MacTutor
At none of its former anniversary meetings has this Society had cause to deplore losses heavier than those it has sustained in the past year. The death of its president, Mr. Baily, was followed, at a short interval, by that of Professor Henderson, of Edinburgh; an astronomer of first-rate merit, and one who, for many years, has been conspicuously distinguished among us by the frequency and importance of his contributions to our publications. His services to the cause for which we are associated have been, indeed, of no ordinary kind; and, although prematurely terminated, have entitled him to a high place among the most deserving of our members. It becomes, therefore, a duty we owe to his memory to recapitulate In this Report, he makes his principal claims to our gratitude, and to place on record a few particulars of his personal history; as well as to testify our respect for his eminent merits and to gratify, however imperfectly, the desire which will be felt to know something of the life and character of one whose labours will henceforth form part of the annals of astronomy.
Thomas Henderson was born at Dundee on the 28th of December, 1798. His father was a tradesman in respectable circumstances, who died early in life, leaving to the care of his widow a family consisting of two sons and three daughters. The eldest son, John, was bred to the legal profession; and, after practising for some time as a writer in Dundee, went to Edinburgh, where he studied for the bar, and was rapidly rising to distinction as an advocate when he died suddenly, at the age of thirty-eight, of aneurysm of the heart. Thomas, the other son and the youngest of the family, was also destined for the legal profession and had the advantage of receiving the best education possible in a town long renowned in Scotland for the excellence of its public schools. After the usual preliminary instruction, he was sent, at the age of nine, to the grammar school, where he pursued the standard course of classical study for four years. He was distinguished by his diligence and quickness of apprehension, generally being the leading student in his class. In 1811, he proceeded to the Academy, where he continued for two more years. The Dundee Academy was at that time under the very capable rectorship of Mr. Duncan, now Professor of Mathematics at the University of St. Andrews. The curriculum included elementary mathematics, natural philosophy, and chemistry, and young Henderson passed through the entire course with the same distinction that had marked his progress at the grammar school. Professor Duncan, in a letter to the writer of this notice, bears the following testimony to the merits of his former pupil. "The two Hendersons," he says, "were the best scholars I had in the entire period of my incumbency. You are aware, I suppose, that John became distinguished at the bar, and was only prevented, by an early death, from rising to great eminence. Thomas, the future astronomer, was remarkable for everything that was good: the diligence and success with which he prepared his lessons, the exactness with which he performed the exercises, the propriety and modesty of his demeanour."
At the age of fifteen he was placed in the office of Mr. Small, a writer (or solicitor) in Dundee, with whom his brother had entered into partnership. In this situation he remained for six years; and it appears to have been during this period that he began to devote his leisure hours to the study of astronomy, though the particular circumstance, or accident (if, indeed, there were any other cause than the promptings of a naturally active and inquisitive mind), which first gave this direction to his inquiries is not known. During his attendance at the Academy, and even at an earlier date, he had evinced a remarkable predilection for works relating to geography and chronology; and his taste for these studies was often gratified at the expense of his health, for he was naturally of a weak constitution and subject to some disorder of the eyes, which at times rendered him nearly blind. From these subjects to astronomy the transition is easy and natural; and, although he received no aid from the lessons of a master, and had no encouragement from example, yet, in a town which could boast of being the birthplace of Ivory, and in which Dr. Small, the expositor of Kepler, had so long resided, it may be supposed there would prevail, among the better informed classes of the inhabitants, some general sentiment of respect for proficiency in astronomy and mathematics, which might not be without its influence on a mind possessing a peculiar aptitude for such studies. However this may be, the fact deserves to be recorded, as an instance of what may be done under circumstances apparently the most adverse, that it was while employed as an attorney's clerk in a provincial town that he laid the foundations of that extensive acquaintance with astronomy for which he afterwards became so distinguished.
Having gone through a six-year apprenticeship, Mr. Henderson, at the age of twenty-one, repaired to Edinburgh for the purpose of completing his legal education and obtaining professional employment. He first obtained a position in the law office of a Writer to the Signet, where his intelligence and abilities were remarked by Mr. (now Sir James) Gibson Craig, who became his steady patron and friend, and by whose recommendation he was appointed secretary, or Advocate's clerk, to the celebrated John Clerk, afterwards one of the judges of the Supreme Court of Scotland, under the title of Lord Eldin. On Lord Eldin's retirement from the bench, he was for some time private secretary to the Earl of Lauderdale; an office which he relinquished for the more profitable appointment as secretary to the Lord Advocate (Jeffrey). In these successive employments, he spent the twelve years from 1819 to 1831; and it may be remarked that, although of a subordinate nature, they were such as would only be entrusted to a person of acknowledged abilities, and one whose character for fidelity, discretion, and general intelligence was already established. It is probable that they allowed him considerable intervals of leisure, but in no other respect were they favourable for scientific pursuits; and, indeed, it may be regarded as one of the most remarkable features in his history that, while engaged in the discharge of multifarious and active duties, in a line of life so foreign to astronomy and physical science of any kind, he should not only retain his tastes for the liberal studies he had commenced at the Dundee Academy, but find leisure to make so many new and important acquisitions.
Soon after he became resident in Edinburgh, his astronomical acquisitions procured him introductions to Professors Leslie and Wallace, Captain Basil Hall, and other distinguished persons, by whom his talents were quickly appreciated, and who afforded him every encouragement to persevere in his scientific pursuits. At that time, the small observatory on Calton Hill, belonging to The Astronomical Institution of Edinburgh was placed under the charge of Professor Wallace, who, finding in Mr. Henderson a person to whom the instruments could be safely entrusted, granted him free access to them, thereby giving him an opportunity to acquire practical knowledge of a subject with which he had already become familiar through study and books. The instruments, it is true, were not of first-rate excellence—a clock and transit telescope with a 30-inch focal length, along with an altitude and azimuth instrument by Troughton—constituted the observatory's equipment. However, for a young astronomer who had no other access to astronomical apparatus, such an opportunity was invaluable; and there is little doubt that this circumstance had a considerable influence on his future career.
The opportunity of making observations, however, did not in any degree withdraw him from the less inviting parts of the science. From the outset of his career he perceived that, in order to be an astronomer, something more is necessary than mere expertise in the use of instruments. He accordingly continued to direct his main attention to the reduction of observations; and, at an early period, acquired a great knowledge of methods, and great facility in calculating eclipses, occultations, cometary orbits, and, generally, in all the computations and reductions which are subservient to practical astronomy.
Mr. Henderson first brought himself into notice as an astronomer in 1824, by communicating in that year to Dr Young, then Secretary to the Board of Longitude, proposed a method for computing an observed occultation of a fixed star by the moon. This accomplished philosopher thought so highly of it that he had it published, under the title of an improvement on his own method, in the Nautical Almanac for 1827 and the four following years. In some of the latter years, this publication was accompanied by a second method also proposed by Mr. Henderson. These methods were also published in the London Quarterly Journal of Science, and he received the thanks of the Board of Longitude for them. Around the same time, or shortly thereafter, he began contributing various useful papers and notices to the Quarterly Journal of Science, among which, in particular, he presented elements for computing the eclipses of the sun and lunar occultations of the planets and satellites for the years 1826, 1827, and 1828. and lists of the principal lunar occultations for the years 1826, 1827, 1828, and 1829. These lists, it is presumed, were the cause of several valuable observations of the phenomena being made, which, but for them, would probably have been neglected.
In 1827 he communicated a paper to the Royal Society of London, "On the Difference of Meridians of the Royal Observatories of London and Paris," which was published in the Philosophical Transactions for that year, and which furnishes a remarkable instance of the value of that habit of scrutinising calculation for which he was particularly distinguished. In the copy of the observations officially furnished from the Royal Observatory to Sir John Herschel, with a view to his operations in 1825 for determining the difference of longitude between Greenwich and Paris by means of fire signals, there was an error of a second in one of the numbers, which had the effect of causing some irregularity in the results of the different days' work; but as the discrepancies were small, they had been ascribed to errors of observation. Mr. Henderson, remarking the irregularity, was led to recalculate the original data, and thereby detected the error; and not content with this, he submitted the entire process to a new calculation. His result differed immaterially from that which had been previously obtained; but the correction of the error, by rendering the single results more consistent, gave a greatly increased confidence to the general conclusion; and, as was said of it by Sir John Herschel himself, "had the effect of raising a result liable to much doubt, from the discordance of the individual days' observations, to the rank of a standard scientific datum, and thus conferring on a national operation all the importance it ought to possess."
Mr. Henderson's connexion with this Society began by his undertaking, upon the request of the Council, to compute an ephemeris of the occultations of Aldebaran by the moon, in the year 1829, for ten different observatories in Europe. In this undertaking he was associated with Mr. Maclear, and the ephemeris, purporting to be their joint production, was read at the December meeting in 1828, and published in No. 15 of the Monthly Notices. His first contribution to the Memoirs (published in Vol. IV.) contained observations of transits of the moon, and stars nearly in the same parallel of declination, over the meridian, made at the Calton Hill Observatory in 1828, from which and corresponding observations made at Greenwich he computed the difference of meridians. This paper deserves notice, as shewing that he had already adopted the practice of estimating and allowing for the weights of the results and determining their probable errors, according to the methods in use among the German astronomers, but of which the examples were not, as yet, frequent in this country. The method of determining differences of longitude by means of observations of moon-culminating stars, then recently proposed by Nicolai, had been strongly recommended by Mr. Baily in a paper published in Vol. II. of the Memoirs, where all the requisite rules and formulæ were given for the computation. Mr. Henderson entered into these views with his accustomed energy, and not only embraced every opportunity of putting the method in practice by computing corresponding observations, but was at much pains to promote such observations by preparing lists of moon-culminating stars for the use of observers. A list of this kind was prepared by him at the request of the Council for the use of the Arctic expedition under the command of Captain (Sir John) Ross in 1830. Another subject on which his talents for computation were frequently exercised in furtherance of the views of the Council, was the calculation of the lunar occultations of fixed stars and planets. Observations of these phenomena, interesting both to Practical and physical astronomy were at that time much sought after by the Society because of their use in determining longitudes; and, since such phenomena are seldom observed unless predicted, it was desirable to ascertain the times of their occurrence by a prior calculation. In this case, Mr. Henderson also rendered most efficient aid by contributing, for several years, monthly lists of the principal lunar occultations calculated for the Greenwich meridian. The promptness and accuracy with which these calculations were made prompted the Council to request that he communicate his methods to the Society; and he accordingly drew up a set of "Practical Rules for the Approximate Prediction of Occultations," which are published in Vol. IV of the Memoirs. These services were duly acknowledged in our Annual Reports and at the anniversary meeting in 1830, the thanks of the Society were voted to him "for the very valuable assistance he had rendered to the cause of astronomy in his various computations presented to the Society."
The amount of Mr. Henderson's contributions to astronomy from 1825 to 1830, consisting of observations, tables, remarks, methods, and calculations of various kinds, published in the Quarterly Journal of Science, the Nautical Almanac, and the Notices and Memoirs of this Society, would have done credit to a professional computer; but, in order to rightly appreciate his zeal, it must be remembered that he was all this while occupied with professional duties of a kind which would be found by most persons to be sufficiently engrossing. His disinterestedness was no less remarkable than his scientific ardour; for, though in the receipt of very moderate emoluments, he declined all remuneration for his calculations; nor would this feature of his character be fully appreciated unless it were told at the same time that a considerable part of his income was appropriated by him to the support of his mother and sisters
Mr. Henderson's official duties, while connected with the Earl of Lauderdale and the Lord Advocate, brought him to London for several months each year. On these occasions, he became personally acquainted with the principal astronomers of the metropolis and had an opportunity, particularly at the observatory of Sir James South, which was freely opened to him, of seeing and handling first-class instruments. His various useful contributions to astronomy had already earned him a considerable reputation; and the high opinion formed of his talents was increased by the worthiness and unaffected simplicity of his character and the range and extraordinary accuracy of his information on all astronomical subjects. Accordingly, the prospect of attaching him to an office by which his services would be secured for the exclusive benefit of astronomy afforded satisfaction to all those who took an active interest in the progress of our science.
