Philosophiæ Naturalis Principia Mathematica

Philosophiæ Naturalis Principia Mathematica is the book Marie-Josèphe de la Croix studied from childhood and later mourned losing. Its importance lies not only in the knowledge she associates with it, but in the independent intellectual life it helps her imagine: a world whose motions can be described and predicted through calculation.

Early Study and Loss

Marie-Josèphe recalls learning alongside her brother, Yves de la Croix, when he was twelve. They studied Greek and Latin, read Herodotus and Galen, and turned to the work of M. Newton. Yves generally had first choice of their books, but he did not object when Marie-Josèphe took Philosophiæ Naturalis Principia Mathematica for herself or slept with it beneath her pillow. The detail makes the book part of her childhood intellectual routine as well as a closely cherished possession.

She grieves for the loss of M. Newton’s book and longs for another copy. The loss is left unexplained, but its consequence is clear: she is separated from a text she wants to consult again, even as she continues to think through the questions its ideas have opened. She wonders what M. Newton has discovered about light, the planets, and gravity during the five years since she last had access to his work.

A Method for Understanding Nature

Walking along the Green Carpet, Marie-Josèphe imagines using a few strokes of a pen and a calculation to describe a small stone’s rise and fall, then predict its effect on the next stone. In her understanding, M. Newton’s discoveries offer a way to describe not just one object in motion but the future paths of stars and planets. The book therefore stands for a method of inquiry that reaches from an ordinary stone to the largest motions she can conceive.

The method is an aspiration rather than an effortless mastery. A breeze stirs the leaves of the potted orange trees, and Marie-Josèphe considers how to predict their fluttering. She cannot yet solve the problem, but believes that time and thought may be enough. Her confidence rests in the possibility that nature can be investigated, including where its motion is less simple than the stone’s.

The Book’s Continuing Absence

Although the physical copy is gone, Philosophiæ Naturalis Principia Mathematica remains present in Marie-Josèphe’s reasoning. Freed from the convent, she feels that no one will forbid her to pursue such questions. Her response to the book’s ideas thus extends beyond remembering what she read: she imagines putting mathematical description to work herself.

The lost book also connects her intellectual hopes to an unfinished exchange with M. Newton. She considers writing to him again, recalling that he had once communicated with her and that she failed to answer. She wishes she had seen the contents of his letter. The possibility of renewed correspondence offers no resolution, but it sharpens the significance of the missing volume: Marie-Josèphe wants both access to the work and a chance to re-enter a conversation about what can be known.