Description

Early Abbe refractometer made by Zeiss about 1890 in Jena. According to one shown at The National Museum of American History, this one was made in 1890-1. Mirror is missing but it can be easily replaced with one with a 33 mm diameter. This one has number #183 engraved in cursive and shows only few signs of use.

A refractometer measures the refractive index of stuff. Ernst Abbé built his first one in 1869 and used it in his work designing lenses for the Carl Zeiss Optical Works in Jena, Germany. Zeiss began advertising Abbé refractometers in 1881.

https://americanhistory.si.edu/collections/object/nmah_1183765