Others took up this problem with gusto. A robust debate arose about whether vision was something “native,” or innate, or whether it had to be learned through experience. In 1688 John Molyneux, an Irish fellow of the Royal Society, expressed the question at issue in a letter to the English philosopher John Locke, by formulating what is now known as Molyneux’s problem. Suppose a man born blind has learned to distinguish a sphere and a cube by his sense of touch. If sight is suddenly restored to him, will he recognize the sphere and the cube solely by sight? Or would he need to touch the two shapes in order to know which is which—in order to match his new visual perception with his accustomed tactile sensations?
Molyneux’s wife had become blind after an illness in their first year of marriage, which is one reason he had become interested in such questions. Molyneux concluded that the man would not recognize the shapes by sight alone; he would need to use his sense of touch to learn by experience which visual sensations corresponded to the familiar tactile sensations of roundness or squareness. Locke agreed with Molyneux’s answer to the problem, arguing in his Essay Concerning Human Understanding (1690) that perception was a matter of acquired custom and the accumulation of knowledge. Without past experience, we would be unable to make sense of the flat patches of color on our retina; we need a means to “translate” these patches into three-dimensional pictures of the world (much as the artist needs to make us see patches of color on a flat canvas in the same way). In 1709 George Berkeley concurred, proposing in his book A New Theory of Vision that a blind man who was suddenly given sight would not be able to discern by his eyes alone what was “high or low, erect or inverted.” There was no necessary connection between the world of sight and the world of touch; experience is needed to establish a link between them.
The idea that we must learn to see gained empirical support in 1728. The English surgeon William Cheselden had invented a new way of safely removing cataracts, which in some cases were so thick that they caused blindness or near blindness. Cheselden operated on a thirteen-year-old boy who had been born blind. After the surgery, the boy was able to see for the first time. Cheselden reported that the boy, who was quite intelligent, found even the simplest visual perceptions difficult. Cheselden recorded that, “when he first saw, he was so far from making any judgements about distances, that he thought all objects whatever touched his eyes … he knew not the shape of anything, nor any one thing from another, however different in shape or magnitude.” The boy had to learn how to make sense of the multiplicity of impressions he received through his newly functioning eyes. The experience he required involved touching the objects he was able to see for the first time, “feeling” their visual characteristics so that he could match them with their tactile properties.
The boy had a particularly difficult time understanding that paintings represented objects in three-dimensional space. As Cheselden related, the boy thought that paintings were only surfaces painted with random shapes and colors. Once the boy realized that the colored surfaces were paintings, he touched them and was further confused by their use of perspective. “Expecting the pictures would feel like the things they represented [he] was amazed when he found those parts, which by their light and shadow appeared now round and uneven, felt flat like the rest and asked, which was the lying sense, feeling or seeing?” After his experience treating the boy, Cheselden came to believe that we learn to see by interacting with the world around us. From 1728 on, his case study was frequently cited in discussions of the Molyneux problem.
If we need to learn how to see the world around us with our eyes, how much more must there be to learn when we use a telescope or, especially, a microscope, to see! The modern-day philosopher Ian Hacking has argued that we do not see through a microscope, but with one, just as we don’t see through our eyes, exactly, but with them. Learning to see with a device like a microscope requires interaction with the microscopic world, not only by repeated viewing with a microscope but by dissecting and manipulating the specimens being observed with it. We know we are seeing the microscopic structures of an insect’s body because we can dissect them, move them around, change their color with the use of dye, and make other interventions. Hacking’s claim is reminiscent of Molyneux’s that we learn shapes by touching them. Interestingly, three years before setting out this problem in the letter to Locke, John Molyneux had visited Leeuwenhoek in Delft with his brother Thomas, in order to examine his microscopes. It is likely that the episode—which caused Molyneux to realize how much training and experience were required to see with the device—sparked his thoughts about how hard it is to see with a different kind of optical instrument: our eyes. After all, the new optical instruments were often compared to the human eye, suggesting that the eye itself was an optical device.
