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Micro polariscope

L.O.132. (old departmental catalogue number aluminium paint). NAT. PHIL. L.O.132., N.P. 671 (on white preprinted gummed label. John Browning London (inscribed on the specimen stage). MANU John Browning second half 19th century London England DES after NORREMBERG,Christian. after 1808 DES after NICOL,William,Professor. 1838 Edinburgh, Scotland. This is a Norremberg style micropolarimeter made by John Browning in about 1870. It is in the form of a simple microscope and was used to observe samples in thin section. The eyepiece holds a crossed tourmaline Nicol prism analyser.

This was a very fine instrument The incident light is reflected from a darkened silver mirror through a pile of plates to polarise it. The plates arehave a very small separation so a diffraction pattern in the form of concentric Newton's rings can be seen in the reflection. The light then passes up through a rotating glass stage with a silvered scale in four quadrants of 90 degrees. Then through the specimen under investigation and tultimately through the [tourmaline] Nicol prism, which is mounted in cork held in a rotatable ocular tube with a silvered scale again marked in four quadrants of 90 degrees. The instrument is pivoted so that natural sunlight or artificial sources could be used. The brass handled carrying case has a drawer which contains 1. A key for the lock of the case. 2. A list of specimens written in pencil on lined note paper. 3. A section of a natural crystal of sodium nitrate. 4. Three crystal of laboratory prepared lead acetate. 5. A section of sodium nitrate mounted in cork and sandwiched between two glass slides. 6.Two blue tinted spectacle or lornette lenses. Two screw for mounting the instrumewnt on a board that slots in to the case for transporting the instrument.