In following the course of the business of the day, I have to announce to you the decision of your Council with respect to the medal of Sir Godfrey Copley's donation to the Society.
It has been awarded this year to the Reverend John Brinkley, D.D. Andrew's, Professor of Astronomy in the University of Dublin, and President Royal Irish Academy, for his various communications printed in the Philosophical Transactions. ...
Dr Brinkley has long been known as an enlightened and profound mathematician. His labours, published in the Memoirs of the Royal Irish Academy, contain abundant proofs of his skill in the higher departments of analysis, but it is not necessary to look anywhere else for a demonstration of this, than in our own Transactions. The volume for 1807 contains an important paper, on the General Term of a Series in the Inverse Method of finite Differences; in which, taking up a subject of investigation on which both Lagrange and Laplace had written, he has surmounted a difficulty which had remained even after the investigations of these illustrious geometers.
Whoever is in possession of the higher resources of the mathematical sciences, may be considered as gifted with a species of power applicable to every department of physical knowledge. It is indeed for this species of knowledge, what muscular strength is for the different branches of human labour; it not only generalizes the results of experiment and observation, but likewise corrects them, and leads to new and more refined methods of investigation. The guide of the mechanical and pneumatical philosopher, and the useful assistant of the chemist, it is of still more importance to the astronomer, whose results depend entirely upon magnitude, time, and motion.
Endowed in so high a degree with one of the essential characters of an accomplished astronomer, his various later communications to the Royal Society, show that Dr Brinkley is equally distinguished as a laborious, acute, and accurate observer. Your Transactions contain seven of his papers, on pure astronomical subjects:-
The second, On the Parallax of certain Fixed Stars.
The third, The Results of Observations made at the Observatory of Trinity College, Dublin, for determining the Obliquity of the Ecliptic, and the Maximum of the Aberration of Light.
The fourth, An Account of Observations made with the eight-feet Astronomical Circle since the beginning of 1818, for investigating the Effects of Parallax and Aberration on the Places of certain Fixed Stars; also the Comparison of them with former Observations for determining the Effects of Lunar Nutation.
The fifth, On the Elements of the Comet seen by Captain Basil Hall at Valparaiso.
The sixth and seventh, two papers communicated in the last year, - the first, On the North Polar Distances of the principal Fixed Stars, - the second, Additional Observations on the Parallax of a Lyrae.
Dr Brinkley has taken up no difficult object of research, without first satisfying himself of the correctness of his instruments by numerous preliminary and delicate trials. He has likewise, in forming his conclusions, examined with philosophical precision all the circumstances which may interfere, and he states the results with the utmost candour, creating difficulties for himself, and proceeding with the greatest caution in these fields of inquiry which had been already entered in vain by so many illustrious men.
You well know, Gentlemen, that Dr Brinkley and the Astronomer Royal are at issue on two great and leading questions of Astronomy - first, the sensible parallax of some of the Fixed Stars, - and secondly, on the apparent southern motion or declination of parts of the sidereal system. You know that sensible parallax is denied by Mr Pond, and believed to exist by Dr Brinkley; that, on the contrary, the southern declination is denied by Dr Brinkley, and believed to exist by Mr Pond.
I mentioned, in announcing the award of the medal last year, that the Council of the Royal Society had no intention of giving its sanction to the opinions of the Astronomer Royal, or of attempting to decide on these important and difficult questions. I again feel it my duty to make the same reservation on this occasion, and to state that the general labours of Dr Brinkley, on the most difficult parts of astronomy, and the approximation to the solution of a great problem, and the high merits of his philosophical inquiries, are the sole grounds on which the Copleian medal has been bestowed.
The Council could not with propriety form an opinion on these subjects, when two such astronomers, possessing such peculiar qualities for observation, and such varied and exalted resources, are at variance; and the difficulty and delicacy of the questions, will perhaps be fully perceived by the addition of some short details to those given last year on these obscure branches of sidereal astronomy.
