Eye of the Beholder: Johannes Vermeer, Antoni van Leeuwenhoek, and the Reinvention of Seeing

by Laura J. Snyder

  De Graaf had been in correspondence with the Royal Society some years before sending his letter introducing Leeuwenhoek. Although the Dutch Republic was leading the way in certain scientific fields, it still had no organized scientific societies; these would arise only in the second half of the eighteenth century. Dutch natural philosophers looked to the Royal Society, as well as the Royal Academy of Sciences in France, as sources of knowledge about developments in the wider scientific community, and as channels for publicizing their own work within it. The Royal Society was a natural outlet for Leeuwenhoek’s discoveries.

  Leeuwenhoek was, at first, nervous to write to the Royal Society, and his early letters show him deferring to its fellows, showering them with honorifics and praise, yet at the same time firm in his self-confidence about his own observations. In these letters he addresses the fellows as “Heeren curiuse Lieffhebbers.” Heeren means “gentlemen,” and shows Leeuwenhoek acknowledging the loftier status of these men, many of whom were of noble family or had studied at Oxford or Cambridge. He himself was not of so lofty a social class, and must have been painfully aware of his lack of university training. We find him frequently apologizing to the Royal Society fellows for his lack of ability in Latin and other languages. Liefhebbers can be translated as “dabblers,” “amateurs,” or “cognoscenti” and was sometimes used to denote laymen in a certain area. The term was employed by Van Hoogstraten in his Inleyding to refer to art lovers without practical knowledge of artistic technique. At the time natural philosophers did not think of themselves as comprising a profession—the fellows of the Royal Society were wealthy men of leisure, or antiquarians, or other amateurs who were “dabblers” in science. Leeuwenhoek thought of himself that way as well, and was trying to connect to the fellows through this shared designation.

  Soon after Leeuwenhoek wrote his first letter to the “Heeren Lieffhebbers” of the Royal Society, Hooke received a note from Constantijn Huygens giving his positive assessment of the former haberdasher from Delft, with whom he had already been in contact.

  He is a person unlearned both in sciences and languages, but of his own nature exceedingly curious and industrious.… I trust you will not be unpleased with the confirmations of so diligent a searcher as this man is, though allways modestly submitting his experiences and conceits about them to the censure and correction of the learned.…

  Here began a fifty-year-long correspondence between Leeuwenhoek and the Royal Society of London, which would end only with Leeuwenhoek’s death in his ninety-first year. During these fifty years he would write around three hundred letters, most of them addressed to the Royal Society. Throughout this period, Leeuwenhoek recorded his observations and discoveries in letters only—he never published a book or a scientific paper. Most of his letters were published in various venues during his lifetime. About half of his letters to the Royal Society were translated into English, in whole or in part, and appeared in the Philosophical Transactions.

  Reading his letters, one gets the sense of a man in a hurry—rushing to record the exhilarating observations he has made so that he can go back and make some more. Leeuwenhoek certainly cultivated that impression, emphasizing his adherence to the Baconian empiricism of the Royal Society, often claiming that he set down his results just as he obtained then, “unarranged promiscuously as put down during my observations.” This could be one reason that Leeuwenhoek never wrote a book, unlike other scientific investigators of the period; he did not wish to take time away from making observations. His lack of academic training may have been another reason he never penned a monograph: he did not have the credentials, the patronage, or the scientific language, Latin, to bolster his writings.

  The epistolary form of Leeuwenhoek’s writings mirrored what was going on in other areas of literature in his time. The last third of the seventeenth century—just when Leeuwenhoek began writing to the Royal Society—saw the rise of the epistolary novel, in which fictional letters, instead of a third-person narrative, were used to tell a story. James Howell’s Familiar Letters, published in three volumes starting in 1645, contained fictionalized accounts of his travels abroad as letters written home. The Letters of a Portuguese Nun, purporting to tell the tale of forbidden love between a cloistered woman and a French officer, was all the rage in literary circles after it appeared in 1669. And Aphra Behn, whose portrait was painted by Hooke’s teacher Peter Lely and was recruited as a spy for the Charles II during the Second Anglo-Dutch War, had great success with her racy Love Letters between a Nobleman and His Sister, published in four volumes between 1684 and 1687.