The death of Dr. Robert Blair in December 1828 had caused a vacancy in the professorship of Practical Astronomy in the University of Edinburgh, Mr. Henderson's qualifications for that office were presented to the Government (the patrons of the appointment) by Dr. Thomas Young and energetically urged by several other astronomers, particularly Captain Basil Hall. From the correspondence with the Secretary of State, it appears that the Government postponed filling the vacancy so that it might be considered what position could best serve science, given that the office had hitherto been neglected. In the summer of 1829, another astronomical appointment became vacant with the untimely death of Dr. Young. This eminent figure had received valuable assistance from Mr. Henderson in the calculations required for the Nautical Almanac and had held him in the most favourable opinion. About a fortnight before his death, he placed a memorandum in the hands of the late Professor Rigaud of Oxford, to be used in case of his death. And when the anticipated event took place, the memorandum was found to contain a request that it might be stated to the Board of Admiralty that he knew no person more competent to be his successor in the superintendency of the Almanac than Mr. Henderson. Professor Rigaud wasted no time in making known in the proper quarter the recommendation of his deceased friend, which he also supported with the weight of his own influence; but, as a consequence of other contemplated arrangements, it was unsuccessful, and the superintendency of the Nautical Almanac was, on that occasion, committed to Mr. Pond, then Astronomer Royal. Mr. Pond was also well aware of the efficiency and value of Mr. Henderson's aid, and immediately preferred a request to him to continue the same computations which he had been accustomed to supplying to Dr. Young; making at the same time offering remuneration, and sufficient employment to occupy a great portion of his time. But, although Mr. Henderson, shortly after, supplied Mr. Pond with some calculations on which he had previously been engaged, this offer appears to have been declined, and for two years longer he continued to pursue his professional occupation.
His character as an astronomer, however, was now fully established; and accordingly, on the death of Mr. Fallows, in 1831, he was regarded as one of the persons best qualified to undertake the direction and management of the observatory established by Government, and then recently completed, at the Cape of Good Hope. Through the intervention of Captain Beaufort, his qualifications were a second time brought under the notice of the Lords Commissioners of the Admiralty, and on this occasion successfully; but the idea of leaving his country was distasteful to him; and he accepted the office with some reluctance, and only in deference to the advice of his friends. The warrant of his appointment is dated in October 1831, and a few months after he embarked for the colony. Mr. Henderson arrived at the Cape in April 1832, and forthwith commenced his observations. The principal instruments were a 10-foot transit by Dollond, and a 6-foot mural circle by Jones; and his only assistant was Lieutenant Meadows, who had been sent out in the previous year. Few examples are upon record of more zealous and successful exertion than that which he furnished during his thirteen-month residence at the Cape. The results of his own personal exertions during that short interval include the determination of the latitude and longitude of his station; the positions of stars near the South Pole for determining the polar positions of his instruments; the amount of refraction near the horizon; observations of the moon and stars for determining the moon's horizontal parallax; of Mars for determining the parallax of that planet, and thus that of the sun; of eclipses of Jupiter's satellites; occultations of fixed stars by the moon; a transit of Mercury; and the locations of Encke's and Biela's comets. and, finally, between 5,000 and 6,000 observations of declination. Such a large mass of work would have been sufficiently creditable under the most advantageous circumstances; but when we consider that he had to contend with all the difficulties incidental to a new and imperfectly organized establishment, where no assistance was to be obtained from artists, and with a notoriously unmanageable instrument, it will be easily admitted that it would be difficult to overrate the zeal, perseverance, and skill with which he laboured to discharge the duties entrusted to him. But the merit of accumulating such a large and valuable mass of observations, great as it must be allowed to be, is completely overshadowed by comparison with that which is due to the persevering industry with which he laboured in their reduction and in deducing from them, the results we shall presently have occasion to mention. When Mr. Henderson accepted the appointment to the Cape Observatory, it was no doubt anticipated (probably even by himself) that his residence there would be of some considerable duration.
These anticipations were not realized, for in May 1833 he resigned the office, and shortly after returned to Europe. The reasons which induced him to take this step were fully stated by him in his letter of resignation addressed to the Secretary of the Admiralty.
After briefly alluding to the exertions necessary to carry out their lordships' instructions, he went on to say that not only did his health render him unable much longer to support the required labour, but the observatory, considered a place of residence, operated under so many disadvantages, required a lifestyle so different from that to which he had been accustomed that he found it impractical to remain any longer; and being thus unable to perform the duties, he felt it incumbent upon him instantly to resign the situation. But with that regard for the interests of science, and that kindness of disposition so eminently characteristic of him, he added that upon his return home he would proceed, with the sanction of their lordships, to the task of reducing the observations and extracting from them the results they were intended to afford; expressed his appreciation for the efficient aid he had received from his assistant, Lieutenant Meadows; modestly proffered such assistance as his experience might enable him to give to his successor; and concluded by recommending the state of the observatory to their lordships' consideration.
Had his state of health permitted him to continue his observations satisfactorily, there can be little doubt that the inconveniences of which he complained would in due time have been removed, or at least have become supportable; but, he had been made aware before he left England, that his physicians already apprehended the germs of that disease which eventually proved fatal to him, and under the depressing influence of this knowledge, aggravated by separation from all his friends and his family to whom he was tenderly attached and by his complete isolation - his spirits gave way, and he became apprehensive that he would be unable to maintain the observatory, from which so much was expected, in a state of requisite efficiency. Impressed with this idea, he took the resolution to give in his resignation, in order that it might have the contingent benefit of another appointment; And thus an act which, hastily judged, might appear to be an abandonment of his post, was the simple and natural result of a high, it may be an exaggerated, sense of public duty. The sacrifice involved in his resignation was of no small importance to him in a pecuniary point of view; for all he had to fall back upon was a pension of £101, a year, to which he had become entitled upon the retirement of Lord Eldin. But no one was ever less influenced by considerations of personal or pecuniary advantage, and under any circumstances he would have disdained the emoluments of office without the most punctilious discharge of its duties.
On his return to this country in 1833, Mr. Henderson took up his abode in Edinburgh, and being now without official engagements, he began the task of reducing the rich store of observations he had brought with him from the Cape The first result of this self-imposed labour was the determination of an important astronomical element, the sun's parallax, from a comparison of observations of the declination of Mars near opposition, made at Greenwich, Cambridge, and Altona, with the corresponding observations at Cape Canaveral. Prior to his departure for that station, he had expressed a wish that a selection should be made of stars that could be conveniently observed with Mars at opposition in November 1832, with a view to determining the parallax, and that a list of these should be circulated among different astronomers in various parts of the world, for the purpose of obtaining corresponding observations. Accordingly, Mr. Sheepshanks, having established the apparent positions of Mars during the requisite period, and Mr. Baily, having selected the stars to be observed, the council arranged for the list to be printed and circulated, along with instructions on how the observations should be made. As a consequence of these preparations, four sets of corresponding observations were obtained, from each of which Mr. Henderson deduced a parallax value. The mean of the whole yielded a parallax of 9°28′, a result which is known from the more certain method of transits of Venus to be somewhat too large, as was the case also in Lacaille's attempt at the Cape, in 1751, to determine the solar parallax by the same method. The determination, he remarks, is chiefly valuable as shewing the probable accuracy of the method, and the limits within which this important datum in physical astronomy may be determined independently of the rare phenomena of the transits of Venus.
Another paper of a more elaborate kind followed soon after, containing an investigation of the anomalies of the 6-foot mural circle in the Cape Observatory. When this instrument was first set up, there were found to be considerable discrepancies in the reading of the different microscopes, a circumstance which occasioned great perplexity to Mr. Fallows; and, although that astronomer ascertained that the mean of the six readings might be depended upon, he did not succeed in arriving at any satisfactory conclusion respecting the cause and the laws of the irregularities. Aware of these anomalies, which, indeed, were confirmed by his first observations. Mr. Henderson, a few weeks after his arrival at the Cape, undertook a laborious examination of the state of the instrument by means of a series of readings of each of the six microscopes at every tenth degree of the limb; and in April and May, 1833, shortly before his departure from the Cape, he repeated the experiment on a more extended scale, by examining the division corresponding to every fifth degree of the circle, and also the divisions immediately before and after it. On the results of this last experiment, which, however, were found to be identical with those of the former one, he grounded the investigation which forms the subject of the paper; an investigation which exhibits in a very advantageous point of view his sagacity, patience, and laborious accuracy, and is an admirable model of a carefully conducted experimental inquiry. The result was, that, in order to explain the observed anomalies it was necessary to suppose the figure of the instrument to be an oval of small eccentricity, that the pivots of the axis were not exactly circular, and that the whole instrument frequently changed its position upon the pier from the defective bearing of one of the pivots. But the most important conclusion deduced from the investigation, as it involved no less important a question than the trustworthiness of the whole of his Cape observations, was that the mean of the readings of the six equidistant microscopes was affected only to a very small extent (if affected at all) by these imperfections, and that the probable error of the instrument is not greater than the errors of the best instruments of similar construction hitherto made. From a similar investigation, founded on a less complete examination of the instrument by Mr. Fallows, Mr. Sheepshanks and Mr. Airy, in a paper which is printed in Vol. V. of the Memoirs, had previously arrived at a similar conclusion.*
While thus busily employed with the reduction of his own observations, on the results of which, he was well aware, his reputation as an astronomer would essentially depend, Mr. Henderson's assistance was still, as it had been in the early part of his career, freely extended to others whenever an opportunity arose to promote the cause of astronomy. Thus, at the request of Mr. Baily, he undertook the reduction of Captain Foster's observations of the comet of 1830, made at Ascension Island. The results of this, together with an ephemeris for facilitating the calculation of observations of the comet made in the southern hemisphere, are published in Vol. VIII of the Memoirs. Fortunately, however (even though this turned out to be true), the interval of leisure was of no long duration; and he was soon called upon for the discharge of more active duties. In 1834, an agreement was concluded between the government and the members of the Astronomical Institution of Edinburgh, whereby the latter relinquished to the University the use of its observatory on Calton Hill, which the former undertook to convert into a public establishment by furnishing it with suitable instruments and providing for an observer and assistant. It was then resolved to fill the office of Professor of Practical Astronomy, which had remained vacant since 1828, and to combine with it the direction and superintendence of the observatory. The Secretary of State did the Society the honour of requesting that a deputation from the Council confer and advise him on the person whom it might be proper to appoint to the situation. As a consequence of this request, a deputation awaited Lord Melbourne and, in the strongest terms, recommended Mr. Henderson, whose appointment accordingly followed immediately. The royal commission, nominating him Professor of Practical Astronomy and His Majesty's Astronomer for Scotland, which was dated the 18th of August of that year, required him to take upon himself the care and custody of the instruments within the observatory, and "to apply himself with diligence and zeal to making astronomical observations at the said observatory, for the extension and improvement of astronomy, geography, and navigation, and other branches of science connected therewith."
Mr. Henderson was now placed in a situation suited in every respect to his tastes, habits, and pursuits; and, as he was still young, those who were best acquainted with the extent of his knowledge, his industrious habits, and his facility and accuracy in all practical matters, formed the highest expectations of the value of his future services to astronomy. Nor were their expectations disappointed. The Annals of the Edinburgh Observatory, his Catalogue of Southern Stars, his investigations of annual parallax, and other deductions from his Cape observations, besides various contributions relative to subjects of a less important, but always of an interesting nature, amply justify the recommendation of our Council; while their very excellence increases our present regrets that a career so auspiciously begun has been so prematurely brought to a close.
As soon as Mr. Henderson had gotten his observatory into working order and had established a regular routine of duty, he resumed the reduction of his Cape observations, an occupation which engrossed the greater part of his leisure time during the remainder of his life, and of which the fruits are a series of papers communicated to the Society and published in our Memoirs, all more or less interesting, and some of them of the first order of excellence
The next result of these reductions, and indeed one of the most intrinsically important of the whole, was a Catalogue of the declinations of 172 principal fixed stars, chiefly in the southern hemisphere, which was presented to the Society at the April meeting in 1837. Due to various causes of delay, the reduction of the right ascensions of the same stars was only completed, and the results presented to the Society, in the course of the last year. They have, however, already been printed and will appear in our forthcoming volume. Although the number of stars contained in this Catalogue is not large, it acquires importance and value both on account of the still relatively defective state of our knowledge of the absolute positions of the southern stars, and from the fact that it is the first to be deduced from observations made in the southern hemisphere with instruments equivalent to those of the best European observatories Indeed, if we exclude Mr. Johnson's excellent Catalogue of Stars Observed at St. Helena, it must be regarded as the first in which the places of stars not visible at our latitudes have been determined with the precision and certainty now aimed at in astronomy. It was principally with a view to the determination of the positions of the principal southern stars, for the aid of navigation, that the establishment of the Cape Observatory was urged upon and undertaken by the government, and this catalogue forms one of the most important installments astronomy has yet received from it.
Although determining the absolute positions of the stars was the observatory's primary business, Mr. Henderson was too zealous an astronomer to omit taking advantage of his position to investigate various important points that can only be determined by comparing observations made at distant locations, or that acquire special interest from the observer's position. One such point is the amount of refraction in the southern hemisphere. In an interesting paper on this subject, published in Vol. X of his Memoirs, he presented the results of a series of observations made at the Cape of Good Hope of stars with a zenith distance greater than 85°, both north and south, and compared the refractions deduced from the tables of Bessel and Ivory. These results, tending to shed light on the important subject of horizontal refractions, are valuable for both general physics and practical astronomy.
