Charles Eugène Delaunay

RAS obituary


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When the intelligence reached England that our esteemed and respected Associate, M. Delaunay, had lost his life by setting up a pleasure boat near Cherbourg, a deep and general regret was felt by his co-workers in astronomy, and especially by the Fellows of this Society, who had little more than two years previously so cordially welcomed his presence among them. Shocked at the time, as we all were, by the suddenness of the calamity which had deprived us of the services of such a distinguished astronomer, we can scarcely even yet realize the extent to which our science has been the loser by his melancholy and premature death.

Charles Eugène Delaunay was born at Lusigny, in the Department of the Aube, in the year 1816. Little is recorded of his early life; till at the usual period, he entered the Ecole Polytechnique in Paris, where he soon became one of the foremost pupils in the school Being at the head of his class in 1836, he passed that year into the Ecole des Mines. While here his vacation reports and journals on the coal seams in the valley of St. Etienne and Creusot, as well as those on the principal iron and steel works of France, gave remarkable evidence of that clarity of thought and skill in theoretical speculations, which have been so marked in all his subsequent investigations. While he was still a pupil at the Ecole des Mines, his former masters, having full confidence in the originality and power of his mathematical knowledge, proposed his appointment as teacher of geodesy at the Ecole Polytechnique. Although Delaunay was willing to accept the offer, certain objections were made by the managers as a consequence of the anomaly of a pupil from one school holding a tutorial position in the other. The council of the school, at the head of which was M. Cordier, appreciating the great talents of young Delaunay, obtained, however, a special sanction for him to accept the office. He thus obtained the position of a teacher, and afterwards of a professor, in the school from which he had only lately passed with so much honour. At a subsequent period he was also appointed a professor at the Ecole des Mines.

It was part of the curriculum of the Ecole des Mines to give a preparatory course of instruction for the benefit of engineers, both for those attached to the Corps des Mines and those connected with the mining industry of France, and thus a void was filled up in the subjects taught which were not included in the course of study at the Ecole Polytechnique. From 1845 to 1850 Delaunay was one of the most successful of the professors in this section, having classes for the teaching of descriptive geometry, stereotomy, machine drawing, analytical mechanics, and elementary physics. His manner of imparting knowledge was so clear and so well appreciated by the pupils that these classes became the most popular division of the school. In 1850, Delaunay attached himself exclusively to the Ecole des Mines and, like his predecessors, Lamé, Regnault, and Sénarmont, was appointed to successive grades in the Corps des Mines, becoming engineer-in-chief in 1858. In 1867, he was raised to the first class of his rank.

In 1841, M. Delaunay published his first memoir entitled, Sur la distinction des Maxima et des Minima dans les questions qui dépendent de la Méthode des Variations. This was followed by other important works on various subjects, such as the theory and precession of equinoxes; the theory of tides; the theory of the motion of the Moon; and elementary treatises on astronomy and mechanics and a large number of miscellaneous papers in the Comptes Rendus, in the Connaissance des Temps, and in the Journal de l' Ecole Polytechnique. His first memoirs exhibited great mathematical power and foreshadowed the scientific rank he soon attained among geometers. Fortunately, his attention was drawn to astronomical questions, in the discussion of which he became so completely engaged that his whole leisure time was devoted to this object. His treatise on the theory of the tides was an important work, and it was around this period that the question of lunar theory first began to occupy his mind. His elementary books on astronomy and mechanics are excellent textbooks for schools, in which he showed the rare talent of how to popularise science without lowering it.

Delaunay's great work on the Lunar Theory is, however, that which has made his name so universally known among us, and for which this Society had the honour of electing him one of its Associates in 1862. Few of us, however, can properly estimate the magnitude of this voluntary labour of Delaunay. Most of us know to what extent an exact acquaintance of the motion of the Moon affects questions in astronomy and navigation; and we also know that there are very great difficulties presented in the process of determining the values ​​of the coefficients of the numerous lunar inequalities. If we were to express the motion of the Moon by analytical formula, in which no sensible term is neglected, from which tables could be formed in which all empiricism was to be excluded, we should then have some faint notion of the immense work which Delaunay had undertaken to investigate. The necessity of carrying the approximation farther than had been previously done increased the labour to an enormous extent

It will be unnecessary in this very brief sketch to enter into the peculiarities of Delaunay's great work on the Lunar Theory. It was only in February, 1870, that Professor Adams presented to him, in the name of the President, the Gold Medal of this Society, as an acknowledgment of the high appreciation which is entertained for his work in this country. On that occasion, Professor Adams gave, with great minuteness, his testimony to the great value and importance of Delaunay's researches on the Lunar Theory, entering at the same time into a complete history of the subject, and pointing out in what Delaunay differed from those who had already published treatises on the theory. To this valuable address of Professor Adams, which is given in extenso in Vol. XXX., No. 4, of the Monthly Notices, anyone who wishes to acquaint himself with the details of the process adopted by Delaunay in his research is referred.