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Even before the philosophers began debating the difficulty of learning to see, natural philosophers grappled with it every time they looked through their instruments. It is not surprising that the debate over whether we must learn to see with our eyes arose at the very time that natural philosophers were struggling to see with their new optical devices. The difficulty with using microscopes and telescopes forced people to realize that sight does not just happen—that it is something we must learn.
Galileo, for example, had to admit to the public that seeing through a telescope was complicated. Those trying to repeat his observations were often flummoxed—sometimes even when Galileo himself set up his own telescope and pointed it in the right direction for them. The physical act of using a telescope itself introduced problems, as Galileo cautioned an eager would-be observer:
The instrument must be held firm, and hence it is good, in order to escape the shaking of the hand that arises from the motion of the arteries and from respiration itself, to fix the tube in some stable place. The glasses should be kept very clear and clean by means of a cloth, or else they become fogged by the breath, humid or foggy air, or by the vapor itself which evaporates from the eye, especially when it is warm.
Even if the viewer could somehow avoid the shaking of his hand holding the telescope caused by the circulation of his own blood, and keep the outside humidity from fogging up the lens, he would still have to contend with the very vapors coming off his eyeball! Leeuwenhoek’s microscopes, with their single lenses held up to the sky “like a telescope,” suffered the same problems—though it was even more difficult for Leeuwenhoek, as he had to contend with keeping the specimen in the right spot for viewing, whereas for Galileo the slow-moving celestial bodies took care of that for him. The double lens tripod-style microscope, known to many of us from our high school science classes, came to dominate in the nineteenth century mainly because of its stability and ease of keeping a specimen in proper place for being observed with the lens (as well as the ease of taking notes while viewing, without having to put the whole contraption down first).
Learning to see with a microscope also involved navigating the range of optical defects plaguing the images viewed through lenses. The true appearance of structures often remained elusive. Robert Hooke would complain that “of these kinds of Objects [that is, those seen with a microscope] there is much more difficulty to discover the true shape, than of those visible to the naked eye, the same Object seeming quite differing, in one position to the Light, from what it really is, and may be discovered in another.” He had observed this himself, while studying the compound eye of the fly: “In one kind of light [the eyes] appear almost like a Lattice, drilled through with abundance of small bodies.… In the sunshine they look like a Surface cover’d with golden Nails; in another posture, like a surface covered with pyramids, in another, with Cones.”
Such defects in optical instruments were caused by the optical problems inherent to the lenses available at the time. Because of the spherical shape of lenses, straight lines at the margins of the field of light appear curved when viewed through a lens; a spherical surface does not focus precisely over its whole surface resulting in an image of uneve
n sharpness and distorted shapes near the edges. This distorts the apparent shape of the object being viewed, a result called spherical aberration. Spherical aberration occurs because the refraction of light at the edge of the lens is greater than in the center, which causes a blurring of the image. In the seventeenth century many philosophers and lens makers thought they could solve this problem by designing machines to grind lenses that were “hyperbolic”: they would have a surface that would exactly focus an image to a point behind the lens so that no blurring would occur. Descartes spent years trying in vain to invent such a machine. By the end of the eighteenth century, the problem was solved by using a combination of lenses to correct for the spherical aberration, allowing the entire image to be in focus at one time.
Another difficulty in looking through lenses resulted from the fact that the surface of a lens, just like a prism, disperses the colors composing white light and produces colored fringes in the image, especially under strong light, an effect called chromatic aberration. Chromatic aberration was not really understood until Isaac Newton’s early optical studies were published in 1672. Newton explained the phenomenon, but concluded, too pessimistically, that all transparent lenses must inevitably suffer from this problem, and so optical devices would always be slightly imperfect. It was only in the late eighteenth century that it was realized that achromatic objectives for microscopes could be created by combining lenses of different kinds of glass. But until then chromatic aberration remained an impediment to seeing with microscopes. The obstacle was compounded for double-lens microscopes, which suffered from the composite aberration of two lenses, rather than only one.
