This is a very large compound microscope of the type constructed by John Marshall circa 1720. It stands about 450 mm (about 18 inches) high. Unsigned, but almost certainly made by John Marshall, one of the leading optical instrument makers of the day. The microscope is an example of Marshall's 'New Invented Double Microscope'. Marshall first made this type of microscope in 1693, and it was first illustrated and described in J Harris - Lexicon technicum: or, an universal English dictionary of arts and sciences, London: Brown, 1704. (In the article on Microscope). The term 'double' refers to the fact that this is a compound microscope, with both an eyepiece and an objective. The instrument stands on a ball joint on an octagonal box with a drawer for accessories.
The ball and socket mounting for the stage is at the base of the square cross-sectioned pillar. It allowed some degree of inclination of the microscope. The body is supported on the pillar by a brass sleeve from which extends an arm supporting the microscope from the nosepiece; a Hevelius screw between that sleeve and another sleeve, facilitates fine focusing. The pasteboard tubes are covered with blue shagreen (outer) and vellum (inner). It is part of the collection of the late Gil Mille. Note it had no substage mirror. Originally designed for opaque objects, when transparent objects were viewed the microscope had to be turned so its axis was over the edge of a table and the object illuminated by light from below.