From the year 1846, M. Delaunay devoted all his available time to the carrying out of this important work. After 14 years of assiduous labour, he published in 1860 the first volume, entitled La Théorie de la Lune, forming one of the volumes of the Memoirs of the French Institute. During this interval, he published, in separate memoirs, papers on several questions relating to the theory, notably that on the secular acceleration of the mean motion of the Moon, which at this time was a subject exciting much controversy. The magnitude of even this supplementary work may be conceived from an extract from an interesting review of the state of this controversy in 1859 by the Rev. R. Main, then President of the Society "The reader who desires to see the exact expression for the acceleration arrived at by M. Delaunay must consult the work referred to, as it is too long for insertion here, consisting, as it does, of 42 terms. Thus much may be said of it, that it takes in every possible term as far as the eighth order, including those terms depending on the inclination and eccentricity of the lunar orbit; and that all the terms calculated by Mr. Adams are in exact accordance with it." In 1867, the second volume appeared in continuation of the first, completing by far the most difficult portion of the work. The third volume, of which the contents have, for the greater part, been prepared for some time, will bring this great undertaking to a conclusion as far as concerns the theory.

"This enormous labour, which has occupied M. Delaunay for nearly 20 years, has been performed by him without assistance from anyone. Indeed, from the nature of the calculations which are required, it would not have been easy to obtain any effective assistance. In order to ensure accuracy, M. Delaunay has omitted no means of verification, and he has performed all the calculations, without exception, at two separate times, with a sufficient interval between them to prevent any special risk of committing the same error twice in succession.

"The volumes before us are perfect models of orderly arrangement. Notwithstanding the great length and complication of the calculations, the whole work is arranged so that any part of it may be quickly examined with the utmost readiness by anyone who may wish to test its accuracy.

"Finally, the analytical expressions which have been obtained for the Moon's coordinates are converted into numbers, by substituting for the elements the most accurate numerical values ​​which the comparison of theory with observation has made known. The work is complete in itself; in it the very difficult and complicated problem of determining the Moon's motion is attacked by a perfectly original method, and that one as powerful and beautiful as it is new. The work has been planned with admirable skill and has been carried out with matchless perseverance. The result is an enduring scientific monument of which our age may well be proud."

M. Delaunay truly considered that the plan which he had laid down for himself would remain incomplete until the analytical expressions of the theory were reduced into the practical form of tables The preparation of lunar tables representing his theory has therefore been going on under his direction. The numerical calculations have been made for a considerable portion, those for the longitude being finished and in the printer's hands, while the remaining portion is far advanced. The Bureau des Longitudes took this part of the work under its patronage and obtained the necessary funds from the Government, so that in a few years we might have expected its completion, for it was hoped that the new duties imposed on Delaunay at the Observatory would not materially impede the progress of the calculations. But all is now in doubt. The master mind has been suddenly taken from this labour of love, and it is not yet certain whether the calculations are far enough advanced to be entrusted to other hands. May we indeed have some hope that they are left in such a condition that others can interpret them, and thus preserve our science from an irreparable loss. In any case, we can sincerely adopt the words of M. Puiseux, Member of the Bureau des Longitudes: " Quoique l'auteur ne soit plus là pour y mettre la dernière main, il ne sera sans doute pas impossible de terminer ce monument scientifique. Espérons pour la gloire de l'astronomie française, que ce service sera rendu à la science, que ce suprême hommage ne manquera pas à notre illustre confrère."

In 1870, M. Delaunay was appointed Director of the Observatory of Paris, in succession to our distinguished associate, M. Le Verrier. Installed in his new office, Delaunay was soon convinced of the importance of the numerous improvements made in the condition of the Observatory since the death of Arago; and many times he has been heard to express his adhesion to the various innovations introduced by his predecessor. He had not, however, long been resident at the Observatory when the terrible war broke out between France and Germany, which was intensified by the disasters consequent on the prolonged siege of Paris. His whole time and thoughts were now concentrated on the best means to be adopted for the preservation of the Observatory from the effects of the bombardment. All his delicate instruments were dismantled and stowed away in sheltered places, and all observations were suspended. Even all this foresight and care nearly failed, for, during the last days of the Commune, their troops took up arms against the building and grounds, which they turned into a military station. Although a few small instruments were destroyed, no very serious damage was done; but in the last moments of their power the soldiers threatened to set fire to the Observatory, making preparations to do so, when the rapid approach of the Versailles troops happily saved the building and its valuable contents from destruction. After the conclusion of peace the Observatory was soon restored to its former condition, and the usual observations were resumed.

