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FRANÇOIS-FÉLIX TISSERAND was born in Nuits-Saint-Georges, in the Côte-d'Or department, on January 13, 1845. After a good literary education, he entered the École Normale Supérieure in 1863. The director took pleasure, in the annual reports of the school's work, in pointing out the student Tisserand to his classmates as setting all the right examples: Tisserand combined a talent that was anticipated with a rare modesty and a sense of duty.
At Le Verrier's invitation, Tisserand joined the Paris Observatory in 1866 as an assistant astronomer. He was successively part of the meridian service, the geodetic service, of which Villarceau was head, and the equatorial service. A thesis devoted to the exposition, according to Jacobi's principles, of the method followed by Delaunay in his theory of the motion of the Moon marked Tisserand's brilliant scientific debut. Shortly after, he left with Messrs. Stephan and Rayet to observe the famous solar eclipse of August 18, 1868, on the shores of the Malacca peninsula
Tisserand was only 28 years old when he was sent to Toulouse to reorganize the observatory. He carried out this task with rare distinction. Resources were modest and staff lacking. Tisserand sensed the astronomical vocation of Messrs. Perrotin and Bigourdan, whom he won over. He established important and varied observations on the satellites of Jupiter and Saturn, shooting stars, and sunspots; several small planets were discovered.
In 1878, Tisserand succeeded Le Verrier at the Academy of Sciences; that same year, he joined the Bureau of Longitudes and was called upon to replace Liouville at the Sorbonne. From 1883, he occupied the chair of Celestial Mechanics, first as a substitute, then as successor to V. Puiseux. His duties as a professor did not prevent him from going to Martinique in 1882 to observe the transit of Venus over the Sun with Messrs. Bigourdan and Puiseux; the same phenomenon had taken him to Japan in 1874 with M. Janssen.
It was from 1883 onward that Tisserand truly took possession of himself. The duty, which was in keeping with his taste, to cover the entire cycle of celestial mechanics would push him to the execution of a major work, The Treatise on Celestial Mechanics whose purpose was to coordinate all research, to facilitate the reading of the original memoirs, in short, to expose the progress made since Laplace. Several parts of science were enriched by him with often very important conclusions, always clear and elegant. His research on the general form of expressions of perturbations, on the role of small divisors and the libration of small planets are related to his doctoral thesis. Tisserand always considered that the theory of the variation of arbitrary Lagrange, from which Delaunay's method proceeds, was sufficient to approach the most complex questions. A few pages from lessons given by the incomparable Professor V. Puiseux on this theory constituted, Tisserand liked to repeat, his best working tool. Calculations, it is true, are often complicated; but algebraic or even numerical calculations did not frighten Tisserand, who carried them through to the end with extraordinary certainty.
The article in the Astronomical Bulletin (1889) "On the Theory of the Capture of Periodic Comets" was one of the most appreciated by astronomers, and the criterion for recognizing whether or not comets are part of the same family is now known to all. It was the reading of Mr. Young's elementary work General Astronomy that prompted Tisserand to examine this theory of comet capture more precisely. This fine piece can be compared with the admirably simple and accurate notices published in the Yearbook of the Bureau of Longitudes. These carefully studied notices are found, for the most part, gathered at the end of Cosmography, published with Mr. Andoyer.
The theories of satellites captivated him most. Volume 4 of his Treatise on Celestial Mechanics shows the full part he plays in these very interesting studies, where the geometer encounters, without being condemned to daunting calculations, the most varied circumstances, including the most serious difficulty of bringing the bodies together. He was one of the first to draw the attention of astronomers to the peculiarities of the Titan-Hyperion system (The Observatory, vol. iii). He highlighted, by the power of calculation alone, the flattening of Neptune, which telescopes could not detect.
