Observations on the Eclipse of the Moon, June 18, 1722. and the Longitude of Port Royal in Jamaica Determined Thereby. By Dr. Halley, Astronomer Royal, F.R.S.

I. Observations on the Eclipse of the Moon, June 18, 1722, and the Longitude of Port Royal in Jamaica determined thereby. By Dr. Halley, Astronomer Royal, F.R.S. The Eclipse of the Moon which happened in June last, 1722, was so far hid by the cloudy Sky, that neither myself, nor any of our Astronomical Friends, in or about London, could furnish an Observation thereof worthy to be laid before the Society. But the same having been well observed at Jamaica, by the late curious Capt. Candler, Commander of his Majesties Ship Launceston, (whose Example it were to be wished, others in the like Post would imitate) and at Berlin, by Mr. Christfried Kirck, Astronomer of the Royal Academy of Sciences there. I thought it not amiss to prefix to their Accounts that little I was able to note concerning it. Sunday, June 18, mane, Having perfectly rectified my Clock so as to shew the Apparent Time, neither the transit of the Moon over the Meridian, nor the beginning of the Eclipse which soon followed, could be seen thro' the very thick Cloud. At 13 h. 12' T. app. a small Particle of the Moons Body was seen through a very little hiatus in the Cloud, by which glimpse I could only be assured that the Eclipse was not yet Total. At 13 h. 29' by such another view. I was satisfied that it was now become Total; but in a Moment, it again disappeared, till 14 h. 49' 10'', when the Cloud beginning to break, I got time to measure with the Micrometer, the Partes Lucidae now recovered in the Moon's Diameter, which I found 14'. 00'', though this not so well as I could wish, by reason of a thinner Sort of Cloud which perpetually intercurr'd, and render'd the Edge of the Shadow somewhat dubious. At 15 h. 15' the Moon was pretty well got out of the thick Cloud, but being very low, and the Daylight become strong, she shone very faintly, and the Shadow became worse and worse defined. From 15 h. 26' to 15 h. 27' T. app. I doubted of the End, and am confident it did not exceed the 27th Minute. It ended over against the North Part of the Palus Maeotis of Mr. Hevelius, much about the middle of the Western or Right-hand Limb of the Moon, she being then very near setting. Capt. Barth. Candler, being then at Port Royal, in Jamaica, had much better Fortune, and a serene Sky from the Beginning to the End; who having used due care to be assured of his Times, by Altitudes taken with an Instrument of three Foot Radius, was pleased to send us the Result of his Observation as follows. | Time | Duration | |------------|----------| | The Eclipse began | 6 59 10 | | Immersion | 8 7 50 | | Emerion | 9 11 0 | | The End | 10 19 40 | | Whence the Middle | 8 39 25 | And supposing the Eclipse to have ended at Greenwich, at 15 h. 26', the Difference of Longitude between Port Royal and Greenwich, will be 5 h. 6' 50'', or 5 h. 6' 1/2 from London, that is, 76 gr. 37'. Mr. Kirck being in a more Easterly Meridian, could see nothing of the Emerion, but has carefully noted the Time of the Beginning and Immersion, as he observed them at Berlin, viz. the Beginning of the Eclipse at 12 h. 59' 55'' and the Immersion at 14 h. 8' 8''. Now by comparing several Observations made at both Places, we have formerly concluded Berlin to be 54 Min. of Time, or 13½ grad. of Longitude more Easterly than London; wherefore at London it began at 12 h. 5' 55'' and immersed at 13 h. 14' 8'', that is, the beginning was later here than at Jamaica 5 h. 6'45'', and the Immersion later 5 h. 6' 18'', punctually agreeing with what resulted from my own Observation of the End as abovesaid; and sufficiently with what I had long since determined from Observations sent me from Jamaica by my old Astronomical Friend Mr. Charles Boucher. II. The