# François de Paule Jacquier

### Quick Info

Vitry-le-François, Champagne, France

Rome, Papal States (now Italy)

**François Jacquier**was a French 18th century mathematician who spent most of his life in the Minim Monastery in Rome. Along with Thomas Le Seur he edited a highly annotated edition of Newton's

*Principia*.

### Biography

**François Jacquier**was born in Vitry-le-François in north eastern France. His parents were Joseph Jacquier (1676-1712), a master baker, and Margueritte Desenlis (1679-1763), the daughter of a master toolmaker. Joseph and Margueritte Jacquier were married on 4 February 1698. They had four children: Hugues-Joseph, born November 1698; Anne, born in March 1700; Marie-Françoise, born in January 1706; and François, the subject of this biography, born in 1711. François never knew his father Joseph who died on 3 April 1762 the year after he was born. His eldest brother Hugues-Joseph joined the Order of Minims, an order of friars founded in 1435 by St Francis of Paola in Calabria, Italy. Jean Desenlis (born 1666), the elder brother of François

**'**mother Margueritte, joined the Order of Minims and probably influenced both Joseph and Margueritte Jacquier's sons to join the Order of Minims. We note that although the spelling of the name Jacquier is constant through generations, the name Desenlis is not, appearing also as de Senlis, Senlis, Sanly, Senly, Sanlys etc. See [30] for many more details of relations of François Jacquier.

Jacquier was taught by the Minim priest Jean Desenlis, his uncle, who quickly saw that his nephew was a talented mathematician who was interested in mathematics and science. When he was sixteen years old, Jacquier followed the example of his elder brother and uncle, and joined the Order of Minims. The Order believed in poverty, chastity, and obedience but the followers also devoted themselves to study and scholarship which suited Jacquier. He studied at the College in Vitry-le-François [7]:-

Originally from Vitry-le-françois in the province of Champagne, Father Jacquier had been in Rome since the early 1730s, when, already professed a Minim, he was sent by the superiors of his province to the College of Trinità dei Monti to continue his studies. Versed in Hebrew and Greek, a scholar of theology and the Holy Scriptures, he had shown above all an exceptional and precocious talent in scientific subjects, in which from 1734 he had had his fellow Minim, Thomas Le Seur, as a teacher.We note that Le Seur, who was born in 1703, so eight years older than Jacquier, had also studied at the College in Vitry-le-François. Jacquier had rapidly gained a high reputation for his mathematical and scientific skills and, in 1734, Cardinal Alessandro Albani consulted him about the hydraulic problems with the harbour of Ravenna and with the river Montone which joins the Ronco before entering the sea just south of Ravenna. After returning to Rome, he was appointed professor of Sacred Scripture at the

*Sacra Congregatio de Propaganda Fide*. In addition, the General Chapter of the Order of Minims in Marseille commissioned him to work on the history of the Order.

Jacquier is best known for his work as an editor and commentator on Newton's

*Principia*Ⓣ. This annotated edition, published in Geneva in three volumes in 1739, 1740 and 1742, gives Le Seur and Jacquier as the editors (listed in that order since the convention was to list the most senior first). In fact the project was suggested by the Calvinist scholar Jean Louis Calandrini, the professor of mathematics at the Academy of Geneva, and although he is not listed, he was a major contributor to the annotations. Niccolò Guicciardini writes [11]:-

As to his authorial identification, it is to be noted that Calandrini did not add his name to those of Le Seur and Jacquier on the title-page. From this, one derives the impression that he wished to achieve recognition of authorship by more oblique means. It is because of his fame and prominent position in the 'république des lettres' that he expected to be recognised as the editor of the Genevan edition of the 'Principia' Ⓣ: he did not need a mention on the title-page, but rather he was keen on being the object of grateful recognition in the Monita signed by Le Seur and Jacquier.There are natural questions regarding how Calandrini cooperated with Le Seur and Jacquier in an era when communication between cities far apart was extremely slow and difficult. It is also interesting that it was a collaboration between Catholic and Protestant scholars [11]:-

