French, c.1888, engraved to the prism holder 'Nachet A Paris' the microscope eyepiece with screw micrometer stagesample stage and mirror in the original leather covered case marked 'COMPATATEUR MICHEL-LEVY' Note: The comparator was used in conjunction with The Michel-Lévy interference color chart to identify mineral composition. The Michel-Lévy interference color chart made its debut in 1888 within the pages of a Paris-published book titled Les Minéraux des Roches. Authored by Auguste Michel-Lévy (1844–1911), Part I of the book delves into the methodologies employed by mineralogists and chemists in the microscopic examination of minerals and the use of the Michel Levy Comparator. In Part 2, Michel-Lévy, in collaboration with Alf. Lacroix, presents a tabulated account of the physical and optical characteristics of rock-forming minerals. Acknowledging the contributions of predecessors such as F.A. Fouqué, his mentor and friend ("mon maître et ami"), with whom he had worked on the production of Minéralogie Micrographique; Roches éruptives Françaises (1879), featuring an exquisite atlas of 55 chromo-lithographed plates. Michel-Lévy also pays tribute to others such as Des Cloizeaux's Manuel de Mineralogie (1862), Mallard's Traité de Cristallographie (1884), DeLapparent's Cours de Minéralogie (1884), and Rosenbusch's second edition of Mikroskopische Physiographie (1885). Additionally, he acknowledges the contributions of Klement and Renard's Reactions Microchimiques (1886) and their predecessors in the realm of microchemistry. However, it is within the pages of this 1888 publication that we witness, for the first time, Michel-Lévy's "Tableau Des Biréfringences" presented in color.