Another important determination, also prompted by the location, was that of the moon's horizontal parallax. It is well known that determining this element was one of the principal objectives of Lacaille's voyage to the Cape; his purpose being to obtain observations of the moon's declination corresponding to others made at different European observatories. A similar investigation was proposed for Mr. Henderson, or rather, several stars had been marked in the Berlin Ephemeris and Nautical Almanac as favourably situated for having their declinations observed alongside the moon's in both hemispheres, by which means the moon's apparent declinations could be obtained free from the effects of errors in the assumed declinations of the stars. But the number of corresponding observations of this kind that could be made was found to be too small to permit the element to be determined from them with sufficient accuracy. Therefore, whenever there was a shortage of moon-culminating stars, Mr. Henderson could use observations of the principal stars that were available for comparison. The investigation, like all others which he undertook, is conducted in the most careful manner; and the result, although, in consequence of the mode of proceeding adopted, it is dependent on the accuracy of the determination of the relative declinations of the principal stars, is probably the best determination of the constant we are in possession of.
It would almost seem as if, in these investigations, Mr. Henderson intended to repeat the labours of Lacaille during his memorable stay at the Cape around the middle of the last century. In another, and more important, aspect, he may be considered an imitator of that great astronomer. Lacaille had remarked that, in the then advanced state of astronomy, no one could any longer be believed on his mere word; and that, in order to employ with confidence an observed position, it was necessary to have all the details of the observation and all the elements of reduction. No astronomer was ever more careful of the observance of this important maxim than Mr. Henderson. From the reading of the circle to the final result of the investigation, everything necessary for the complete understanding of the process or verification of the work is carefully set forth and explained; and, accordingly, all his investigations and results are characterised by an air of truthfulness, which would be in vain to seek where a different practice is followed.
But of all the results which he deduced from this persevering examination of his Cape observations, the one which will be considered the most interesting is the annual parallax of the double star Centauri, amounting to about a second of space. This binary system was recognized to be a double about a century ago; and, on comparing the observations of Lacaille with those of the present time, it is found to have an annual proper motion of about 3″-6″. Being situated within about 30° of the South Pole, it is always above the horizon at the Cape, and, consequently, favourably placed for being accurately observed at all times. The intrinsic brightness of the two component stars is also remarkable; and from this, and their large proper motion-circumstances indicative of proximity to our system Mr. Henderson was led to suspect they might have a sensitive parallax. He was not, however, aware of their large proper motion until he was about to leave the Cape; and the observations from which the result was first deduced, were accordingly not made with special reference to the question of parallax, but for the purpose of determining their mean positions. The first indications of parallax were detected upon a comparison of their declinations with those of such of the standard stars as were observed on the same day throughout the year; but he deferred the announcement of the discovery until he had completed the reduction of the right ascensions, and obtained, by this means, a further test of the accuracy of his conclusion. A similar investigation of these latter observations confirmed the previous deduction; and, in a paper read to the Society at the January meeting of 1839, he announced a parallax of the double star amounting to about a second of space. With his habitual caution and accuracy, he applied every means of testing the result the observations afforded, deducing the parallax separately from the observations of right ascension, from the direct observations of declination, and from the reflected observations of declination, and this in respect. of each of the two stars; and although the resulting parallax differed somewhat in the different cases, the general agreement was satisfactory, and the amount much too large to be ascribable to probable errors of observation. But notwithstanding the corroboration which the results of these different modes of deduction afforded each other, if the question of the parallax of this binary star had been allowed to rest in the state in which it was placed in Mr. Henderson's first paper, astronomers would probably have agreed in thinking his investigation only went the length of establishing a strong probability in favour of its existence. Mr. Main, after an elaborate comparison of the result with the individual observations from which it was deduced, observes, "For the present it must be considered that the star well deserves a rigorous examination by all the methods which the author himself has so well pointed out; and that, in the event of a parallax at all comparable with that assigned by Mr. Henderson being found, he will deserve the merit of its discovery, and the warmest thanks of astronomers, as an extender of the knowledge we possess of ours connection with the sidereal system." Memoirs, vol. xii. p. 36. The result, however, was far too curious to be allowed long to remain without an attempt being made to confirm it. No sooner was Mr. Henderson's paper communicated to Mr. Maclear, than that energetic astronomer undertook a series of observations of the double altitudes of the two stars with the mural circle, with an express view to the question. They extend over seventeen months, from March 26, 1839, to August 12, 1840; and, as the mural circle at the Cape was changed shortly after their commencement, they have the further advantage of having been made, for the The greater part, with a different instrument. These observations being transmitted to Mr. Henderson, he immediately undertook to reduce them; and, in an elaborate paper inserted in Vol. XII of the Memoirs, he deduced the parallax for each of the two stars from both the direct and reflected observations. The results entirely confirmed his former deductions, but, as was to be expected from the greater number of observations, they were more consistent. The mean gave, as before, a parallax of about 1 arcsecond; whereas it is inferred that this system, perhaps the nearest of the stellar bodies, is separated from us by an interval exceeding 200,000 times the distance of the sun from the earth.
Looking to the history of this interesting subject, to the consistent results given by the Dublin circle, which have been disproved by other instruments, and considering that the present determination has as yet been only partially confirmed by the observations of right ascension, the cautious astronomer will, perhaps, be inclined to maintain some reserve until the star has been examined with an instrument affording the means of exact micrometric measurement, or, at least, until a longer series of meridian observations has been made; for, as has been remarked by Sir John Herschel, "It is only on a very long series of observations of absolute places, affected, as they are, by instrumental error and uncertainty of refraction, that any conclusion of this kind can rest with security." But whatever the ultimate decision of astronomers may be with respect to the parallax in question, there will be but one opinion as to the merit of Mr. Henderson's investigations, and the interest which attaches to the subject: and, in the meantime, it will be remembered that this is the first determination of the parallax of a star which has been confirmed by a different observer using a different instrument; and that if future observations shall continue to give similar results, which now seems a reasonable anticipation, to Mr. Henderson will indisputably belong the enviable distinction of having been the first to succeed in an inquiry so often, but fruitlessly, attempted by astronomers, namely, the discovery of a fixed star whose distance from our system is capable of measurement and expression. For these researches he was proposed to the Council at the meeting in November last, as deserving of the Society's gold medal for the present year, but his untimely death prevented the question from being addressed.
Another attempt made by him to determine the annual parallax was less successful. Sirius, the brightest star in the heavens, might be supposed to be one of the least remote; and some astronomists—Cassini, Lacaille, and Piazzi—had assigned it a parallax of several seconds. The Cape observations being well adapted for the investigation of the question, Mr. Henderson undertook the examination of those made by himself, and also a series by Mr. Maclear, in order to ascertain if they indicated any sensible parallax; but, in this case, the result amounted only to about a quarter of a second, a quantity not exceeding, perhaps, the probable error of the determination.
Mr. Henderson's work on the subject of parallax did not end there. In a letter to Mr. Main, which was read at the December meeting of 1842, he presented the results of an investigation into the parallaxes, as they appear from his Cape observations, of twenty stars that had been observed frequently enough to reduce the errors of observation within reasonable limits. These stars comprised the majority of those located in the same region of the heavens as Centauri, which Sir John Herschel had identified as deserving of investigation for parallax and which, on that account, are currently objects of particular attention at the Cape Observatory. In a few instances, considerable parallaxes appeared; in the greater number of cases, the results were so small as to offer little hope of finding a measurable parallax, and in some, they were negative. The mean of the twenty parallaxes is +0.29, a result which, on the whole, may be considered encouraging to continue the research.
It is a matter of much regret that the reduction of the entire series of Mr. Henderson's Cape observations—the rich store from which the above interesting results have been extracted—has not been completed by him; and that the observations must consequently be deprived of the advantage of his final revision. From the examination of his papers, it appears that the number of positions determined both with the mural circle and transit instrument, from April 10, 1832, to May 24, 1833, is between 5,000 and 6,000. The transit observations (made chiefly by Lieutenant Meadows) are found to be carefully written out, with the column headed "correction of instrument" filled in for the whole period and that headed "correction of clock" from the commencement to October 31, 1832. The circle observations, which were all made by himself, are in a similar state of forwardness; and it may be inferred from the appearance of the papers that if he had lived a few months longer, and the work had proceeded at the ordinary rate, the whole would have been ready for the press.
A statement of the results deduced by Mr. Henderson from his Cape observations could not be properly concluded without an expression of admiration for that disinterested zeal which led him to undertake and execute so great an amount of extra-official labour. The observations, it will be remembered, were made at a public establishment, and their reduction was a matter of public concern and importance; and after his resignation of the appointment, the public had no claim on his services more than on those of any other individual. But, as already remarked, considerations of this kind never, in any degree, influenced his conduct; and, for ten long years, he gratuitously devoted himself to this purpose all the time he could spare from his official duties. In the same circumstances, almost any other person would have claimed, and undoubtedly have obtained, both assistance and remuneration. In addition to the results now mentioned, he rendered yet another important service to the astronomy of the southern heavens, in supervising the reduction of the stars observed at the Cape by Lacaille. This work, which he undertook on behalf of Mr. Baily for the British Association, was announced as completed in our Annual Report for 1843; but it has not yet been published. Mr. Henderson's work at the Edinburgh Observatory is well known to astronomers from the five volumes of observations published for 1834–1839. A sixth volume is understood to be left nearly ready for publication; and the observations for the remaining years will, no doubt, still be made available to science. The published volumes are prefaced by an Introduction, containing a minute and most lucid description of the instruments and methods used in the observations and reductions, with every detail and explanation that can contribute to giving authenticity and value to the work. His first year's observations, having been referred to this Society by the Home Secretary, were reported by a committee of the Council to be of first-rate excellence, and their publication was recommended as a matter of scientific importance. This report has been ratified by all astronomers; and, so far as they have been published, the Edinburgh observations not only do credit to the astronomer and his assistant, Mr. Wallace, but have conferred on the Observatory a high reputation among the similar institutions of Europe
Although the periodical publication of the Edinburgh observations rendered it largely unnecessary for him to resort to other channels of publicity, he continued, from time to time, to communicate to this Society various observations of phenomena, either occasional or of immediate interest, and notices likely to be useful to practical astronomers. Among these may be mentioned observations of the planets near their oppositions and inferior conjunctions, of moon-culminating stars, of the annular eclipse of the sun on May 15, 1836; and, more especially, elements of cometary orbits. Indeed, if he had no other claim on our regard, his care in disseminating the earliest information respecting the orbits of newly discovered comets would alone have entitled him to the applause due to a useful labourer in the cause of astronomy Various observations and notices of the kind now referred to were also communicated by him to Professor Schumacher and published in the Astronomische Nachrichten, whereby they obtained immediate circulation over the Continent.
His attention at Edinburgh was chiefly directed to planetary observations and the creation of an extensive catalogue of zodiacal stars. He had progressed far in the latter work; and in one of his last letters, written to an intimate friend, he spoke of being engaged in fixing the positions of some of those stars in Argelander's recent catalogue, which, though visible to the naked eye, had escaped the notice of all former astronomers.
In recounting Mr. Henderson's labours at the Edinburgh Observatory, we would fail to do justice to his zeal if we omitted all reference to other aspirations which occasionally placed large demands on his time. His office as professor, though he gave no lectures in his own, the department entailed various duties for him. During one entire semester (1835-1836) he delivered the mathematical lectures for Professor Wallace, then became incapacitated by illness; and in the last year he undertook, for some time, a similar duty for Professor Forbes in the class of Natural Philosophy. In short, he was one whose general talents and business acumen, coupled with extreme benevolence and great common sense, made him a most useful assistant; and, accordingly, the largest share of any public business with which he happened to be connected was sure to fall into his hands.
Having none of the accessory advantages of birth, fortune, or early introduction, Mr. Henderson had to rely on his own energy and talents alone in conquering his way to fame; and he was only beginning to enjoy his well-earned reputation, both in his own country and abroad. He was admitted a Fellow of this Society in 1832, and of the Royal Society in 1840, and he had been a member of the Royal Society of Edinburgh since 1834. It does not appear that he was a member of any foreign society, but he was in frequent correspondence with Schumacher, Bessel, Encke, and other distinguished astronomers on the continent, by whom his talents and opinion on astronomical subjects were held in high estimation
In 1836 he married Miss Adie, eldest daughter of the well-known optician and ingenious inventor of the sympiesometer. The death of this lady in 1842, a few weeks after the birth of their only child, affected his sensitive temper from which he never completely recovered. In the summer of that year he was gratified by an event which afforded him at the time the liveliest pleasure, and ever after formed a bright spot in his memory. This was the visit to Edinburgh of Professor Bessel, whom he had always been accustomed to regard as his master in science; and for whose character and writings he entertained an unbounded admiration. In company with the great astronomer, and his countryman and colleague, the celebrated mathematician Jacobi, he made a short excursion to the Highlands; and his friends well remember the delight with which he used to recount the incidents of that journey, and relate anecdotes of his illustrious companions
Although his constitution was never robust, and he was occasionally subject to low spirits, during the influence of which he would express misgivings as to his hold on life, his health did not undergo any visible change until the autumn of 1844, when he was suddenly seized with an illness of such alarming a kind that, happening at the time he was on a visit to a friend, some days elapsed before he could be removed to his own house. From this attack he partially recovered, and hopes were entertained that he would soon be enabled to resume his usual duties; but a relapse having occurred, he expired suddenly on the 23rd of November, a few weeks before he would have completed his forty-sixth year. The disease was then ascertained to be hypertrophy of the heart; and there can be little doubt that, in the state of health induced by this organic disorder, the fatigue of the nightly observations and of climbing the steep hill on the summit of which the observatory is built had been extremely prejudicial to him and contributed to accelerating its fatal termination.
