Compound microscope, 1715.

One of the few microscopes made by John Marshall (1663-1725) that bears a date. The bottom of the drawer is stamped with the date 1715, and bears the signature 'J Marshall, London'. The first Marshall microscopes of this type were made in 1693 and embodied many improvements on earlier instruments, such as that of Robert Hooke. These include the supporting of the body on a rigid bras arm which slides on the pillar, the ball-and-socket joint for the inclining motion placed at the foot of the pillar, and the addition of a fine adjustment which moves the arm carrying the body along the pillar. The upper part of the body slides into the lower half to focus the instrument. The optical system consists of a single-lens objective, a field-lens and an eye-lens.