PETROGRAPHIC MICROSCOPE
MODEL: 'NEW PETROLOGICAL' or 'DICK PETROLOGICAL'(Achromatic condenser with iris diaphragm and stops)
MAKER: JAMES SWIFT & SON
c. 1900
SERIAL NUMBER: 10829
The achromatic condenser has an iris diaphragm controlled by a knurled ring at its bottom end. An insert fits inside the bottom of this condenser and has a tiny ridge inside of its top to hold the dark field stop or oblique illumination stop which are also present. The top element of this condenser can be unscrewed to remove it and reveal the lower element.