Robert Hooke's Micrographia (1665): Life Under the Microscope

Micrographia, published by the English scientist Robert Hooke in January 1665, was the first major book devoted to observations made through a microscope. Its giant engravings of a flea, a louse, a fly’s eye and other tiny things showed readers a hidden world, and its description of cork introduced the word “cell” into biology. Sponsored by the young Royal Society, it became one of the best-selling scientific books of its age.

Background: Hooke and the Royal Society

Robert Hooke (1635–1703) was born at Freshwater on the Isle of Wight, the son of a clergyman. After studying at Westminster School and Oxford, he worked as an assistant to Robert Boyle, building the air pump used in the experiments that led to Boyle’s law. In 1662 he became Curator of Experiments to the Royal Society, responsible for demonstrating new experiments at its weekly meetings.

Microscopes had existed since the early 17th century, but few people had used them systematically. The society wanted a showcase for its experimental approach. The architect and astronomer Christopher Wren had begun microscopic drawings for King Charles II, and when he moved on to other work the task passed to Hooke. From 1663 Hooke presented a series of observations to the society, which formed the core of the book.

Making the book

Hooke used a compound microscope with an objective lens, a field lens and an eyepiece, built by the London instrument maker Christopher Cock. Its images were dim and distorted, so Hooke devised a lighting arrangement: an oil lamp whose light was concentrated through a glass globe of brine and a lens onto the specimen.

Drawing what he saw was difficult. Live insects would not keep still, and the depth of focus was very shallow, so Hooke looked at each object many times under different light before producing a composite drawing. He is generally thought to have drawn most of the images himself, and they were engraved on copper plates. Hooke reported making an ant drunk with brandy so that it would stay still long enough to be observed.

The book was licensed by the Royal Society in November 1664 and published by its printers, John Martyn and James Allestry, at the start of 1665. It was a large folio volume, expensive to buy but eagerly sought.

What Micrographia contains

The book presents 60 numbered observations, most made with the microscope and a few with the telescope, illustrated by 38 engraved plates. Hooke began with man-made objects, such as the point of a needle, the edge of a razor and printed full stops, showing how rough they looked when magnified. He contrasted them with the fine structures of nature.

He went on to describe:

• Minerals and crystals: frozen urine crystals, snowflakes and the shapes of sand grains.
• Plants: moulds, mosses, the stinging hairs of nettles and the structure of charcoal and cork.
• Animals: a flea and a louse on huge fold-out plates, the compound eye of a fly, the sting of a bee, the gnat and its larva, and feathers.
• Astronomy: observations of the Moon’s craters and of stars, at the end of the book.

Hooke also used the book to set out ideas well beyond microscopy. He discussed the colours of thin films such as soap bubbles, proposed that light might travel as rapid pulses or waves, offered a theory of combustion involving a substance in the air, and argued that fossils were the remains of once-living creatures rather than tricks of nature.

The word “cell”

In Observation 18, Hooke described a thin slice of cork cut with a sharp penknife. Under the microscope it appeared “all perforated and porous”, divided into small boxes that reminded him of a honeycomb. He called these compartments “cells”, a word that then meant small rooms, such as those of monks. He even calculated that a cubic inch of cork must contain well over a thousand million of them.

Hooke was seeing the empty walls of dead plant cells, not living cells with their contents. He did not suggest that cells were the basic units of life; that theory was developed by Matthias Schleiden and Theodor Schwann in 1838–1839. But his term stuck and became one of the most important words in biology.

Reception

Micrographia was an immediate success. The diarist Samuel Pepys bought a copy in January 1665, stayed up until two in the morning reading it, and called it the most ingenious book he had ever read. Others mocked the new science: the playwright Thomas Shadwell satirised virtuosi peering at insects in The Virtuoso (1676), a figure partly modelled on Hooke.

Within months the Great Plague of London closed much of the city’s public life, but the book’s reputation spread across Europe. It inspired the Dutch draper Antonie van Leeuwenhoek, whose more powerful single-lens instruments revealed microorganisms a decade later.

Hooke after Micrographia

The book made Hooke’s name, and the following decades were the busiest of his life. In 1665 he was appointed Gresham Professor of Geometry in London, a post he held until his death, and he lived in rooms at Gresham College in the City. After the Great Fire of 1666 he became one of the surveyors appointed by the City of London to oversee rebuilding, and he worked closely with Christopher Wren on many buildings, including the Monument to the fire.

He continued to experiment on an extraordinary range of subjects. In 1678 he published the law of elasticity that bears his name, stating that the extension of a spring is proportional to the force applied. He designed clocks and watch springs, studied the motion of planets, and corresponded with Isaac Newton about the idea that gravity weakens with the square of distance. His later quarrels with Newton over priority, especially on gravitation and optics, damaged his reputation after his death, when Newton dominated the Royal Society.

Interest in Hooke revived strongly in the late 20th century. Historians now see him as one of the most inventive experimenters of his age, and Micrographia as his most lasting achievement.

The microscope after Hooke

Ironically, Hooke himself grew frustrated with the microscope. Few English scientists followed up his work systematically, and by the 1690s he complained that microscopy had been neglected and was used chiefly for amusement. The most important advances came from abroad: from the Dutch observers Leeuwenhoek and Jan Swammerdam, and the Italian anatomist Marcello Malpighi, who used the instrument to study the lungs, glands and the development of the chick embryo.

Myths and facts

• Myth: Hooke invented the microscope. Compound microscopes had existed since around the early 1600s in the Netherlands and Italy. Hooke improved their use and illumination.
• Myth: Hooke discovered living cells. He named the structures in cork, but saw only dead cell walls.
• Myth: We know what Hooke looked like. No portrait confirmed as Hooke from his lifetime is known to survive; modern images are reconstructions from written descriptions.

Timeline

• 1635, 18 July: Robert Hooke born at Freshwater, Isle of Wight.
• 1662: Hooke becomes Curator of Experiments to the Royal Society.
• 1663: Hooke begins presenting microscopic observations to the society.
• 1664, November: The Royal Society licenses publication.
• 1665, January: Micrographia published in London; Pepys reads it.
• 1676: Leeuwenhoek reports microscopic “animalcules” to the Royal Society.
• 1703, 3 March: Hooke dies in London.

Why it matters

Micrographia showed that a whole new realm of nature lay beyond the reach of the naked eye, and it made the microscope an accepted tool of science. By combining careful observation, striking images and bold theory, Hooke helped set the pattern for scientific publishing and gave biology its most basic term.