Editing Joseph-Louis Lagrange (section)

=== Paris ===
In 1786, following Frederick's death, Lagrange received similar invitations from states including Spain and [[Naples]], and he accepted the offer of [[Louis XVI of France|Louis XVI]] to move to Paris. In France he was received with every mark of distinction and special apartments in the Louvre were prepared for his reception, and he became a member of the [[French Academy of Sciences]], which later became part of the [[French Institute|Institut de France]] (1795). At the beginning of his residence in Paris, he was seized with an attack of melancholy, and even the printed copy of his ''Mécanique'' on which he had worked for a quarter of a century lay for more than two years unopened on his desk. Curiosity as to the results of the [[French Revolution]] first stirred him out of his lethargy, a curiosity which soon turned to alarm as the revolution developed.

It was about the same time, 1792, that the unaccountable sadness of his life and his timidity moved the compassion of 24-year-old Renée-Françoise-Adélaïde Le Monnier, daughter of his friend, the astronomer [[Pierre Charles Le Monnier]]. She insisted on marrying him and proved a devoted wife to whom he became warmly attached.

In September 1793, the [[Reign of Terror]] began. Under the intervention of [[Antoine Lavoisier]], who himself was by then already thrown out of the academy along with many other scholars, Lagrange was specifically exempted by name in the decree of October 1793 that ordered all foreigners to leave France. On 4 May 1794, Lavoisier and 27 other [[Tax farming|tax farmers]] were arrested and sentenced to death and guillotined on the afternoon after the trial. Lagrange said on the death of Lavoisier:

: ''It took only a moment to cause this head to fall and a hundred years will not suffice to produce its like.''<ref name="St Andrew" />

Though Lagrange had been preparing to escape from France while there was yet time, he was never in any danger; different revolutionary governments (and at a later time, [[Napoleon I of France|Napoleon]]) gave him honours and distinctions. This luckiness or safety may to some extent be due to his life attitude he expressed many years before: "''I believe that, in general, one of the first principles of every wise man is to conform strictly to the laws of the country in which he is living, even when they are unreasonable''".<ref name="St Andrew" /> A striking testimony to the respect in which he was held was shown in 1796 when the French commissary in Italy was ordered to attend in the full state on Lagrange's father and tender the congratulations of the republic on the achievements of his son, who "had done honour to all mankind by his genius, and whom it was the special glory of [[Piedmont]] to have produced". It may be added that Napoleon, when he attained power, warmly encouraged scientific studies in France, and was a liberal benefactor of them. Appointed [[Sénat conservateur|senator]] in 1799, he was the first signer of the [[Sénatus-consulte]] which in 1802 annexed his fatherland Piedmont to France.<ref name=laei/> He acquired French citizenship in consequence.<ref name=laei/> The French claimed he was a French mathematician, but the Italians continued to claim him as Italian.''<ref name="St Andrew" />

==== Units of measurement ====
Lagrange was involved in the development of the [[metric system]] of measurement in the 1790s. He was offered the presidency of the Commission for the reform of weights and measures (''[[General Conference on Weights and Measures|la Commission des Poids et Mesures]]'') when he was preparing to escape. After Lavoisier's death in 1794, it was largely Lagrange who influenced the choice of the [[metre]] and [[kilogram]] units with [[decimal]] subdivision, by the commission of 1799.<ref name="Delambre1816">{{cite book |last1=Delambre |first1=Jean Baptiste Joseph |title=Mémoires de la classe des Sciences mathématiques et physiques de l'Institut de France, Année 1812, Seconde Partie |location=Paris |publisher=Firmin Didot |date=1816 |pages=xxvii–lxxx |chapter=Notice sur la vie et les ouvrages de M. Malus, et de M. le Comte Lagrange |chapter-url=https://books.google.com/books?id=BbxeAAAAcAAJ&pg=PR1 }}</ref> Lagrange was also one of the founding members of the [[Bureau des Longitudes]] in 1795.