When Copernicus first developed that sublime system of the planetary worlds which has since been called after his name, he was obliged to suppose the fixed stars at an almost infinite distance; and the astronomical instruments of that day offered no means even of attempting the discovery of their parallax. The importance of such a discovery was, however, immediately felt, as a demonstration of it would, in fact, become likewise an absolute demonstration of the Copernican system of the universe.
Galileo seems to have suggested the method of inquiry for parallax, by examining the relative position of double stars, at the two extremities of the earth's orbit; a method founded on the supposition that the stars differ greatly in distance. This method, likewise strongly recommended by Dr Wallis, was first, I believe, practised and pursued with great sagacity and industry by Sir William Herschel: and though it has furnished many important results, with respect to the proper motions of their stars, and the arrangement and groups of these heavenly bodies, it has as yet afforded no observations forming data for reasoning on the distance of the fixed stars from the sun.
The other method, and that which has been most insisted upon, seems likewise to have originated with the illustrious Florentine philosopher, that of observing stars about the summer and winter solstice in or near the zenith, for the purpose of avoiding the errors of refraction, by fixed instruments. The celebrated Robert Hooke, who erected at Chelsea a telescope thirty-six feet long, for examining γ-Draconis, imagined that he had discovered a very considerable parallax for this star, but Hooke's observations were contradicted by those of Molyneux. Flamsteed drew a similar conclusion from his experiments on the pole star, but the results which he ascribed to parallax, were explained by Bradley's great discoveries of the aberration of light, and the nutation of the earth's axis; and it is remarkable that Hooke reasoned correctly on inaccurate observations, while Flamsteed formed wrong conclusions from exceedingly correct results.
Jacques Cassini, in observing Sirius, attributed a parallax of six seconds to this star; and La Caille, from observations made at the Cape of Good Hope, supposed it four seconds.
Piazzi, in researches pursued from 1800 to 1806, supposed that several of the fixed stars exhibit parallax. He assumes for Sirius nearly the same parallax as La Caille; for Procyon, three seconds; for Capella, less than a second. His conclusions are, however, given with great diffidence, and his object seemed to be, rather to call the attention of astronomers to a subject which had been for some time neglected, than to press his opinions upon them with anything like confidence.
In all these observations made upon the stars, it must be confessed nothing like southern motion had ever been suspected.
Dr Brinkley, in his first communication to the Royal Society on Parallax, in 1810, rated it for α-Lyrae, at two seconds and a half. The Astronomer Royal, in endeavouring to confirm this result, has had no satisfactory indications of such a fact; and his general conclusions, as you know, both from observations made with a fixed instrument, and with the mural circle, are unfavourable to the existence of sensible parallax for any of the fixed stars; and he refers apparent parallax to the imperfection of the instrument with which the observations have been made, and offers as a proof, the diminution of the indications in proportion as instruments have become more delicate; and estimating the Greenwich as superior to the Dublin circle, thus accounts for the difference of his results and those of Dr Brinkley.
This gentleman, in his last three papers on Parallax, has replied to all the arguments, and has endeavoured to overturn all the objections of the Astronomer Royal. He does not allow the superiority of the principle of the Greenwich instrument, and he shows the consistency of the Dublin instrument with itself, by thirteen summer solstices, for which observations on eighty-seven days were made, and which give the maximum of lunar nutation 9". 60, exactly what he had used for the sun, and very nearly the same result as that from the stars; placing the permanent state of the instrument beyond all doubt. The results of two hundred and sixty-two observations on α-Lyrae, in 1811, give the mean difference between the summer and winter zenith distances at 1". 32; and repeated observations made in the last ten years, give sensible parallax, though with less consistency, for α-Aquilae, α-Cygni, and Arcturus, but none for γ-Draconis.
