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URBAIN JEAN JOSEPH LE VERRIER was born on March 11, 1811, in the department of the Manche. Of his earlier education we have no record; but at twenty years of age he joined the École Polytechnique at Paris, where he studied two years, and on leaving the institution in 1833 had attained a rank which entitled him to make choice of one of the higher public services, and he accordingly became attached by preference to the "Administration des Tabacs," as engineer. In this position his duties also involved employment in the laboratory, and it thus probably arose that the first scientific papers published in his name were upon chemical subjects, viz. "Sur les combinaisons du phosphore avec l'hydrogène" and "Sur les combinaisons du phosphore avec l'oxigène," which appeared in the Annales de Chimie in 1836 and 1837 respectively. Notwithstanding, however, that Le Verrier's earlier memoirs were upon subjects connected with a department of science at that time distinct from astronomy, it is evident, from a very interesting note communicated by Sir George Airy to М. Tresca a few months since, that Le Verrier's attention had been directed to the particular science in which he has left so illustrious a name previously to his joining the "Administration des Tabacs" – or during his course of study at the École Polytechnique. Sir George states that he was probably Le Verrier's oldest scientific friend – that he believes his name had been known to him since the year 1832, about which time the Astronomer Royal's researches on the motions of the Earth and Venus were made public.
Le Verrier's first astronomical memoir was presented to the Academy of Sciences on September 16, 1839. It is entitled "On the Secular Variations of the Elements of the Orbits of the Seven Principal Planets," and was printed in extenso in the addi. tions to the Connaissance des Temps for 1843, which appeared in August 1840. Thus Le Verrier's first memoir has reference to one of the most interesting and important questions in astronomy, the stability of the planetary system. Lagrange and Laplace had shown that the mean distances of the planets from the Sun are invariable. With regard to the eccentricities and inclinations it had been shown by Laplace that neither would increase indefinitely with the time, though without indication of the limits within which their variations must be confined. The first attempt in this direction was made by Lagrange, as regards the elements of Jupiter and Saturn in 1776, and for the four smaller planets a few years later; but the values of the masses employed in his researches, particularly of the mass of Venus, were open to considerable corrections, and hence a degree of uncertainty attached to his inferences. Le Verrier undertook the long and difficult numerical calculation still necessary to decide whether the elements of the planetary system are liable only to changes of moderate magnitude about a mean state, and in the investigation in question he takes into account the simultaneous action of the seven principal planets. The first part of the memoir treats upon the eccentricities and apsides, one of the most interesting results referring to the eccentricity of the Earth's orbit, which it is found will diminish during nearly 24,000 years, attaining then a minimum equal to 0.0033; it then again increases until some 70,000 years hence a maximum of about 0.021 is attained, though Le Verrier finds that the highest value the Earth's eccentricity can reach is 0.07775. Jupiter, Saturn, and Uranus he found to compose a system independent of the other planets, the eccentricities and the lines of apsides returning to the same condition after a lapse of 900,000 years. The maxima and minima of the eccentricity of Saturn he found to be separated by an interval of 16,114 years. The change in the eccentricity of Mars is exceedingly slow, a period of 1,800,000 years being required for the exhibition of the most pronounced maxima. Le Verrier then treats of the secular variations of the inclinations and longitudes of the nodes, and assigns the limits of the inclinations upon the ecliptic of 1800 and also the limits of the relative inclinations of the planetary orbits. Finally he appends tables showing the elements of Mercury, Venus, the Earth, and Mars for a period of 200,000 years, or for every 10,000 years from -100,000 to +100,000 counted from 1800. It should be noted that the superior limits of the eccentricities of these four planets assigned by Le Verrier are very similar to the results obtained by Lagrange, an agreement which arises from the fact, pointed out by Le Verrier, that this higher limit will change only to a trifling extent, though considerable variation may be introduced in the values of the adopted masses.
A year later Le Verrier returned to this subject in a paper printed in the Connaissance des Temps for 1844, in which the approximations are carried further than in the previous memoir. The stability of the system formed by Jupiter, Saturn, and Uranus is confirmed, but the method of successive approximations is shown to be affected in its application to Mercury, Venus, the Earth, and Mars by uncertainty still remaining in the values of their masses. Le Verrier leaves his investigation in such manner that, when the definitive corrections to the masses he has employed are known, a comparatively simple calculation will lead to the corresponding corrected results without the necessity of repeating the laborious numerical computations previously involved.
In 1843 Le Verrier presented to the Paris Academy a "Theory of the Motion of Mercury," which was subsequently handled more completely, and definitely finished in 1859. The first part contains the calculation of the perturbations of the heliocentric motion of the planet; in the second part the theory thus formed is compared with meridian observations made at Paris from 1801 to 1842, and with the whole series of observed transits of Mercury, which are thoroughly reduced and discussed. In this section he determines the diameter of the Sun from the durations of the transits of Mercury across his disk. The third part relates to the construction of the usual tables for the calculation of the planet's geocentric positions; tables in which he intended to introduce modifications from previous forms calculated to greatly abridge the preparation of ephemerides.
During several following years Le Verrier's attention was more or less directed to the motions of the comets of short period, particularly that of 1770, commonly termed Lexell's Comet, and those of Faye and De Vico, discovered in the years 1843 and 1844 respectively. The amount of labour and research involved in these investigations, more especially in that relating to the comet of 1770, was enormous, and their publication excited a high degree of interest amongst astronomers.
The comet of 1770 was discovered by Messier on June 15, and approached the Earth until on July 1 it was distant only 363 terrestrial semi-diameters. It was observed until the beginning of October, and thus a wide extent of observation was afforded for the determination of the orbit. Pingré, Prosperin, Lambert, and others failed to represent the comet's path by a parabolic orbit, and to Lexell was due the merit of having first determined its true form an ellipse of very limited dimensions, the period of revolution, while the comet was visible, being only five and a half years. Lexell further explained a circumstance which at first excited surprise, that a comet revolving in so short a period should have been observed at a single appearance only. He remarked that the comet must have passed so near to the planet Jupiter in May 1767 that its influence would be considerably greater than that of the Sun, and hence he thought the form of orbit in which the comet was moving in 1770 might have been impressed upon it as late as 1767. And he further accounted for its non-appearance since 1770 by the near approach which the comet might again make to Jupiter in the summer of the year 1779. In 1806 Burckhardt, at the instance of Laplace, verified Lexell's calculations, and further applying formulæ by the French mathematician, he determined the actual effect of the two near approximations to the planet upon the comet's orbit. Burckhardt's results were published in the Mécanique Céleste, and were received with confidence by astronomers generally.
