At the beginning of 1720, after the death of Flamsteed, Halley was appointed astronomerroyal. In the previous years be had been employed in completing Via lunar and planetary tables, which were then ready to be published. But upon his appointment to Greenwich be revived his old idea of observing the moon through a revolution of her nodes. It was doubtful that at tho age of sixty-four he should live to complete an undertaking which required nineteen years of health ; but he did undertake it, and did live to finish it. The result is the comparison of nearly 2000 observed lunar places with his pre viously formed tables. He died on the 14th of January 1741-42, in the eighty-sixth year of his age. • The remarks on the personal character of Halley which appear in the &op of Mairan were furnished, it is asserted, by his friend Mr. Folkes, and their justice must be allowed so far as they speak of his prodigious information and activity. His disinterestedness in money matters is supposed to be attested by his request to Queen Caroline not to increase the salary of the astronomer-royal on his appointment to that office, lest it should afterwards become an object of ambition to incompetent persons; but, though allowing that Halley was not greedy of gain, we see but little to commend in this act of a man of independent fortune. The social qualifications of Halley were such as endeared him to his friends ; and he could, when no partiality stood in the way, be fair and just to others. Thus Mairan remarks on his not having treated either Des Cartes or Vista with the injustice which their memory received from several English writers. It were to be wished that he had been as free from personal as from national prepossessions, and that Liebnitz and Flamsteed had received their due from the friend of Newton. In his edition of the observations of the latter [FlastsrEED) he inserted a preface containing culpable misrepresentations, an account of which is to be found in Mr. Baily's work. We shall also cite the following suppression. In all the editions of the Synopsis Cometica ' published during Halley's life, a numerical deduction from observations is given, to which the following is appended :—" At the moment of the first example the comet was observed at London to be close to the second star of Aries, of which it was nine minutes north, and three minutes east ; the observer being Robert Hook." But in the augmented edition left by Halley to be published with his tables, the comet, at the same hour as in the pre ceding, is nine or ten minutes north of the star of Aries, and nearly in the same longitude; the observer being no longer Robert Hook, but Auzout and another. Doubtless Halley had quarrelled with Hook (as almost everybody was obliged to do) in the interval ; and though the example was evidently worked for comparison with Hook's observation, at the same moment, we find it struck out in favour of one by Auzout in the same hour.
But though the scientific fame of a philosopher be no excuse for that suppression of his faults to which biographers are prone, still less should the latter be allowed to colour our views of the former.
Among the Englishmen of his day Halley stands second only to Newton, and probably for many years_ after the publication of the 'Principle,' he was the only one who both could and would rightly appreciate the character and coining utility of that memorable work. His own attention was too much divided to permit of his being the mathematician which be might have been; but nevertheless his papers on pure mathematics show a genius of the same order of power, though of much less fertility, than that of John Bernoulli. We shall close this article with a brief account of his printed writings, sod of the most remarkable points in them.
The separate works of Halley consist of the Catalogus Stollarum Australium: &c., London, 1679, translated into French by M. Royer in the same year; the work of Apollonius `De Sectione Ratiouis,' Oxford, 1706; the ' Conic Sections of Apollonius,' Oxford, 1710; the unfortunate edition of Flamsteed's Historia Ccelestis,' London, 1712; and the planetary tables published in 1749, though printed for the most part in 1717-19. Tho superintendence of this work is attributed to Bradley, though it is evident that he did not write the preface. Besides the preceding there are from eighty to a hundred memoirs, including many of small importance, in the 'Philosophical Trans actions.' In astronomy we owe to Halley—I, the discovery and the detection of the amount of what is called the long inequality of Jupiter and Saturn, which he confidently expected would be shown to be a conse quence of the law of gravitation, as was afterwards done ; 2, the detection, by comparison of ancient and modern observations of eclipses, of the slow acceleration of the moon's mean motion; 3, the first prediction of the return of a comet—' Halley's Comet ; ' 4, the explanation of the appearance of Venus in the day-time at particular seasons, arising out of the now well-known method of estimating the brilliancy of the planet ; 5, the recommendation to observe the transit of Venus for the determination of the sun's parallax.
The following is a list of the most remarkable labours of Halley out of astronomy, arranged in the order of publication :—I, on the variation of the compass; 2, the law according to which the mercury falls in the barometer while the instrument ascends, being the first application of this instrument to the measurement of heights ; 3, theory of the trade-winds ; 4, construction of equations of the third and fourth degree; 5, estimation of the quantity of vapour raised from the sea; 6, inquiry into the point at which Julius Cwser made his entry into Britain; 7, tables of mortality, from observations made at Breslau, the first of the kind constructed; 8, application of Algebra to the problem of lenses ; 9, method of constructing logarithms, a celebrated paper, reprinted in Sherwin's 'Logarithms ;' 10, improve ments in the diving-bell Those papers only have been mentioned which refer to points on which Halley's name is inseparably connected with the history of the progress of science.
(Biographic Britannica.)