How Calandrini, Le Seur and Jacquier planned to comment the 'Principia' Ⓣ in the 1730s is not known. Unfortunately, their correspondence is lost. It may well be that Calandrini came to know about the two Minims via his cooperation with Bourguet and the 'Bibliothèque Italique', which promoted many exchanges with the literati active in the peninsula. Be that as it may, a cooperation between scholars living in two cities as distant (geographically and culturally) as Geneva and Rome does not seem the easiest or most obvious choice, but Le Seur and Jacquier were amongst the few in all of Europe who possessed the competence and the stamina to carry out the first, complete, line-by-line, commentary of Newton's 'Principia' Ⓣ.Le Seur and Jacquier fully acknowledge Calandrini's contribution, writing in the first volume:-

We do not wish to omit public evidence of our gratitude towards the illustrious Calandrini, Professor in the Academy of Geneva, very proficient in matters mathematical, who arranged that our edition of Newton's 'Principia' Ⓣ, enriched by many additions, would be readied to the elegant standard of the edition that appeared in London in the year 1726. Furthermore, that very learned man took upon himself the labour not only of checking carefully that the figures be engraved, and placed in the appropriate places, and that the typographical errors be corrected, but also of writing those elements of conic sections that we have already praised, and those things that appeared as not treated clearly enough by us, he occasionally elucidated with his own notes.Charles de Brosses (1709-1777) was a writer on history and language whose writing were used by Diderot and D'Alembert in their

*Encyclopaedia*. In 1739 he met Jacquier who was busy working at Trinità dei Monti on the annotated edition of the

*Principia*Ⓣ. In the

*Lettres Familières Écrites d'Italie*Ⓣ, de Brosses describes his encounter with Jacquier in the Trinità dei Monti [5]:-

The convent is well placed, and has a fine view; it has a garden, a good reading room, and a very pious collection of monks, who know more than what merely pertains to their profession. I made the acquaintance of one, Father Jacquier, a very able mathematician, who is working with one of his brethren on a commentary, in four quarto volumes, regarding the principles of Newton's philosophy. The earlier volumes are now being printed in Geneva. I have heard great praise of this work. You know Malebranche used to say that Newton had climbed to the top of the tower, and had taken the ladder up with him. Father Jacquier is making a new ladder in order to get to the top of that tower. I made fun of him for his ungrateful way of preferring the Newtonian method to that of Wolff, who has done so well by the Order of the Minims through his treatise 'De Minimis et Maximis' Ⓣ: foolish banter on my part!In January 1741 Jacquier and Le Seur sent the first two volumes of their edition of Newton's

*Principia*Ⓣ to the Royal Society in London. In a letter to Cromwell Mortimer, Secretary of the Royal Society, dated 9 January 1741, they explain that they were printed in Geneva since the Inquisitor would not suffer them to be printed at Rome, for fear of offending the Holy Church. This refers to an interesting aspect of Le Seur and Jacquier's annotated edition of the

*Principia*Ⓣ, namely the problem of whether the Earth orbits the Sun. The

*Principia*Ⓣ certainly presents a heliocentric solar system, yet the Roman Catholic Church at this time banned the teaching this since the

*Index*banned:-

... all books teaching the Earth's motion and the Sun's immobility.In fact this prohibition was dropped from the

*Index*in 1758 but it was certainly in place in 1739-42 when Le Seur and Jacquier's

*Principia*Ⓣ was published. They had, therefore, to make sure that their work did not end up on the

*Index*by making it clear that they were complete believers in Roman Catholic orthodoxy. They managed this with the following statement:-

Newton assumes the hypothesis of the moving earth. The author's propositions could not be explained without granting that hypothesis. Therefore we were compelled to wear an alien mask. For the rest, we profess ourselves observant of the decrees against the motion of the earth promulgated by the holy pontiffs.We note that the Royal Society was very impressed with the annotated

*Principia*Ⓣ and elected Jacquier a fellow of the Society on 10 December 1741.