In this state the subject remained until it was taken up by Le Verrier. The principal results of his researches were communicated to the Paris Academy in 1844 and 1848, but the details were not fully published until the year 1857, when they appeared in the third volume of Annales of the Observatory at Paris. He found, from a minute discussion of the observations, that the mean motion of the comet could not be precisely determined in 1770, the observations leaving a degree of uncertainty as to the exact value of this important element which rendered the calculation of the comet's subsequent path to some extent doubtful, and thus it became necessary to consider the possible limits of uncertainty of elements in the investigation of the effect of the near approach of the comet to Jupiter in 1779. Following the comet in this way through the several orbits in which it might have moved after its disappearance in 1770, Le Verrier found that it is impossible it could have been retained in the system of Jupiter so as to have become a satellite of that planet: it is not impossible that after the great perturbation in 1779 its orbit may have become a hyperbola, while, on the contrary, it may have continued an ellipse, or rather, he showed that there were many possible elliptical trajectories. And finally he tabulates all these possible ellipses, so that, if a new periodical comet were detected, on examining the course previously followed by it, and comparing with the possible tracks of the comet of 1770, it should be practicable to pronounce upon the identity of the bodies or otherwise. Le Verrier also ascertained that Burckhardt's calculations for the year 1767, in the Mécanique Céleste, were vitiated by errors, the cause of which has since been explained by D'Arrest.
The comet of Faye, discovered on November 22, 1843, which was soon found to be moving in an elliptical orbit, with short period, was also made the subject of an immense work by Le Verrier, who had to some extent favoured the idea of its identity with the comet of 1770. He did not shrink from the laborious calculation of the effect of planetary perturbations from 1843 to 1781, the result of which negatived the conjectured identity. Continuing his researches still further backwards, he ultimately came to the conclusion that "it is possible the comet of Faye, in the year 1747, may have passed so near to Jupiter that its path was completely changed: it is at least to this year that it is necessary to remount to fix an epoch when the comet commenced describing the restricted ellipse in which we have observed it in our days. It was not until its thirteenth return to perihelion that it was at last seized by M. Faye."
Similarly, the comet of De Vico, detected on August 22, 1844, engaged the attention of Le Verrier. Remarking that, like Faye's comet, it offered vague resemblance to the comet of 1770, and that, from the circumstances under which the comet near aphelion would approach the orbit of Jupiter, the large difference in the line of nodes did not discourage investigation, he proceeded to calculate the perturbations previous to 1844, starting from a system of elements obtained by Professor Brünnow from a very complete discussion of the observations in that year. The first case of great perturbation was found to occur in 1814, and after a careful study of their effect, it was found necessary to include the uncertainty of the previous elements in continuing the research to a more distant period. A table is presented, showing the elements for various epochs, as far back as 1753, on the supposition that the comet underwent the greatest possible amount of perturbation. As bearing upon the conjectured identity of this comet with the comet of 1770, Le Verrier found that between 1844 and 1787 the line of nodes would have retrograded 109°, so that perturbation sufficed to explain the great difference in this element; but he also ascertained that in other elements the differences were so great as to be incompatible with the hypothesis of identity, and thus he adds: "The two comets of Faye and De Vico, amongst which we had hoped to find again the comet of 1770, have in the result disappointed our expectations." Upon further considerations, Le Verrier inferred that the comet of De Vico had been a denizen of the planetary system for many centuries prior to its discovery in 1844, and he was thus led to seek for the comet amongst those of comparatively early date. The comet of 1585, observed by Tycho Brahe and Rothmann with a degree of precision very great for the epoch, and the elements of which presented some similarity to those of De Vico's comet, was first examined. Laugier and Mauvais had obtained for the comet of 1585 an ellipse of short period. Le Verrier concluded that there is no plausible reason for admitting the identity of the comets of 1585 and 1844; and, not satisfied with this inference, from a consideration of the relative position of the line of apsides, he showed that it is possible to represent the observations of 1585 within their probable limits of error by a parabolic orbit, a result which was verified by an independent investigation by Professor Peters, of Kiel.
The case is entirely different with the comet of 1678, observed only by La Hire at Paris, which in several of the elements of its orbit presented some degree of similarity to the comet of De Vico. Le Verrier examined if it were possible the perturbations of the latter would admit of its passing through the four positions observed by La Hire, and he found a system of elements from a consideration of the perturbations which, with trifling variation – the semi-axis remaining unchanged – sufficiently well represented the observed positions, and thus he decides in favour of the identity of the comets of 1678 and 1844. He concludes the account of his researches on the motion of De Vico's comet thus: "The comet of 1844 has, like others, come to us from the most distant regions of space, and has been fixed amongst the planets under the powerful influence of the action of Jupiter. Its advent ante-dates, without doubt, many centuries. Since that epoch it has often passed in the neighbourhood of the Earth, but has only been once observed in past centuries, 166 years before its appearance in 1844." He considered that the comet will describe the orbit in which we have observed it for a long time to come, and that, after a certain number of centuries, it will again attain the orbit of Jupiter in a direction opposite to that from which it arrived in the planetary system, and its course will again be wholly changed.
It was while he was engaged upon these researches relating to the comets of short period that Le Verrier's attention was first specially directed to the anomalous motion of the planet Uranus. In the formation of the Tables of Uranus, published in 1821, Bouvard had experienced unforeseen difficulties in reconciling the older observations of the planet with the modern ones. If the early observations were combined with the later series, while the first were passably represented, the latter showed differences much exceeding the admissible errors of observation; while, if the ancient observations were omitted from the discussion, the modern series could be represented satisfactorily, but at the expense of large differences, when the theory was compared with the early observations of Flamsteed, Bradley, Mayer, and Lemonnier. Under these circumstances, Bouvard decided to found his tables upon the modern observations exclusively, leaving, as he says, to a future time the decision whether the difficulties he had encountered were attributable to inaccuracies in the older observations, or whether they arose from some extraneous action which had been exercised upon Uranus. Writing to the Astronomer Royal in October 1837, Eugène Bouvard, the nephew of the author of the Tables of Uranus, mentions that the latter had deputed to him their reconstruction; he referred to the constantly increasing differences between calculation and observation, and suggests whether they could be owing to the action of a body situated beyond the planet. Such, at least, he states to have been the opinion of the elder Bouvard. Again, in 1840, Bessel, in a letter addressed to Humboldt, expresses the opinion that a time would come when "the mystery of Uranus" would be solved by a new planet, the elements of which would be recognised from its action upon Uranus, and verified by that which it might also exercise upon Saturn.
