Nachet Petrographic Microscope (No. 343)
Scope 343
Age:  1892
Made by: Nachet
Made in: France
scope 343 alternate
Rotating lower body
This is a large petrographic microscope introduced in 1892 by Nachet et Fils of 17, Rue Saint-Séverin, 17 Paris. It was sold as a high-end microscope for the study of mineralogy and petrography. Nachet stated that the construction of this microscope was based on the principle that "if the objective can be rotated at the same time as the object, there can be no movement of the latter in the field of vision." As such this microscope has a separate upper and lower body tube. Rotating a control knob rotates the sample, objective and Analyzer relative to the polarizer. The stage also has rotational movement, with a calibration vernier. Thus, precise rotations can be made and the resultant birefringent image can be noted. Between the upper and lower body tubes is a dovetail cutout for the insertion of a Bertrand lens (for conoscopic investigation) or a Lambda plate for crystal identification using the Michel Lévy chart. There are separate coarse and fine focus adjustments for the top and bottom body tubes.

The Analyzer is mounted on a swing arm allowing it to be moved out of position for non-PLM imaging. The Polarizer (a Nicol prism) is mounted traditionally below the stage. The mirror is mounted on an articulated arm below the Polarizer. There is a small mirror mounted on the side of the body tube next to a cutout. It is designed to illuminate the eyepiece wires obliquely. The body is supported by a large horseshoe base with a double pillar construction supporting a large compass joint. Objectives were attached using a spring-loaded mount allowing for rapid replacement. The microscope is approximately 40cm tall. "Nachet..." is engraved on the horseshoe base.

Originally this microscope came with six objectives, three eyepieces (plain, cross wires, and micrometer scale), a 1/4 wave mica slide, a Lambda plate, a quartz compensator, and three red and blue slides. The entire set came in a mahogany case. The Nachet catalog states that this microscope comes with the "highest appoval from professors Foqué, Michel Lévy, Rosenbusch, etc." The set sold originally for 1200Fr.

Microscope featured 10/2023

Sun, Dec 3, 2023