Chapter 8

Eulogies, said an ancient authority, should be deferred until we have lost the true measure of the dead. Then we could make giants of them without any one opposing us. On the contrary, I am of opinion that biographers, especially those of academicians, ought to make all possible haste, so that every one may be represented according to his true measure, and that well-informed people may have the opportunity of rectifying the mistakes which, notwithstanding every care, almost inevitably slip into this sort of composition. I regret that our former secretaries did not adopt this rule. By deferring from year to year to analyze the scientific and political life of Bailly with their scruples, and with their usual talents, they allowed time for inconsiderateness, prejudice, and passions of every kind, to impregnate our minds with a multitude of serious errors, which have added considerably to the difficulty of my task. When I was led to form very different opinions from those that are found spread through some of the most celebrated works, on the events of the great revolution of 1789, in which our fellow-academician took an active part, I could not be so conceited as to expect to be believed on my own word. To propound my opinions then was insufficient; I had also to combat those of the historians with whom I differed. This necessity has given to the biography that I am going to read an unusual length. I solicit the kind sympathy of the assembly on this point. I hope to obtain it, I acknowledge, when I consider that my task is to analyze before you the scientific and literary claims of an illustrious colleague, to depict the uniformly noble and patriotic conduct of the first President of the National Assembly; to follow the first Mayor of Paris in all the acts of an administration, the difficulties of which appeared to be above human strength; to accompany the virtuous magistrate to the very scaffold, to unroll the mournful phases of the cruel martyrdom that he was made to undergo; to retrace, in a word, some of the greatest, some of the most terrible events of the French Revolution.

INFANCY OF BAILLY.--HIS YOUTH.--HIS LITERARY ESSAYS.--HIS MATHEMATICAL STUDIES.

John Sylvain Bailly was born at Paris in 1736. His parents were James Bailly and Cecilia Guichon.

The father of the future astronomer had charge of the king's pictures. This post had continued in the obscure but honest family of Bailly for upwards of a century.

Sylvain, while young, never quitted his paternal home. His mother would not be separated from him; it was not that she could give him the instruction required from masters in childhood, but a tenderness, allowed to run to the utmost extreme, entirely blinded her. Bailly then formed his own mind, under the eye of his parents. Nothing could be better, it seemed, than the boyhood of our brother academician, to verify the oft-repeated theory, touching the influence of imitation on the development of our faculties. Here, the result, attentively examined, would not by a great deal agree with the old hypothesis. I know not but, every thing considered, whether it would rather furnish powerful weapons to whoever would wish to maintain that, in its early habits, childhood rather seeks for contrasts.

James Bailly had an idle and light character; whilst young Sylvain from the beginning showed strong reasoning powers, and a passion for study.

The grown man felt in his own element while in noisy gayety.

But the boy loved retirement.

To the father, solitude would have been fatal; for to him life consisted in motion, sallies, witty conversations, free and easy parties, the little gay suppers of those days.

The son, on the contrary, would remain alone and quite silent for whole days. His mind sufficed to itself; he never sought the fellowship of companions of his own age. Extreme steadiness was at once his habit and his taste.

The warder of the king's pictures drew remarkably well, but did not appear to have troubled himself much with the principles of art.

His son Sylvain studied those principles deeply, and to some purpose; he became a theoretic artist of the first class, but he never could either draw or paint even moderately well.

There are few young people who would not, at some time or other, have wished to escape from the scrutinizing eyes of their parents. The contrary was the case in Bailly's family, for James used sometimes to say to his friends or to his servants, "Do not mention this peccadillo to my son. Sylvain is worth more than I am; his morals are very strict. Under the most respectful exterior, I should perceive in his manner a censure which would grieve me. I wish to avoid his tacit reproaches, even when he does not say a word."

The two characters resembled each other only in one point--in their taste for poetry, or perhaps we ought to say versification, but even here we shall perceive differences.

The father composed songs, little interludes, and farces that were acted at the _Italian Comedy_; but the son commenced at the age of sixteen by a serious work of time,--a tragedy.

This tragedy was entitled _Clothaire_. The subject, drawn from the early centuries of the French History, had led Bailly by a curious and touching coincidence to relate the tortures inflicted on a Mayor of Paris by a deluded and barbarous multitude. The work was modestly submitted to the actor Lanoue, who, although he bestowed flattering encouragement on Bailly, dissuaded him frankly from exposing _Clothaire_ to the risk of a public representation. On the advice of the comedian-author, the young poet took _Iphygenia in Tauris_ for the subject of his second composition. Such was his ardour, that by the end of three months, he had already written the last line of the fifth act of his new tragedy, and hastened to Passy, to solicit the opinion of the author of _Mahomet II_. This time Lanoue thought he perceived that his confiding young friend was not intended by nature for the drama, and he declared it to him without disguise. Bailly heard the fatal sentence with more resignation than could have been expected from a youth whose budding self-esteem received so violent a shock. He even threw his two tragedies immediately into the fire. Under similar circumstances, Fontenelle showed less docility in his youth. If the tragedy of _Aspar_ also disappeared in the flames, it was not only in consequence of the criticism of a friend; for the author went so far as to call forth the noisy judgment of the pit.