Prospero Lorenzo Lambertini (1675-1758) became Pope Benedict XIV in August 1740. He was a scholar who was well disposed towards learning and impressed with the work of Le Seur and Jacquier. One of the long running problems for the Vatican had been the stability of the dome of St Peter's basilica and the new Pope tackled it. Architects had for many years argued over the solution and, in 1742, the Pope asked three mathematicians, Le Seur, Jacquier and Ruggero Boscovich, to advise on stabilising the dome. They studied the problem and produced the report

*Parere di tre mattematici sopra i dani, che si sono trovati nella cupola di S Pietro sul fine dell'anno MDCCXLII data per ordi ne di Nostro Signore Papa Benedetto XIV*Ⓣ (Rome, 1742).

This report is an interesting document for it is clearly aimed at criticising architects for lacking the necessary mathematical knowledge to properly design buildings. It begins with a description of the damage that the three mathematicians had observed during their visits to the site. In particular they give details of the numerous cracks which they observed in all parts of the building. They then compare the many faults they have observed with those observed by people in earlier times. They dispute earlier theories that attribute the damage to natural settlement and the incompetence of the masons. The mathematicians want to put the blame on the architects, not on those carrying out the architects' design. They state clearly that mathematicians would have avoided the errors made by the architects. The cracks, they say, come from natural movements in the ground, not from exceptional events such as earthquakes or lightning strikes.

The three mathematicians then devise a "system" using Newton's laws of motion and Philippe de La Hire's papers as the basis for their calculations [6]:-

The method consists of starting from theoretical knowledge then to observe its application in reality, and it is used here on several occasions, each time making the case presented more and more complex in order to gradually approach as close as possible to the real situation studied. However, it contradicts the declared organisation of their discourse, which started from observations on the ground before proposing an analysis of the problem. ... The conclusion resulting from these calculations does not fail to surprise us: the recommendation now consists of planning a doubling of the reaction forces as a precaution, "so that if, by an unforeseen accident, one part were to fail, the other would remain. Their calculations indicate the need to place a new iron circle which would prove sufficient to offset the three million pounds.The authors of [6] give the following conclusion:-

Newton's theories on the exercise of forces, and the debates at the Royal Academy of Sciences, constitutes for Jacquier and Le Seur the opportunity to prove the validity of a system which, through mathematics, claims to be universal. In their eyes, drawing inspiration from the principles of Newton, of which they published a critical edition three years earlier, with the aim of settling the interminable debates on the dome can be an important issue. In this, their approach meets the expectations of the Holy See, which wishes an indisputable solution. Their conclusion is categorical, and is, in this respect, a figure of expertise: "everything else that we have heard planned for the desired restoration seems to us superfluous, useless or harmful." Convinced of the correctness of their "system", they refuse to "review all the projects because it would be too long and useless."As one might expect, architects reacted strongly to the criticisms by Jacquier, Le Seur and Boscovich, claiming that architects understood real situations while mathematicians only understood ideal theoretical situations. Pope Benedict XIV, however, sought the advice of another mathematician, Gabriele Manfredi, in 1743. In the same year he also sought advice from Giovanni Poleni who, like Jacquier, Le Seur and Boscovich, proposed fitting large iron rings to strengthen the dome and the rings were fitted in 1748.

Jacquier visited France in 1744 writing back to Le Seur in January of that year [22]:-

Here they esteem both of us more highly than they do in Rome.He met Alexis Clairaut who gave him an enthusiastic reception and arranged for him to be elected to the Académie des Sciences. Clairaut was friendly with many of the leading scientists and mathematicians in Paris, in particular with Maupertuis and D'Alembert who Jacquier met. Clairaut was also very friendly with Voltaire and Émilie du Châtelet and Jacquier spent two months in the summer of 1744 at the Chateau de Cirey in Cirey-sur-Blaise, Haute-Marne, the home of Voltaire and Émilie du Châtelet. Jacquier liked du Châtelet's

*Fundamentals of Physics*and had arranged for an Italian translation to be made which was being used at this time by Laura Bassi. The discussions between Jacquier and du Châtelet led to her beginning her French translation of Newton's

*Principia*Ⓣ. Her two-volume translation and commentary was published in 1759 under the title

*Principes Mathématiques de la Philosophie Naturelle*Ⓣ.

