Greenough’s prism rotator
A Victorian curiosity
By Brian Davidson
The Zeiss catalogue of microscopes and accessories for 1902 includes this accessory, which it states was, “constructed in accordance with Mr Greenough’s suggestions, more especially designed to facilitate the examination, from different sides in succession, of objects so small that the control of their movements under the microscope would be difficult to accomplish by hand”.
The Rotator was intended for the observation of small opaque objects of between 0.5 and 0.3 mm diameter, such as insect eggs. The upper surface of the object is viewed directly from above, the lower side is seen by double reflection through one half of the lower prism, whilst resting on the other half. Rotation of the subject round its axis allows lateral observation of all remaining sides through the upper double-reflecting prism, which remains static, whilst the lower prism on which the object is placed, rotates through 360 degrees.
These three modes of observation can be carried out with any pair of objectives up to 6×. Greenough model stereoscopic binocular microscopes are ideal for use with this accessory, but it will also give good results with a monocular instrument. This accessory remained in production until the end of the 1930s.
Editor’s note: Brian also included a slide of the page of the Zeiss Catalogue describing and picturing the device. My scan of the slide does not do justice to the original, but I think enough remains visible for the workings of the device to be clear.