These circumstances would, no doubt, be well known to Arago; and accordingly, in the summer of 1845, we find him representing to Le Verrier the importance of the question, and the duty which it imposed upon every astronomer to cooperate towards clearing up the difficulty. In his Première Mémoire sur la théorie d'Uranus, presented to the Paris Academy on November 10, 1845, Le Verrier writes: "I therefore abandoned for the moment, to occupy myself upon Uranus, the researches which I had undertaken relating to the comets, of which many fragments have already appeared. Such is the origin of the work which I have the honour to present to the Academy today." This distinct acknowledgment that it was Arago who first engaged him to study the theory of Uranus will be found in the Comptes Rendus for the above date.
In this first memoir the perturbations produced by Jupiter and Saturn were newly and completely developed and calculated, the most important numbers being verified by a duplicate process, involving entirely different methods. Le Verrier found corrections which materially affected the places deduced from the Tables of Bouvard, but which nevertheless failed to reconcile the observed and computed positions. This work was one of great labour, and as the consequence of it, to quote the words of the Astronomer Royal: "Perhaps it may be truly said, that the theory of Uranus was now, for the first time, placed on a satisfactory foundation."
The second memoir was presented to the Academy on June 1, 1846. Le Verrier first reduced anew nearly all the reliable existing observations of Uranus, and compared them with the theory established in his first memoir, and he arrived at the definite conclusion that it was impossible to represent the observed motion of Uranus without admitting the presence of some extraneous action. The failure of the law of gravitation at the distance of Uranus, which had been already suggested, he at once rejected, remarking that every suspicion of the kind had but served to afford a further confirmation of the universality of the Newtonian law; and, dismissing other explanations that offered themselves as insufficient or inapplicable, he is led to the consideration of the problem involved in the following question: "Is it possible that the irregularities of Uranus can be due to the action of a planet situate in the ecliptic at a distance double that of Uranus? And if so, where is that planet actually situated? What is its mass? What are the elements of the orbit which it describes?" The problem thus distinctly announced, he proceeded, as he states, to solve rigorously. He found that there was but one region of the ecliptic where a disturbing body could be placed so as to satisfy the observed irregularities in the motion of Uranus, and concluded that on January 1, 1847, its heliocentric longitude must be very nearly 325°. This he announced as the capital result of his researches, adding that, to arrive at it, he had been under the necessity of undertaking the calculation of the perturbations exercised by Jupiter upon Uranus, determining also those due to Saturn, carrying the approximations to the squares and products of the masses, which had introduced notable modifications in the existing or admitted theories; of reducing nearly three hundred meridian observations of Uranus; of calculating the corresponding heliocentric positions of the planet, supposing that it was subject only to the action of the Sun, Jupiter, and Saturn, and of deducing the geocentric coordinates with the help of the Solar Tables, thus proving the absolute incompatibility between the places calculated and those observed. The existence of an undiscovered perturbing body being thus indicated, there remained, in order to assign its place in the heavens, the inverse solution of the problem of perturbations in its usual form, or the investigation of the elements of the unseen body from its measured effect upon the motion of Uranus. Recalling a remark of Clairaut's, when making known the result of his calculation of the perturbations experienced by Halley's Comet from 1682 to 1759, that it might be subject to the influence of planets too distant to be perceived from the Earth, Le Verrier in conclusion expresses the hope that these distant planets may not be all invisible, and that it might be practicable to discover the body of which he had made known the position.
Le Verrier's third memoir, the most remarkable production of the three, was communicated to the Academy of Sciences on August 31, 1846. In the former investigation it had been assumed that the mean distance of the disturbing body was twice that of Uranus. Le Verrier now considered the mean distance one of the unknown elements to be determined, like the others, from the solution of his equations of condition; from which also the mass of the undiscovered planet would result. The necessary treatment of these equations was found to be very tedious and difficult, but finally the following definitive results were obtained :-
From which elements Le Verrier found for the true longitude of the perturbing body on January 1, 1847, 326° 32′ and for its radius vector 33'06. He then proceeds to assign limits within which the elements given above might be varied without ceasing to represent the observations, and thus effectually to limit the space of the heavens within which it would be necessary to search for the planet so as to insure its true position being included. This space he found to be comprised between 321 and 335° of heliocentric longitude; but he considered that positions differing much from 326° 32', the value directly found, possessed little probability, and suggested that the search for the planet should be commenced at the point immediately indicated by the solution of his equations. Further, with the mass he had derived for the disturbing body, and on the assumption that its density might be the same as that of Uranus, he considered the apparent diameter might be three seconds of arc, and therefore would be easily measurable in large telescopes. One of the most striking characteristics of this memorable paper is the confidence displayed by its author in the result of his investigations, or, as the Astronomer Royal has expressed it, "the calmness and clearness with which he limited the field of observation, and the firmness with which he proclaimed to observing astronomers, 'look in the place which I have indicated, and you will see the planet well.' It is here, if I mistake not, that we see a character far superior to that of the able, or enterprising, or industrious mathematician – it is here that we see the philosopher."
On September 18 Le Verrier addressed a letter to Dr. Galle, then in charge of the powerful refractor of the Royal Observatory at Berlin, begging him to make a search for the planet, of whose existence he felt so confident. The letter arrived on September 23, and the result is well known. Availing himself of Bremiker's Chart for Hour xxi. of R.A., one of the series issued by the Berlin Academy (which, though quite ready for publication, had not yet been circulated), he remarked, on the same evening, an object shining as a star of the eighth magnitude in a position where none was entered upon the map, the motion of which was strongly suspected on this night, and established beyond doubt on the following one, the change of place corresponding nearly to that which Le Verrier's elements of the new planet indicated. On the same night also a measurable disk was recognised, which the micrometer showed to have a diameter of between two and three seconds. The observed longitude was within 55' of that which Le Verrier had predicted. It is unnecessary to expatiate here upon the admiration, and, as regards astronomers generally, the astonishment at the successful issue of the unprecedented labours of Le Verrier, which the announcement of this great discovery produced. It was only limited to the civilised world. Honours showered upon him from all quarters and his name may truly be said to have suddenly become "a household word" wherever astronomical science is cultivated.
The actual discovery of the planet was known in this country on September 30 by letters from the Berlin Observatory. Up to this time the entirely independent work of Professor Adams in the explanation of the irregularities in the observed motion of Uranus by the action of an undiscovered planet, and the determination of its actual position, was known only to a limited circle in this country, and, so far as appears, was not at all known abroad. Hence, when the official astronomers to whom Professor Adams' results, which were almost identical with those of Le Verrier, had been communicated, came forward immediately after the actual discovery of the planet at Berlin was announced, to state the circumstances under which his investigation had been conducted and had become known to them, animated and heated discussions arose, to which further allusion need not be made here, than to add that they soon subsided into a general feeling of respect and admiration for the two distinguished mathematicians who, unknown to each other, had successfully treated a problem which it had previously been considered almost impossible to solve.
