Etienne Louis Mills, a French engineer and physicist, born in Paris June 23, 1775, died there, Feb. 23, 1812. He belonged to a distinguished family, and bis intellectual precocity manifested itself while he was at school in the composition of an epic poem and of two tragedies. At the same time he was roticient in mathematics, and passed a brilliant examination as a military engineer. In 1793 he received the rank of sub-lieutenant but as the school of Mezieres which had conferred it was closed, he enlisted as a volun-and exhibited so much talent while employed on the fortifications of Dunkirk, that he was sent as a pupil to the newlv established polytechnic school, which he left in 1796 with the grade of sub-lieutenant; and next year he entered the army as captain He d.stmjru.shed himself at the capture of Malta and of Jaffa, where he narrowly escaped losing his lift, by the plague. He was among the ear membersof the Egyptian institute, and in 1799 he was made by Kleber chief of bat-talion. shortly after his return from the Fast he married the daughter of Chancellor Koch of the German university of Giessen, whose acquaintance he had made while formerly stationed there.

In 1804 he was commissioned by Napoleon to draw up plans for the enlargement of the harbor and fortifications of Antwerp, and he subsequently superintended the reconstruction of the fort at Kehl, opposite Strasburg. In 1810 he became mayor, member of the academy, and examiner at the polytechnic school, and next year provisional director of that institution. His chief publications include a mathematical Traite d'ojjtique, first published in 1810, in which he promulgated some valuable discoveries respecting the refraction of light in transparent media; and the "Theory of Double Refraction" (Memoires presentes d Vinstitute vol. ii.), containing an account of his discoveries respecting the polarization of light, and showing that light may acquire properties identical with either of two rays yielded by refraction through Iceland spar by the process of simple reflection at a particular angle from any transparent body. This famous memoir received an academical prize at the suggestion of Laplace. He also published an "Essay on the Measurement of the Refractive Force of Opaque Bodies;" "Remarks on some new Optical Phenomena," intended to prove that two portions of light are always polarized together in opposite directions; a paper " On Phenomena accompanying Refraction and Reflection," and one "On the Axis of Refraction of Crystals".