  We cannot know whether Leeuwenhoek’s ease with this format for publishing his discoveries was related to the literature being read and discussed in educated circles around him (such as the learned members of his new wife’s family). But we know that soon, in his letters, truth would become stranger than fiction.

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  By the time Leeuwenhoek wrote his first letter to Oldenburg, microscopic studies had undergone a metamorphosis since the publication of Hooke’s Micrographia in 1665, in part because of the popularity of that book. The initial use—marveling at the wonders of tiny creatures—had evolved to the more systematic study of organic beings. Natural philosophers had begun to realize that merely looking at an insect with a microscope was not enough. It was exciting for a time to see “flies the size of an elephant,” but eventually natural philosophers yearned to know what was inside those tiny creatures. Soon after Micrographia appeared, Huygens’s friend Margaret Cavendish—who had used a microscope in the 1640s—dismissed the “art of Micrography” for not doing enough: it described only the outside of tiny animals, and did not “discover their interior, corporeal, figurative motions, and the obscure actions of Nature, or the causes which make such or such Creatures.” She had missed Odierna’s earlier efforts to meticulously open the eye of the fly to uncover the workings of its vision. But Cavendish was expressing a common disenchantment with what seemed to be the limits of the microscope. She was correct that Hooke himself was not particularly interested in looking inside organic beings, and had concentrated on looking at the outside of both organic and inorganic objects. Still, his methodical study of organic beings—and his careful cross-sectioning of the cork—heralded a new stage in microscopic research. Soon the microscope would be used the way Cavendish had hoped: to look at the “interior” of creatures, to try and discern “the causes which make” them.

  At this time Marcello Malpighi, who held the chair of practical medicine at the University of Bologna, was taking the first steps in this direction. He was using a microscope to study the structure and “textures” of various organs in the human and animal body: lungs, skin, brain, liver, and kidney. Malpighi had been influenced by his acquaintance with Giovanni Alfonso Borelli, one of the founding members of the Accademia del Cimento, a scientific society begun in Florence in 1657 by students of Galileo’s. Like the Royal Society in London, the Accademia stressed experimentation and eschewed speculation; its motto was Provando e riprovando—Test and retest. Borelli held that the operations of organic structures are caused by the action of the parts of living bodies that are not visible to the naked eye. These parts were often described as familiar machines; as Borelli put it, “The operations of animals are accomplished by mechanical causes, instruments, and procedures, that is, by the scale, the lever, the pulley, the tympanum, the wedge, the screw, and so forth.” Borelli’s view was in keeping with the time’s general mechanistic outlook.

  This mechanistic program had been kick-started by Descartes with his first publication, the Discours de la méthode in 1637, in which he outlined a plan for explaining all the physical aspects of the human body in terms of machinelike structures. Descartes’s championing of the mechanistic philosophy dates back to his meeting Isaac Beeckman in Breda in 1618. Beeckman, a mathematician, physicist, and theologian, known as a man of encyclopedic knowledge, welcomed Descartes when he arrived in Breda and became, in Descartes’s words, a “promoter�
�� of his studies (Beeckman would later sniff that he had been more like Descartes’s teacher). Like Beeckman, Descartes came to believe that the underlying cause of actions and processes observed in natural bodies were invisible tiny mechanisms throughout nature, specifically small, unobservable “corpuscles” of matter that cause natural phenomena by their contact with one another. Unlike proponents of atomism, such as Boyle, Descartes rejected the idea that there is a smallest, indivisible particle of matter; on his view, God can always divide any particle further. Descartes also rejected the view, held by atomists, that there exists a “void,” or vacuum, in which the corpuscles move. His corpuscles somehow move through other matter.

