The letter was found within a copy of Voltaire’s Essai sur l’histoire universelle, tome troisième : contenant les temps depuis Charles VII roi de France jusqu’à l’empereur Charlesquint (Leipzig & Dresden, 1754), housed at the BCU Lausanne (1D 110 Armoire 46). This book contains numerous additions in a secretarial hand, themselves corrected by Voltaire, which were written on separate slips of paper and affixed to the book.