Certainly no astronomer will regret that any opinions either off-hand or well digested, on the first literary productions of Bailly, contributed to throw him into the pursuit of science. Still, for the sake of principle, it seems just to protest against the praises given to the foresight of Lanoue, to the sureness of his judgment, to the excellence of his advice. What was it in fact? A lad of sixteen or seventeen years of age, composes two tolerable tragedies, and these essays are made irrevocably to decide on his future fate. We have then forgotten that Racine had already reached the age of twenty-two, when he first appeared, producing _Theagenes and Charicles_, and the _Inimical Brothers_; that Crébillon was nearly forty years of age when he composed a tragedy on _The Death of the Sons of Brutus_, of which not a single verse has been preserved; finally, that the two first comedies of Molière, _The three rival Doctors_ and _The Schoolmaster_, are no longer known but by their titles. Let us recall to mind that reflection of Voltaire's: "It is very difficult to succeed before the age of thirty in a branch of literature that requires a knowledge of the world and of the human heart."

A happy chance showed that the sciences might open an honourable and glorious path to the discouraged poet. M. de Moncaville offered to teach him mathematics, in exchange for drawing-lessons that his son received from the warder of the king's pictures. The proposal being accepted, the progress of Sylvain Bailly in these studies was rapid and brilliant.

BAILLY BECOMES THE PUPIL OF LACAILLE.--HE IS ASSOCIATED WITH HIM IN HIS ASTRONOMICAL LABOURS.

The mathematical student soon after had one of those providential meetings which decide a young man's future fate. Mademoiselle Lejeuneux cultivated painting. It was at the house of this female artist, known afterwards as Madame La Chenaye, that Lacaille saw Bailly. The attentive, serious, and modest demeanour of the student charmed the great astronomer. He showed it in a most unequivocal manner, by offering, though so avaricious of his time, to become the guide of the future observer, and also to put him in communication with Clairaut.

It is said that from his first intercourse with Lacaille, Bailly showed a decided vocation for astronomy. This fact appears to me incontestable. At his first appearance in this line, I find him associated in the most laborious, difficult, and tiresome investigations of that great observer.

These epithets may perhaps appear extraordinary; but they will be so only to those who have learnt the science of the stars in ancient poems, either in verse or in prose.

The Chaldæans, luxuriously reclining on the perfumed terraced roofs of their houses in Babylon, under a constantly azure sky, followed with their eyes the general and majestic movements of the starry sphere; they ascertained the respective displacements of the planets, the moon, the sun; they noted the date and hour of eclipses; they sought out whether simple periods would not enable them to foretell these magnificent phenomena a long time beforehand. Thus the Chaldæans created, if I may be allowed the expression, _Contemplative Astronomy_. Their observations were neither numerous nor exact; they both made and discussed them without labour and without trouble.

Such is not, by a great deal, the position of modern astronomers. Science has felt the necessity of the celestial motions being studied in their minutest details. Theories must explain these details; it is their touchstone; it is by details that theories become confirmed or fall to the ground. Besides, in Astronomy, the most important truths, the most astonishing results, are based on the measurement of quantities of extreme minuteness. Such measures, the present bases of the science, require very fatiguing attention, infinite care, to which no learned man would bind himself, were he not sustained, and encouraged by the hope of attaining some capital determination, through an ardent and decided devotion to the subject.

The modern astronomer, really worthy of the name, must renounce the distractions of society, and even the refreshment of uninterrupted sleep. In our climates during the inclement season, the sky is almost constantly overspread by a thick curtain of clouds. Under pain of postponing by some centuries the verification of this or that theoretic point, we must watch the least clearing off, and avail ourselves of it without delay.