The minute accuracy with which Dr Brinkley has investigated the subject, can only be estimated by accomplished mathematicians and astronomers. He has examined all Mr Pond's results, reasoning upon the law of the aberration of light, the effects of refraction and of differences of temperature, and has compared his own series of observations with those of other astronomers, and he seems entirely convinced of the accuracy of his general conclusions. If any circumstances depending upon change of temperature, flexion of the instrument, or other causes of error existed.
"Why," he says, "should they not be general for all the stars?" "Why," he asks, "should such causes exist for α-Lyrae, and not for the pole star, which shows no sensible parallax?"
In his last paper, he makes some further corrections in the coefficient of aberration and solar nutation, and his ultimate result is 1". 14 for the annual parallax of a Lyrae.
On the question of southern motion. Dr Brinkley expresses himself with much more confidence than on that of parallax. He compares M Bessel's, Mr Pond's, M Piazzi's, and the Dublin catalogues; and after endeavouring to prove a discordance in the Astronomer Royal's mode of applying the data in these catalogues to the question, he says, "from the weight of external testimony adduced, it will, I think, be readily conceded to me that the southern motion does not exist, and that it must be regarded as an error belonging to one or both of the Greenwich catalogues of 1813 or 1823."
Such is the state of these two questions.
They are not, however, questions of useless controversy, or connected with hostile feelings. The two rival astronomers seem equally animated with the love of truth and justice, and have carried on their discussions in that conciliatory, amicable, and dignified manner, which distinguishes the true philosopher. I cannot give a stronger proof of this, than in stating, that the Astronomer Royal was amongst the first of the Members of the Council, to second and applaud the proposition for the award of this day.
I have said, that these questions are not questions of useless controversy, nor are they questions of mere curiosity. No important changes can take place in the sidereal system without affecting the whole of astronomy: the fixed stars are, indeed, to space in the heavens, what land-marks or the extremities of base lines are to distances upon the earth; and all our conclusions upon the great problems of the system of the universe, have been formed upon the idea of the general permanency of their arrangements.
With respect to parallax, it is not a little remarkable, that Dr Bradley, from his varied and refined observations with Graham's sector, concluded that α-Lyrae could not possess a parallax of as much as 2", and that Dr Brinkley's conclusions, from his most refined observations, come far within these limits. Mr Mitchell, likewise, from photometrical considerations concludes, that if the largest fixed stars are the nearest, and about the size of the sun, their parallax, taken from the quantity of light they emit, can not much exceed one second; and Mr Gauss, in a conversation that I had with him this summer, he informed me, that he had drawn a similar conclusion, from ascertaining the distance and size of the image of the sun upon the helioscope; the new instrument that has been used with so much success in triangulation.
There is one circumstance which seems to have perplexed Dr Brinkley a little, namely, that some of the smaller stars seem to show a greater parallax than those of a larger apparent size: this, at first sight, might appear to throw some doubt upon the results; yet it, perhaps, admits of explanation, on the idea that if the stars are disposed in groups or systems, as Mr Mitchell and Sir William Herschel believe, the bodies possessing the greatest masses, may be in the centre of these groups, and the smallest stars in consequence most contiguous to the largest. It is to be regretted, that on the subject of parallax, no star has yet been observed absolutely in the zenith, which might easily be done in a part of the globe, for instance, under the equator, when almost precisely the same circumstances of temperature, moisture, and pressure of the atmosphere, would constantly exist. An instrument fixed on granite, or an aperture made in a solid stratum of rock, would destroy the probability of interference from foreign causes, and reduce the problem to the simplest possible conditions.
In waiting for new elucidations on these important questions (and no persons are more capable of giving them than the two distinguished astronomers now engaged in the discussion), I cannot but congratulate the Society, that the state of scientific inquiry, and the number of scientific men, render it scarcely possible that any great problem can long remain unsolved, any considerable object of interest uninvestigated. No question is now limited to one observatory, to one country, or even to one quarter of the globe. While such men as Brinkley observe at Dublin, Bessel at Königsberg, Arago at Paris, Olbers at Bremen, Schumacher at Altona, and Gauss and Harding at Göttingen, astronomy must be progressive, her results cannot but become more refined.