King Charles-Emmanuel III of Sardinia offered Jacquier the chair of physics at the University of Turin in 1745. Cardinal Valenti, Pope Benedict XIV's secretary of state, however, wanted to keep Jacquier in Rome and offered him the chair of experimental physics at La Sapienza. This Papal University had been founded in 1303 but was only known as La Sapienza from the 1650s. In 1755 Jacquier published his Italian translation of Brook Taylor's

*New principles*, with additions, as

*Elementi di perspettiva secondo li principii di Brook Taylor, con varii aggiunti*Ⓣ.

In 1765, Philip, Duke of Parma (1720-1765), asked Jacquier and Le Seur to come Parma to educate his son Ferdinand (1751-1802). Philip died unexpectedly on 18 July 1765 in Alessandria, Italy but Jacquier and Le Seur still went to Parma teaching Ferdinand in the year 1766-67. While there they co-authored the two-volume work

*Elements du calcul integral*Ⓣ (1768) which they dedicated to Ferdinand who had become Duke of Parma following the death of his father. They write in the Preface:-

It is customary to expose in the Prefaces, the preliminary notions of the subject that must be treated. We will not enter into this in detail, and we will limit ourselves to prescribing the knowledge that we require in those who will want to read these Elements.From the Trinità dei Monti, Jacquier conducted a correspondence with many of the leading mathematicians and scientists in Europe, including d'Alembert, Clairaut, Bézout, Lalande, de l'Hôpital, Maupertuis, and Montucla. We have seen, however, that Jacquier did not spent his time completely within the Trinità dei Monti. He had many links to other leading French people in Rome and was very much a part of this society. For example the French painter Joseph-Marie Vien (1716-1809) was appointed director of the Académie de France in Rome in 1776 and he sent his sons to be taught mathematics and Latin by Jacquier. He also went to the Palazzo De Carolis, where the French embassy was situated, to teach Sophie du Puy-Montbrun, the granddaughter of the French ambassador. He also taught Felix Francois Dorothée de Berton, comte de Crillon (1748-1820).

Although we have explained in the first Chapter the principles of the Differential Calculus, we have however only done it succinctly, and as much as it was necessary to lead to the Integral Calculus. It is therefore understood that one must, before reading this work, be exercised in differential calculus, and know how to handle it with ease. It is therefore even more necessary to have thoroughly studied the finite Calculus, and to have become very familiar with its use. Finally, our readers must be perfectly educated in Elementary Geometry, Conic Sections, and have some knowledge of the general theory of curves; nor should they ignore the doctrine of sequences, as it belongs to finite calculus. We are convinced that with these aids, anyone with good understanding for Calculation and the Sciences, will be able by themselves to understand our Work, and to overcome its difficulties, without the help of any Master.

But since we already have several Treatises on the Integral Calculus, you are entitled to ask us the reason for our work, and how this work differs from the others that have appeared. Among the different Treatises that we know, some seem to us too elementary, and not very suitable for making known this material; the others are deep and contain the most beautiful discoveries of this kind; but their illustrious authors are great men, who, occupied with the glory of invention, have thought little of the benefits to those who aspire to understand them.

It is from these considerations that we attempt, in the Work that we give to the Public, to put our readers within reach of understanding what is most sublime in the Calculus, by requiring no other preparations than those which we have just indicated.

