The book. Let it be said, mathematics is not a masculine science. In the XVIIe century, they were already taught to young girls. Not all of them, of course. But among the Ursulines, the knowledge of numbers was considered part of the general culture. Similarly, young women of good society had to be educated. This is, moreover, about all that we know of Marie Crous: tutor to Mme.me of Caumont La Force, it had opened the aristocrat to the happiness of maths. Her date and place of birth or death, her social status and her life, the way in which she herself discovered arithmetic remain, on the other hand, unknown. Since Friday, March 24, however, his work has been accessible to the greatest number, digitized by the Mazarine library, holder of the only known copies.
Funny objects that this “abbreviated” dated in 1636 and this summary, written in 1641. In the first, she details her educational approach and provides some biographical details. Aged in her twenties, from a family « humble »she wishes to address “to the girls my companions”, as she writes in the introduction to the first book. To these sisters « exercise[ant] Arithmetic “, she intends to taste the delights of calculation in base 10. It is that at the time the units used in France appear far removed from the decimal system. Whether volume, length, weight or currency, the calculation bases adopted do not facilitate operations.
Addressed to his companions
The young mathematician made a point of popularizing the advances of the Belgian Simon Stévin (1548-1620) on the subject. And even to push them a little further. It thus creates in France the ancestor of the comma, in this case a high point which separates the unit and the first decimal. To initiate her companions, she offers conversion tables between existing units and the decimal system. It also poses problems: simple subtractions, but also more complex exercises, requiring you to compose different operations or even to master the rule of three. “If it is aimed at girls, it does not want to confine them to domestic matters”, observes the mathematician Roger Mansuy. The fields of application offered range from the beads of a necklace to the construction of a moat around a castle.
Marie Crous had not been forgotten. Since the 19the century, it appeared in the work of science historians, always very briefly, because of the lack of information about it. As for his two books, they were only listed in a single copy. Having entered Mazarin’s library by an equally unknown route, they remained at the Mazarine library, heiress to the cardinal’s collection. Well preserved under their parchment cover but not very accessible. Roger Mansuy, teacher in preparatory classes at Saint-Louis high school, asked for their digitization. Request immediately accepted by the management of the establishment. The companions, and perhaps also the companions of Marie Crous, will be able to immerse themselves in it. Hear, hear!
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