Although France can boast of having had among its mathematicians some of the greatest astronomers, there has yet been a complete absence in that country of those numerous public and private observatories which are to be found in England and Germany, and even in Italy. No one was more sensible of this lack of means for the practical advancement of astronomy in France than Delaunay. Seeing thus the importance of an increased number of observatories in France, he, in conjunction with M. Le Verrier, made an application to the government for the pecuniary assistance which would be needed to establish a certain number of astronomical and geodetic stations in different parts of the country. These observatories were intended to be established according to a joint plan arranged by M. Delaunay and the Bureau des Longitudes We owe, also, to Delaunay the independence of the Observatory of Marseilles, which had formerly only been a branch of the Observatory of Paris, the foundation of an Observatory at Toulouse, and the project for an Observatory at Besançon.

When, in 1854, the administration of the Observatory of Paris was separated from that of the Bureau des Longitudes, several of the members of its staff, who were naturally "of the school of Arago," retired to a common residence in the Rue Nôtre Dame des Champs, where they established a small observatory. Delaunay, whose sympathies and affinities were akin to those of Mathieu and Laugier, occupied an apartment in the same house. Hence arose that undivided friendship which lasted throughout his life. It was here where he carried on most of his research; he seldom went out, except to give his accustomed lessons at the École des Mines or the Sorbonne. At five in the morning he was often at his work, never finally quitting it until late in the evening. It was while passing his life in this peaceable, and, to him, happy, manner, that he was called by the late Emperor to the control of the Observatory of Paris. He considered it to be his duty to accept the charge, but it was at the sacrifice of some peace of mind that he did so. In the early part of his directorship he often looked with sorrow on his late modest apartment, to the many hours consecrated to his research, either within its walls or at his small country residence in Champagne. Delaunay soon, however, saw that he now had a public duty to perform. He perceived that the rapid advancement of astronomy required corresponding efforts, on the part of a great national establishment like that under his direction, to meet the demand for observations suitable to the present state of science. Had his life been spared, he would no doubt have succeeded in making the Observatory the great centre of astronomy in France. Shortly before his death he remarked: "We are going to do many things; the Observatory intends to devote all its energies to the re-observation of Lalande's Catalogue; to continue the ecliptic star-charts commenced by Chacornac; to observations of double stars; and finally we are making preparations for new determinations of the longitude of Brest, Greenwich, and Neuchâtel." The observation of the minor planets during the second half of the lunation, according to the original convention agreed upon by the Astronomer Royal and M. Le Verrier, has been continued by M. Delaunay with great success, except only during the siege.

M. Delaunay had the misfortune to lose his wife a few years after their marriage, leaving an only son, Gaston Delaunay, now principal guardian of the forests of Vitry-le-François. His aged mother survived him, and his devotion to her was well known. The moment it was possible for him to leave Paris after the siege, his first thought was of his poor old mother, of whom he had heard no tidings since the investment of Paris by the Germans. He hastened to Ramerupt and in person related all his cares and anxieties and then returned to his duties of reconstruction with a lightened heart.

Delaunay was a member of several of the learned societies; he also had received the honorary degree of Doctor in Science. He was a member of the Academy of Sciences of Paris, the chair of which he had only lately filled. He was a foreign member of the Royal Society and, as we have already remarked, an Associate of the Royal Astronomical Society.

The circumstances of Delaunay's death will always remain a sad episode in the history of astronomy. In his full mental power, but needing some temporary recreation, he left the meeting of the Bureau des Longitudes on Tuesday, July 30, 1872, for the purpose of spending a few days on the coasts of Normandy, in company with his cousin, M. Millot, Controller of the Post. On Sunday, August 4, he wrote from Bayeux that his health was excellent, that he intended passing one or two days at Cherbourg, and returning to Paris on Thursday following. On Tuesday morning a telegram was received in Paris in these words: "Hier, à Cherbourg, un canot monté par quatre personnes a chaviré dans la rade. Les quatre personnes ont peri; l'une d'elles est M. Delaunay, Directeur de l'Observatoire de Paris. Son corps a été retrouvé à l'île Pelée, à cinq kilomètres de Cherbourg." Thus, with his cousin and two boatmen, our distinguished and lamented Associate suddenly met his death at the age of fifty-six, amid the regrets of the whole scientific world, and in the full powers of that gifted intellect which had so long been devoted to the successful development of some of the most important branches of mathematical astronomy.

It is a singular fact that the family of M. Delaunay have, on former occasions, been called upon to mourn the loss of relations by drowning. Delaunay himself had a natural dread of the sea, and indeed of ships and boats of all kinds. Having this great aversion for boating, he must have been enjoying a great buoyancy of health and spirits at Cherbourg to have accompanied M. Millot on this fatal excursion. His friends cannot understand how he could have prevailed upon to form one of the party, as the loss of his father and brother was ever present in his mind on an occasion of this kind. His father perished in the presence of his wife and son while bathing in an open river near Troyes; while his brother shared a similar fate some years afterwards, also while bathing, very nearly at the same spot as his father.

E. D

Charles Eugène Delaunay's obituary appeared in Journal of the Royal Astronomical Society 33:4 (1873), 203-209.