Learning to see through a microscope not only involved learning to cope with optical defects; it also had to do with understanding the way that our underlying beliefs influence what we see—an idea that emerged during this period. Because of the difficulty of seeing with the devices, and the newness of the images seen with them, it was easier for a viewer’s beliefs and expectations to influence how he or she interpreted what was seen through a telescope or microscope. It wasn’t only Galileo’s training in perspective theory that allowed him to see the moon’s splotches as craters and shadows; it was also his acceptance of the Copernican theory. If one accepted Copernicus’s theory there was no conceptual barrier to imagining that the moon’s surface resembled that of Earth, because both bodies were the same kind of thing: celestial bodies orbiting the Sun. But on the old Aristotelian view, Earth resided in a special terrestrial realm at the center of the universe, and everything going around Earth was made up of a perfect celestial “ether” that was “luminiferous,” or shining. An observer who believed with all his might that the moon’s surface must be perfectly smooth and shining just could not see the craters and mountains—that observer was not pretending not to see, he was really not seeing, because his expectations were coloring his sight. Instead, he saw blotchy clouds over the moon’s shining, perfectly smooth surface, or he blamed defects of the telescope for causing the mottled appearance of the moon viewed with it. Later, when studying sperm, Leeuwenhoek’s own beliefs influenced his observations, causing him to spend hour upon hour seeking the homunculus or “little man” within; he sometimes thought he caught a glimpse of him. In the nineteenth century William James coined the phrase “will to believe,” noting that sometimes we convince ourselves to believe what we chose to believe, even without rational evidence; so too, it can be said, we sometimes will ourselves to see what we want to see, or what we are accustomed to seeing.
But the natural philosopher of the seventeenth century sought to see the natural world as it was, not how he was accustomed to believe it was on the basis of a favorite theory or other beliefs. It was necessary to train the mind, as it were, to allow it to see what was there, even if it was hard to see with the new optical instruments, and even if what was seen went against strongly held beliefs. Galileo recognized this problem when he said of one of his critics that he should use “not just the eyes in his head, but those of his mind as well.” It was necessary to realize that expectations, beliefs, even desires can cause us to see something other than what is present to our eyes. Like the painters using mirrors to focus their attention and disrupt their visual habits, natural philosophers, too, needed to take pains to suspend their expectations while viewing nature through optical instruments. Only once they succeeded could the Scientific Revolution take place; only then could the ancient texts and theories be overthrown. And so Leeuwenhoek, and all the men and women using the new optical instruments, needed to learn how to discern what was really there and what was not, what was merely an artifact of the device itself, what was an artifact of the mind’s expectations or desires, and what was being revealed by the lens.
Learning to see with the microscope was more difficult than learning to see with a telescope in one crucial way. Telescopes revealed that the heavens were remarkably similar to the known, familiar world. Indeed, what was so controversial about the new discoveries made with the telescope was the forced recognition that there was no distinct, Aristotelian celestial realm, where heavenly bodies were made of the luminiferous ether and were completely unlike Earth. Instead, the telescope showed us that the moon was just like Earth—pockmarked, with mountains and craters—and so was Jupiter, which had its own moons circling about it, just as Earth has a moon cycling around us. Telescopes showed us that there were even more stars than we had imagined; but these were not strange new things, just more of the same. In this way, the new awareness of the vastness of the universe—which made the world stranger than it seemed to be—was balanced by the idea that this vast universe was familiar, that the parts of it we cannot see with the naked eye are similar to the parts we can see.