The character of Mr. Henderson as an astronomer stands high, and his name will go down to posterity as an accurate observer, an industrious computer, a skillful manipulator, and an improver of methods in that department to which he devoted himself. Endowed by nature with perceptive powers of great acuteness, and accustomed by his early professional training to examine and sift the evidence of every fact or statement presented to his mind and to keep it before him until he had obtained a clear conception of it in all its bearings, every acquisition he made was perfect; and all his knowledge was stored up in a memory of unusually retentive powers, in such an orderly manner as to be always available at the moment it was wanted A keen eye, and habits of order, regularity, and attention, enabled him to become an excellent observer; but the services for which he will be remembered consist not so much in numerous and accurate observations, as in the use he made of them and the manner in which he worked out their results. At the outset of his career, he was led (probably by the commendation of them in our Memoirs) to study attentively the methods of the German astronomers, particularly those of Bessel and Struve, upon whose model he formed his practice, and from which he never departed. All his memoirs and investigations are characterized by the excellences of those illustrious masters. Every observation is scrupulously discussed, and its results drawn out in the most concise and useful form. His processes are fully explained; his formula for reduction carefully chosen; no labour is evaded; and no circumstance that could affect the accuracy of the final result is passed unnoticed. Nor is the manner in which his results are presented and communicated inferior to the skill displayed in deducing them. His descriptions of instruments, methods, and details of practice are characterized by a simplicity, neatness, and precision that simultaneously demonstrate his good taste and mastery of his subject. His introductions to the Edinburgh observations may be cited as admirable examples of astronomical writing. Nothing, indeed, is more remarkable in all his compositions than good taste and the complete absence of any trace of exaggeration of his own merits or affectation of singularity. Distinguishing clearly his object, he pursues it in a direct, undeviating course; never stepping aside for the sake of display, yet skillfully availing himself of every means of reaching it that science had placed at his disposal. To represent him as profoundly skilled in the higher departments of physical astronomy would be to make a pretension from which the modesty of his nature would have been reconciled. but he had a sufficiently accurate knowledge of the analytical processes by which the phenomena of the universe are deduced from, or connected with, the theory of gravitation, to appreciate correctly their bearings on the practical branches, to which he directed his attention. To a very considerable knowledge of mathematics he added great powers of calculation, which he never abused. Though less liable than most men to make mistakes, he, in no case, allowed himself to dispense with the most scrupulous revision of his work. One of his most distinguishing qualities was sound judgment. He never attempted anything to which his powers were not fully equal; and, as a consequence of this, whatever he did, he did well.
Few men have been more conversant with the modern history of astronomy, especially that branch of it with which he was more immediately connected. It may be said, without any exaggeration, that he knew, and could name the author of every invention or contrivance, whether mathematical or mechanical, bearing on his professional duties.
In his private character and the relations of domestic life, Mr. Henderson was distinguished by great warmth of affection and amiability of disposition. Naturally modest and retiring, he shrunk from the most distant contact with obtrusiveness and ostentation; but he knew his position well enough and was by no means deficient in spirit to defend it. His disposition was cheerful and sociable, and when released from official duties, he took great pleasure in the company of his friends, to whom he was endeared by the worth of his character, the unaffected simplicity of his manners, his kind-hearted benevolence, and enthusiastic admiration of anything noble and excellent. His reputation for astronomical knowledge and his readiness to assist in its promotion involved him in extensive correspondence; but, however occupied he might be, when reference was made to him on any point connected with his professional pursuits, he was always to be depended upon for a prompt answer, either containing (as was most frequently the case) a full exposition of the matter at hand, or a frank acknowledgment that he had no information to give. Notwithstanding his slender appointments, he had already collected an extensive and valuable astronomical library; but the proceeds of its sale were the principal part of the inheritance he left for his orphan daughter. He was
The loss of such an excellent member, at an age when his knowledge and faculties had only attained maturity, and when past triumphs justified the brightest anticipations for the future, cannot be regarded by the Society with feelings of ordinary regret. Let us hope there will never be wanting among us examples of similar and equally successful devotion.
The following is a list of Mr. Henderson's Astronomical Papers.
I. In the Memoirs of the Royal Astronomical Society:
Observed Transits of the Moon and Stars nearly in the same Parallel of Declination over the Meridian. Vol. IV. p. 189
Note on the difference of meridians between the Observatories of Greenwich and Edinburgh. Vol. IV, p. 191.
Practical Rules for the Approximate Prediction of Occultations. Vol. IV, p. 587.
On the Latitude and Longitude of the Observatory at the Cape of Good Hope. Vol. VI, p. 125.
Positions of several stars near the South Pole, deduced from observations made at the Observatory at the Cape of Good Hope. Vol. VI, p. 133.
Observations of the Periodic Comet of 67 years, made at the Observatory, Cape of Good Hope, between November 18, 1832, and January 3, 1833. Vol. VI, p. 159.
Observations of the Moon and stars made with the Mural Circle at the Observatory, Cape of Good Hope, for the determination of the Moon's parallax. Vol. VI, p. 205
Observations of Mars and Stars made with the Mural Circle at the Observatory, Cape of Good Hope, for the determination of the Parallax of Mars. Vol. VI, p. 207.
Letter to Professor Airy, on the Sun's Parallax, as deduced from various observations made at Greenwich, Cambridge, and the Cape of Good Hope. Vol. VIII, p. 95.
Supplement to a paper entitled "On the Latitude and Longitude of the Observatory at the Cape of Good Hope." Vol. VIII, p. 137.
On the Mural Circle of the Observatory at the Cape of Good Hope. Vol. VIII, p. 141.
Observations of the Comet of 1830, made at Ascension Island, by the late Captain Foster. Reduced by Mr. Henderson. Vol. VIII, p. 191
Observations of Vesta at the Opposition in 1834, made at Edinburgh. Vol. VIII, p. 232. Observations of Jupiter at the Opposition in 1834, made at Edinburgh.
Edinburgh. Vol. VIII, p. 234. Observations of Venus at the Inferior Conjunction, in December 1834, made at Edinburgh. Vol. VIII, p. 236.
Observations of Mars at the Opposition in January 1835, made at Edinburgh. Vol. VIII, p. 238.
Places of the Comet of Biela, deduced from Observations at Slough and the Cape of Good Hope. Vol. VIII, p. 240.
Places of Encke's Comet, from Observations made at the Cape of Good Hope. Vol. VIII, p. 243
Notes on Mossotti's Observations of the Comet of Encke. Vol. VIII, p. 250.
Notes on Mr. Dunlop's Observations of Two Comets in 1833 and 1834. Vol. VIII, p. 264.
Results of the Lunar Observations made at Edinburgh in the years 1834 and 1835. Vol. IX, p. 272.
On the Declinations of the Principal Fixed Stars, deduced from Observations made at the Observatory, Cape of Good Hope, in the years 1832 and 1833. Vol. X, p. 49
Refractions of Stars near the Horizon, observed at the Cape of Good Hope. Vol. X, p. 271.
The Constant Quantity of the Moon's Equatorial Horizontal Parallax, deduced from Observations made at Greenwich, Cambridge, and the Cape of Good Hope, in 1832 and 1833. Vol. X.
p. 283. On the Parallax of a Centauri. Vol. XI, p. 61.
On the Parallax of Sirius. Vol. XI, p. 239.
The Parallax of a Centauri, deduced from Mr. Maclear's Observations at the Cape of Good Hope, in the years 1839 and 1840. Vol. XII, p. 329.
The Right Ascensions of the Principal Fixed Stars, deduced from Observations made at the Observatory, Cape of Good Hope, in the years 1832 and 1833. Vol. XV, p. 129.
II. In the Monthly Notices of the Royal Astronomical Society:
Occultations of Aldebaran by the Moon, in the year 1829, computed for ten different observatories in Europe, by T. Henderson, Esq. and T. Maclear, Esq. Vol. I, p. 89.
A List of the Occultations of Aldebaran by the Moon, in the year 1830, computed for ten different observatories in Europe, by T. Henderson, Esq. and T. Maclear, Esq. Vol. I, p. 133.
Various Observations made at the Royal Observatory, Edinburgh. Vol. III, p. 129.
Opposition of Uranus, August 1835, observed at Edinburgh. Vol. III, p. 143
Oppositions of Jupiter in January 1836, of Juno in January 1836, and Vesta in March 1836, observed at Edinburgh. Vol. III, p. 200.
On the Annular Eclipse of the Sun, on May 15, 1836. Vol. IV, p. 165.
Apparent Positions of Galle's First Comet. Vol. V, p. 9.
Elements of Galle's First Comet. Vol. V, p. 16.
On the Parallaxes of Certain Southern Stars. Vol. V, p. 223.
Elements of the Comet of 1668. Vol. V, p. 266.
Elements and Ephemeris of the Great Comet of 1843. Vol. V, p. 266.
Letter to the Secretary on the Great Comet of 1843, p. 267. Vol. V
Approximate Elements of the Comet of Faye. Vol. VI, p. 15.
On the Orbit of the Comet of Faye. Vol. VI, p. 18.
Elements and Ephemeris of the Comet of Faye. Vol. VI, p. 57.
III. In the Philosophical Transactions of the Royal Society of London:
On the Difference of Meridians of the Royal Observatories of Greenwich and Paris. Vol. for 1827, p. 286.
Observations of the Comet of Encke made in 1832. Vol. for 1833, p. 549
IV. In the Philosophical Magazine:-
On Mr. Burns' Method of Finding the Latitude by Double Altitudes Vol. LXVI. p. 283.
Some Remarks on Captain Sabine's Pendulum Experiments. Vol. II. (New Series), p. 126.
V. In the London Quarterly Journal of Science:-
Rules for Computing an Observed Occultation of a Fixed Star by the Moon. No. XXXVI. p. 343. Also in New Series, No. II. p. 434. Annexed also to the Nautical Almanacs for 1827-1831.
Remarks on the Determination of the Longitude from Observations of the Moon's Right Ascension. No. XXXVII. p. 109.
Discordance of the Lunar Observations Made at Greenwich and Paris. No. XXXVII. p. 116
Corrections of the Catalogue of Zodiacal Stars. No. XXXVIII. p. 239.
A Method of Computing the Sun's Horizontal Parallax from Observations of the Transits of Venus. No. XXXIX. p. 94.
Remarks on the Discordances Observed Between the Lunar Observations at Greenwich and Paris. No. XXXIX. p. 96.
Remarks on M. Mendoza Rios' Method of Computing the True from the Apparent Lunar Distances. No. XL. p. 315.
In the Quarterly Journal, New Series: -
Remarks on the Solar Tables. No. II. p. 438.
Answer to Some Objections Stated Against the Method for Computing an Observed Occultation. No. VIII. p. 411.
VI. In Schumacher's Astronomische Nachrichten:-
Note on the Occultation of Mercury by the Moon on Aug. 9, 1831. No. 190, col. 437.
Astronomical Observations made at Edinburgh in 1831. No. 242, col. 25.
Note on Mossotti's Observations of Encke's Comet. No. 243, col. 39.
Account of Observations made at the Cape of Good Hope in 1832 and 1833. No. 257, col. 293.
On the Longitude of the Cape Observatory, and the Sun's Mean Equatoral Horizontal Parallax. No. 262, col. 403.
Elements of Two Comets observed at Paramatta in 1833 and 1834. No. 271, col. 117
Mean Declinations of 172 Principal Fixed Stars, deduced from observations made at the Cape of Good Hope. No. 318, col. 81.
Refractions of Stars near the Horizon, observed at the Cape of Good Hope. No. 319, col. 103.
On the Moon's Equatoral Horizontal Parallax. No. 338, col. 25
On the Comet of 1668. No. 476, col. 333. Elliptic Elements of Faye's Comet. No. 495, col. 235.
Computations of the principal Lunar Occultations of the Fixed Stars, during the years 1826, 1827, 1828, and 1829, made for the Royal Observatory at Greenwich.
Elements for Computing the Eclipses of the Sun, and Lunar Occultations of the Planets and their Satellites, for the years 1826, 1827, and 1828. In various issues of the Quarterly Journal.
Computations of the principal Lunar Occultations of the Fixed Stars and Planets, for the years 1830, 1831, and 1832. In Monthly Notices of the Royal Astronomical Society, and in the Nautical Almanac
Ephemeris of the Comet of 6.7 years, in Supplement to Nautical Almanac for 1832.
