An Advertisement to Astronomers, of the Advantages That May Accrue from the Observation of the Moon's Frequent Appulses to the Hyades, during the Three Next Ensuing Years

CONTENTS. VIII An Account of a Small Telescopical Comet seen at London on the 10th of June 1717. by Edm. Halley, LL.D. R. Soc. Secr. IX An Account of Books: I. Joannis Poleni in Gymnasio Patavino Phil Ord. Prof & Scient. Societatum Regalium, qua Londini & Berolini iunt, Sodalis, De Motu Aque mixto, Libri duo, &c. 4to. Patavii 1717. II. Apollonii Pergai Conicorum Libri Octo & Sereni Antissensis de Sectione Cylindri & Coni Libri duo. Fol. Reg. E Theatro Oxon. 1710. I. An Advertisement to Astronomers, of the Advantages that may accrue from the Observation of the Moon's frequent Appulses to the Hyades, during the Three next ensuing Years. Of all the Methods hitherto proposed for finding the Longitudes of Places for Geographical Uses, none seems more adapted to the purpose, than that by the Occultations of the fixt Stars by the Moon observed in distant Parts: For those Immersions of the Stars which happen on the dark Semicircle of the Moon, and their Emergences from the same, are perfectly momentaneous, without that Ambiguity, to which the Observations of the Eclipses of the Moon and those of Jupiter's Satellites are subject. Besides, whilst the Moon is horned, and her weaker Light less dazzling, an ordinary short Telescope, such as by Experience is found to be manageable on Ship board, suffices to observe those Moments, even in the Occultations of very minute Stars: On which account, this way seems to bid fairest for the desired Solution of the grand Problem of finding the Longitude at sea. But since it would be needless to enquire exactly what Longitude a Ship is in, when that of the Port to which she is bound is still unknown, it were to be wished that the Princes of the Earth would cause such Observations to be made, in the Ports and on the principal Head-Lands of their Dominions, each for his own, as might might once for all settle truly the Limits of the Land and Sea. This Work however being likely to be left to the Care and Curiosity of private Persons, it may not be amiss hereby to give notice of the present Opportunity of performing it, in this our Northern Hemisphere, by help of the frequent Appulses of the Moon to the more Southerly of the Hyades, many of which she eclipses in each monthly Revolution, and will continue so to do, during the Years 1718, 1719, and 1720. These Stars are but Three or Four in all former Catalogues, but the British of Mr Flamsteed encreases them to Sixteen; to them we have added Three others somewhat smaller, viz. c, i, and n in the Figure of the Hyades hereunto annexed. In it the principal Stars are marked with Bayer's Marks, and the rest with the Letters of the Italick Alphabet; their Longitudes are fitted to the beginning of the Year 1718, and being truly laid down, may serve to instruct the curious Observer, when and where to look for them, when the Moon is among them. It appears by this Scheme that the Distance between α and η or Pallicitum, is about Nine Hours Motion of the Moon, in which time supposing her to pass from one to the other, she must eclipse γ and ε, and Four or Five of those about θ, and must apply very close, with her Southern Limb, to all those which have about Six Degrees South-Latitude; which would be a very entertaining Sight for the Lovers of these Arts. But if the Times of the Occultations of any One of these Stars, or even of any Two of them in the same Night, be accurately observed under distant Meridians, the difference of those Meridians may be truly obtained thereby; especially since the Moon's Parallax, and all other parts of her Theory thereto required, are at present sufficiently stated and known. For the sake of such as are willing to make use of this Method, we have added the Places of all the Hyades fitted to the present Time, and chiefly taken from the British Catalogue, which being faulty in the Stars we call k and l, we have here rectified them. Catalogus Hyadum, incunte Anno 1718. | Stelarum NOMINA. | Long. | Lat. Aul. | Ma. | |------------------|-------|-----------|-----| | Quae praecedit γ Tauri | a | 0° 51' 35" 50' 14" | 7 | | In naribus Tauri, Bayero γ | b | 1° 50' 54" 5' 46" 22" | 3 | | Quae sub γ | c | 2° 54' 25" 4' 47" 5" | 7 | | In Origine Nasi Tauri | d | 3° 10' 33" 4' 9" 4" | 6 | | Inter nares & oculum Tauri | e | 3° 17' 21" 5' 41" 50" | 8 | | Boreum | f | 3° 25' 32" 6' 2" 4" | 6 | | Huic contigua ad Australium | g | 3° 35' 2" 3' 43" 2" | 5 | | Precedentium θ Borealis | h | 4° 0' 21" 5' 52" 55" | 4 | | Earum Australis clarior. | i | 4° 7' 44" 5' 36" 40" | 8 | | Quae sequitur δ | j | 4° 19' 27" 6' 9" 45" | 4 | | Contiguarum inter nares & Palilicum Borea | k | 4° 26' 55" 6' 7" 35" | 5 | | Earundem Australior | l | 4° 30' 26" 5' 37" 49" | 7 | | Duarum supra θ Borea | m | 4° 30' 31" 2' 35" 58" | 3 | | Earundem Australior | n | 4° 32' 35" 5' 41" 00" | 8 | | Sub θ trium in recta pracedens | o | 4° 45' 55" 6' 0" 35" | 7 | | Earum media | p | 5° 50' 20" 5' 29" 50" | 1 | | 2nd θ sequentium Borea | q | 6° 17' 35" 6' 3" 20" | 7 | | Oculus Boreus Tauri | r | 6° 30' 34" 6' 19" 19" | 6 | | Sequentium θ Australis | s | 6° 33' 12" 6' 12" 35" | 7 | II. Solutio