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.

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.

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' Ⓣ.

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.

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!

... all books teaching the Earth's motion and the Sun's immobility.

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.

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.

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."

Here they esteem both of us more highly than they do in Rome.

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.

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.

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.