III. Annual Report of the Royal Astronomical Society of London, dated Feb. 12, 1836. Printed for the Society.

AN early copy of this Report having been kindly put into our hands, we gladly avail ourselves of the opportunity of presenting to our readers a portion of its interesting contents, though we are obliged to use some editorial privileges to make room for our notice. It is not, however, that we intend to enter into any account of the affairs of the Society, or to notice here the progress which the science it cultivates has made within the last year, gratifying as both are; it is the tribute of respect paid in the report to the memory of three of its most distinguished Fellows, whom it has lost during that period, which solicits our attention.

The debt of gratitude which society at large owes to such of its departed members who have promoted the welfare of their race, is sometimes discharged in part by the monument erected by the artist, and by the biography of the literary man; each helps to extend the knowledge of the benefits which the community has received from those who are no more. And as the desire of posthumous fame must ever be the strongest stimulant to the rightly ambitious,-to those who, by their talents, are capable of bettering the condition of their fellow-creatures; it behoves mankind, even from selfish considerations, diligently and faithfully to acquit itself of this obligation; we, on our parts, will not be backward in paying our quota.

The precise and formal nature of an official report, necessarily keeps down the expression of those feelings in which a writer would otherwise naturally indulge, when recording his recollections of a deceased associate; conscious that his memoir may be read by thousands who never saw, if they even ever heard of him whose character he is drawing, he thinks it necessary to restrict himself to a simple enunciation of the events, or of the labours and discoveries which have entitled his subject to celebrity. Hence arises, as we presume, the subdued tone of eulogy in the biographical sketches before us; but as we do not feel ourselves under such restrictions, we, while we avail ourselves of the substance and words of the memoir, shall unhesitatingly give expression, in one instance at least (the second in the following series), to that enthusiasm which we feel for a man not known as he deserved to be, whose moral virtues were even more rare than the professional genius and extensive knowledge, which placed him in the foremost ranks of his contemporaries.

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Dr. BRINKLEY,

Bishop of Cloyne, was for a long time Andrews Professor of Astronomy at Trinity College, Dublin, and Director of the Observatory near that city. Indeed, he had spent so much of the latter period of his life in Ireland, that he has been considered by some as a native of that country. He was, however, born in England, and of English parents. He distinguished himself in early life at the University of Cambridge, where he was the senior wrangler of 1788. He was for a short time an assistant at the Observatory of Greenwich, where probably he acquired the taste for astronomy which he afterwards cultivated with so much success: and it is to this eircumstance also that he was indebted for the appointment of Director of the Observatory in Ireland. For when Dr. Maskelyne was requested to point out the most

qualified person that he knew, as a successor to Usher, he instantly named Brinkley. The observatory at that time was furnished only with a transit; and this state of comparative leisure gave him opportunities of attaining greater proficiency in transcendental mathematics than any of his contemporaries, and at a much earlier period. Most of his papers on subjects of this nature are inserted in the Memoirs of the Royal Irish Academy, and are duly appreciated by those who are conversant with such inquiries. On the erection of the circle, he applied himself more assiduously to practical astronomy; and justly estimating the powers and advantages of such an instrument he devoted his time to the elucidations of certain minute subjects in astronomy, which had hitherto either evaded the researches of former observers, or had been the subject of much dɔubt and even controversy: such as the aberration and parallax of the fixed stars, the solar and lunar mutation, and the varied amount of astronomical refraction, more especially at low altitudes. In the investigation of these subjects we trace the same master-hand as in all his other inquiries: and although the result of his deductions relative to the subject of parallax does not appear to accord with those obtained from the mural circle at Greenwich, yet so highly did the Royal Society estimate the talent and skill displayed in the inquiry, that they awarded him the Copley medal for his paper on this subject. The constants of aberration and lunar mutation, determined by Dr. Brinkley, are those which have been adopted by this Society, in the formation of their catalogue of stars: the former deduced from 2633, and the latter from 1618, comparisons of various stars. This attempt to deduce from observation the constant of solar mutation (the existence of which was only known from theory) is at once a proof of his skill in the manipulation of the instrument, and of his confidence in its accuracy and its powers. His tables of refraction, when adapted to the external thermometer, are found to possess a degree of merit far above what has been generally attributed to them. In private life, Dr. Brinkley was remarkable for the kindness of his disposition, and the urbanity and mildness of his manners; and was ever ready to communicate information to the zealous and earnest inquirer after knowledge. On his promotion to the see of Cloyne, he devoted himself almost entirely to ecclesiastical affairs; and for the last ten years he had not contributed a paper to any scientific society. He was for a long time the President of the Royal Irish Academy; and for two years filled also the chair of this Society. He died on the 13th of September last, at an advanced age.

"The following particulars of Brinkley's earlier life have been communieated by a Fellow of the Society. Both he and Vince, when boys, were under the care of Mr. Tinley of Harleston, to whose assistance and influence over others both owed the means of maintaining themselves at the university. Brinkley wrote in the Ladies' Diary from 1780 or 1781 to 1785; and mention is made of his name by Maskelyne, in the Greenwich books, from June 1787 to March 1788, in which interval he also took his degree at Cambridge.”

