This brass Wilson type screw-barrel, or pocket, microscope dates from the mid-18^th century. It is unsigned and its manufacturer is unknown. It consists of a short two inch long outer brass case which is completely open at the bottom and has a small diameter hole at the top. Within this body are a number of thin brass plates kept in place by a spring. The bottom of the barrel of the microscope, which has a convex glass lens to provide illumination at the bottom, is screwed into the outer case.

The microscope comes with a number of different strength magnifiers which are attached by screwing them into to the small diameter hole at the bottom of the case. The slider, into which objects for study may be placed, is inserted between the thin brass plates where it will be held in place by the spring. To use the microscope an object is placed on the slider and placed in position between the holding plates. A magnifier is selected and screwed into the top of the case, the microscope pointed at a light source and the screw barrel adjusted until the object comes into focus.

James Wilson was a maker of optical instruments in business in Hatton Garden during the late 16^th and early 17^th centuries. He first described this type of microscope to the Royal Society in 1702 although it should be noted that, as Wilson himself acknowledged, it borrowed very heavily from the Dutch mathematician Nicolass Hartsoeker’s earlier design. Wilson probably died in the early 18^th century but his design remained popular throughout the 18^th and even into the 19^th centuries. It was produced by a large number of manufacturers and was particularly popular with botanists due to its easy portability.

Despite remaining popular with amateur naturalists into the 19^th Century the design was rendered defunct by developments in microscopy in the 1830s and eventually disappeared from production.