In November 1846 Le Verrier published, as an Appendix to the Connaissance des Temps for 1849, Recherches sur les mouvements de la Planète Herschel (dite Uranus), in which he gave a detailed account of the processes, analytical and numerical, involved in the course of his investigations, of which, previous to the telescopic discovery of the disturbing body, he had only given the particulars found in the three memoirs presented to the Academy and referred to above. It is to these Recherches that recourse must be had in order to follow Le Verrier through the various steps by which he accomplished the solution of the grand problem which added Neptune to the known great planets of the Solar System.
On the death of Arago, in 1853, Le Verrier was appointed to the direction of the Observatory at Paris, an institution which by his indomitable energy he raised from a position inferior to other principal national establishments, until he left it second to none. In 1870, in consequence of differences with the staff of the Observatory, he ceased his connection with it for a time, but on the melancholy death of Delaunay in 1872, he was reinstated, and retained the management of the institution during the rest of his life. It was while director of the Observatory of Paris that Le Verrier undertook and accomplished the immense work with which his name will be mainly associated in future times – no less than the complete revision of the planetary theories – the theories of Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus, and Neptune, and the formation of tables of their motions. On two occasions these researches, which have been well termed appalling in their magnitude, have formed the subject of addresses from the Chair of the Royal Astronomical Society, first in the year 1868, when the Gold Medal of the Society was presented to Le Verrier at the hands of Professor Pritchard for his theories and tables of Mercury, Venus, the Earth, and Mars; and again in 1876, when, during the presidency of Professor Adams, the Society's Medal was for the second time adjudged to Le Verrier for the similar investigation of the theories of the four great planets, Jupiter, Saturn, Uranus, and Neptune, and for his Tables of Jupiter and Saturn founded upon them. (The Tables of Uranus and Neptune were published at a later period.) The addresses delivered on these occasions, which, as usual, are printed in the Monthly Notices, enter into particulars of the nature and extent of Le Verrier's work in the planetary theories; Professor Adams' valuable analysis of the more intricate and laborious researches connected with the larger affording an admirable outline of Le Verrier's greater achievements. The circumstance that our late distinguished Associate's work upon the planetary theories has thus twice been the subject of detailed comment in the publications of the Society may render it unnecessary to enter into recapitulation here; but it may be useful for reference to subjoin the brief résumé as presented by Le Verrier to the Academy of Sciences at the beginning of the year 1875.
The general developments formed the object of five memoirs, presented and published in 1840, 1843, 1849, and 1855.
The formulæ relating to the secular inequalities were specially treated in the memoirs of 1840 and 1841. The same subject was taken up again, in a more general and complete form, in a work communicated to the Academy on November 11, 1872, concerning the four great planets, Jupiter, Saturn, Uranus, and Neptune.
The theory of Mercury, presented in 1843, afterwards completely revised, was definitively finished in 1859; the theory of Venus was given in 1861; that of the Sun (the Earth) in 1853 and 1858; that of Mars in 1861; the theories of Jupiter and Saturn in 1872 and 1873. The theory of Uranus, first communicated in 1846 on the occasion of the discovery of Neptune, was the subject of a new investigation, presented on November 15, 1874. Lastly, the theory of Neptune was presented to the Academy of Sciences in the first days of 1875.
These theories, and the tables constructed upon them, have been given to the world in the noble series of Annales de l'Observatoire de Paris, vols. iv. to xiv., which will remain a lasting monument to the great Astronomer.
One of the last subjects that engaged Le Verrier's attention was connected with the unexplained motion in the perihelion of the planet Mercury, to which he had pointedly referred upwards of twenty years previously, and which he considered to be due to the action of matter, in one form or another, between Mercury and the Sun; and on this point Professor Adams has remarked that "the theory of the planet has been established with so much care, and the transits of the planet across the Sun's disk furnish such accurate observations, as to leave no doubt of the reality of the phenomenon in question and the only way of accounting for it appears to be to suppose, with M. Le Verrier, the existence of several minute planets, or of a certain quantity of diffused matter circulating about the Sun within the orbit of Mercury." Le Verrier was first led to suppose that the telescope might furnish proof of the existence of at least one such minute planet when he became acquainted with the observation of Lescarbault in March 1859. In 1876, on collecting five or six observations of a similar nature, he treated them with the view to discover whether they could be attributed to the transit of a single intraMercurial body across the Sun's disk, and, with a skill almost peculiar to himself, he found that they might be represented, so far as regards the times of conjunction with the Sun, by the motion of a single planet, the heliocentric longitude of which is given by a formula, with an indeterminate, admitting however of only two values without deviating considerably from observation. The period of revolution of such a planet will be either 27.96 days or 33'02 days, according as one or other of these values is adopted. Le Verrier considered that a transit of the hypothetical planet was possible in the spring of 1877, but that no other could occur before 1885. As is known, an energetic watch was maintained upon the Sun's disk at the critical period without success.
Le Verrier's health had long been in an indifferent state, and for some six months previous to his decease he had been unable to take part in the proceedings of the Academy of Sciences. Towards the close of his life he had been greatly assisted by M. Gaillot, when from painful and depressing illness he was prevented from giving active personal superintendence to the completion of his planetary tables. To the exertions of M. Gaillot it is believed to be owing that the last sheets of the Tables of Neptune were ready a few days prior to Le Verrier's death, and that thus he was enabled to see the greatest work of his life brought to a close. Le Verrier expressed in strong terms to the writer of this notice his feeling of appreciation of the value of the services which M. Gaillot had rendered him.
The death of M. Le Verrier occurred early on the morning of September 23, 1877. He was buried on the 25th, in the Cemetery of Mont Parnasse, at Paris. The funeral cortège left the Observatory under a military escort, with muffled drums – as usual at the funeral of a Grand Officer of the Legion of Honour – proceeding by way of the Avenue de l'Observatoire and Rue Val de Grace to the Church of Saint Jacques de Haut-pas, where the religious ceremony took place in the presence of a crowded assembly. The cordons of the pall were held by M. Peligot, President of the Academy of Sciences; M. Dumas, Vice-President of the Superior Council of Public Instruction; M. Fizeau, Vice-President of the Academy and Member of the Scientific Council of the Observatory; M. Faye, President of the Bureau des Longitudes; General Morin, Vice-President of the Association Scientifique (which active institution was founded by Le Verrier); General Baron Wrede, of the Academy of Stockholm; Captain Mouchez, of the Institut; and Mr. Hind, Superintendent of the Nautical Almanac. The Marshal-President of the French Republic was represented by one of his staff, the General-Commandant of Paris; and deputations from the École Polytechnique, at which Le Verrier completed his studies, and from other institutions with which he had been connected, were also present. Discourses were pronounced at the grave at Mont Parnasse by MM. Dumas, Faye, Janssen, Tresca, and Yvon Villarceau. These éloges will be found in the Comptes Rendus.