Jacquier, however, was more involved in Roman society than his religious life might suggest. For example, he frequently visited the scholarly salons in Rome, especially that of Margherita Sparapani Gentili Boccapadule (1735-1820). She was a highly educated woman who invited to her home the most cultured Italian and foreign men in Rome. Perhaps more surprising was his friendship with Giacomo Casanova. They corresponded about games of chance involving questions of probability. Their close friendship is evident, however, when Casanova's lifestyle led to him having to pawn one of his most elegant suits and Jacquier lent him money to repay the loan so that the suit would not be sold by the pawnbroker.

The Roman College was founded in Rome by Ignatius of Loyola in 1551 about ten years after the founding of the Jesuits. It continued to be run by the Jesuits but, in 1773, the Jesuit Order was suppressed. Teaching at the College was taken over by religious men of other Orders and at this time Jacquier was appointed as Professor of Mathematics.

The Pontifical Academy of Arcadia was a literary society founded in Rome in 1690. It was not unusual for men of religion to be members although most of its members were nobles or artists. Jacquier was a member and gave orations to the Society. One such talk he gave in 1780 was on the shape of the Earth. Galileo had argued that the fact that the Earth was an oblate spheroid showed that it rotated, the flattening being cause by centrifugal forces. Jacquier argued, following the Roman Catholic doctrine at that time, that God could shape the static Earth any way he wished, so he could have chose to flatten the poles. Although there is no doubt that Jacquier was a devoted Catholic, one is left to wonder if he really believed in a geocentric solar system or whether he argued for it simply because he felt obliged to follow doctrine. Pope Benedict XIV approved the publication of Galileo's

*Dialogo*Ⓣ in Padua in 1744 and removed the prohibition from the

*Index*against teaching the Earth's motion in 1758. There is no direct evidence that Jacquier in any way influenced these decisions, but there is just the possibility that he might have done so.

Jacquier continued to live at the Trinità dei Monti and Johann Wolfgang von Goethe, the poet and playwright, visited him there in January 1787 writing in his diary:-

A few days ago I visited Father Jacquier, a Franciscan, at Trinità dei Monti. He is French by birth, known for his mathematical writings, old in years, very agreeable and intelligent. He knew the best men of his time, and even spent a few months with Voltaire, who affected him greatly.

### References (show)

- G B Avanzo ,
*Elogio dei celebre P Jacquier*(G Puccinelli, Rome, 1790). - R Arianrhod,
*Seduced by Logic. Émilie Du Châtelet, Mary Somerville and the Newtonian Revolution*(Oxford University Press, Oxford, 2012). - J Bellot, François Jacquier, moine mathématicien au temps des Lumières. Interview with Gilles Montègre,
*L'Histoire*(26 June 2018).

