## The History of Mathematics## Mathematics After the Middle Ages |

## What was in Joseph-Louis Lagrange’s letter to Jean le Rond d’Alembert? |

Italian-French astronomer and mathematician Comte Joseph-Louis Lagrange (1736–1813) was most known for his work in mathematical astronomy, including many functions, theories, etc. that bear his name (for example, Lagrange point, Lagrange’s equations, Lagrange’s theorem, Lagrangian function). His mentor was none other than French scientist Jean le Rond d’Alembert (1717–1783)—a physicist who expanded on Newton’s laws of motion, contributed to the field of fluid motion, described the regular changes in the Earth axis, and was the first to use partial differential equations in mathematical physics. He even had time to edit, along with French philosopher Denis Diderot (1713–1784), the *Encyclopedié,* a 17-volume encyclopedia of scientific knowledge published from 1751 to 1772.

But apparently living in the years of such mathematical enlightenment had its drawbacks. In 1781, Lagrange wrote a letter to d’Alembert about his greatest fear: that the field of mathematics had reached its limit. At that point in time, Lagrange believed everything mathematical had been discovered, uncovered, and calculated. Little did he realize that mathematics was only in its infancy.