J. R. H.
Le Verrier's first astronomical memoir was presented to the Academy of Sciences on September 16, 1839. It is entitled "On the Secular Variations of the Elements of the Orbits of the Seven Principal Planets," and was printed in extenso in the addi. tions to the Connaissance des Temps for 1843, which appeared in August 1840. Thus Le Verrier's first memoir has reference to one of the most interesting and important questions in astronomy, the stability of the planetary system. Lagrange and Laplace had shown that the mean distances of the planets from the Sun are invariable. With regard to the eccentricities and inclinations it had been shown by Laplace that neither would increase indefinitely with the time, though without indication of the limits within which their variations must be confined. The first attempt in this direction was made by Lagrange, as regards the elements of Jupiter and Saturn in 1776, and for the four smaller planets a few years later; but the values of the masses employed in his researches, particularly of the mass of Venus, were open to considerable corrections, and hence a degree of uncertainty attached to his inferences. Le Verrier undertook the long and difficult numerical calculation still necessary to decide whether the elements of the planetary system are liable only to changes of moderate magnitude about a mean state, and in the investigation in question he takes into account the simultaneous action of the seven principal planets. The first part of the memoir treats upon the eccentricities and apsides, one of the most interesting results referring to the eccentricity of the Earth's orbit, which it is found will diminish during nearly 24,000 years, attaining then a minimum equal to 0.0033; it then again increases until some 70,000 years hence a maximum of about 0.021 is attained, though Le Verrier finds that the highest value the Earth's eccentricity can reach is 0.07775. Jupiter, Saturn, and Uranus he found to compose a system independent of the other planets, the eccentricities and the lines of apsides returning to the same condition after a lapse of 900,000 years. The maxima and minima of the eccentricity of Saturn he found to be separated by an interval of 16,114 years. The change in the eccentricity of Mars is exceedingly slow, a period of 1,800,000 years being required for the exhibition of the most pronounced maxima. Le Verrier then treats of the secular variations of the inclinations and longitudes of the nodes, and assigns the limits of the inclinations upon the ecliptic of 1800 and also the limits of the relative inclinations of the planetary orbits. Finally he appends tables showing the elements of Mercury, Venus, the Earth, and Mars for a period of 200,000 years, or for every 10,000 years from -100,000 to +100,000 counted from 1800. It should be noted that the superior limits of the eccentricities of these four planets assigned by Le Verrier are very similar to the results obtained by Lagrange, an agreement which arises from the fact, pointed out by Le Verrier, that this higher limit will change only to a trifling extent, though considerable variation may be introduced in the values of the adopted masses.
A year later Le Verrier returned to this subject in a paper printed in the Connaissance des Temps for 1844, in which the approximations are carried further than in the previous memoir. The stability of the system formed by Jupiter, Saturn, and Uranus is confirmed, but the method of successive approximations is shown to be affected in its application to Mercury, Venus, the Earth, and Mars by uncertainty still remaining in the values of their masses. Le Verrier leaves his investigation in such manner that, when the definitive corrections to the masses he has employed are known, a comparatively simple calculation will lead to the corresponding corrected results without the necessity of repeating the laborious numerical computations previously involved.
In 1843 Le Verrier presented to the Paris Academy a "Theory of the Motion of Mercury," which was subsequently handled more completely, and definitely finished in 1859. The first part contains the calculation of the perturbations of the heliocentric motion of the planet; in the second part the theory thus formed is compared with meridian observations made at Paris from 1801 to 1842, and with the whole series of observed transits of Mercury, which are thoroughly reduced and discussed. In this section he determines the diameter of the Sun from the durations of the transits of Mercury across his disk. The third part relates to the construction of the usual tables for the calculation of the planet's geocentric positions; tables in which he intended to introduce modifications from previous forms calculated to greatly abridge the preparation of ephemerides.
During several following years Le Verrier's attention was more or less directed to the motions of the comets of short period, particularly that of 1770, commonly termed Lexell's Comet, and those of Faye and De Vico, discovered in the years 1843 and 1844 respectively. The amount of labour and research involved in these investigations, more especially in that relating to the comet of 1770, was enormous, and their publication excited a high degree of interest amongst astronomers.
The comet of 1770 was discovered by Messier on June 15, and approached the Earth until on July 1 it was distant only 363 terrestrial semi-diameters. It was observed until the beginning of October, and thus a wide extent of observation was afforded for the determination of the orbit. Pingré, Prosperin, Lambert, and others failed to represent the comet's path by a parabolic orbit, and to Lexell was due the merit of having first determined its true form an ellipse of very limited dimensions, the period of revolution, while the comet was visible, being only five and a half years. Lexell further explained a circumstance which at first excited surprise, that a comet revolving in so short a period should have been observed at a single appearance only. He remarked that the comet must have passed so near to the planet Jupiter in May 1767 that its influence would be considerably greater than that of the Sun, and hence he thought the form of orbit in which the comet was moving in 1770 might have been impressed upon it as late as 1767. And he further accounted for its non-appearance since 1770 by the near approach which the comet might again make to Jupiter in the summer of the year 1779. In 1806 Burckhardt, at the instance of Laplace, verified Lexell's calculations, and further applying formulæ by the French mathematician, he determined the actual effect of the two near approximations to the planet upon the comet's orbit. Burckhardt's results were published in the Mécanique Céleste, and were received with confidence by astronomers generally.
In this state the subject remained until it was taken up by Le Verrier. The principal results of his researches were communicated to the Paris Academy in 1844 and 1848, but the details were not fully published until the year 1857, when they appeared in the third volume of Annales of the Observatory at Paris. He found, from a minute discussion of the observations, that the mean motion of the comet could not be precisely determined in 1770, the observations leaving a degree of uncertainty as to the exact value of this important element which rendered the calculation of the comet's subsequent path to some extent doubtful, and thus it became necessary to consider the possible limits of uncertainty of elements in the investigation of the effect of the near approach of the comet to Jupiter in 1779. Following the comet in this way through the several orbits in which it might have moved after its disappearance in 1770, Le Verrier found that it is impossible it could have been retained in the system of Jupiter so as to have become a satellite of that planet: it is not impossible that after the great perturbation in 1779 its orbit may have become a hyperbola, while, on the contrary, it may have continued an ellipse, or rather, he showed that there were many possible elliptical trajectories. And finally he tabulates all these possible ellipses, so that, if a new periodical comet were detected, on examining the course previously followed by it, and comparing with the possible tracks of the comet of 1770, it should be practicable to pronounce upon the identity of the bodies or otherwise. Le Verrier also ascertained that Burckhardt's calculations for the year 1767, in the Mécanique Céleste, were vitiated by errors, the cause of which has since been explained by D'Arrest.