https://www.lhistoire.fr/entretien/françois-jacquier-moine-mathématicien-au-temps-des-lumières - R Coronado,
*A World Not to Come*(Harvard University Press, 2013). - C de Brosses, Lettres Familières,
*Écrites d'Italie a Quelques Amis en 1739 et 1740*(Poulet-Malassis et de Broise, Paris, 1858). - P Dubourg Glatigny and M Le Blanc, Architecture et expertise mathématique: la contribution des Minimes Jacquier et Le Seur aux polémiques de 1742 sur la coupole de Saint-Pierre de Rome,
*Mélanges de l'école française de Rome***117**(1) (2005), 189-218. - F Favino, Minimi in "Sapienza": François Jacquier, Thomas Le Seur e il rinnovamento dell'insegnamellto scientifico allo Studium Urbis,
*Mélanges de l'École française de Rome. Italie et Méditerranée modernes et contemporaines***117**(1) (2005), 159-187. - François Jacquier,
*Prabook*(World Biographical Encyclopedia, Inc., 2021). - A M Galluzzi, P Francesco Jacquier. Un erudito nella Roma dei '700,
*Bollettino ufficiale dell'ordine dei Minimi***7**(1) (1971), 29-65. - H Gross,
*Rome in the Age of Enlightenment. The Post-Tridentine Syndrome and the Ancien Régime*(Cambridge University Press, Cambridge, 1990). - N Guicciardini, Editing Newton in Geneva and Rome: The Annotated Edition of the
*Principia*by Calandrini, Le Seur and Jacquier,*Annals of Science***72**(3) (2015), 337-380. - J L Heilbron,
*Electricity in the 17th and 18th Centuries. A Study of Early Modern Physics*(University of California Press, 1979). - R Herr,
*The Eighteenth-Century Revolution in Spain*(Princeton University Press, 1958). - F Jacquier,
*Institutiones philosophicae ad theologica potissimum accommodarae*(Venetiis, 1785). - F Jacquier,
*Elementi di perspettiva secondo li principii di Brook Taylor con varie aggiunte spettanti all'ottica, e alla geometria*(Generoso Salomoni, Rome, 1755). - D W Kurtz (ed.),
*Transits of Venus (IAU C196). New Views of the Solar System and Galaxy*(Cambridge University Press, Cambridge, 2005). - T Le Seur and F Jacquier,
*Elemens du calcul intégral*(Heritiers Monti, 1768). - G Maheut,
*François Jacquier*(Société des Sciences et Arts de Vitry-le-François, 1988). - G Maheut, Les trois mathématiciens de Vitry-le-François: Abraham de Moivre (1667-1754), François Jacquier (1711-1788), René Gateaux (1889-1914),
*Association des professeurs de mathématiques de l'enseignement*(2011).

https://www.apmep.fr/Les-trois-mathematiciens-de-Vitry - G Montègre and P Crépel,
*François Jacquier. Un savant des Lumières entre le cloître et le monde*(Presses Universitaires de Lorraine, 2018). - G Montègre, Des couvents romains foyers de science et d'érudition : l'activité des pères François Jacquier et Gabriel Fabricy, in
*La Rome des Français au temps des Lumières : capitale de l'antique et carrefour de l'Europe: 1769-1791*(École Française de Rome, 2011), 289-371. - G Montègre, Un médiateur culturel français dans la Rome des Lumières: le père François Jacquier. 1744-1788, in
*Olivier Forlin ed.), Anticléricalisme, minorités religieuses et échanges culturels entre la France et l'Italie*(L'harmattan, 2006), 181-202. - L Pepe, Tra matematica e fisica : François Jacquier in Italia e le sue Institutiones philosophicae,
*Bollettino di storia delle scienze matematiche***36**(2) (2016), 255-268. - R Pisano and P Bussotti, A Newtonian tale details on notes and proofs in the Geneva edition of Newton's 'Principia',
*Journal of the British Society for the History of Mathematics***31**(3) (2016), 160-178. - H Schlimme, Construction Knowledge in Comparison: Architects, Mathematicians and Natural Philosophers Discuss the Damage to St Peter's Dome in 1743,
*Department of Architecture, University of Cambridge*.

https://www.arct.cam.ac.uk/system/files/documents/vol-3-2853-2868-schlimme.pdf - S Stewart,
*The Ruins Lesson. Meaning and Material in Western Culture*(University of Chicago Press, 2021). - F J Swetz and S J Kolpas, Mathematical Treasure: Critical Edition of Newton's Principia,
*Convergence*(May 2019).

https://www.maa.org/press/periodicals/convergence/mathematical-treasure-critical-edition-of-newtons-principia - E Tivnan, François Jacquier, in
*The Catholic Encyclopedia*(Robert Appleton Company, New York, 1910). - E P Tivnan, François Jacquier,
*Catholic Answers*.

https://www.catholic.com/encyclopedia/francois-jacquier - M Valentin, Généalogie du R P François Jacquier,
*Société des Sciences et Arts de Vitry-le-Françoi*s**III**(1868-1869), 104-114. - P J S Whitmore,
*The Order of Minims in Seventeenth-Century France*(Springer, Netherlands, 1967).

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Honours awarded to François Jacquier

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Written by J J O'Connor and E F Robertson

Last Update July 2022

Last Update July 2022