Microscopes, by contrast, revealed a new and strange world to viewers, a “color-charged, glistening world,” as one writer has put it, in which new textures, hues, forms, and light effects were revealed for the very first time. Learning to see through a microscope required coming to accept that the world was, after all, very different from the way it had always seemed. Huygens had remarked on this when he described people looking at a specimen with Drebbel’s microscopes for the first time. They at first complained that they could see nothing. Then they cried out with surprise at the sight of unbelievable, marvelous things. “For in fact,” Huygens explained, “this concerns a new theater of nature, another world.” In the early part of his self-imposed microscopic apprenticeship, Leeuwenhoek began to train himself to see the “color-charged, glistening world,” a world newly revealed to be unfamiliar and strange.
*1 The ell was a measure based on the distance from armpit to fingertips, and it differed slightly from place to place. A Delft ell was 68.2 centimeters, about 2.25 feet. 16 pennings = 1 stuiver, 20 stuivers = 1 guilder, 28 stuivers =1 florin.
*2 Her family name sometimes appears in the archives as de Mey.
*3 Maria Virlin also appears in the archives as Maria Virulij.
*4 It is interesting that the glass sphere hanging over the scene of Vermeer’s Allegory of the Catholic Faith (representing heaven) and glass spheres appearing in some still-life paintings of the time (such as by Claesz and Kalf) are similar to the glass balls used for making lenses. Since such spheres were not common in homes at the time, one wonders whether the Dutch painters had seen glassblowers preparing these balls for lens makers.
*5 As we saw earlier, the glassworkers in the Dutch Republic were paid about 24 stuivers a day, which would be 144 per week (assuming a six-day workweek) and about 7,488 per year (assuming pay over fifty-two weeks). A florin was 28 stuivers, so that yearly income would be 267 florins.
PART 5
Ut pictura, ita visio
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ON A FINE summer day in 1623, Constantijn Huygens hosted a group of acquaintances and friends at his father’s house in The Hague. Huygens had just returned home after his second trip to England as the diplomatic secretary of the Dutch delegation. He was eager to demonstrate some newly invented d
evices he had brought home with him. Several painters were in attendance, including Huygens’s neighbors, the Jacob de Gheyns—both the father (Jacob II), a painter, and the son (Jacob III), a painter and engraver who had accompanied Huygens to London—and Johannes Symonsz. van der Beeck, known as Johannes Torrentius (the Latin equivalent of his Dutch surname, which means brook or torrent).
During the afternoon, Huygens showed his guests an instrument he had purchased in England from a close friend, the inventor Cornelis Drebbel. Huygens explained to his guests that this “machine” was “a kind of viewing device, by [means of] which likenesses of things presented to it from outside are directed on to a white [or bright] plate within its enclosed space.” Huygens had set up a wooden box on the windowsill of his dining room. The box had a brass extendable tube—like the kind Drebell made for his microscopes—facing outdoors. The tube held a glass lens, which projected an image of the people outside onto a bright white plate inside the box. Huygens informed his friends that he had been using the device for making paintings, with great “delight” at the results.
As Huygens later recalled, his guests crowded around the box excitedly, watching the moving image on the white screen inside the box. Torrentius, however, acted strangely, asking, “Are the little people that are seen on the plate … [the ones] observed going about outside the dining room?” Huygens felt certain that the painter had feigned ignorance about the camera obscura, which, Huygens knew, “now-a-days is familiar to every one” in its whole-room or tented configurations—though the box type was still new. Huygens suspected that “this cunning fox” used a camera obscura when painting—that must be how he was able to depict objects made of glass, tin, earthenware, and iron with such exquisite realism, showing the different textures and sheens of each—but was trying to keep his use of the device a secret so that “the simple, uncritical public in this way would ascribe [his skill] to bursts of Divine Inspiration.” Torrentius’s still-life paintings, Huygens and his friend De Gheyn agreed, resembled nothing so much as projections of objects in a camera obsura. Although he continued to admire Torrentius’s work, Huygens concluded that afternoon that the artist was a “holy quack” for pretending to create his pictures without the instrument.*1
Eye of the Beholder: Johannes Vermeer, Antoni van Leeuwenhoek, and the Reinvention of Seeing Page 14