It is impossible to pass over in silence a work to which Tisserand devoted much of his time: the Astronomical Bulletin. For him, it was not only a useful working instrument, but also a means of activating the astronomical movement. By comparing the last volumes of the collection with the first, one can judge the fruitful transformation of Tisserand's mind. His authority as a scholar was strengthened, and at the same time the flexibility and breadth of his mind became ever more evident. Thus, the 1895 volume alone deals simultaneously with: shooting stars; Jupiter's new satellite; the calculation of circular orbits; a long-period inequality of the variable star Algol, the cause of which is linked to the flattening of the main star; and the speed of radial motion of nebulae; of the Sun's proper motion; and finally, of the libration of small planets.
Tisserand's appointment as director of the Paris Observatory, after the unexpected death of the late Admiral Mouchez in 1892, laid out new duties for him. No doubt he was keen to complete the principal work of his life as a scientist; but for this, he neglected no detail of the establishment's administration. He knew how to find time for everything, putting everything in its place. What a valuable guide one would have had in him, when, satisfied with having completed his treatise, he would have given the best of himself to questions of practical astronomy! His very recent study of the variations of the normal pendulum caused by variations in the barometer marked a first attempt in this direction He was not, like his predecessor, the man of bold initiatives, but to what extent he contributed as president of the Committee of the Photographic Map of the Sky, by his direction, at the same time so benevolent and so firm, to smoothing out the difficulties, to ensuring the success of the great scientific enterprise of Admiral Mouchez! It was for him a deep joy to receive the testimonies of esteem of all the astronomers gathered in Paris, last May, on the occasion of the Astrophotographic Congress.
A few months later, on the night of October 20, Tisserand was suddenly taken from the affection of his family, his friends, and his students, from the deep esteem of all. Rarely could one see such unanimity of regret around a coffin. This was because Tisserand had received as a gift, to an eminent degree, the qualities of French genius: clarity, elegance, accuracy, good sense; at the same time, people mourned the disappearance of an upright man, guided by the principles of equity and justice, simple and modest as at the beginning of his career, naturally kind, eager to reconcile everything, full of solicitude for young people beginning their scientific careers
O. CALLANDREAU.
[For the above notice the Council is indebted to M. O. Callandreau.]
At Le Verrier's invitation, Tisserand joined the Paris Observatory in 1866 as an assistant astronomer. He was successively part of the meridian service, the geodetic service, of which Villarceau was head, and the equatorial service. A thesis devoted to the exposition, according to Jacobi's principles, of the method followed by Delaunay in his theory of the motion of the Moon marked Tisserand's brilliant scientific debut. Shortly after, he left with Messrs. Stephan and Rayet to observe the famous solar eclipse of August 18, 1868, on the shores of the Malacca peninsula
Tisserand was only 28 years old when he was sent to Toulouse to reorganize the observatory. He carried out this task with rare distinction. Resources were modest and staff lacking. Tisserand sensed the astronomical vocation of Messrs. Perrotin and Bigourdan, whom he won over. He established important and varied observations on the satellites of Jupiter and Saturn, shooting stars, and sunspots; several small planets were discovered.
In 1878, Tisserand succeeded Le Verrier at the Academy of Sciences; that same year, he joined the Bureau of Longitudes and was called upon to replace Liouville at the Sorbonne. From 1883, he occupied the chair of Celestial Mechanics, first as a substitute, then as successor to V. Puiseux. His duties as a professor did not prevent him from going to Martinique in 1882 to observe the transit of Venus over the Sun with Messrs. Bigourdan and Puiseux; the same phenomenon had taken him to Japan in 1874 with M. Janssen.