The comet of Faye, discovered on November 22, 1843, which was soon found to be moving in an elliptical orbit, with short period, was also made the subject of an immense work by Le Verrier, who had to some extent favoured the idea of its identity with the comet of 1770. He did not shrink from the laborious calculation of the effect of planetary perturbations from 1843 to 1781, the result of which negatived the conjectured identity. Continuing his researches still further backwards, he ultimately came to the conclusion that "it is possible the comet of Faye, in the year 1747, may have passed so near to Jupiter that its path was completely changed: it is at least to this year that it is necessary to remount to fix an epoch when the comet commenced describing the restricted ellipse in which we have observed it in our days. It was not until its thirteenth return to perihelion that it was at last seized by M. Faye."
Similarly, the comet of De Vico, detected on August 22, 1844, engaged the attention of Le Verrier. Remarking that, like Faye's comet, it offered vague resemblance to the comet of 1770, and that, from the circumstances under which the comet near aphelion would approach the orbit of Jupiter, the large difference in the line of nodes did not discourage investigation, he proceeded to calculate the perturbations previous to 1844, starting from a system of elements obtained by Professor Brünnow from a very complete discussion of the observations in that year. The first case of great perturbation was found to occur in 1814, and after a careful study of their effect, it was found necessary to include the uncertainty of the previous elements in continuing the research to a more distant period. A table is presented, showing the elements for various epochs, as far back as 1753, on the supposition that the comet underwent the greatest possible amount of perturbation. As bearing upon the conjectured identity of this comet with the comet of 1770, Le Verrier found that between 1844 and 1787 the line of nodes would have retrograded 109°, so that perturbation sufficed to explain the great difference in this element; but he also ascertained that in other elements the differences were so great as to be incompatible with the hypothesis of identity, and thus he adds: "The two comets of Faye and De Vico, amongst which we had hoped to find again the comet of 1770, have in the result disappointed our expectations." Upon further considerations, Le Verrier inferred that the comet of De Vico had been a denizen of the planetary system for many centuries prior to its discovery in 1844, and he was thus led to seek for the comet amongst those of comparatively early date. The comet of 1585, observed by Tycho Brahe and Rothmann with a degree of precision very great for the epoch, and the elements of which presented some similarity to those of De Vico's comet, was first examined. Laugier and Mauvais had obtained for the comet of 1585 an ellipse of short period. Le Verrier concluded that there is no plausible reason for admitting the identity of the comets of 1585 and 1844; and, not satisfied with this inference, from a consideration of the relative position of the line of apsides, he showed that it is possible to represent the observations of 1585 within their probable limits of error by a parabolic orbit, a result which was verified by an independent investigation by Professor Peters, of Kiel.
The case is entirely different with the comet of 1678, observed only by La Hire at Paris, which in several of the elements of its orbit presented some degree of similarity to the comet of De Vico. Le Verrier examined if it were possible the perturbations of the latter would admit of its passing through the four positions observed by La Hire, and he found a system of elements from a consideration of the perturbations which, with trifling variation – the semi-axis remaining unchanged – sufficiently well represented the observed positions, and thus he decides in favour of the identity of the comets of 1678 and 1844. He concludes the account of his researches on the motion of De Vico's comet thus: "The comet of 1844 has, like others, come to us from the most distant regions of space, and has been fixed amongst the planets under the powerful influence of the action of Jupiter. Its advent ante-dates, without doubt, many centuries. Since that epoch it has often passed in the neighbourhood of the Earth, but has only been once observed in past centuries, 166 years before its appearance in 1844." He considered that the comet will describe the orbit in which we have observed it for a long time to come, and that, after a certain number of centuries, it will again attain the orbit of Jupiter in a direction opposite to that from which it arrived in the planetary system, and its course will again be wholly changed.
It was while he was engaged upon these researches relating to the comets of short period that Le Verrier's attention was first specially directed to the anomalous motion of the planet Uranus. In the formation of the Tables of Uranus, published in 1821, Bouvard had experienced unforeseen difficulties in reconciling the older observations of the planet with the modern ones. If the early observations were combined with the later series, while the first were passably represented, the latter showed differences much exceeding the admissible errors of observation; while, if the ancient observations were omitted from the discussion, the modern series could be represented satisfactorily, but at the expense of large differences, when the theory was compared with the early observations of Flamsteed, Bradley, Mayer, and Lemonnier. Under these circumstances, Bouvard decided to found his tables upon the modern observations exclusively, leaving, as he says, to a future time the decision whether the difficulties he had encountered were attributable to inaccuracies in the older observations, or whether they arose from some extraneous action which had been exercised upon Uranus. Writing to the Astronomer Royal in October 1837, Eugène Bouvard, the nephew of the author of the Tables of Uranus, mentions that the latter had deputed to him their reconstruction; he referred to the constantly increasing differences between calculation and observation, and suggests whether they could be owing to the action of a body situated beyond the planet. Such, at least, he states to have been the opinion of the elder Bouvard. Again, in 1840, Bessel, in a letter addressed to Humboldt, expresses the opinion that a time would come when "the mystery of Uranus" would be solved by a new planet, the elements of which would be recognised from its action upon Uranus, and verified by that which it might also exercise upon Saturn.
These circumstances would, no doubt, be well known to Arago; and accordingly, in the summer of 1845, we find him representing to Le Verrier the importance of the question, and the duty which it imposed upon every astronomer to cooperate towards clearing up the difficulty. In his Première Mémoire sur la théorie d'Uranus, presented to the Paris Academy on November 10, 1845, Le Verrier writes: "I therefore abandoned for the moment, to occupy myself upon Uranus, the researches which I had undertaken relating to the comets, of which many fragments have already appeared. Such is the origin of the work which I have the honour to present to the Academy today." This distinct acknowledgment that it was Arago who first engaged him to study the theory of Uranus will be found in the Comptes Rendus for the above date.
In this first memoir the perturbations produced by Jupiter and Saturn were newly and completely developed and calculated, the most important numbers being verified by a duplicate process, involving entirely different methods. Le Verrier found corrections which materially affected the places deduced from the Tables of Bouvard, but which nevertheless failed to reconcile the observed and computed positions. This work was one of great labour, and as the consequence of it, to quote the words of the Astronomer Royal: "Perhaps it may be truly said, that the theory of Uranus was now, for the first time, placed on a satisfactory foundation."