On gamma Virginis. In Smyth's Cycle of Celestial Objects, vol. i. p. 483
* It may not be without interest to state that, when this instrument was sent back to England some years afterwards, and examined at the Royal Observatory, it was found that, owing probably to some oversight in the construction, the large steel collar carried by the conical axis was quite loose. It is well, perhaps, the discovery was not made sooner, or the instrument would probably have been condemned, and the observations lost,
Thomas Henderson was born at Dundee on the 28th of December, 1798. His father was a tradesman in respectable circumstances, who died early in life, leaving to the care of his widow a family consisting of two sons and three daughters. The eldest son, John, was bred to the legal profession; and, after practising for some time as a writer in Dundee, went to Edinburgh, where he studied for the bar, and was rapidly rising to distinction as an advocate when he died suddenly, at the age of thirty-eight, of aneurysm of the heart. Thomas, the other son and the youngest of the family, was also destined for the legal profession and had the advantage of receiving the best education possible in a town long renowned in Scotland for the excellence of its public schools. After the usual preliminary instruction, he was sent, at the age of nine, to the grammar school, where he pursued the standard course of classical study for four years. He was distinguished by his diligence and quickness of apprehension, generally being the leading student in his class. In 1811, he proceeded to the Academy, where he continued for two more years. The Dundee Academy was at that time under the very capable rectorship of Mr. Duncan, now Professor of Mathematics at the University of St. Andrews. The curriculum included elementary mathematics, natural philosophy, and chemistry, and young Henderson passed through the entire course with the same distinction that had marked his progress at the grammar school. Professor Duncan, in a letter to the writer of this notice, bears the following testimony to the merits of his former pupil. "The two Hendersons," he says, "were the best scholars I had in the entire period of my incumbency. You are aware, I suppose, that John became distinguished at the bar, and was only prevented, by an early death, from rising to great eminence. Thomas, the future astronomer, was remarkable for everything that was good: the diligence and success with which he prepared his lessons, the exactness with which he performed the exercises, the propriety and modesty of his demeanour."
At the age of fifteen he was placed in the office of Mr. Small, a writer (or solicitor) in Dundee, with whom his brother had entered into partnership. In this situation he remained for six years; and it appears to have been during this period that he began to devote his leisure hours to the study of astronomy, though the particular circumstance, or accident (if, indeed, there were any other cause than the promptings of a naturally active and inquisitive mind), which first gave this direction to his inquiries is not known. During his attendance at the Academy, and even at an earlier date, he had evinced a remarkable predilection for works relating to geography and chronology; and his taste for these studies was often gratified at the expense of his health, for he was naturally of a weak constitution and subject to some disorder of the eyes, which at times rendered him nearly blind. From these subjects to astronomy the transition is easy and natural; and, although he received no aid from the lessons of a master, and had no encouragement from example, yet, in a town which could boast of being the birthplace of Ivory, and in which Dr. Small, the expositor of Kepler, had so long resided, it may be supposed there would prevail, among the better informed classes of the inhabitants, some general sentiment of respect for proficiency in astronomy and mathematics, which might not be without its influence on a mind possessing a peculiar aptitude for such studies. However this may be, the fact deserves to be recorded, as an instance of what may be done under circumstances apparently the most adverse, that it was while employed as an attorney's clerk in a provincial town that he laid the foundations of that extensive acquaintance with astronomy for which he afterwards became so distinguished.
Having gone through a six-year apprenticeship, Mr. Henderson, at the age of twenty-one, repaired to Edinburgh for the purpose of completing his legal education and obtaining professional employment. He first obtained a position in the law office of a Writer to the Signet, where his intelligence and abilities were remarked by Mr. (now Sir James) Gibson Craig, who became his steady patron and friend, and by whose recommendation he was appointed secretary, or Advocate's clerk, to the celebrated John Clerk, afterwards one of the judges of the Supreme Court of Scotland, under the title of Lord Eldin. On Lord Eldin's retirement from the bench, he was for some time private secretary to the Earl of Lauderdale; an office which he relinquished for the more profitable appointment as secretary to the Lord Advocate (Jeffrey). In these successive employments, he spent the twelve years from 1819 to 1831; and it may be remarked that, although of a subordinate nature, they were such as would only be entrusted to a person of acknowledged abilities, and one whose character for fidelity, discretion, and general intelligence was already established. It is probable that they allowed him considerable intervals of leisure, but in no other respect were they favourable for scientific pursuits; and, indeed, it may be regarded as one of the most remarkable features in his history that, while engaged in the discharge of multifarious and active duties, in a line of life so foreign to astronomy and physical science of any kind, he should not only retain his tastes for the liberal studies he had commenced at the Dundee Academy, but find leisure to make so many new and important acquisitions.
Soon after he became resident in Edinburgh, his astronomical acquisitions procured him introductions to Professors Leslie and Wallace, Captain Basil Hall, and other distinguished persons, by whom his talents were quickly appreciated, and who afforded him every encouragement to persevere in his scientific pursuits. At that time, the small observatory on Calton Hill, belonging to The Astronomical Institution of Edinburgh was placed under the charge of Professor Wallace, who, finding in Mr. Henderson a person to whom the instruments could be safely entrusted, granted him free access to them, thereby giving him an opportunity to acquire practical knowledge of a subject with which he had already become familiar through study and books. The instruments, it is true, were not of first-rate excellence—a clock and transit telescope with a 30-inch focal length, along with an altitude and azimuth instrument by Troughton—constituted the observatory's equipment. However, for a young astronomer who had no other access to astronomical apparatus, such an opportunity was invaluable; and there is little doubt that this circumstance had a considerable influence on his future career.
The opportunity of making observations, however, did not in any degree withdraw him from the less inviting parts of the science. From the outset of his career he perceived that, in order to be an astronomer, something more is necessary than mere expertise in the use of instruments. He accordingly continued to direct his main attention to the reduction of observations; and, at an early period, acquired a great knowledge of methods, and great facility in calculating eclipses, occultations, cometary orbits, and, generally, in all the computations and reductions which are subservient to practical astronomy.
Mr. Henderson first brought himself into notice as an astronomer in 1824, by communicating in that year to Dr Young, then Secretary to the Board of Longitude, proposed a method for computing an observed occultation of a fixed star by the moon. This accomplished philosopher thought so highly of it that he had it published, under the title of an improvement on his own method, in the Nautical Almanac for 1827 and the four following years. In some of the latter years, this publication was accompanied by a second method also proposed by Mr. Henderson. These methods were also published in the London Quarterly Journal of Science, and he received the thanks of the Board of Longitude for them. Around the same time, or shortly thereafter, he began contributing various useful papers and notices to the Quarterly Journal of Science, among which, in particular, he presented elements for computing the eclipses of the sun and lunar occultations of the planets and satellites for the years 1826, 1827, and 1828. and lists of the principal lunar occultations for the years 1826, 1827, 1828, and 1829. These lists, it is presumed, were the cause of several valuable observations of the phenomena being made, which, but for them, would probably have been neglected.
In 1827 he communicated a paper to the Royal Society of London, "On the Difference of Meridians of the Royal Observatories of London and Paris," which was published in the Philosophical Transactions for that year, and which furnishes a remarkable instance of the value of that habit of scrutinising calculation for which he was particularly distinguished. In the copy of the observations officially furnished from the Royal Observatory to Sir John Herschel, with a view to his operations in 1825 for determining the difference of longitude between Greenwich and Paris by means of fire signals, there was an error of a second in one of the numbers, which had the effect of causing some irregularity in the results of the different days' work; but as the discrepancies were small, they had been ascribed to errors of observation. Mr. Henderson, remarking the irregularity, was led to recalculate the original data, and thereby detected the error; and not content with this, he submitted the entire process to a new calculation. His result differed immaterially from that which had been previously obtained; but the correction of the error, by rendering the single results more consistent, gave a greatly increased confidence to the general conclusion; and, as was said of it by Sir John Herschel himself, "had the effect of raising a result liable to much doubt, from the discordance of the individual days' observations, to the rank of a standard scientific datum, and thus conferring on a national operation all the importance it ought to possess."
Mr. Henderson's connexion with this Society began by his undertaking, upon the request of the Council, to compute an ephemeris of the occultations of Aldebaran by the moon, in the year 1829, for ten different observatories in Europe. In this undertaking he was associated with Mr. Maclear, and the ephemeris, purporting to be their joint production, was read at the December meeting in 1828, and published in No. 15 of the Monthly Notices. His first contribution to the Memoirs (published in Vol. IV.) contained observations of transits of the moon, and stars nearly in the same parallel of declination, over the meridian, made at the Calton Hill Observatory in 1828, from which and corresponding observations made at Greenwich he computed the difference of meridians. This paper deserves notice, as shewing that he had already adopted the practice of estimating and allowing for the weights of the results and determining their probable errors, according to the methods in use among the German astronomers, but of which the examples were not, as yet, frequent in this country. The method of determining differences of longitude by means of observations of moon-culminating stars, then recently proposed by Nicolai, had been strongly recommended by Mr. Baily in a paper published in Vol. II. of the Memoirs, where all the requisite rules and formulæ were given for the computation. Mr. Henderson entered into these views with his accustomed energy, and not only embraced every opportunity of putting the method in practice by computing corresponding observations, but was at much pains to promote such observations by preparing lists of moon-culminating stars for the use of observers. A list of this kind was prepared by him at the request of the Council for the use of the Arctic expedition under the command of Captain (Sir John) Ross in 1830. Another subject on which his talents for computation were frequently exercised in furtherance of the views of the Council, was the calculation of the lunar occultations of fixed stars and planets. Observations of these phenomena, interesting both to Practical and physical astronomy were at that time much sought after by the Society because of their use in determining longitudes; and, since such phenomena are seldom observed unless predicted, it was desirable to ascertain the times of their occurrence by a prior calculation. In this case, Mr. Henderson also rendered most efficient aid by contributing, for several years, monthly lists of the principal lunar occultations calculated for the Greenwich meridian. The promptness and accuracy with which these calculations were made prompted the Council to request that he communicate his methods to the Society; and he accordingly drew up a set of "Practical Rules for the Approximate Prediction of Occultations," which are published in Vol. IV of the Memoirs. These services were duly acknowledged in our Annual Reports and at the anniversary meeting in 1830, the thanks of the Society were voted to him "for the very valuable assistance he had rendered to the cause of astronomy in his various computations presented to the Society."
The amount of Mr. Henderson's contributions to astronomy from 1825 to 1830, consisting of observations, tables, remarks, methods, and calculations of various kinds, published in the Quarterly Journal of Science, the Nautical Almanac, and the Notices and Memoirs of this Society, would have done credit to a professional computer; but, in order to rightly appreciate his zeal, it must be remembered that he was all this while occupied with professional duties of a kind which would be found by most persons to be sufficiently engrossing. His disinterestedness was no less remarkable than his scientific ardour; for, though in the receipt of very moderate emoluments, he declined all remuneration for his calculations; nor would this feature of his character be fully appreciated unless it were told at the same time that a considerable part of his income was appropriated by him to the support of his mother and sisters
Mr. Henderson's official duties, while connected with the Earl of Lauderdale and the Lord Advocate, brought him to London for several months each year. On these occasions, he became personally acquainted with the principal astronomers of the metropolis and had an opportunity, particularly at the observatory of Sir James South, which was freely opened to him, of seeing and handling first-class instruments. His various useful contributions to astronomy had already earned him a considerable reputation; and the high opinion formed of his talents was increased by the worthiness and unaffected simplicity of his character and the range and extraordinary accuracy of his information on all astronomical subjects. Accordingly, the prospect of attaching him to an office by which his services would be secured for the exclusive benefit of astronomy afforded satisfaction to all those who took an active interest in the progress of our science.
The death of Dr. Robert Blair in December 1828 had caused a vacancy in the professorship of Practical Astronomy in the University of Edinburgh, Mr. Henderson's qualifications for that office were presented to the Government (the patrons of the appointment) by Dr. Thomas Young and energetically urged by several other astronomers, particularly Captain Basil Hall. From the correspondence with the Secretary of State, it appears that the Government postponed filling the vacancy so that it might be considered what position could best serve science, given that the office had hitherto been neglected. In the summer of 1829, another astronomical appointment became vacant with the untimely death of Dr. Young. This eminent figure had received valuable assistance from Mr. Henderson in the calculations required for the Nautical Almanac and had held him in the most favourable opinion. About a fortnight before his death, he placed a memorandum in the hands of the late Professor Rigaud of Oxford, to be used in case of his death. And when the anticipated event took place, the memorandum was found to contain a request that it might be stated to the Board of Admiralty that he knew no person more competent to be his successor in the superintendency of the Almanac than Mr. Henderson. Professor Rigaud wasted no time in making known in the proper quarter the recommendation of his deceased friend, which he also supported with the weight of his own influence; but, as a consequence of other contemplated arrangements, it was unsuccessful, and the superintendency of the Nautical Almanac was, on that occasion, committed to Mr. Pond, then Astronomer Royal. Mr. Pond was also well aware of the efficiency and value of Mr. Henderson's aid, and immediately preferred a request to him to continue the same computations which he had been accustomed to supplying to Dr. Young; making at the same time offering remuneration, and sufficient employment to occupy a great portion of his time. But, although Mr. Henderson, shortly after, supplied Mr. Pond with some calculations on which he had previously been engaged, this offer appears to have been declined, and for two years longer he continued to pursue his professional occupation.