A favourable wind arises and dissipates the vapours in the very direction where some important phenomenon will manifest itself, and is to last only a few seconds. The astronomer, exposed to all the transitions of weather, (it is one of the conditions of accuracy,) the body painfully bent, directs the telescope of a great graduated circle in haste upon the star that he impatiently awaits. His lines for measuring are a spider's threads. If in looking he makes a mistake of half the thickness of one of these threads, the observation is good for nothing; judge what his uneasiness must be; at the critical moment, a puff of wind occasioning a vibration in the artificial light adapted to his telescope, the threads become almost invisible; the star itself, whose rays reach the eye through atmospheric strata of various density, temperature, and refrangibility, will appear to oscillate so much as to render the true position of it almost unassignable; at the very moment when extremely good definition of the object becomes indispensable to insure correctness of measures, all becomes confused, either because the eye-piece gets steamed with vapour, or that the vicinity of the very cold metal occasions an abundant secretion of tears in the eye applied to the telescope; the poor observer is then exposed to the alternative of abandoning to some other more fortunate person than himself, the ascertaining a phenomenon that will not recur during his lifetime, or introducing into the science results of problematical correctness. Finally, to complete the observation, he must read off the microscopical divisions of the graduated circle, and for what opticians call _indolent vision_ (the only sort that the ancients ever required) must substitute _strained vision_, which in a few years brings on blindness.[6]

When he has scarcely escaped from this physical and moral torture, and the astronomer wishes to know what degree of utility is deducible from his labours, he is obliged to plunge into numerical calculations of repelling length and intricacy. Some observations that have been made in less than a minute, require a whole day's work in order to be compared with the tables.

Such was the view that Lacaille, without any softening, exhibited to his young friend; such was the profession into which the adolescent poet plunged with great ardour, and without having been at all prepared for the transition.

A useful calculation constituted the first claim of our tyro to the attention of the learned world.

The year 1759 had been marked by one of those great events, the memory of which is religiously preserved in scientific history. A comet, that of 1682, had returned at the epoch foretold by Clairaut, and very nearly in the region that mathematical analysis had indicated to him. This reappearance raised comets out of the category of sublunary meteors; it gave them definitely closed curves as orbits, instead of parabolas, or even mere straight lines; attraction confined them within its immense domain; in short, these bodies ceased for ever to be liable to superstition regarding them as prognostics.

The stringency, the importance of these results, would naturally increase in proportion as the resemblance between the announced orbit and the real orbit became more evident.

This was the motive that determined so many astronomers to calculate the orbit of the comet minutely, from the observations made in 1759, throughout Europe. Bailly was one of those zealous calculators. In the present day, such a labour would scarcely deserve special mention; but we must remark that the methods at the close of the eighteenth century were far from being so perfect as those that are now in use, and that they greatly depended on the personal ability of the individual who undertook them.

Bailly resided in the Louvre. Being determined to make the theory and practice of astronomy advance together, he had an observatory established from the year 1760, at one of the windows in the upper story of the south gallery. Perhaps I may occasion surprise by giving the pompous name of _Observatory_ to the space occupied by a window, and the small number of instruments that it could contain. I admit this feeling, provided it be extended to the Royal Observatory of the epoch, to the old imposing and severe mass of stone that attracts the attention of the promenaders in the great walk of the Luxembourg. There also, the astronomers were obliged to stand in the hollow of the windows; there also they said, like Bailly: I cannot verify my quadrants either by the horizon or by the zenith, for I can neither see the horizon nor the zenith. This ought to be known, even if it should disturb the wild reveries of two or three writers, who have no scientific authority: France did not possess an observatory worthy of her, nor worthy of the science, and capable of rivalling the other observatories of Europe, until within these ten or twelve years.

The earliest observations made by Bailly, from one of the windows in the upper story of the Louvre gallery that looks out on the Pont des Arts, are dated in the beginning of 1760. The pupil of Lacaille was not yet twenty-four years old. Those observations relate to an opposition of the planet Mars. In the same year he determined the oppositions of Jupiter and of Saturn, and compared the results of his own determinations with the tables.

The subsequent year I see him associated with Lacaille in observing the transit of Venus over the sun's disk. It was an extraordinary piece of good fortune, Gentlemen, at the very commencement of his scientific life, to witness in succession two of the most interesting astronomical events: the first predicted and well established return of a comet; and one of those partial eclipses of the sun by Venus, that do not recur till after the lapse of a hundred and ten years, and from which science has deduced the indirect but exact method, without which we should still be ignorant of the fact that the sun's mean distance from our earth is thirty-eight millions of leagues.

I shall have completed the enumeration of Bailly's astronomical labours performed before he became an academician, when I have added, from observations of the comet of 1762, the calculation of its parabolic orbit; the discussion of forty-two observations of the moon by La Hire, a detailed labour destined to serve as a starting point for any person occupying himself with the lunar theory; finally, also the reduction of 515 zodiacal stars, observed by Lacaille in 1760 and 1761.

