Hooke's Microscope

These two- and three-lens microscopes were designed and used by Robert Hooke and made by Christopher Cock, London, shortly before 1665. It was the one he used for the observations in his landmark best-seller Micrographia.

The main tube of the replica microscope on the right, from Hooke's design, is 7 inches long and 4 inches in diameter, made of leather-covered cardboard. The brass rod that it slid up and down on is 15 inches high.

Starting with Kepler's design of two bi-convex lenses, these microscopes added a field lens mounted close to the eyepiece lenses to widen the field of view. This middle lens could be removed. It was focused by moving the tube, not the specimen. This was basically the same design that Galileo had presented to Prince Federico Cesi in 1624.

In Micrographia, Hooke discussed these lenses (emphasis added):

The Microscope, which for the most part I made use of, ... was contriv'd with three Glasses; a small Object Glass, a thinner Eye Glass, and a very deep one:

This I made use of only when I had occasion to see much of an Object at once; the middle Glass conveying a very great company of radiating Pencils, which would go another way, and throwing them upon the deep Eye Glass. But when ever I had occasion to examine the small parts of a Body more accurately, I took out the middle Glass, and only made use of one Eye Glass with the Object Glass.

Three lenses just compounded the aberrations, so two were better, trading "accuracy", what we call resolution, for size.

The microscope is Hooke's own drawing in Micrographia of his microscope, "which for the most part I made use of" (emphasis added):

The Tube being for the most part not above six or seven inches long, though, by reason it had four Drawers, it could very much be lengthened, as occasion required; ...

My way for fixing both the Glass and Object to the Pedestal most conveniently was thus:

Upon one side of a round Pedestal AB, ..., was fixt a small Pillar CC,

on this was fitted a small Iron Arm D, which could be mov'd up and down, and fixt in any part of the Pillar, by means of a small Screw E;

on the end of this Arm was a small Ball fitted into a kind of socket F, made in the side of the Brass Ring G, through which the small end of the Tube was screw'd; by means of which contrivance I could place and fix the Tube in what posture I desir'd (which for many Observations was exceeding necessary) and adjusten it most exactly to any Object.

For placing the Object, I made this contrivance; upon the end of a small brass Link or Staple HH, I so fastned a round Plate II, that it might be turn'd round upon its Center K, and going pretty stiff, would stand fixt in any posture it was set;

on the side of this was fixt a small Pillar P, about three quarters of an inch high, and through the top of this was thrust a small Iron pin M, whose top just stood over the Center of the Plate;