His character as an astronomer, however, was now fully established; and accordingly, on the death of Mr. Fallows, in 1831, he was regarded as one of the persons best qualified to undertake the direction and management of the observatory established by Government, and then recently completed, at the Cape of Good Hope. Through the intervention of Captain Beaufort, his qualifications were a second time brought under the notice of the Lords Commissioners of the Admiralty, and on this occasion successfully; but the idea of leaving his country was distasteful to him; and he accepted the office with some reluctance, and only in deference to the advice of his friends. The warrant of his appointment is dated in October 1831, and a few months after he embarked for the colony. Mr. Henderson arrived at the Cape in April 1832, and forthwith commenced his observations. The principal instruments were a 10-foot transit by Dollond, and a 6-foot mural circle by Jones; and his only assistant was Lieutenant Meadows, who had been sent out in the previous year. Few examples are upon record of more zealous and successful exertion than that which he furnished during his thirteen-month residence at the Cape. The results of his own personal exertions during that short interval include the determination of the latitude and longitude of his station; the positions of stars near the South Pole for determining the polar positions of his instruments; the amount of refraction near the horizon; observations of the moon and stars for determining the moon's horizontal parallax; of Mars for determining the parallax of that planet, and thus that of the sun; of eclipses of Jupiter's satellites; occultations of fixed stars by the moon; a transit of Mercury; and the locations of Encke's and Biela's comets. and, finally, between 5,000 and 6,000 observations of declination. Such a large mass of work would have been sufficiently creditable under the most advantageous circumstances; but when we consider that he had to contend with all the difficulties incidental to a new and imperfectly organized establishment, where no assistance was to be obtained from artists, and with a notoriously unmanageable instrument, it will be easily admitted that it would be difficult to overrate the zeal, perseverance, and skill with which he laboured to discharge the duties entrusted to him. But the merit of accumulating such a large and valuable mass of observations, great as it must be allowed to be, is completely overshadowed by comparison with that which is due to the persevering industry with which he laboured in their reduction and in deducing from them, the results we shall presently have occasion to mention. When Mr. Henderson accepted the appointment to the Cape Observatory, it was no doubt anticipated (probably even by himself) that his residence there would be of some considerable duration.
These anticipations were not realized, for in May 1833 he resigned the office, and shortly after returned to Europe. The reasons which induced him to take this step were fully stated by him in his letter of resignation addressed to the Secretary of the Admiralty.
After briefly alluding to the exertions necessary to carry out their lordships' instructions, he went on to say that not only did his health render him unable much longer to support the required labour, but the observatory, considered a place of residence, operated under so many disadvantages, required a lifestyle so different from that to which he had been accustomed that he found it impractical to remain any longer; and being thus unable to perform the duties, he felt it incumbent upon him instantly to resign the situation. But with that regard for the interests of science, and that kindness of disposition so eminently characteristic of him, he added that upon his return home he would proceed, with the sanction of their lordships, to the task of reducing the observations and extracting from them the results they were intended to afford; expressed his appreciation for the efficient aid he had received from his assistant, Lieutenant Meadows; modestly proffered such assistance as his experience might enable him to give to his successor; and concluded by recommending the state of the observatory to their lordships' consideration.
Had his state of health permitted him to continue his observations satisfactorily, there can be little doubt that the inconveniences of which he complained would in due time have been removed, or at least have become supportable; but, he had been made aware before he left England, that his physicians already apprehended the germs of that disease which eventually proved fatal to him, and under the depressing influence of this knowledge, aggravated by separation from all his friends and his family to whom he was tenderly attached and by his complete isolation - his spirits gave way, and he became apprehensive that he would be unable to maintain the observatory, from which so much was expected, in a state of requisite efficiency. Impressed with this idea, he took the resolution to give in his resignation, in order that it might have the contingent benefit of another appointment; And thus an act which, hastily judged, might appear to be an abandonment of his post, was the simple and natural result of a high, it may be an exaggerated, sense of public duty. The sacrifice involved in his resignation was of no small importance to him in a pecuniary point of view; for all he had to fall back upon was a pension of £101, a year, to which he had become entitled upon the retirement of Lord Eldin. But no one was ever less influenced by considerations of personal or pecuniary advantage, and under any circumstances he would have disdained the emoluments of office without the most punctilious discharge of its duties.
On his return to this country in 1833, Mr. Henderson took up his abode in Edinburgh, and being now without official engagements, he began the task of reducing the rich store of observations he had brought with him from the Cape The first result of this self-imposed labour was the determination of an important astronomical element, the sun's parallax, from a comparison of observations of the declination of Mars near opposition, made at Greenwich, Cambridge, and Altona, with the corresponding observations at Cape Canaveral. Prior to his departure for that station, he had expressed a wish that a selection should be made of stars that could be conveniently observed with Mars at opposition in November 1832, with a view to determining the parallax, and that a list of these should be circulated among different astronomers in various parts of the world, for the purpose of obtaining corresponding observations. Accordingly, Mr. Sheepshanks, having established the apparent positions of Mars during the requisite period, and Mr. Baily, having selected the stars to be observed, the council arranged for the list to be printed and circulated, along with instructions on how the observations should be made. As a consequence of these preparations, four sets of corresponding observations were obtained, from each of which Mr. Henderson deduced a parallax value. The mean of the whole yielded a parallax of 9°28′, a result which is known from the more certain method of transits of Venus to be somewhat too large, as was the case also in Lacaille's attempt at the Cape, in 1751, to determine the solar parallax by the same method. The determination, he remarks, is chiefly valuable as shewing the probable accuracy of the method, and the limits within which this important datum in physical astronomy may be determined independently of the rare phenomena of the transits of Venus.
Another paper of a more elaborate kind followed soon after, containing an investigation of the anomalies of the 6-foot mural circle in the Cape Observatory. When this instrument was first set up, there were found to be considerable discrepancies in the reading of the different microscopes, a circumstance which occasioned great perplexity to Mr. Fallows; and, although that astronomer ascertained that the mean of the six readings might be depended upon, he did not succeed in arriving at any satisfactory conclusion respecting the cause and the laws of the irregularities. Aware of these anomalies, which, indeed, were confirmed by his first observations. Mr. Henderson, a few weeks after his arrival at the Cape, undertook a laborious examination of the state of the instrument by means of a series of readings of each of the six microscopes at every tenth degree of the limb; and in April and May, 1833, shortly before his departure from the Cape, he repeated the experiment on a more extended scale, by examining the division corresponding to every fifth degree of the circle, and also the divisions immediately before and after it. On the results of this last experiment, which, however, were found to be identical with those of the former one, he grounded the investigation which forms the subject of the paper; an investigation which exhibits in a very advantageous point of view his sagacity, patience, and laborious accuracy, and is an admirable model of a carefully conducted experimental inquiry. The result was, that, in order to explain the observed anomalies it was necessary to suppose the figure of the instrument to be an oval of small eccentricity, that the pivots of the axis were not exactly circular, and that the whole instrument frequently changed its position upon the pier from the defective bearing of one of the pivots. But the most important conclusion deduced from the investigation, as it involved no less important a question than the trustworthiness of the whole of his Cape observations, was that the mean of the readings of the six equidistant microscopes was affected only to a very small extent (if affected at all) by these imperfections, and that the probable error of the instrument is not greater than the errors of the best instruments of similar construction hitherto made. From a similar investigation, founded on a less complete examination of the instrument by Mr. Fallows, Mr. Sheepshanks and Mr. Airy, in a paper which is printed in Vol. V. of the Memoirs, had previously arrived at a similar conclusion.*
While thus busily employed with the reduction of his own observations, on the results of which, he was well aware, his reputation as an astronomer would essentially depend, Mr. Henderson's assistance was still, as it had been in the early part of his career, freely extended to others whenever an opportunity arose to promote the cause of astronomy. Thus, at the request of Mr. Baily, he undertook the reduction of Captain Foster's observations of the comet of 1830, made at Ascension Island. The results of this, together with an ephemeris for facilitating the calculation of observations of the comet made in the southern hemisphere, are published in Vol. VIII of the Memoirs. Fortunately, however (even though this turned out to be true), the interval of leisure was of no long duration; and he was soon called upon for the discharge of more active duties. In 1834, an agreement was concluded between the government and the members of the Astronomical Institution of Edinburgh, whereby the latter relinquished to the University the use of its observatory on Calton Hill, which the former undertook to convert into a public establishment by furnishing it with suitable instruments and providing for an observer and assistant. It was then resolved to fill the office of Professor of Practical Astronomy, which had remained vacant since 1828, and to combine with it the direction and superintendence of the observatory. The Secretary of State did the Society the honour of requesting that a deputation from the Council confer and advise him on the person whom it might be proper to appoint to the situation. As a consequence of this request, a deputation awaited Lord Melbourne and, in the strongest terms, recommended Mr. Henderson, whose appointment accordingly followed immediately. The royal commission, nominating him Professor of Practical Astronomy and His Majesty's Astronomer for Scotland, which was dated the 18th of August of that year, required him to take upon himself the care and custody of the instruments within the observatory, and "to apply himself with diligence and zeal to making astronomical observations at the said observatory, for the extension and improvement of astronomy, geography, and navigation, and other branches of science connected therewith."
Mr. Henderson was now placed in a situation suited in every respect to his tastes, habits, and pursuits; and, as he was still young, those who were best acquainted with the extent of his knowledge, his industrious habits, and his facility and accuracy in all practical matters, formed the highest expectations of the value of his future services to astronomy. Nor were their expectations disappointed. The Annals of the Edinburgh Observatory, his Catalogue of Southern Stars, his investigations of annual parallax, and other deductions from his Cape observations, besides various contributions relative to subjects of a less important, but always of an interesting nature, amply justify the recommendation of our Council; while their very excellence increases our present regrets that a career so auspiciously begun has been so prematurely brought to a close.
As soon as Mr. Henderson had gotten his observatory into working order and had established a regular routine of duty, he resumed the reduction of his Cape observations, an occupation which engrossed the greater part of his leisure time during the remainder of his life, and of which the fruits are a series of papers communicated to the Society and published in our Memoirs, all more or less interesting, and some of them of the first order of excellence
The next result of these reductions, and indeed one of the most intrinsically important of the whole, was a Catalogue of the declinations of 172 principal fixed stars, chiefly in the southern hemisphere, which was presented to the Society at the April meeting in 1837. Due to various causes of delay, the reduction of the right ascensions of the same stars was only completed, and the results presented to the Society, in the course of the last year. They have, however, already been printed and will appear in our forthcoming volume. Although the number of stars contained in this Catalogue is not large, it acquires importance and value both on account of the still relatively defective state of our knowledge of the absolute positions of the southern stars, and from the fact that it is the first to be deduced from observations made in the southern hemisphere with instruments equivalent to those of the best European observatories Indeed, if we exclude Mr. Johnson's excellent Catalogue of Stars Observed at St. Helena, it must be regarded as the first in which the places of stars not visible at our latitudes have been determined with the precision and certainty now aimed at in astronomy. It was principally with a view to the determination of the positions of the principal southern stars, for the aid of navigation, that the establishment of the Cape Observatory was urged upon and undertaken by the government, and this catalogue forms one of the most important installments astronomy has yet received from it.
Although determining the absolute positions of the stars was the observatory's primary business, Mr. Henderson was too zealous an astronomer to omit taking advantage of his position to investigate various important points that can only be determined by comparing observations made at distant locations, or that acquire special interest from the observer's position. One such point is the amount of refraction in the southern hemisphere. In an interesting paper on this subject, published in Vol. X of his Memoirs, he presented the results of a series of observations made at the Cape of Good Hope of stars with a zenith distance greater than 85°, both north and south, and compared the refractions deduced from the tables of Bessel and Ivory. These results, tending to shed light on the important subject of horizontal refractions, are valuable for both general physics and practical astronomy.
Another important determination, also prompted by the location, was that of the moon's horizontal parallax. It is well known that determining this element was one of the principal objectives of Lacaille's voyage to the Cape; his purpose being to obtain observations of the moon's declination corresponding to others made at different European observatories. A similar investigation was proposed for Mr. Henderson, or rather, several stars had been marked in the Berlin Ephemeris and Nautical Almanac as favourably situated for having their declinations observed alongside the moon's in both hemispheres, by which means the moon's apparent declinations could be obtained free from the effects of errors in the assumed declinations of the stars. But the number of corresponding observations of this kind that could be made was found to be too small to permit the element to be determined from them with sufficient accuracy. Therefore, whenever there was a shortage of moon-culminating stars, Mr. Henderson could use observations of the principal stars that were available for comparison. The investigation, like all others which he undertook, is conducted in the most careful manner; and the result, although, in consequence of the mode of proceeding adopted, it is dependent on the accuracy of the determination of the relative declinations of the principal stars, is probably the best determination of the constant we are in possession of.