  Descartes’s mechanistic and corpuscular program was wildly influential. A widening circle of university professors and medical doctors held that the workings of the body—and its malfunctions—were to be explained in terms of the shape, arrangement, and movement of particles so small they could not be seen with the naked eye. It became common to use machine metaphors for understanding these mechanistic processes; in his later work L’Homme, published in the early 1660s, Descartes had described the human brain as a system of ropes and strings. Earlier, Kepler had said that “the heavenly machine is … a kind of clockwork.” Boyle claimed more expansively that the entire natural world is “a great piece of clock-work.” In his inaugural lecture at the University of Messina in 1662, Malpighi praised the mechanistic philosophy of Descartes as putting anatomy on a firmer footing.

  Not only properties of the body but also sense perception was described mechanistically. For instance, taste was described in terms of the contact of particles of different shapes on the tongue, much as the Roman poet Lucretius had argued in the first century BCE. Followers of Descartes, known as Cartesians, speculated about the pointed shapes of the particles making up salt and vinegar, which would hurt the tongue and cause the sharp, acidic tastes of these substances. Later, when Leeuwenhoek examined the infusion of pepper and other spices, he seems to have been looking for the jagged shape of their particles. He subsequently concluded that the pungency of pepper is due to “its sharp parts, [which] leads to stinging or wounding of the tongue.” Leeuwenhoek could have known about Cartesian mechanism either by reading the Dutch edition of Descartes’s Principia philosophiae, published in 1657, or through his conversations with Constantijn Huygens or other of his acquaintances, such as the Utrecht physician Lambert van Velthuysen, who was a staunch Cartesian.

  Some writers, however, like Nicolas Steno, complained that proponents of mechanism were not doing enough: you could not just observe a machine from the outside, but had to take it apart, in order to fully understand its workings. This led to a new program of study in human anatomy, called subtle anatomy, which focused on peering inside the body to uncover its tiniest parts, employing the microscope as needed. Steno himself would use subtle anatomy to prove that Descartes was wrong to claim that the pineal gland in the head was unique to humans (and the center of the soul); by numerous careful dissections, Steno found the gland in other animals. Johannes de Raey noted that human bodies are like buildings, in that the façade is surpassed by the skill and beauty within. When studying the human body, one must “descend into the interior, reveal the structure, nexus and spaces of the tiniest parts, observe hidden movements, and fully expose at last the causes and ingenious art of nature.” This meant the rejection of Descartes’s own scientific method of theorizing from ideas in the mind, and the acceptance of Bacon’s method of observation and experimentation. Just four years after his inaugural lecture praising Descartes, Malpighi turned against Cartesianism, denying it any role in anatomy. The only way to “come to know the structure of the kidneys,” he explained, is “not by any means” through books or pure reason, but by many dissections, and by “the patient, long-continued and varied use of the microscope.”

  Like the microscope, the telescope, and the camera obscura, dissections, by opening up human bodies, made visible the invisible. It was inevitable, perhaps, that microscopes would soon be deployed during dissections, or with parts retrieved by dissections, as physicians sought to understand the structures exposed by laying open the body. By the 1680s, microscopical descriptions and illustrations based on microscopic observations were to be found in major anatomical publications by leading Amsterdam physicians. As one writer would declare toward the end of the seventeenth century, never before had there been such a “rummaging through the human body” in search of surprising structures.

  To accommodate this new interest in dissection, Padua built the first anatomical theater for human dissection in 1594; three years later Leiden built one, followed by Delft in 1614 and Amsterdam in 1639. These “theaters,” as the name suggests, not only allowed physicians and philosophers to perform dissections of human corpses for their own research, but they also hosted public displays. Generally held around Christmas—when the cold weather ensured slower decay of the body—dissections of executed criminals became spectacles, conducted under the watchful eye of the public. Just as the Dutch Republic had put its criminals to work as a way of enabling them to be of use to society, it put the corpses of criminals “to work” so that they could be of use to anatomical science and to public education. Members of the public, who generally were charged a modest admission fee, would sit in carefully marked-out sections, and were forbidden to take any body parts home with them (these were often passed around the audience for closer inspection, and were highly sought-after trophies for cabinets of curiosity). Public anatomy became a kind of public entertainment. As this fad was described later, “nor was it spurned by gentlewomen, who, clad in sumptuous raiment, attended to the lugubrious exercises of the anatomist during the day, and later went on to gay balls and parties.”

