This type of instrument is known as a Wilson screw microscope. The design shown here, that is, a single-lens instrument with a screw focusing mechanism, was initially devised by the Dutch mathematician Nicolaas Hartsoeker from Campani's focusing idea and the spring mechanism used by Bonanni. The microscope is basically a magnifying glass that, by means of a thread, allows you to modify the focal length and focus on the object. In 1702 the microscope manufacturer James Wilson added the handle to use it more comfortably and popularized it, becoming known by name for this type of microscope. He also added an accessory for observations of opaque objects that had to be placed outside the barrel.
The screw or barrel microscope consists on a small cylinder with an external thread at both ends. The optics are an objective lens, in its bronze mount, screwed into one end of the body, while a condenser lens for specimen illumination is screwed into the other end. The sample to be examined is inserted through the opening in one side of the tube and is held in place by a spring inside the tube. Focusing is achieved by threading the outer tube. The dimensions of the microscope are 72 mm in height and 27 mm in diameter. It has six objectives with different focal lengths numbered from 1 to 6, five bone slides with four samples each, an ivory talc box, a tube for analize liquids and for observing opaque objects, a forceps with platform and filter, together with the necessary extension when using it. The whole set is housed in a beautiful leather goods box.
References: G. Turner, "Collecing Microscopes", pag 9, 30, 36
H. Moe, "The Story of the Microscopes", pag 70-71
G. Turner, "Great Age of the Microscope", pag 30,251-256