HISTORY OF PHYSICAL ASTRONOMY.

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Board of Visitors, which was composed of members of the Royal Society ,were authorized to demand of the Astronomer Royal, within six monthsafter the lapse of each successive year, “a true and fair copy of theannual observations he had made.” At a meeting of the Royal Society ,held on the 2nd of March, 1727, Sir Isaac Newton, who was then Pre-sident , took occasion to remark that this regulation had not been recentlyobserved; and stated at the same time, that, as the continued neglect ofit might be attended with detriment to the public interest, he thought itproper to remind the Astronomer Royal of the circumstance of such aregulation being in force. Halley, who was present, replied to Newtonby asserting that he had already executed a great number of observations,especially of the moon ; but that on account of the utility of such observa-tions towards ascertaining the longitude, for which a large reward hadbeen offered by the Government, he had hitherto kept them in his owncustody, that he might have time to finish the theory he designed to buildupon them, before others might take the advantage of reaping the benefitof his labours*.

Halley died on the 14th of January, 1742, in the 86th year of his age.It appears that for some time previous, he had ceased to attend to theduties of the observatory, a circumstance which is not to be wondered atwhen his extreme old age is taken into consideration. His last observa-tion is dated December 31, 1739. The only part of the observationsmade by him at Greenwich that has ever been published, is a collectionof observed places of the moon, which are to be found at the end of hisAstronomical Tables, which were published in 1749f. These tables wereprinted off in 1719, with a view to their immediate publication; but theirauthor being in the meantime appointed Astronomer Royal, they wereretained by him for his own exclusive advantage, since there was now anincreased probability of his bringing the lunar theory to such a state ofperfection as would lead to a practical solution of the problem of thelongitude. With a view to this object, he had no sooner entered uponhis duties at Greenwich, than he commenced instituting a comparisonbetween the places of the moon deduced from his observations, and thecorresponding places calculated from the tables. These results wereprinted off at successive intervals during Halley’s lifetime, and the wholecollection was finally published along with his Astronomical Tables, as hasbeen already mentioned. It exhibits a comparison between the observedand calculated places of the moon, extending from 1722 to 1739. Theerror of the tables in longitude is frequently less than U, but in someinstances it rises to 5' or 6'. In general, it may be said to range between2' and 4'. It does not appear that Halley employed these residual errorsin any researches for the purpose of obtaining an improvement of histables of 1719.

The original records of Halley’s observations are deposited at Green-wich in four small quarto volumes. Upon the recommendation of Mr.Daily, a manuscript copy of them was taken hy the order of the Lordsof the Admiralty, and presented to the Astronomical Society, in the year

* Mem. Ast. Soc„ vol. viii., p. 188, cited by Mr. Baily, from the Minute Book ofthe Royal Society.

t In the preface to these tables it is stated that they were mainly constructed byHalley, upon the observations of Flamsteed.