  In Delft and the other anatomical cities in the Dutch Republic, the theaters played, to some degree, the social role played by the Royal Society in London: as a place where natural philosophers could gather and share their findings. But the theaters were also places for artists to gather. Some would be moved to paint large-scale pictures depicting anatomical lessons in action, like Michiel Jansz. van Mierevelt’s Anatomy Lesson of Dr. Willem van der Meer (1617), Rembrandt’s Anatomy Lesson of Dr. Nicolaes Tulp (1631), and De Man’s Anatomy Lesson of Cornelis ’s Gravesande (1681). Artists were drawn to the anatomy theaters not only for the demonstrations of dissections—which gave them insights into human anatomy they could not get elsewhere—but also to the collections, or small museums, attached to the theaters. The Leiden theater possessed skins of tigers, leopards, and a sloth; an anteater, the “hand of a mermaid,” and paintings, etchings, and gravures, in biblical, historical, and allegorical styles. The Delft theater displayed several skeletons of famous criminals, skeletons of a crocodile, rhinoceros, and shark and collections of plants, eggs, shells, and other curiosities from around the world. The anatomical theaters served as research centers for artists as well as for natural philosophers.

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  In Bologna’s anatomical theater, built in 1637, Malpighi was opening up humans and other creatures to reveal their inner structures, and examining these structures with his microscope. He applied the techniques of anatomical preparation to these microscopic studies: he injected colored liquids into tiny vessels, cooked, dried, and macerated excised materials, poured colored ink over dissected parts of brains, kidneys, and male genitalia, and blew gases such as carbon dioxide into vessels to expand them for easier examination. By such methods Malpighi was able to see many details in the texture of animal organs not recognized by others, including some later named for him, such as the “Malpighian bodies” of the kidney (the glomeruli, or network of capillaries), the capillaries of the frog lung, and the “Malpighian” (or “reticular”) layer in the skin. He was the first to realize that the lungs of animals and men were not merely a homogenous mass of flesh, as had previously been thought, but instead had a complex structure, composed of thin membranes shaped into vesicles that sprouted from the branches of the
trachea, like a tree. He was also the first to see capillaries in animals, thus giving an explanation for the connection between veins and arteries that had eluded the English physician William Harvey, when he had published the first correct and mostly complete description of circulation of the blood in 1628. Harvey had used only a magnifying glass, not a more powerful microscope, and his investigation of the blood and its circulation throughout the body was hampered by his lack of a stronger instrument.

  Malpighi’s work soon became known outside of Bologna. In 1667 Malpighi was contacted by Henry Oldenburg, who challenged him to participate in the scientific program of the Royal Society. Oldenburg specifically suggested a study of the silkworm (such as those that the children raised in Delft). Oldenburg was, perhaps, aware of the importance of the silkworm to the industrial life of Bologna; silk weaving was one of the mainstays of the Bologna economy in the seventeenth century. By the end of the seventeenth century there were 119 silk mills, run by waterwheels powered by the canals running through the city. By the end of the eighteenth century twelve thousand of the city’s seventy thousand residents worked in the silk industry.

  Malpighi found it easy to acquire silkworms for his examination. He began to breed large numbers of them in his home in order to examine them at every stage in their development. At each phase from chrysalis to moth, Malpighi dissected the insects and observed them both with the naked eye and under the microscope. His observations proved that the silkworm does not use lungs to breathe, but rather the tracheal system, a series of tiny holes in their skin. He also detected the reproductive organs of the moth. In 1669 he published his book on the silkworm, De bombyce, which was dedicated to the Royal Society and published under its auspices. The book was lavishly illustrated, in the tradition begun by Hooke, displaying Malpighi’s observations in careful detail.