FOOTNOTE:

[6] This long list of supposed difficulties in making an exact observation is hardly worthy of a zealous astronomer. Our author shows no enthusiasm for his subject here, and ends by ascribing the whole jeremiad to Lacaille, a man of very great practical perseverance. It is to be regretted that Arago never refers to observations of his own, but constantly quotes from others, nor does he always select the best. --_Translator's Note_.

BAILLY A MEMBER OF THE ACADEMY OF SCIENCES.--HIS RESEARCHES ON JUPITER'S SATELLITES.

Bailly was named member of the Academy of Sciences the 29th January, 1763. From that moment his astronomical zeal no longer knew any bounds. The laborious life of our fellow-academician might, on occasion, be set up against a line, more fanciful than true, by which an ill-natured poet stigmatized academical honours. Certainly no one would say of Bailly, that after his election,

"Il s'endormit et ne fit qu'un somme."

"He fell asleep and made but one nap (or sum)."

On the contrary, we cannot but be surprised at the multitude of literary and scientific labours that he accomplished in a few years.

Bailly's earliest researches on Jupiter's satellites began in 1763.

The subject was happily chosen. Studying it in all its generalities, he showed himself both an indefatigable computer, a clear-sighted geometer, and an industrious and able observer. Bailly's researches on the satellites of Jupiter, will always be his first and chief claim to scientific glory. Before him, the Maraldis, the Bradleys, the Wargentins had discovered empirically some of the principal perturbations that those bodies undergo, in their revolving motions around the powerful planet that rules them; but they had not been traced up to the principles of universal attraction. The initiative honour in this respect belongs to Bailly. Nor is this honour decreased by the ulterior and considerable improvements that the science has since received; even the discoveries of Lagrange and of Laplace have left this honour intact.

The knowledge of the satellitic motions rests almost entirely on the observation of the precise moment when each of those bodies disappears, by entering into the conical shadow, which the immense opaque globe of Jupiter projects on the opposite side from the sun. In the course of discussing a multitude of these eclipses, Bailly was not long in perceiving that the computers of the Satellitic Tables worked on numerical data that were not at all comparable with each other. This seemed of little consequence previous to the birth of the theory; but, after the analytical discovery of the perturbations, it became desirable to estimate the possible errors of observation, and to suggest means for remedying them. This was the object of the very considerable work that Bailly presented to the Academy in 1771.

In this beautiful memoir, the illustrious astronomer developes the series of experiments, by the aid of which each observation may give the instant of the real disappearance of a satellite, distinguished from the instant of the apparent disappearance, whatever be the power of the telescope used, whatever be the altitude of the eclipsed body above the horizon, and consequently, whatever be the transparency of the atmospheric strata through which the phenomenon is observed, also whatever be the distance from that body to the sun, or to the planet; finally, whatever be the sensibility of the observer's sight, all which circumstances considerably influence the time of apparent disappearance. The same series of ingenious and delicate observations led the author, very curiously, to the determination of the true diameters of the satellites, that is to say, of small luminous points, which, with the telescopes then in use, showed no perceptible diameter.

I will rest contented with these general considerations; only remarking, in addition, that the diaphragms used by Bailly were not intended only to diminish the quantity of light contributing to the formation of the images, but that they considerably increase the diameter, and in a variable way, at least in the instance of stars.

Under this new aspect, it will be requisite to submit the question to a new examination.

Any geometers and astronomers who wish to know all the extent of Bailly's labours, must not content themselves with consulting the collections in the Academy of Sciences; for he published, at the beginning of 1766, a separate work under the modest title of _Essay on the Theory of Jupiter's Satellites_.

The author commences with the _Astronomical History of the Satellites_. This history contains an almost complete analysis of the discoveries by Maraldi, by Bradley, by Wargentin. The labours of Galileo and his contemporaries are given with less detail and exactness. I have thought that I ought to fill up the lacunæ, by availing myself of some very precious documents published a few years since, and which were unknown to Bailly.

But this I will do in a separate notice, free from all preconceived ideas, and free from all party spirit; I will not forget that an honest man ought not to calumniate any one, not even the agents of the Inquisition.

BAILLY'S LITERARY WORKS.--HIS BIOGRAPHIES OF CHARLES V.--OF LEIBNITZ--OF PETER CORNEILLE--OF MOLIÈRE.

When Bailly entered the Academy of Sciences, the perpetual secretary was Grandjean de Fouchy. The bad health of this estimable scholar occasioned an early vacancy to be foreseen. D'Alembert cast his views on Bailly, hinted to him the survivorship to Fouchy, and proposed to him, by way of preparing the way, to write some biographies. Bailly followed the advice of the illustrious geometer, and chose as the subject of his studies, the éloges proposed by several academies, though principally by the French Academy.