In Micrographia, Robert Hooke described the structure of cork as seen through a microscope. He called its rows of small compartments cells, helping the term spread.

He was primarily observing cell walls left by dead plant tissue. This was a different step from later discoveries about living cells and the development of cell theory.

Microscopy

In 1663 and 1664, Hooke made his microscopic, and some astronomic, observations, which he collated in Micrographia in 1665. His book, which describes observations with microscopes and telescopes, as well as original work in biology, contains the earliest-recorded observation of a microorganism, the microfungus Mucor. Hooke coined the term "cell", suggesting a resemblance between plant structures and honeycomb cells.The hand-crafted, leather-and-gold-tooled microscope he designed and used to make the observations for Micrographia, which Christopher Cock made for him in London, is on display at the National Museum of Health and Medicine in Maryland. Hooke's work developed from that of Henry Power, who published his microscopy work in Experimental Philosophy (1663); in turn, the Dutch scientist Antonie van Leeuwenhoek went on to develop increased magnification and so reveal protozoa, blood cells, and spermatozoa.

Micrographia also contains Hooke's, or perhaps Boyle's and Hooke's, ideas on combustion. Hooke's experiments led him to conclude combustion involves a component of air, a statement with which modern scientists would agree but that was not understood widely, if at all, in the seventeenth century. He also concluded respiration and combustion involve a specific and limited component of air. According to Partington, if "Hooke had continued his experiments on combustion, it is probable that he would have discovered oxygen".

Samuel Pepys wrote of the book in his diary on 21 January 16⁠64/65⁠: "Before I went to bed I sat up till two o'clock in my chamber reading of Mr. Hooke's Microscopicall Observations, the most ingenious book that ever I read in my life".

Observations

Hooke most famously describes a fly's eye and a plant cell (where he coined that term because plant cells, which are walled, reminded him of the cells of a monastery). Known for its spectacular copperplate of the miniature world, particularly its fold-out plates of insects, the text itself reinforces the tremendous power of the new microscope. The plates of insects fold out to be larger than the large folio itself, the engraving of the louse in particular folding out to four times the size of the book. Although the book is best known for demonstrating the power of the microscope, Micrographia also describes distant planetary bodies, the wave theory of light, the organic origin of fossils, and other philosophical and scientific interests of its author.

Hooke also selected several objects of human origin; among these objects were the jagged edge of a honed razor and the point of a needle, seeming blunt under the microscope. His goal may well have been to contrast the flawed products of mankind with the perfection of nature (and hence, in the spirit of the times, of biblical creation).

Methods

In 2007, Janice Neri, a professor of art history and visual culture, studied Hooke's artistic influences and working processes using newly rediscovered notes and drawings associated with Micrographia. These materials helped trace the preparation of some of the book's images. Neri interpreted Hooke's description of his plates as schemas as evidence that he approached them as diagrams. In this reading, the pictures were tools for examining and organizing what the microscope revealed. They did more than reproduce an object's surface appearance: their arrangement helped readers understand the structures Hooke wanted them to notice.

Additionally: "Hooke often enclosed the objects he presented within a round frame, thus offering viewers an evocation of the experience of looking through the lens of a microscope."

Reception

Published under the aegis of the Royal Society, the popularity of the book helped further the society's image and mission of being England's leading scientific organization. Micrographia's illustrations of the miniature world captured the public's imagination in a radically new way; Samuel Pepys called it "the most ingenious book that ever I read in my life".