The second memoir was presented to the Academy on June 1, 1846. Le Verrier first reduced anew nearly all the reliable existing observations of Uranus, and compared them with the theory established in his first memoir, and he arrived at the definite conclusion that it was impossible to represent the observed motion of Uranus without admitting the presence of some extraneous action. The failure of the law of gravitation at the distance of Uranus, which had been already suggested, he at once rejected, remarking that every suspicion of the kind had but served to afford a further confirmation of the universality of the Newtonian law; and, dismissing other explanations that offered themselves as insufficient or inapplicable, he is led to the consideration of the problem involved in the following question: "Is it possible that the irregularities of Uranus can be due to the action of a planet situate in the ecliptic at a distance double that of Uranus? And if so, where is that planet actually situated? What is its mass? What are the elements of the orbit which it describes?" The problem thus distinctly announced, he proceeded, as he states, to solve rigorously. He found that there was but one region of the ecliptic where a disturbing body could be placed so as to satisfy the observed irregularities in the motion of Uranus, and concluded that on January 1, 1847, its heliocentric longitude must be very nearly 325°. This he announced as the capital result of his researches, adding that, to arrive at it, he had been under the necessity of undertaking the calculation of the perturbations exercised by Jupiter upon Uranus, determining also those due to Saturn, carrying the approximations to the squares and products of the masses, which had introduced notable modifications in the existing or admitted theories; of reducing nearly three hundred meridian observations of Uranus; of calculating the corresponding heliocentric positions of the planet, supposing that it was subject only to the action of the Sun, Jupiter, and Saturn, and of deducing the geocentric coordinates with the help of the Solar Tables, thus proving the absolute incompatibility between the places calculated and those observed. The existence of an undiscovered perturbing body being thus indicated, there remained, in order to assign its place in the heavens, the inverse solution of the problem of perturbations in its usual form, or the investigation of the elements of the unseen body from its measured effect upon the motion of Uranus. Recalling a remark of Clairaut's, when making known the result of his calculation of the perturbations experienced by Halley's Comet from 1682 to 1759, that it might be subject to the influence of planets too distant to be perceived from the Earth, Le Verrier in conclusion expresses the hope that these distant planets may not be all invisible, and that it might be practicable to discover the body of which he had made known the position.
Le Verrier's third memoir, the most remarkable production of the three, was communicated to the Academy of Sciences on August 31, 1846. In the former investigation it had been assumed that the mean distance of the disturbing body was twice that of Uranus. Le Verrier now considered the mean distance one of the unknown elements to be determined, like the others, from the solution of his equations of condition; from which also the mass of the undiscovered planet would result. The necessary treatment of these equations was found to be very tedious and difficult, but finally the following definitive results were obtained :-
| Semi-axis of the orbit | 36.154 | |
| Duration of the sidereal revolution | 217.387 years. | |
| Eccentricity | 0.10761 | |
| Longitude of perihelion | 284° 45' | |
| Mean longitude 1847, January 1 | 318° 47' | |
| Mass (the Sun's mass 1). |
From which elements Le Verrier found for the true longitude of the perturbing body on January 1, 1847, 326° 32′ and for its radius vector 33'06. He then proceeds to assign limits within which the elements given above might be varied without ceasing to represent the observations, and thus effectually to limit the space of the heavens within which it would be necessary to search for the planet so as to insure its true position being included. This space he found to be comprised between 321 and 335° of heliocentric longitude; but he considered that positions differing much from 326° 32', the value directly found, possessed little probability, and suggested that the search for the planet should be commenced at the point immediately indicated by the solution of his equations. Further, with the mass he had derived for the disturbing body, and on the assumption that its density might be the same as that of Uranus, he considered the apparent diameter might be three seconds of arc, and therefore would be easily measurable in large telescopes. One of the most striking characteristics of this memorable paper is the confidence displayed by its author in the result of his investigations, or, as the Astronomer Royal has expressed it, "the calmness and clearness with which he limited the field of observation, and the firmness with which he proclaimed to observing astronomers, 'look in the place which I have indicated, and you will see the planet well.' It is here, if I mistake not, that we see a character far superior to that of the able, or enterprising, or industrious mathematician – it is here that we see the philosopher."
On September 18 Le Verrier addressed a letter to Dr. Galle, then in charge of the powerful refractor of the Royal Observatory at Berlin, begging him to make a search for the planet, of whose existence he felt so confident. The letter arrived on September 23, and the result is well known. Availing himself of Bremiker's Chart for Hour xxi. of R.A., one of the series issued by the Berlin Academy (which, though quite ready for publication, had not yet been circulated), he remarked, on the same evening, an object shining as a star of the eighth magnitude in a position where none was entered upon the map, the motion of which was strongly suspected on this night, and established beyond doubt on the following one, the change of place corresponding nearly to that which Le Verrier's elements of the new planet indicated. On the same night also a measurable disk was recognised, which the micrometer showed to have a diameter of between two and three seconds. The observed longitude was within 55' of that which Le Verrier had predicted. It is unnecessary to expatiate here upon the admiration, and, as regards astronomers generally, the astonishment at the successful issue of the unprecedented labours of Le Verrier, which the announcement of this great discovery produced. It was only limited to the civilised world. Honours showered upon him from all quarters and his name may truly be said to have suddenly become "a household word" wherever astronomical science is cultivated.
The actual discovery of the planet was known in this country on September 30 by letters from the Berlin Observatory. Up to this time the entirely independent work of Professor Adams in the explanation of the irregularities in the observed motion of Uranus by the action of an undiscovered planet, and the determination of its actual position, was known only to a limited circle in this country, and, so far as appears, was not at all known abroad. Hence, when the official astronomers to whom Professor Adams' results, which were almost identical with those of Le Verrier, had been communicated, came forward immediately after the actual discovery of the planet at Berlin was announced, to state the circumstances under which his investigation had been conducted and had become known to them, animated and heated discussions arose, to which further allusion need not be made here, than to add that they soon subsided into a general feeling of respect and admiration for the two distinguished mathematicians who, unknown to each other, had successfully treated a problem which it had previously been considered almost impossible to solve.
In November 1846 Le Verrier published, as an Appendix to the Connaissance des Temps for 1849, Recherches sur les mouvements de la Planète Herschel (dite Uranus), in which he gave a detailed account of the processes, analytical and numerical, involved in the course of his investigations, of which, previous to the telescopic discovery of the disturbing body, he had only given the particulars found in the three memoirs presented to the Academy and referred to above. It is to these Recherches that recourse must be had in order to follow Le Verrier through the various steps by which he accomplished the solution of the grand problem which added Neptune to the known great planets of the Solar System.
