Voltaire writes that Leibniz was known in the universe by his works and was respected in his home country. He adds that Leibniz instructed kings and enlightened the wise, concluding that he knew how to doubt. A provenance note added to the MS states that the poem was written for Pierre Soubeyran who was tasked with engraving the portrait of Leibniz that the verse would accompany. This portrait first appeared in the Mercure de France in August 1748 (p.161), but was engraved by one Gilles Edme Petit rather than Soubeyran as the note suggests.

A letter of more than 2700 words from Frederick II, King of Prussia to Voltaire discussing his literary works and philosophical ideas. Frederick opens the letter by expressing his concerns about Voltaire’s frequent ill health. He has consulted doctors who have provided a long-range diagnosis, and he asks for a full statement of Voltaire’s symptoms. He then complains that Voltaire has added no criticised the poems he sent, and encloses revisions of two poems in response to Voltaire’s critiques, with a self-deprecating note on his incurable ‘mania’ for poetry, and an expression of admiration for Voltaire’s genius in rising above his physical weakness. Frederick expresses admiration for Voltaire’s ‘Épitre sur l’Envie’ and for his tragedy Mérope, offering his views on the role of love in modern theatre, and adding a verse encomium on the diversity of Voltaire’s achievements from history to science (citing his elucidation of Newton) to tragedy. Turning from literature to philosophy, the heart of the letter is a detailed consideration of some of the defining metaphysical debates of the Age of Enlightenment. Frederick expresses his scepticism at the arguments in favour of determinism, but declares himself concinced of the principle of ‘sufficient reason’ (that a rational cause lies behind every effect, and that in this sense ‘chance is the synonym of nothing’. He therefore argues that the true determinant of human actions is reason itself, and describes the idea of the deity which he deduces from this. In the last section of the letter, Frederick expresses mock-scepticism at the reported admiration for him of the Marquise du Châtelet, mentioning that he has discussed it with Leibniz, and joking that he now considers himself a rival of Newton’s for her favours.

Voltaire writes that after leaving Paris in July he asked a young man named Delamare to give de Mairan the text on the driving forces that he had kindly lent Voltaire, adding that he does not know if the young man returned it to him. He adds that it would be happy for the young man if he had stolen it in order to learn but notes that it is a treasure that is not for his use. Voltaire writes that the day before his departure, he asked Mr Pitot if he had read the text and that he replied that he had not. From this, Voltaire concludes that in de Mairan’s academy the same thing happens as at assemblies of actors: everyone thinks only of their own role and they play is worse for it. He writes that he asked Pitot if he thought that the quantity of motion was the product of the mass by the square of the velocities and that Pitot had agreed, saying that Leibnitz and Bernoulli seemed convincing to him. However, Voltaire notes that shortly after his arrival at Cirey, Pitot sent him a letter claiming to have read de Mairan’s text, which he describes as a masterpiece, and noting that it had changed his mind on the matter. Voltaire then thanks de Mairan for the enlightenment and pleasure he gained from studying under his instruction, flattering de Mairan, and remarking that he greatly admires how de Mairan distinguishes accelerated movements which are like the square of speeds and times, from forces that are only due to speeds and times. He makes reference to three articles (Articles 22, 23, and 24) that he particularly admired.

Voltaire then asks de Mairan for his help on a problematic matter that has been occupying him for a few days. He states that it is an experiment contrary to the first foundations of catoptrics and notes that the foundation of the experiment is that one must see the object at the point of intersection of the cathetus and of the reflected ray but that his fundamental rule is, on many occasions, false. He provides a diagram to explain his findings, noting that he should see the object A at the point of intersection D but instead sees it at L, K, I, H, and G successively. He asks if this does not prove that we do not perceive distances by means of angles that are formed in our eyes, noting that he often sees the object as very close and large although the angle is small.

He ends the letter by saying that Taquet and Barrou have been unable to solve the problem he poses and asks if de Mairan would mind giving him his opinion. He adds that Gabrielle Émilie Le Tonnelier de Breteuil, marquise Du Châtelet is worthy of reading de Mairan’s work and finds that there is no one who is more made to give a taste of the truth than him. She has ordered Voltaire to assure de Mairan of his esteem and pays him he compliments.

Voltaire writes that César de Missy will no doubt accuse him of laziness, but he has been unwell and forced to take the water which has interrupted his business for some time. He writes that as a citizen of the world he takes great interest in the maxims of antimachiavellianism, but so few share his interest that he had abandonned his work entirely. He adds that he published it hoping to do some good, but only prduced money for booksellers. Voltaire sends his best to Monsieur de Nency and asks how he can get hold of nova reperta et antiqua deperdita printed recently in London with notes. He discusses his Lettres philosophiques and comments on their flaws, suggesting that they were turned upside down and truncated. He then notes that he lives in a barren country for literature as foreign newspapers are forbidden and only almanacs are printed there, remarking that the Univerdity of Louvain does not yet know of Sir Isaac Newton. He adds that Émilie du Châtelet is the only philosopher in Brabant, and that it is a pity that she prefers Leibnitz to Newton.

De Missy writes that although Voltaire’s last letter was long overdue and that he would have liked to have received it sooner, he does not accuse him of laziness. He then quotes from a poem. He adds that he almost accuses Voltaire of the opposite given his poor health. Again, he quotes from a poem. De Missy then questions whether one still studies after one’s death, concluding that at the very least one would not study for the benefit of one’s fellow citizens of the lower world, and that one could avoid the excesses of study which hasten death. He quotes again from a poem. De Missy then remarks that although he writes with the intention of slowing Voltaire’s ardor for study a litte, it is not up to him or to suppress his desire to devour the books Voltaire had asked him for. He then turns to Émilie du Châtelet and composes a poem in her honour. At the conclusion of the poem, he asks that if Voltaire finds it too frivolous to be presented to a lady then he should remove it. He concludes with a brief remark on the philosophy of Leibnitz.

Voltaire thanks Gravesande for the figure he sent him of the machine used to fix the image of the sun. He notes that he will have one made according to the design and will be freed from great embarassment because he is clumsy and has lots of trouble in his dark room with his mirrors. He remarks that the package from Gravesande also included the work he had asked for in which his adversary uses c.300 pages on the subject of some thoughts of Pascal that Voltaire had examined in less than one sheet. He goes on to provide some excerpts of quotes that the editors of Pascal’s works suppressed from print. Voltaire claims that Pascal was blighted by melancholy, stating that Leibnitz makes this claim a little harshly. Voltaire then discusses the original sin, melancholy states, and the nature of the soul.