It would almost seem as if, in these investigations, Mr. Henderson intended to repeat the labours of Lacaille during his memorable stay at the Cape around the middle of the last century. In another, and more important, aspect, he may be considered an imitator of that great astronomer. Lacaille had remarked that, in the then advanced state of astronomy, no one could any longer be believed on his mere word; and that, in order to employ with confidence an observed position, it was necessary to have all the details of the observation and all the elements of reduction. No astronomer was ever more careful of the observance of this important maxim than Mr. Henderson. From the reading of the circle to the final result of the investigation, everything necessary for the complete understanding of the process or verification of the work is carefully set forth and explained; and, accordingly, all his investigations and results are characterised by an air of truthfulness, which would be in vain to seek where a different practice is followed.
But of all the results which he deduced from this persevering examination of his Cape observations, the one which will be considered the most interesting is the annual parallax of the double star Centauri, amounting to about a second of space. This binary system was recognized to be a double about a century ago; and, on comparing the observations of Lacaille with those of the present time, it is found to have an annual proper motion of about 3″-6″. Being situated within about 30° of the South Pole, it is always above the horizon at the Cape, and, consequently, favourably placed for being accurately observed at all times. The intrinsic brightness of the two component stars is also remarkable; and from this, and their large proper motion-circumstances indicative of proximity to our system Mr. Henderson was led to suspect they might have a sensitive parallax. He was not, however, aware of their large proper motion until he was about to leave the Cape; and the observations from which the result was first deduced, were accordingly not made with special reference to the question of parallax, but for the purpose of determining their mean positions. The first indications of parallax were detected upon a comparison of their declinations with those of such of the standard stars as were observed on the same day throughout the year; but he deferred the announcement of the discovery until he had completed the reduction of the right ascensions, and obtained, by this means, a further test of the accuracy of his conclusion. A similar investigation of these latter observations confirmed the previous deduction; and, in a paper read to the Society at the January meeting of 1839, he announced a parallax of the double star amounting to about a second of space. With his habitual caution and accuracy, he applied every means of testing the result the observations afforded, deducing the parallax separately from the observations of right ascension, from the direct observations of declination, and from the reflected observations of declination, and this in respect. of each of the two stars; and although the resulting parallax differed somewhat in the different cases, the general agreement was satisfactory, and the amount much too large to be ascribable to probable errors of observation. But notwithstanding the corroboration which the results of these different modes of deduction afforded each other, if the question of the parallax of this binary star had been allowed to rest in the state in which it was placed in Mr. Henderson's first paper, astronomers would probably have agreed in thinking his investigation only went the length of establishing a strong probability in favour of its existence. Mr. Main, after an elaborate comparison of the result with the individual observations from which it was deduced, observes, "For the present it must be considered that the star well deserves a rigorous examination by all the methods which the author himself has so well pointed out; and that, in the event of a parallax at all comparable with that assigned by Mr. Henderson being found, he will deserve the merit of its discovery, and the warmest thanks of astronomers, as an extender of the knowledge we possess of ours connection with the sidereal system." Memoirs, vol. xii. p. 36. The result, however, was far too curious to be allowed long to remain without an attempt being made to confirm it. No sooner was Mr. Henderson's paper communicated to Mr. Maclear, than that energetic astronomer undertook a series of observations of the double altitudes of the two stars with the mural circle, with an express view to the question. They extend over seventeen months, from March 26, 1839, to August 12, 1840; and, as the mural circle at the Cape was changed shortly after their commencement, they have the further advantage of having been made, for the The greater part, with a different instrument. These observations being transmitted to Mr. Henderson, he immediately undertook to reduce them; and, in an elaborate paper inserted in Vol. XII of the Memoirs, he deduced the parallax for each of the two stars from both the direct and reflected observations. The results entirely confirmed his former deductions, but, as was to be expected from the greater number of observations, they were more consistent. The mean gave, as before, a parallax of about 1 arcsecond; whereas it is inferred that this system, perhaps the nearest of the stellar bodies, is separated from us by an interval exceeding 200,000 times the distance of the sun from the earth.
Looking to the history of this interesting subject, to the consistent results given by the Dublin circle, which have been disproved by other instruments, and considering that the present determination has as yet been only partially confirmed by the observations of right ascension, the cautious astronomer will, perhaps, be inclined to maintain some reserve until the star has been examined with an instrument affording the means of exact micrometric measurement, or, at least, until a longer series of meridian observations has been made; for, as has been remarked by Sir John Herschel, "It is only on a very long series of observations of absolute places, affected, as they are, by instrumental error and uncertainty of refraction, that any conclusion of this kind can rest with security." But whatever the ultimate decision of astronomers may be with respect to the parallax in question, there will be but one opinion as to the merit of Mr. Henderson's investigations, and the interest which attaches to the subject: and, in the meantime, it will be remembered that this is the first determination of the parallax of a star which has been confirmed by a different observer using a different instrument; and that if future observations shall continue to give similar results, which now seems a reasonable anticipation, to Mr. Henderson will indisputably belong the enviable distinction of having been the first to succeed in an inquiry so often, but fruitlessly, attempted by astronomers, namely, the discovery of a fixed star whose distance from our system is capable of measurement and expression. For these researches he was proposed to the Council at the meeting in November last, as deserving of the Society's gold medal for the present year, but his untimely death prevented the question from being addressed.
Another attempt made by him to determine the annual parallax was less successful. Sirius, the brightest star in the heavens, might be supposed to be one of the least remote; and some astronomists—Cassini, Lacaille, and Piazzi—had assigned it a parallax of several seconds. The Cape observations being well adapted for the investigation of the question, Mr. Henderson undertook the examination of those made by himself, and also a series by Mr. Maclear, in order to ascertain if they indicated any sensible parallax; but, in this case, the result amounted only to about a quarter of a second, a quantity not exceeding, perhaps, the probable error of the determination.
Mr. Henderson's work on the subject of parallax did not end there. In a letter to Mr. Main, which was read at the December meeting of 1842, he presented the results of an investigation into the parallaxes, as they appear from his Cape observations, of twenty stars that had been observed frequently enough to reduce the errors of observation within reasonable limits. These stars comprised the majority of those located in the same region of the heavens as Centauri, which Sir John Herschel had identified as deserving of investigation for parallax and which, on that account, are currently objects of particular attention at the Cape Observatory. In a few instances, considerable parallaxes appeared; in the greater number of cases, the results were so small as to offer little hope of finding a measurable parallax, and in some, they were negative. The mean of the twenty parallaxes is +0.29, a result which, on the whole, may be considered encouraging to continue the research.
It is a matter of much regret that the reduction of the entire series of Mr. Henderson's Cape observations—the rich store from which the above interesting results have been extracted—has not been completed by him; and that the observations must consequently be deprived of the advantage of his final revision. From the examination of his papers, it appears that the number of positions determined both with the mural circle and transit instrument, from April 10, 1832, to May 24, 1833, is between 5,000 and 6,000. The transit observations (made chiefly by Lieutenant Meadows) are found to be carefully written out, with the column headed "correction of instrument" filled in for the whole period and that headed "correction of clock" from the commencement to October 31, 1832. The circle observations, which were all made by himself, are in a similar state of forwardness; and it may be inferred from the appearance of the papers that if he had lived a few months longer, and the work had proceeded at the ordinary rate, the whole would have been ready for the press.
A statement of the results deduced by Mr. Henderson from his Cape observations could not be properly concluded without an expression of admiration for that disinterested zeal which led him to undertake and execute so great an amount of extra-official labour. The observations, it will be remembered, were made at a public establishment, and their reduction was a matter of public concern and importance; and after his resignation of the appointment, the public had no claim on his services more than on those of any other individual. But, as already remarked, considerations of this kind never, in any degree, influenced his conduct; and, for ten long years, he gratuitously devoted himself to this purpose all the time he could spare from his official duties. In the same circumstances, almost any other person would have claimed, and undoubtedly have obtained, both assistance and remuneration. In addition to the results now mentioned, he rendered yet another important service to the astronomy of the southern heavens, in supervising the reduction of the stars observed at the Cape by Lacaille. This work, which he undertook on behalf of Mr. Baily for the British Association, was announced as completed in our Annual Report for 1843; but it has not yet been published. Mr. Henderson's work at the Edinburgh Observatory is well known to astronomers from the five volumes of observations published for 1834–1839. A sixth volume is understood to be left nearly ready for publication; and the observations for the remaining years will, no doubt, still be made available to science. The published volumes are prefaced by an Introduction, containing a minute and most lucid description of the instruments and methods used in the observations and reductions, with every detail and explanation that can contribute to giving authenticity and value to the work. His first year's observations, having been referred to this Society by the Home Secretary, were reported by a committee of the Council to be of first-rate excellence, and their publication was recommended as a matter of scientific importance. This report has been ratified by all astronomers; and, so far as they have been published, the Edinburgh observations not only do credit to the astronomer and his assistant, Mr. Wallace, but have conferred on the Observatory a high reputation among the similar institutions of Europe
Although the periodical publication of the Edinburgh observations rendered it largely unnecessary for him to resort to other channels of publicity, he continued, from time to time, to communicate to this Society various observations of phenomena, either occasional or of immediate interest, and notices likely to be useful to practical astronomers. Among these may be mentioned observations of the planets near their oppositions and inferior conjunctions, of moon-culminating stars, of the annular eclipse of the sun on May 15, 1836; and, more especially, elements of cometary orbits. Indeed, if he had no other claim on our regard, his care in disseminating the earliest information respecting the orbits of newly discovered comets would alone have entitled him to the applause due to a useful labourer in the cause of astronomy Various observations and notices of the kind now referred to were also communicated by him to Professor Schumacher and published in the Astronomische Nachrichten, whereby they obtained immediate circulation over the Continent.
His attention at Edinburgh was chiefly directed to planetary observations and the creation of an extensive catalogue of zodiacal stars. He had progressed far in the latter work; and in one of his last letters, written to an intimate friend, he spoke of being engaged in fixing the positions of some of those stars in Argelander's recent catalogue, which, though visible to the naked eye, had escaped the notice of all former astronomers.
In recounting Mr. Henderson's labours at the Edinburgh Observatory, we would fail to do justice to his zeal if we omitted all reference to other aspirations which occasionally placed large demands on his time. His office as professor, though he gave no lectures in his own, the department entailed various duties for him. During one entire semester (1835-1836) he delivered the mathematical lectures for Professor Wallace, then became incapacitated by illness; and in the last year he undertook, for some time, a similar duty for Professor Forbes in the class of Natural Philosophy. In short, he was one whose general talents and business acumen, coupled with extreme benevolence and great common sense, made him a most useful assistant; and, accordingly, the largest share of any public business with which he happened to be connected was sure to fall into his hands.
Having none of the accessory advantages of birth, fortune, or early introduction, Mr. Henderson had to rely on his own energy and talents alone in conquering his way to fame; and he was only beginning to enjoy his well-earned reputation, both in his own country and abroad. He was admitted a Fellow of this Society in 1832, and of the Royal Society in 1840, and he had been a member of the Royal Society of Edinburgh since 1834. It does not appear that he was a member of any foreign society, but he was in frequent correspondence with Schumacher, Bessel, Encke, and other distinguished astronomers on the continent, by whom his talents and opinion on astronomical subjects were held in high estimation
In 1836 he married Miss Adie, eldest daughter of the well-known optician and ingenious inventor of the sympiesometer. The death of this lady in 1842, a few weeks after the birth of their only child, affected his sensitive temper from which he never completely recovered. In the summer of that year he was gratified by an event which afforded him at the time the liveliest pleasure, and ever after formed a bright spot in his memory. This was the visit to Edinburgh of Professor Bessel, whom he had always been accustomed to regard as his master in science; and for whose character and writings he entertained an unbounded admiration. In company with the great astronomer, and his countryman and colleague, the celebrated mathematician Jacobi, he made a short excursion to the Highlands; and his friends well remember the delight with which he used to recount the incidents of that journey, and relate anecdotes of his illustrious companions
Although his constitution was never robust, and he was occasionally subject to low spirits, during the influence of which he would express misgivings as to his hold on life, his health did not undergo any visible change until the autumn of 1844, when he was suddenly seized with an illness of such alarming a kind that, happening at the time he was on a visit to a friend, some days elapsed before he could be removed to his own house. From this attack he partially recovered, and hopes were entertained that he would soon be enabled to resume his usual duties; but a relapse having occurred, he expired suddenly on the 23rd of November, a few weeks before he would have completed his forty-sixth year. The disease was then ascertained to be hypertrophy of the heart; and there can be little doubt that, in the state of health induced by this organic disorder, the fatigue of the nightly observations and of climbing the steep hill on the summit of which the observatory is built had been extremely prejudicial to him and contributed to accelerating its fatal termination.