66

EDWARD TROUGHTON

was born, it is believed*, in October, 1753, in the parish of Corney, in the county of Cumberland, the third son of a small farmer. An uncle of the same name, and his elder brother, John, were settled in London as mathematical instrument makers, and as his second brother was apprenticed to the same business, Edward was designed to be a farmer, and continued to be his father's assistant till the age of seventeen. To persons acquainted with the condition of that part of England, it need not be said that his education was better than is usual for his rank, and was of a sound

* The parish register for this time was destroyed.

though homely cast. There has always been there, so far as memory goes back, a considerable stock of mathematical and general knowledge floating amongst the people; and a large proportion of persons distinguished for their attainments in the university of Cambridge have arisen among the Cumberland and Westmoreland yeomanry. The death of his second brother altered Edward's destination, and he was immediately placed with his brother John, then chiefly employed in dividing and engraving for the trade and the higher branches of the art. Under his instruction, Troughton made most rapid progress, and, at the expiration of his time, was admitted as a partner. About 1782, the Troughtons established themselves in Fleet-street, where they commenced an independent business, as successors to a series of wellknown artists (Wright, and subsequently Colex), who had previously occupied the same premises. Ramsden was then in the zenith of his reputation, but his dilatory habits were little suited to the wants and impatience of astronomers; this, and their own instrinsic merits, speedily advanced the brothers in their profession, and in the estimation of competent judges. Considerable rivalry ensued, and Edward Troughton, who felt his own powers, was not a person to conceal his feelings or to propitiate an adversary. After the death of his brother John, Edward alone continued the business till 1826*, when his increasing age and dislike to routine employment, induced him to take Mr. William Simms as his partner and successor.

"The life of an artist is generally contained in the history of his works, and this is peculiarly true of Mr. Troughton. Of him it may be said, with truth, that he improved and extended the use of every instrument he touched, and that every astronomical instrument was in its turn the subject of his attention. In this branch he has no equal, except the celebrated Graham, the object of his unbounded admiration. To describe all his improvements or inventions would require a detailed account of almost every instrument, astronomical, nautical, or geodæsical, in actual use; we must, therefore, limit ourselves to a brief and very imperfect notice.

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'The instruments which facilitate navigation were peculiar objects of interest to Mr. Troughton; and long after his infirmities were an effectual bar to the applications of his most esteemed friends, he exerted himself to supply the seamen with well-adjusted and accurate sextants. Your fancies,' he would say, 'may wait; their necessities cannot.' In 1788, he took out a patent for the double-framed sextant, a construction which, combining firmness and lightness, yet admitted of a considerable radius in this invaluable instrument. In the various adjustments of his sextants, the selection of their mirrors and glasses, he was most scrupulous, and for many years scarcely any other were seen in the hands of the most scientific navigators of our own or foreign navies, But there is a fault in the construction of the sextant, which the maker can only imperfectly guard against-that of a sensible excentricity; and the detection and correction of this, though not very difficult, is beyond the skill of ordinary observers. After trying and rejecting the repeating reflecting circle of Borda, Mr. Troughton (1796) hit upon one of his happiest constructions, the British reflecting circle, which bears his name, an instrument which, in right hands, is capable of wonderful accuracy. The additional weight of the circle, and the trouble of the extra readings, have hitherto prevented its introduction into common use, and perhaps at sea, where the errors of observation are necessarily of as large an order as those of a good sextant, the superior accuracy of the circle may not come into play; but

The last capital instrument made by Mr. Troughton alone was a seven feet transit for Sir J. South, in 1820, on the model of that at Greenwich.

for observations on shore, and with a stand, no sensible observer can hesitate between the instruments. It is a characteristic trait of Mr. Troughton, that in order to bring his favourite circle into general use, he reduced its price below the usual profits of trade; and if he had succeeded in his attempt he might have been ruined by his success, for his sextants were by far the most gainful article of his business. With the same earnestness to promote navigation, he invented the dip-sector (afterwards reinvented by Dr. Wollaston,) and expended time, money, and ingenuity to no inconsiderable amount, in attempting to perfect the marine top for producing a true horizontal reflecting surface at sea. The marine barometer, the snuff-box sextant, and the portable universal dial, owe to him all their elegance, and much of their accuracy. Where others invented or sketched, he perfected.