The observatories established by enlightened public patronage, at the Cape of Good Hope, and by private munificence at Paramatta, in New South Wales, cannot fail of giving us almost a new sidereal world in the southern hemisphere. Already, Sir Thomas Brisbane has sent to the Royal Society an extensive catalogue; and we may expect everything from him that indefatigable zeal, ardour of pursuit, and intense love of the science can afford.
With the increase of the popularity and the means of astronomy, facilities for procuring the necessary instruments, have likewise been greatly increased; and it must be a gratifying circumstance to the lovers of science to know, that even on the continent, extensive and accurate researches meet with no obstacle from the want of proper apparatus; and though Germany cannot boast of a Ramsden, a Troughton, or a Dollond, yet it possesses a Reichenbach, and a Fraunhofer, whose instruments even the Astronomer Royal, I am sure, would examine with pleasure.
All these circumstances ought to be subjects of congratulation to us, not of uneasiness; and if they produce any strong feeling, it should be that of emulation and of glory; the desire of maintaining the pre-eminence which, since the foundation of the Royal Observatory, has belonged to us in this science. And, amongst the cultivators of the different branches of human knowledge, astronomers particularly, whose subject is the heavens, should be above the feelings of low, or even national jealousy: their results are for all nations, and for future ages, and they require even for their perfection, the peaceful co-operations of philosophers in the remote parts of the globe.
I cannot give a more happy instance of this, than the manner in which the comet, of the shortest known period, of M Encke, was observed by Sir Thomas Brisbane's assistants, in New South Wales, and the calculations of its return so fully verified.
There is no more gratifying subject of contemplation than the present state and future prospects of astronomy; and when it is recollected, what this science was two centuries ago, the contrast affords a sublime proof of the powers and resources of the human mind. The notions of Ptolemy of cycles and epicycles, and the moving spheres of the heavens, were then current. The observations existing were devoted rather to the purposes of judicial astrology, than to the philosophy of the heavenly bodies, to objects of superstition, rather than of science.
If it were necessary to fix upon the strongest characteristic of the superiority of modern over ancient times, I know not whether the changes in the art of war, from the application of gunpowder, or in literary resources, from the press, or even the wonderful power created by the steam-engine, could be chosen with so much propriety as the improved state of astronomy.
Even the Athenians, the most enlightened people of antiquity, condemned a philosopher to death for denying the divinity of the sun; and it will be sufficient to mention, the idolatry and utter ignorance of the other great nations of antiquity, with regard to the laws or motions of the heavenly bodies.
Take the most transient and simplest view of the science, as it now exists, and what a noble subject for contemplation! Not only the masses and distances of the sun, planets, and their satellites are known, but even the weight of bodies upon their surface ascertained, and all their motions, appearances, and changes predicted with the utmost certainty for years to come, and even carried back through past ages to correct the chronology, and fix the epochas in the history of ancient nations. Attempts have been made to measure the almost inconceivable distances of the fixed stars: and, with this, what sublime, practical, and moral results! The pathless ocean navigated, and in unknown seas, the exact point of distance from known lands ascertained. All vague and superstitious notions banished from the mind, which, trusting to its own powers and analogies, sees an immutable and eternal order in the whole of the universe, intended, after the designs of the most perfect beneficence, to promote the happiness of millions of human beings, and where the whole of created nature offers its testimony to the existence of a Divine and Supreme intelligence.
I shall now conclude: Mr Baily, you have been so good as to undertake to transmit the medal to Dr Brinkley; no one is more capable of appreciating the high estimation in which his talents and character are held by the Royal Society. Assure him of our respect and admiration; inform him, that presiding, as he does, over another kindred scientific body, we receive his communications not merely with pleasure but with gratitude, and that we trust he will continue them, both for the advancement of astronomy, and for the increase of his own high reputation.