The character of Mr. Henderson as an astronomer stands high, and his name will go down to posterity as an accurate observer, an industrious computer, a skillful manipulator, and an improver of methods in that department to which he devoted himself. Endowed by nature with perceptive powers of great acuteness, and accustomed by his early professional training to examine and sift the evidence of every fact or statement presented to his mind and to keep it before him until he had obtained a clear conception of it in all its bearings, every acquisition he made was perfect; and all his knowledge was stored up in a memory of unusually retentive powers, in such an orderly manner as to be always available at the moment it was wanted A keen eye, and habits of order, regularity, and attention, enabled him to become an excellent observer; but the services for which he will be remembered consist not so much in numerous and accurate observations, as in the use he made of them and the manner in which he worked out their results. At the outset of his career, he was led (probably by the commendation of them in our Memoirs) to study attentively the methods of the German astronomers, particularly those of Bessel and Struve, upon whose model he formed his practice, and from which he never departed. All his memoirs and investigations are characterized by the excellences of those illustrious masters. Every observation is scrupulously discussed, and its results drawn out in the most concise and useful form. His processes are fully explained; his formula for reduction carefully chosen; no labour is evaded; and no circumstance that could affect the accuracy of the final result is passed unnoticed. Nor is the manner in which his results are presented and communicated inferior to the skill displayed in deducing them. His descriptions of instruments, methods, and details of practice are characterized by a simplicity, neatness, and precision that simultaneously demonstrate his good taste and mastery of his subject. His introductions to the Edinburgh observations may be cited as admirable examples of astronomical writing. Nothing, indeed, is more remarkable in all his compositions than good taste and the complete absence of any trace of exaggeration of his own merits or affectation of singularity. Distinguishing clearly his object, he pursues it in a direct, undeviating course; never stepping aside for the sake of display, yet skillfully availing himself of every means of reaching it that science had placed at his disposal. To represent him as profoundly skilled in the higher departments of physical astronomy would be to make a pretension from which the modesty of his nature would have been reconciled. but he had a sufficiently accurate knowledge of the analytical processes by which the phenomena of the universe are deduced from, or connected with, the theory of gravitation, to appreciate correctly their bearings on the practical branches, to which he directed his attention. To a very considerable knowledge of mathematics he added great powers of calculation, which he never abused. Though less liable than most men to make mistakes, he, in no case, allowed himself to dispense with the most scrupulous revision of his work. One of his most distinguishing qualities was sound judgment. He never attempted anything to which his powers were not fully equal; and, as a consequence of this, whatever he did, he did well.
Few men have been more conversant with the modern history of astronomy, especially that branch of it with which he was more immediately connected. It may be said, without any exaggeration, that he knew, and could name the author of every invention or contrivance, whether mathematical or mechanical, bearing on his professional duties.
In his private character and the relations of domestic life, Mr. Henderson was distinguished by great warmth of affection and amiability of disposition. Naturally modest and retiring, he shrunk from the most distant contact with obtrusiveness and ostentation; but he knew his position well enough and was by no means deficient in spirit to defend it. His disposition was cheerful and sociable, and when released from official duties, he took great pleasure in the company of his friends, to whom he was endeared by the worth of his character, the unaffected simplicity of his manners, his kind-hearted benevolence, and enthusiastic admiration of anything noble and excellent. His reputation for astronomical knowledge and his readiness to assist in its promotion involved him in extensive correspondence; but, however occupied he might be, when reference was made to him on any point connected with his professional pursuits, he was always to be depended upon for a prompt answer, either containing (as was most frequently the case) a full exposition of the matter at hand, or a frank acknowledgment that he had no information to give. Notwithstanding his slender appointments, he had already collected an extensive and valuable astronomical library; but the proceeds of its sale were the principal part of the inheritance he left for his orphan daughter. He was
The loss of such an excellent member, at an age when his knowledge and faculties had only attained maturity, and when past triumphs justified the brightest anticipations for the future, cannot be regarded by the Society with feelings of ordinary regret. Let us hope there will never be wanting among us examples of similar and equally successful devotion.
The following is a list of Mr. Henderson's Astronomical Papers.
I. In the Memoirs of the Royal Astronomical Society:
Observed Transits of the Moon and Stars nearly in the same Parallel of Declination over the Meridian. Vol. IV. p. 189
Note on the difference of meridians between the Observatories of Greenwich and Edinburgh. Vol. IV, p. 191.
Practical Rules for the Approximate Prediction of Occultations. Vol. IV, p. 587.
On the Latitude and Longitude of the Observatory at the Cape of Good Hope. Vol. VI, p. 125.
Positions of several stars near the South Pole, deduced from observations made at the Observatory at the Cape of Good Hope. Vol. VI, p. 133.
Observations of the Periodic Comet of 67 years, made at the Observatory, Cape of Good Hope, between November 18, 1832, and January 3, 1833. Vol. VI, p. 159.
Observations of the Moon and stars made with the Mural Circle at the Observatory, Cape of Good Hope, for the determination of the Moon's parallax. Vol. VI, p. 205
Observations of Mars and Stars made with the Mural Circle at the Observatory, Cape of Good Hope, for the determination of the Parallax of Mars. Vol. VI, p. 207.
Letter to Professor Airy, on the Sun's Parallax, as deduced from various observations made at Greenwich, Cambridge, and the Cape of Good Hope. Vol. VIII, p. 95.
Supplement to a paper entitled "On the Latitude and Longitude of the Observatory at the Cape of Good Hope." Vol. VIII, p. 137.
On the Mural Circle of the Observatory at the Cape of Good Hope. Vol. VIII, p. 141.
Observations of the Comet of 1830, made at Ascension Island, by the late Captain Foster. Reduced by Mr. Henderson. Vol. VIII, p. 191
Observations of Vesta at the Opposition in 1834, made at Edinburgh. Vol. VIII, p. 232. Observations of Jupiter at the Opposition in 1834, made at Edinburgh.
Edinburgh. Vol. VIII, p. 234. Observations of Venus at the Inferior Conjunction, in December 1834, made at Edinburgh. Vol. VIII, p. 236.
Observations of Mars at the Opposition in January 1835, made at Edinburgh. Vol. VIII, p. 238.
Places of the Comet of Biela, deduced from Observations at Slough and the Cape of Good Hope. Vol. VIII, p. 240.
Places of Encke's Comet, from Observations made at the Cape of Good Hope. Vol. VIII, p. 243
Notes on Mossotti's Observations of the Comet of Encke. Vol. VIII, p. 250.
Notes on Mr. Dunlop's Observations of Two Comets in 1833 and 1834. Vol. VIII, p. 264.
Results of the Lunar Observations made at Edinburgh in the years 1834 and 1835. Vol. IX, p. 272.
On the Declinations of the Principal Fixed Stars, deduced from Observations made at the Observatory, Cape of Good Hope, in the years 1832 and 1833. Vol. X, p. 49
Refractions of Stars near the Horizon, observed at the Cape of Good Hope. Vol. X, p. 271.
The Constant Quantity of the Moon's Equatorial Horizontal Parallax, deduced from Observations made at Greenwich, Cambridge, and the Cape of Good Hope, in 1832 and 1833. Vol. X.
p. 283. On the Parallax of a Centauri. Vol. XI, p. 61.
On the Parallax of Sirius. Vol. XI, p. 239.
The Parallax of a Centauri, deduced from Mr. Maclear's Observations at the Cape of Good Hope, in the years 1839 and 1840. Vol. XII, p. 329.
The Right Ascensions of the Principal Fixed Stars, deduced from Observations made at the Observatory, Cape of Good Hope, in the years 1832 and 1833. Vol. XV, p. 129.
II. In the Monthly Notices of the Royal Astronomical Society:
Occultations of Aldebaran by the Moon, in the year 1829, computed for ten different observatories in Europe, by T. Henderson, Esq. and T. Maclear, Esq. Vol. I, p. 89.
A List of the Occultations of Aldebaran by the Moon, in the year 1830, computed for ten different observatories in Europe, by T. Henderson, Esq. and T. Maclear, Esq. Vol. I, p. 133.
Various Observations made at the Royal Observatory, Edinburgh. Vol. III, p. 129.
Opposition of Uranus, August 1835, observed at Edinburgh. Vol. III, p. 143
Oppositions of Jupiter in January 1836, of Juno in January 1836, and Vesta in March 1836, observed at Edinburgh. Vol. III, p. 200.
On the Annular Eclipse of the Sun, on May 15, 1836. Vol. IV, p. 165.
Apparent Positions of Galle's First Comet. Vol. V, p. 9.
Elements of Galle's First Comet. Vol. V, p. 16.
On the Parallaxes of Certain Southern Stars. Vol. V, p. 223.
Elements of the Comet of 1668. Vol. V, p. 266.
Elements and Ephemeris of the Great Comet of 1843. Vol. V, p. 266.
Letter to the Secretary on the Great Comet of 1843, p. 267. Vol. V
Approximate Elements of the Comet of Faye. Vol. VI, p. 15.
On the Orbit of the Comet of Faye. Vol. VI, p. 18.
Elements and Ephemeris of the Comet of Faye. Vol. VI, p. 57.
III. In the Philosophical Transactions of the Royal Society of London:
On the Difference of Meridians of the Royal Observatories of Greenwich and Paris. Vol. for 1827, p. 286.
Observations of the Comet of Encke made in 1832. Vol. for 1833, p. 549
IV. In the Philosophical Magazine:-
On Mr. Burns' Method of Finding the Latitude by Double Altitudes Vol. LXVI. p. 283.
Some Remarks on Captain Sabine's Pendulum Experiments. Vol. II. (New Series), p. 126.
V. In the London Quarterly Journal of Science:-
Rules for Computing an Observed Occultation of a Fixed Star by the Moon. No. XXXVI. p. 343. Also in New Series, No. II. p. 434. Annexed also to the Nautical Almanacs for 1827-1831.
Remarks on the Determination of the Longitude from Observations of the Moon's Right Ascension. No. XXXVII. p. 109.
Discordance of the Lunar Observations Made at Greenwich and Paris. No. XXXVII. p. 116
Corrections of the Catalogue of Zodiacal Stars. No. XXXVIII. p. 239.
A Method of Computing the Sun's Horizontal Parallax from Observations of the Transits of Venus. No. XXXIX. p. 94.
Remarks on the Discordances Observed Between the Lunar Observations at Greenwich and Paris. No. XXXIX. p. 96.
Remarks on M. Mendoza Rios' Method of Computing the True from the Apparent Lunar Distances. No. XL. p. 315.
In the Quarterly Journal, New Series: -
Remarks on the Solar Tables. No. II. p. 438.
Answer to Some Objections Stated Against the Method for Computing an Observed Occultation. No. VIII. p. 411.
VI. In Schumacher's Astronomische Nachrichten:-
Note on the Occultation of Mercury by the Moon on Aug. 9, 1831. No. 190, col. 437.
Astronomical Observations made at Edinburgh in 1831. No. 242, col. 25.
Note on Mossotti's Observations of Encke's Comet. No. 243, col. 39.
Account of Observations made at the Cape of Good Hope in 1832 and 1833. No. 257, col. 293.
On the Longitude of the Cape Observatory, and the Sun's Mean Equatoral Horizontal Parallax. No. 262, col. 403.
Elements of Two Comets observed at Paramatta in 1833 and 1834. No. 271, col. 117
Mean Declinations of 172 Principal Fixed Stars, deduced from observations made at the Cape of Good Hope. No. 318, col. 81.
Refractions of Stars near the Horizon, observed at the Cape of Good Hope. No. 319, col. 103.
On the Moon's Equatoral Horizontal Parallax. No. 338, col. 25
On the Comet of 1668. No. 476, col. 333. Elliptic Elements of Faye's Comet. No. 495, col. 235.
Computations of the principal Lunar Occultations of the Fixed Stars, during the years 1826, 1827, 1828, and 1829, made for the Royal Observatory at Greenwich.
Elements for Computing the Eclipses of the Sun, and Lunar Occultations of the Planets and their Satellites, for the years 1826, 1827, and 1828. In various issues of the Quarterly Journal.
Computations of the principal Lunar Occultations of the Fixed Stars and Planets, for the years 1830, 1831, and 1832. In Monthly Notices of the Royal Astronomical Society, and in the Nautical Almanac
Ephemeris of the Comet of 6.7 years, in Supplement to Nautical Almanac for 1832.
On gamma Virginis. In Smyth's Cycle of Celestial Objects, vol. i. p. 483
* It may not be without interest to state that, when this instrument was sent back to England some years afterwards, and examined at the Royal Observatory, it was found that, owing probably to some oversight in the construction, the large steel collar carried by the conical axis was quite loose. It is well, perhaps, the discovery was not made sooner, or the instrument would probably have been condemned, and the observations lost,