Among ordinary physical apparatus may be mentioned, considerable improvement in the construction of the balance, the mountain-barometer, and the form given to the compensated mercurial pendulum, his pyrometer, by which some very valuable expansions have been determined; and the apparatus by which Sir George Shuckburgh ascertained the density of water, and that which, in the hands of Mr. Baily, has given the true length of the simple seconds pendulum. On the length of the simple pendulum Mr. Troughton himself made many very careful and extensive experiments, according to views and after a procedure of his own; but his ideas, though ingenious and elegant, were not pursued after Captain Kater's happy application of Huyghens' theorem. In the ordinary geodæsical instruments, Mr. Troughton greatly improved the surveying level and staff, and reduced them both in weight and price with increased convenience and accuracy. The errors of the common surveying chain, which are sometimes enormous*, and the complexity and expense of that made by Ramsden for the trigonometrical survey, led to the construction of a more simple and accurate chain, at a reasonable cost, and of easy use. The larger theodolites by Mr. Troughton, those, for instance, of twelve inches diameter, are remarkable for simplicity and power. In the refined and delicate instruments which have been applied to the most accurate geodæsical measurements, we may mention the large theodolite for the American coast-survey (1815), and those for the Irish (1822), and for the Indian surveys (1830), which may be advantageously contrasted, for their design and simplicity, with those, however otherwise excellent, of Ramsden; and also the apparatus for measuring a base line (1827), employed by Colonel Colby in Ireland, and Colonel Everest in India (1829). It must not, however, be forgotten, that the idea of this last most exquisite apparatus, and very much of the novelty of the construction, are due to our excellent members, Colonel Colby and Lieutenant Drummond. Mr. Troughton made some very beautiful and manageable zenith sectors, which were capable of great accuracy, considering their dimensions: one of these is, we believe, in the possession of the Danish gevernment, and was employed in the Holstein survey by Professors Schumacher and Gauss. He had designed one with a six-feet telescope and arc for America on the same construction, but it was never completed, though considerable progress had been made.

"It is, however, more properly with the astronomical instruments of this great artist that we are immediately concerned; and here he reigns without a rival. In the small altitude and azimuth circle (1792), the portable transit, and the portable universal equatorial, and the theodolite, it is not easy to state accurately the line between his improvements or inventions, and those of preceding

* On one occasion when two surveyors differed in their measurements their chains were sent to Mr. Troughton to compare; one was found two inches too short, the other three inches too long,

artists; but it is from him that these instruments received their present form and perfection. The repeating circle of Borda, an instrument which he disliked, first received its beauty and accuracy from his hands; and for it he invented his very elegant double-foot screw, to give minute adjustments. The ordinary reading micrometer, and the position micrometer commonly employed in the measurement of double stars, were greatly improved by him in simplicity, and brought to perfection; and he first applied the former to dividing. In the class of larger altitude circles, revolving freely in azimuth, we find the circle for Count Bruhl (1792), the Westbury circle (1806), that for Sir T. M. Brisbane, the Society's Lee circle, the substance and form of Dr. Pearson's circle, those employed in the Indian survey for determining latitudes (1830), and that at the Edinburgh observatory (1830), with many others which it would be tedious to mention. In Groombridge's transit circle (1806), the beauty of the form and accuracy of the divisions satisfied every body but the artist himself*, whose experience and matured powers were finally exhibited in the mural circle. This finished specimen of sound engineering and mechanical construction at first met with much opposition; and many were the objections, both before and after the erection of the Greenwich mural (1812), with which its inventor was assailed. To these he resolutely turned a deaf ear, for nothing could shake his confidence in what he knew; and he had the pleasure of finding, before his death, the mural circle established in the Royal Observatory of Paris, and safely lodged on its massive pier at the Cape, St. Helena, Madras, Cracow (1832), Edinburgh (1834), Brussels (1835), Cadiz, Armagh, and Cambridge (1832). A small model, of two feet in diameter, was made for Sir T. M. Brisbane prior to the Greenwich mural, and is now at the observatory of Paramatta. The principal equatorial instruments of Mr. Troughton, with accurately divided circles, are those of Coimbra (1788), Armagh, and Brussels (1834). When we add to this long catalogue the large transits at Greenwich (1816), Camden Hill (1820), Cracow (1828), Markrea (1832), &c., in which the differential screws are so beautifully applied to form what he called the bones of the instrument, and the gigantic zenith tube at Greenwich, which he just finished before his strength failed, we have reason to wonder that even his long and active life should have sufficed for works of such variety and extent, and may form some estimate of the value of Mr. Troughton's labours, and their effect on modern astronomy. It may, perhaps, be remarked, that the only astronomical instrument which is not greatly indebted to Mr. Troughton is the telescope; and he was deterred from any attempt in this branch of his art, by a singular physical defect, which existed in many members of his family. He could not distinguish colours, and had little idea of them, except generally as they conveyed the idea of greater or less light. The ripe cherry and its leaf were to him of one hue, only to be distinguished by their form; and he was in the habit of relating some curious mistakes committed by himself, and others of his relations, in confounding green and red. With this defect in his vision, he never attempted any experiments in which colour was concerned; and it is difficult to see how he could have done so with success.

"The most remarkable of Mr. Troughton's writings are, 'An account of a method of dividing astronomical and other instruments by ocular inspection,' &c., printed in the Phil. Trans., 1809, which was rewarded with the Copley medal; 'A comparison of the repeating circle of Borda with the altitude and

Mr. Troughton was, upon reflection, so little satisfied with the design of this transit circle, that he broke up a second, on a somewhat smaller scale, after he had spent 1507. upon it. "I was afraid," he said, "I might grow covetous as I grew old, and so be tempted to finish it, and I don't think it is a good kind of instrument."