**Mary Emily Sinclair** (September 27, 1878 – June 3, 1955) was an American mathematician whose research concerned
algebraic surfaces and the
calculus of variations. She was the first woman to earn a doctorate in mathematics at the
University of Chicago, and became Clark Professor of Mathematics at
Oberlin College.^{
[1]}^{
[2]}

Sinclair was born on September 27, 1878, in
Worcester, Massachusetts; she was the fourth of five children of John Elbridge Sinclair and Marietta S. Fletcher Sinclair. Her father was a mathematics professor at the
Worcester Polytechnic Institute, and also had two daughters from an earlier marriage. Her mother, originally from Worcester, taught English and modern languages at the Worcester Polytechnic Institute but stopped when her children were born. After graduating in 1896 from the Worcester Classical High School, Mary Emily Sinclair became a student at Oberlin, and as a student served as president of the Oberlin branch of the
YWCA. She graduated
Phi Beta Kappa in 1900 with an
A.B.^{
[1]}^{
[2]}

While working as a teacher at a seminary in
Hartford, Connecticut, Sinclair continued her studies through the
University of Chicago, earning a master's degree in mathematics in 1903.^{
[1]}^{
[2]} After briefly teaching at
Lake Erie College in 1903, she taught at the
University of Nebraska from 1904 through 1907, while continuing her graduate study at the University of Chicago.^{
[1]}^{
[2]} She completed her Ph.D. in 1908, with the dissertation *On a Compound Discontinuous Solution Connected with the Surface of Revolution of Minimum Area* in the
calculus of variations, supervised by
Oskar Bolza.^{
[1]}^{
[2]}^{
[3]} She became the first woman to earn a doctorate in mathematics at the University of Chicago,^{
[1]}^{
[4]} and her doctorate marked the beginning of a period in which the university gave over 50 doctorates to women through 1946, likely the most of any American university.^{
[5]}

Meanwhile, in 1907, Sinclair had taken a position as instructor at Oberlin College, where she would remain for the rest of her career, teaching there for 37 years. The next year, on receiving her doctorate, she was promoted to associate professor. Although unmarried, she adopted two children as infants in 1914 and 1915. Also in 1915, she became one of the founding members of the
Mathematical Association of America. She was promoted to professor in 1925, and became head of the mathematics department at Oberlin in 1939. In 1941 she was named Clark Professor of Mathematics. She retired in 1944, but continued to teach mathematics to US Navy students for two more years through
Berea College.^{
[1]}^{
[2]}

She returned to Oberlin in 1947, but was heavily injured in a
carjacking incident in 1950. She moved to
Belfast, Maine, in 1953, living there with her daughter-in-law, and died there on June 3, 1955.^{
[1]}

Sinclair's 1903 master's thesis was *Concerning the discriminantal surface for the quintic in the normal form: *.^{
[2]}
In it, she uses
Tschirnhaus transformations to put
quintic functions with real coefficients into the form given in the title, and uses the
discriminant, a polynomial of the coefficients , , and , to classify polynomials of this form by their numbers of real roots. Physical models of her discriminant surface were made from her design by a German company,^{
[6]} and a stone carving based on it was created in 2003 by sculptor
Helaman Ferguson.^{
[6]}^{
[7]}

- ^
^{a}^{b}^{c}^{d}^{e}^{f}^{g}^{h}Riddle, Larry (25 February 2016), "Mary Emily Sinclair",*Biographies of Women Mathematicians*, Agnes Scott College - ^
^{a}^{b}^{c}^{d}^{e}^{f}^{g}Green, Judy; LaDuke, Jeanne (2008),*Pioneering Women in American Mathematics — The Pre-1940 PhD's*, History of Mathematics, vol. 34 (1st ed.), American Mathematical Society, The London Mathematical Society, ISBN 978-0-8218-4376-5; biography on p. 559–562 of the Supplementary Material at AMS **^**Mary Emily Sinclair at the Mathematics Genealogy Project**^**Murray, Margaret A. M. (January 2009), "A Celebration of Women in Mathematics at MIT" (PDF),*Notices of the American Mathematical Society*,**56**(1): 42–47**^**Mac Lane, Saunders (1989), "Mathematics at the University of Chicago: a brief history" (PDF), in Duren, Peter; Askey, Richard A.; Merzbach, Uta C. (eds.),*A Century of Mathematics in America, Part II*, History of Mathematics, Providence, Rhode Island: American Mathematical Society, pp. 127–154, doi: 10.1080/10724117.2018.1546504, MR 1003124; see Section "Ph.D.s to Women at Chicago", pp. 144–146- ^
^{a}^{b}Top, Jaap; Weitenberg, Erik (2011), "Models of discriminant surfaces",*Bulletin of the American Mathematical Society*, New Series,**48**(1): 85–90, doi: 10.1090/S0273-0979-2010-01315-X, MR 2738907 **^**Ferguson, Helaman,*a parametric form of the quintic discriminant, very remarkable and deserves to be better known*, archived from the original on 2006-05-08