Marie Crous ( fl. 1641) was a French

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, mathematical structure, structure, space, Mathematica ...

. She is known for two publications: a 1636 study in which she contributed to the further development of

arithmetic Arithmetic is an elementary branch of mathematics that deals with numerical operations like addition, subtraction, multiplication, and division. In a wider sense, it also includes exponentiation, extraction of roots, and taking logarithms. ...

using

decimal fractions The decimal numeral system (also called the base-ten positional numeral system and denary or decanary) is the standard system for denoting integer and non-integer numbers. It is the extension to non-integer numbers (''decimal fractions'') of the ...

, and a 1641 textbook of practical arithmetic rules. She proposed the introduction of the decimal system in France as early as 1636.

Life and work

Little is known about Crous's life; the dates of her birth and death are also unclear. By her own statement, she was of modest origins. She was the tutor of Charlotte de Caumont La Force, a girl from a noble

Huguenot The Huguenots ( , ; ) are a Religious denomination, religious group of French people, French Protestants who held to the Reformed (Calvinist) tradition of Protestantism. The term, which may be derived from the name of a Swiss political leader, ...

family, and enjoyed the

patronage Patronage is the support, encouragement, privilege, or financial aid that an organization or individual bestows on another. In the history of art, art patronage refers to the support that princes, popes, and other wealthy and influential people ...

of the salonnière Madame de Combalet, the Duchess d'Aiguillion, a niece of

Cardinal Richelieu Armand Jean du Plessis, 1st Duke of Richelieu (9 September 1585 – 4 December 1642), commonly known as Cardinal Richelieu, was a Catholic Church in France, French Catholic prelate and statesman who had an outsized influence in civil and religi ...

. Crous has remained well known through two publications: * ''Advis de Marie Crous aux filles exersantes l'arithmetique: sur les dixmes ou dixiesme du sieur Stevin.'' 1636 - a study on decimals building on the work of

Simon Stevin Simon Stevin (; 1548–1620), sometimes called Stevinus, was a County_of_Flanders, Flemish mathematician, scientist and music theorist. He made various contributions in many areas of science and engineering, both theoretical and practical. He a ...

* ''Abbrégé recherché de Marie Crous. Pour tirer la solution de toutes propositions d'aritmetique, dependantes des reigles y contenuës''. 1641 - a textbook of rules of arithmetic especially for use in trade and industry. Crous's work goes beyond the common arithmetic books of her time. The ''Advis'' includes a presentation of decimal fractions, based on Simon Stevin's work ''

De Thiende ''De Thiende'', published in 1585 in the Dutch language by Simon Stevin, is remembered for extending positional notation to the use of decimals to represent fractions. A French version, ''La Disme'', was issued the same year by Stevin. Stevin intr ...

''. She introduced a change from Stevin's work: the introduction of a period (now a comma in many countries) to separate the units from the decimal part, and the

zero 0 (zero) is a number representing an empty quantity. Adding (or subtracting) 0 to any number leaves that number unchanged; in mathematical terminology, 0 is the additive identity of the integers, rational numbers, real numbers, and compl ...

to indicate that a given position is empty. The ''Abbrégé'' is a survey of arithmetic rules, including for use in mental arithmetic. Crous argues that both her books should be used in conjunction. She presented her work as study material for women and girls who wanted to study arithmetic "out of interest or necessity". The Advis is dedicated to her pupil Charlotte de Caumont La Force. The Abbrégé is dedicated to Madame de Combalet, her patroness. In the preface to the Advis, she proposed the introduction of a decimal metric system of weights and measures in France; this would not happen until the end of the eighteenth century.

References

{{DEFAULTSORT:Crous, Marie 17th-century French mathematicians French women mathematicians 17th-century French women scientists