On the death of Arago, in 1853, Le Verrier was appointed to the direction of the Observatory at Paris, an institution which by his indomitable energy he raised from a position inferior to other principal national establishments, until he left it second to none. In 1870, in consequence of differences with the staff of the Observatory, he ceased his connection with it for a time, but on the melancholy death of Delaunay in 1872, he was reinstated, and retained the management of the institution during the rest of his life. It was while director of the Observatory of Paris that Le Verrier undertook and accomplished the immense work with which his name will be mainly associated in future times – no less than the complete revision of the planetary theories – the theories of Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus, and Neptune, and the formation of tables of their motions. On two occasions these researches, which have been well termed appalling in their magnitude, have formed the subject of addresses from the Chair of the Royal Astronomical Society, first in the year 1868, when the Gold Medal of the Society was presented to Le Verrier at the hands of Professor Pritchard for his theories and tables of Mercury, Venus, the Earth, and Mars; and again in 1876, when, during the presidency of Professor Adams, the Society's Medal was for the second time adjudged to Le Verrier for the similar investigation of the theories of the four great planets, Jupiter, Saturn, Uranus, and Neptune, and for his Tables of Jupiter and Saturn founded upon them. (The Tables of Uranus and Neptune were published at a later period.) The addresses delivered on these occasions, which, as usual, are printed in the Monthly Notices, enter into particulars of the nature and extent of Le Verrier's work in the planetary theories; Professor Adams' valuable analysis of the more intricate and laborious researches connected with the larger affording an admirable outline of Le Verrier's greater achievements. The circumstance that our late distinguished Associate's work upon the planetary theories has thus twice been the subject of detailed comment in the publications of the Society may render it unnecessary to enter into recapitulation here; but it may be useful for reference to subjoin the brief résumé as presented by Le Verrier to the Academy of Sciences at the beginning of the year 1875.
The general developments formed the object of five memoirs, presented and published in 1840, 1843, 1849, and 1855.
The formulæ relating to the secular inequalities were specially treated in the memoirs of 1840 and 1841. The same subject was taken up again, in a more general and complete form, in a work communicated to the Academy on November 11, 1872, concerning the four great planets, Jupiter, Saturn, Uranus, and Neptune.
The theory of Mercury, presented in 1843, afterwards completely revised, was definitively finished in 1859; the theory of Venus was given in 1861; that of the Sun (the Earth) in 1853 and 1858; that of Mars in 1861; the theories of Jupiter and Saturn in 1872 and 1873. The theory of Uranus, first communicated in 1846 on the occasion of the discovery of Neptune, was the subject of a new investigation, presented on November 15, 1874. Lastly, the theory of Neptune was presented to the Academy of Sciences in the first days of 1875.
These theories, and the tables constructed upon them, have been given to the world in the noble series of Annales de l'Observatoire de Paris, vols. iv. to xiv., which will remain a lasting monument to the great Astronomer.
One of the last subjects that engaged Le Verrier's attention was connected with the unexplained motion in the perihelion of the planet Mercury, to which he had pointedly referred upwards of twenty years previously, and which he considered to be due to the action of matter, in one form or another, between Mercury and the Sun; and on this point Professor Adams has remarked that "the theory of the planet has been established with so much care, and the transits of the planet across the Sun's disk furnish such accurate observations, as to leave no doubt of the reality of the phenomenon in question and the only way of accounting for it appears to be to suppose, with M. Le Verrier, the existence of several minute planets, or of a certain quantity of diffused matter circulating about the Sun within the orbit of Mercury." Le Verrier was first led to suppose that the telescope might furnish proof of the existence of at least one such minute planet when he became acquainted with the observation of Lescarbault in March 1859. In 1876, on collecting five or six observations of a similar nature, he treated them with the view to discover whether they could be attributed to the transit of a single intraMercurial body across the Sun's disk, and, with a skill almost peculiar to himself, he found that they might be represented, so far as regards the times of conjunction with the Sun, by the motion of a single planet, the heliocentric longitude of which is given by a formula, with an indeterminate, admitting however of only two values without deviating considerably from observation. The period of revolution of such a planet will be either 27.96 days or 33'02 days, according as one or other of these values is adopted. Le Verrier considered that a transit of the hypothetical planet was possible in the spring of 1877, but that no other could occur before 1885. As is known, an energetic watch was maintained upon the Sun's disk at the critical period without success.
Le Verrier's health had long been in an indifferent state, and for some six months previous to his decease he had been unable to take part in the proceedings of the Academy of Sciences. Towards the close of his life he had been greatly assisted by M. Gaillot, when from painful and depressing illness he was prevented from giving active personal superintendence to the completion of his planetary tables. To the exertions of M. Gaillot it is believed to be owing that the last sheets of the Tables of Neptune were ready a few days prior to Le Verrier's death, and that thus he was enabled to see the greatest work of his life brought to a close. Le Verrier expressed in strong terms to the writer of this notice his feeling of appreciation of the value of the services which M. Gaillot had rendered him.
The death of M. Le Verrier occurred early on the morning of September 23, 1877. He was buried on the 25th, in the Cemetery of Mont Parnasse, at Paris. The funeral cortège left the Observatory under a military escort, with muffled drums – as usual at the funeral of a Grand Officer of the Legion of Honour – proceeding by way of the Avenue de l'Observatoire and Rue Val de Grace to the Church of Saint Jacques de Haut-pas, where the religious ceremony took place in the presence of a crowded assembly. The cordons of the pall were held by M. Peligot, President of the Academy of Sciences; M. Dumas, Vice-President of the Superior Council of Public Instruction; M. Fizeau, Vice-President of the Academy and Member of the Scientific Council of the Observatory; M. Faye, President of the Bureau des Longitudes; General Morin, Vice-President of the Association Scientifique (which active institution was founded by Le Verrier); General Baron Wrede, of the Academy of Stockholm; Captain Mouchez, of the Institut; and Mr. Hind, Superintendent of the Nautical Almanac. The Marshal-President of the French Republic was represented by one of his staff, the General-Commandant of Paris; and deputations from the École Polytechnique, at which Le Verrier completed his studies, and from other institutions with which he had been connected, were also present. Discourses were pronounced at the grave at Mont Parnasse by MM. Dumas, Faye, Janssen, Tresca, and Yvon Villarceau. These éloges will be found in the Comptes Rendus.
J. R. H.
Jean Joseph Le Verrier's obituary appeared in Journal of the Royal Astronomical Society 38:4 (1878), 155-166.