It was from 1883 onward that Tisserand truly took possession of himself. The duty, which was in keeping with his taste, to cover the entire cycle of celestial mechanics would push him to the execution of a major work, The Treatise on Celestial Mechanics whose purpose was to coordinate all research, to facilitate the reading of the original memoirs, in short, to expose the progress made since Laplace. Several parts of science were enriched by him with often very important conclusions, always clear and elegant. His research on the general form of expressions of perturbations, on the role of small divisors and the libration of small planets are related to his doctoral thesis. Tisserand always considered that the theory of the variation of arbitrary Lagrange, from which Delaunay's method proceeds, was sufficient to approach the most complex questions. A few pages from lessons given by the incomparable Professor V. Puiseux on this theory constituted, Tisserand liked to repeat, his best working tool. Calculations, it is true, are often complicated; but algebraic or even numerical calculations did not frighten Tisserand, who carried them through to the end with extraordinary certainty.
The article in the Astronomical Bulletin (1889) "On the Theory of the Capture of Periodic Comets" was one of the most appreciated by astronomers, and the criterion for recognizing whether or not comets are part of the same family is now known to all. It was the reading of Mr. Young's elementary work General Astronomy that prompted Tisserand to examine this theory of comet capture more precisely. This fine piece can be compared with the admirably simple and accurate notices published in the Yearbook of the Bureau of Longitudes. These carefully studied notices are found, for the most part, gathered at the end of Cosmography, published with Mr. Andoyer.
The theories of satellites captivated him most. Volume 4 of his Treatise on Celestial Mechanics shows the full part he plays in these very interesting studies, where the geometer encounters, without being condemned to daunting calculations, the most varied circumstances, including the most serious difficulty of bringing the bodies together. He was one of the first to draw the attention of astronomers to the peculiarities of the Titan-Hyperion system (The Observatory, vol. iii). He highlighted, by the power of calculation alone, the flattening of Neptune, which telescopes could not detect.
It is impossible to pass over in silence a work to which Tisserand devoted much of his time: the Astronomical Bulletin. For him, it was not only a useful working instrument, but also a means of activating the astronomical movement. By comparing the last volumes of the collection with the first, one can judge the fruitful transformation of Tisserand's mind. His authority as a scholar was strengthened, and at the same time the flexibility and breadth of his mind became ever more evident. Thus, the 1895 volume alone deals simultaneously with: shooting stars; Jupiter's new satellite; the calculation of circular orbits; a long-period inequality of the variable star Algol, the cause of which is linked to the flattening of the main star; and the speed of radial motion of nebulae; of the Sun's proper motion; and finally, of the libration of small planets.
Tisserand's appointment as director of the Paris Observatory, after the unexpected death of the late Admiral Mouchez in 1892, laid out new duties for him. No doubt he was keen to complete the principal work of his life as a scientist; but for this, he neglected no detail of the establishment's administration. He knew how to find time for everything, putting everything in its place. What a valuable guide one would have had in him, when, satisfied with having completed his treatise, he would have given the best of himself to questions of practical astronomy! His very recent study of the variations of the normal pendulum caused by variations in the barometer marked a first attempt in this direction He was not, like his predecessor, the man of bold initiatives, but to what extent he contributed as president of the Committee of the Photographic Map of the Sky, by his direction, at the same time so benevolent and so firm, to smoothing out the difficulties, to ensuring the success of the great scientific enterprise of Admiral Mouchez! It was for him a deep joy to receive the testimonies of esteem of all the astronomers gathered in Paris, last May, on the occasion of the Astrophotographic Congress.
A few months later, on the night of October 20, Tisserand was suddenly taken from the affection of his family, his friends, and his students, from the deep esteem of all. Rarely could one see such unanimity of regret around a coffin. This was because Tisserand had received as a gift, to an eminent degree, the qualities of French genius: clarity, elegance, accuracy, good sense; at the same time, people mourned the disappearance of an upright man, guided by the principles of equity and justice, simple and modest as at the beginning of his career, naturally kind, eager to reconcile everything, full of solicitude for young people beginning their scientific careers
O. CALLANDREAU.
[For the above notice the Council is indebted to M. O. Callandreau.]
François Félix Tisserand's obituary appeared in Journal of the Royal Astronomical Society 57:4 (1897), 231-233.