The Remarkable Vision of Robert Hooke (1635–1703)
First Observer of the Microbial World
Robert Hooke played important roles in the early development of the Royal Society of London. As Curator of Experiments of the Society, he became a pioneering microscopist, prolific inventor, astronomer, geologist, architect, and an effective surveyor of the City of London following the Great Fire of 1666. Hooke's Micrographia (1665) revealed the microscopic structures of numerous biological and inorganic objects and became an important source of information for later studies. Aside from the body of detailed observations reported and depicted in Micrographia, the Preface is in itself an extraordinary document that exhibits Hooke's fertile mind, philosophical insights, and rare ability to look into the future.
What Galileo's Sidereus Nuncias had done for the telescope and its heavenly vistas, Hooke's Micrographia now did for the microscope. Just as Galileo did not invent the telescope, neither did Hooke invent the microscope. But what he described seeing in his compound microscope awakened learned Europe to the wonderful world within. . . .
Micrographia, published by Robert Hooke in 1665, is one of the great classics of science. It was the first publication that illustrated objects as seen in a microscope, and it included the first accurate description and depiction of a microorganism, the microfungus Mucor (Figure 1). Hooke's discovery of a microorganism was made long before Antoni van Leeuwenhoek reported the existence of bacteria and other single-cell microbes. It has become clear that, contrary to conventional wisdom, Leeuwenhoek's initial microscopic observations were not made in isolation, but were based on findings and technical details in Hooke's Micrographia (Ford 1991; Gest 2004 a, 2004b,).
Hooke's description of Mucor was one of 60 detailed "Observations," many of which were of diverse biological objects such as the head of a fly, a flea, an ant, the sting of a bee, the teeth of a snail, hair, surfaces of leaves, and a thin section of cork tissue. Hooke observed that cork and other plant tissues consisted of "a great many little Boxes," for which he introduced the word cells. He estimated that there were more than 1 million cells in a square inch of cork tissue. Since [End Page 267] Hooke had broad interests in nature, he used Micrographia to speculate on a variety of topics including: "Of diamonds in flints; Of fantastical colours; On the inflection of the rays of light in the air; Of the fixt stars; Of the moon."
The Head of a Fly
The style of Hooke's writing in Micrographia is exemplified by Observation 39, "The Head of a Fly." The index entry reads:
1. All the face of a Drone-fly is nothing almost but eyes. 2. Those are of two magnitudes. 3. They are Hemispheres, and very reflective and smooth. 4. Some directed towards every quarter. 5. How the fly cleanses them. 6. Their number. 7. Their order: divers particulars observ'd in the dissecting a head. That these are very probably the eyes of the Creature; argued from several Observations and Experiments, that Crabs, Lobsters, Shrimps, seem to be water Insects, and to be framed much like Air Insects. Several Considerations about their manner of Vision.
The text of Observation 39 is almost six pages long. The following short section (slightly abbreviated) shows Hooke's literary skill, and Figure 2 exemplifies his excellent ability as a draughtsman.
I took a large grey Drone-Fly that had a large head and cutting off its head, I fix'd it with the forepart or face upon my Object Plate. . . . I found this Fly to have the biggest cluster of eyes in proportion to his head of any small kind of Fly that I have yet seen . . . the greatest part of the face, nay, of the head, was nothing else but two large and protuberant bunches . . . the surface of each of these was shaped into a multitude of small Hemispheres, plac'd in a triagonal order, that being the closest and most compacted, and in that order, rang'd over the whole surface of the eye in very lovely rows . . . which I was assured of by the regularly reflected Image of certain Objects which I mov'd to and fro between the head and the light. . . . Every one of these Hemispheres reflects as exact, regular and perfect an Image of any Object from the surface of them, as a small Ball of Quick-silver of that bigness would do . . . in each of these Hemispheres I have been able to discover a Landscape of those things which lay before my window, one thing of which was a large Tree, whose trunk and top I could plainly discover, as I could also the parts of my window, and my hand and fingers, if I held it between the Window and the Object.
Toward the end of Observation 39, Hooke says:
We may be sure that the filaments or sensitive parts of the Retina must be most exceedingly curious and minute, since the whole Picture itself is such; what must needs the component parts be of that Retina which distinguishes part of an object's Picture that must be many millions of millions less than that in a man's eye? And how exceeding curious and subtile must the component parts of the [End Page 268] medium that conveys light be, when we find the instrument made for its reception or refraction to be so exceedingly small?
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Head of a "drone-fly" (dragon-fly). According to Hooke, there were close to 14,000 hemispheres in the eye.
Source: from "Micrographia," reproduced courtesy of the Lilly Library, Indiana University, Bloomington, Indiana.