| 54 56 1/4| Sun | | | | 55 35 | 56 22 | 57 8 | | | | 28 | 7 9 | ix 7 56 | 8 43 | β Leonis | | | | 59 41 | x 0 26 1/2| 1 11 | γ Virginis | | | | 13 30 | 14 25 1/2 | 15 10 | δ Virginis | | | | 42 36 1/2| 43 23 | 44 8 | Spica V | | | | 53 10 | xxiii 53 57 1/2| 54 44 | Sun | | | | 55 21 1/2| 56 9 | 56 55 | | | | 29 | 3 10 1/2| ix 3 58 | 4 44 | β Leonis | | | | 53 0 | xxiii 53 47| 54 33 1/2| Sun | | | | 55 13 | 56 0 | 56 46 | | Corresponding altitudes taken with an Hadley's quadrant of seven inches radius, by reflection from water. | Sun | April 25, 1770 | |-----|----------------| | Double Alt. 65° | Index err. + 1m | | Time by the clock. | | Eastern Az. | Western Az. | Meridian | | Up. limb | v 11 21 48 1/2 | 11 30 43 | xi 56 15 1/2 | | Center | 23 42 | 28 52 | 17 | | Low. limb | 25 37 | 26 54 1/2 | 15 3/4 | | Second set. Doub. Alt. 67° 30' | | Up. limb | v 11 30 45 | 11 21 45 | 15 | | Center | 32 49 | 19 49 | 14 1/2 | | Low. limb | 34 35 1/2 | 17 53 | 14 1/4 | | Third set. Doub. Alt. 70° | | Up. limb | v 11 39 53 | 11 12 34 1/2 | 13 3/2 | | Center | 41 50 | 10 41 | 15 1/2 | | Low. limb | 43 48 | | | | Mean of all three sets | xi 56 15 1/2 | | Cor. for 1/2 interval 3h 20' | - 16 3 | | Passage over true meridian | xi 55 58 9 | | Clock too slow | 1 46 8 | Sun | April 28, 1770 | |-----|----------------| | Double Alt. 79° 11' | Index err. + 1m | | Time by the clock. | | Eastern Az. | Western Az. | Meridian | | Up. limb | ix 8 12 1/2 | 11 43 6 1/2 | xi 55 39 1/2 | | Center | 10 16 | 4 1 3 | 39 1/2 | | Low. limb | 12 22 1/2 | 38 56 | 38 3/4 | | Mean | xi 55 39 5 | | Cor. for 1/2 interval 2h 20' | - 13 5 | | Passage over true meridian | xi 55 26 | | Clock too slow | 1 50 | XXX. Extract