==== École Normale ====
In 1795, Lagrange was appointed to a mathematical chair at the newly established [[École Normale Supérieure|École Normale]], which enjoyed only a short existence of four months. His lectures there were elementary; they contain nothing of any mathematical importance, though they do provide a brief historical insight into his reason for proposing [[undecimal#Undecimal in the history of measurement|undecimal]] or Base 11 as the base number for the reformed system of weights and measures.<ref>{{cite book |last1=Lagrange |first1=Joseph-Louis |last2=Laplace |first2=Pierre-Simon |chapter=Mathématiques |title=Séances des écoles normales, recueillies par des sténographes, et revues par les professeurs. Seconde partie. Débats. Tome premier |location=Paris |publisher=L. Reynier |date=1795 |pages=3–23 |oclc=780161317}}</ref>{{rp|23}} The lectures were published because the professors had to "pledge themselves to the representatives of the people and to each other neither to read nor to repeat from memory" ["Les professeurs aux Écoles Normales ont pris, avec les Représentants du Peuple, et entr'eux l'engagement de ne point lire ou débiter de mémoire des discours écrits"<ref name="Book1">{{cite book |title=Séances des Écoles normales, recueillies par des sténographes, et revues par les professeurs. Nouvelle édition. Leçons. Tome premier |chapter=Avertissement |pages=iii–viii |location=Paris |publisher=Cercle-Social |date=1795 |oclc=490193660 }}</ref>{{rp|iii}}]. The discourses were ordered and taken down in shorthand to enable the deputies to see how the professors acquitted themselves. It was also thought the published lectures would interest a significant portion of the citizenry ["Quoique des feuilles sténographiques soient essentiellement destinées aux élèves de l'École Normale, on doit prévoir quיelles seront lues par une grande partie de la Nation"<ref name="Book1"/>{{rp|v}}].

==== École Polytechnique ====
In 1794, Lagrange was appointed professor of the [[École Polytechnique]]; and his lectures there, described by mathematicians who had the good fortune to be able to attend them, were almost perfect both in form and matter.{{Citation needed|date=February 2008}} Beginning with the merest elements, he led his hearers on until, almost unknown to themselves, they were themselves extending the bounds of the subject: above all he impressed on his pupils the advantage of always using general methods expressed in a symmetrical notation.

However, Lagrange does not seem to have been a successful teacher. [[Joseph Fourier|Fourier]], who attended his lectures in 1795, wrote:
:his voice is very feeble, at least in that he does not become heated; he has a very marked Italian accent and pronounces the ''s'' like ''z'' [...] The students, of whom the majority are incapable of appreciating him, give him little welcome, but the ''professeurs'' make amends for it.<ref>Ivor Grattan-Guinness. Convolutions in French Mathematics, 1800–1840. Birkhäuser 1990. Vol. I, p.108. [https://books.google.com/books?id=dHe00X4MDKMC&q=%22His+voice+is+very+feeble%22&pg=PA108]</ref>

==== Late years ====
[[File:Lagrange's tomb at the Pantheon.jpg|thumb|right|250px|Lagrange's tomb in the crypt of the [[Panthéon, Paris|Panthéon]]]]
In 1810, Lagrange started a thorough revision of the ''Mécanique analytique'', but he was able to complete only about two-thirds of it before his death in Paris in 1813, in 128 [[rue du Faubourg Saint-Honoré]]. Napoleon honoured him with the Grand Croix of the Ordre Impérial de la Réunion just two days before he died. He was buried that same year in the [[Panthéon]] in Paris. The inscription on his tomb reads in translation:<blockquote>JOSEPH LOUIS LAGRANGE. Senator. Count of the Empire. Grand Officer of the Legion of Honour. Grand Cross of the Imperial [[Order of the Reunion]]. Member of the Institute and the Bureau of Longitude. Born in Turin on 25&nbsp;January 1736. Died in Paris on 10&nbsp;April 1813.</blockquote>