Because Van Leeuwenhoek sometimes made his observations in a dark room with only a candle for illumination, and because he often described what he was seeing—like the blood corpuscles—as looking like “grains of sand on a piece of dark taffeta,” it appears that Van Leeuwenhoek at least occasionally used a method known as “dark ground illumination.” This is an observation technique still used in microscopy today, as it is excellent for live and unstained biological specimens, such as a tissue culture or individual water-borne single-cell organisms. With this method, direct light is blocked so that only scattered light reaches the objective lens of the microscope. This would have been fairly simple for Leeuwenhoek to achieve. In the twentieth century the researcher Barnett Cohen succeeded in viewing blood corpuscles by using a Leeuwenhoek-like setup and dark-ground illumination. He put the blood in a capillary tube with a very small globe about two millimeters in diameter at the bottom, and trained the single-lens microscope on this tube. He used lateral (sideways) illumination, such as Van Leeuwenhoek could have achieved by putting a single candle on one side of his microscope while observing through it. In this way Cohen saw the blood corpuscles clearly against a dark background, exactly like grains of sand on black taffeta.
Cohen found that it was somewhat more difficult to observe a single bacterium in a tube of water in this manner, but it was possible to do so by putting a drop of water on the lens of the microscope. This drop of water acted as an additional lens that further magnifies the specimen. If Van Leeuwenhoek had used this method, it would have provided him with three levels of magnification: one provided by the lens of the microscope, another by the glass tube, and a third by a drop of water. We cannot know whether this does accurately replicate Van Leeuwenhoek’s observational methods, but it is clear that he used some similar method, at least some of the time. Van Leeuwenhoek would later describe observing sperm by candlelight, with a small concave mirror to enhance the illumination. When Thomas Molyneux visited him on behalf of the Royal Society in 1685, he marveled at how his microscope surpassed all others he had ever used in its “extreme clearness and … representing all objects so extraordinary distinctly,” even though the instrument had been used “in a dark room.”
It is also possible that Van Leeuwenhoek sometimes used a type of camera obscura—a kind later called a solar microscope. It is generally believed that this type of camera obscura microscope was not invented until Daniel Fahrenheit, the German glassblower and natural philosopher living in The Hague, designed it in 1736. But I think it likely that Van Leeuwenhoek constructed and used one earlier than this. A solar microscope consists of a mirror, two convex lenses fitted inside a tube, and a square wooden or metal mounting plate. The plate is positioned in a small opening in a closed window shutter, with the mirror outside and the tube inside. The mirror can be tilted in different positions to direct the sun’s rays into the tube with the lenses. The room is kept dark. The mirror outside the shutter reflects the sun’s rays into the tube, so that the light passes through the condensing lens, the specimen on a slide, and then the objective lens. As with a room-type camera obscura, an image of the specimen is projected onto a wall or screen opposite the shuttered window. Unlike most camera obscuras, this type casts a magnified image.
A solar microscope produces a bright and strongly contrasted image of the specimen, and allows the image to be visible to a number of observers at once. The image can be traced over, ensuring an easy way to draw the magnified specimen. In the second half of the eighteenth century, solar microscopes were used to entertain crowds with shows of gigantic, magnified fleas the “size of sheep,” hair “as large as a broomstick,” and the circulation of blood in the tail of a tadpole, which was, one observer noted, “like looking at a geographical map in which all the streams and rivers are animated by actual flowing water.”
The solar microscope was, basically, a very small camera obscura attached to a scioptric ball, a universal ball joint that allows a microscope or camera obscura to be swiveled into any position. Often the scioptric ball was fitted into a small hole in a window shutter. Daniel Schwenter had invented the scioptric ball in 1636. After this it would have been simple to construct a microscope version of the scioptric ball and place it in a hole in a closed shutter. Histories of technology are written from remaining objects and documents, and since Van Leeuwenhoek never disclosed his methods or the construction of his best microscopes it is possible that history has overlooked his invention of an early solar microscope. A visitor to Delft wrote that besides the microscopes Van Leeuwenhoek had shown him, “he told me he has another sort, which he reserves solely for his own observations.” In one of his letters to Oldenberg, Van Leeuwenhoek explained that though he is a poor draftsman, he has a special method of producing drawings that he was “resolved not to let anyone know.” A solar microscope would have solved that problem, since the image could be simply traced over. Whether or not Van Leeuwenhoek intimately knew Vermeer, his connection to so many of Delft’s artists could have led him to learn about the camera obscura. Some writers have casually conjectured—with no evidence—that Van Leeuwenhoek introduced Vermeer to the camera obscura. But it might have been the other way around, the artist showing the natural philosopher how to cast an image on a wall. And, ironically, Van Leeuwenhoek, not Vermeer, may have been the one tracing a camera obscura image.*2
Although Van Leeuwenhoek sometimes made his own drawings, at other times he deployed artists to depict the images seen through his microscopes. He is scrupulous in giving them credit, though not by name. In the summer of 1698 he reported, “I sent for a painter who is very observant and also has an accurate eye.” Van Leeuwenhoek put a little eel in the glass tube in front of the microscope and handed it to the painter. When he saw the circulation of blood through the vessels in the eel, “the Painter could not stop marvelling.” Sometimes, the draftsmen saw what Van Leeuwenhoek himself could not see. Their expertise in perspective, as well as, perhaps, their experience in using mirrors, lenses, and camera obscuras in their own work, might have made them more suited to these observations than Van Leeuwenhoek himself. They might have had more experience than did Van Leeuwenhoek with looking through lenses—at least at the beginning of his investigations.
As we have seen, Van Leeuwenhoek had numerous connections to artists, through his mother’s family, his stepfather and stepbrothers, and his second wife, Cornelia Swalmius. He was painted by Cornelis de Man and Johannes Verkolje and, perhaps, by Vermeer himself. When he worked as a haberdasher, he might have sold material to be used in Alberti’s veils to artists of the nearby Guild of St. Luke. So he had many opportunities to find draftsmen to help him. But Van Leeuwenhoek never revealed the names of his illustrators. Boitet, who wrote about Delft in 1729, claimed to know who made Van Leeuwenhoek’s drawings. Tomas van der Wilt or Wildt (born 1659) was a painter in Delft who had been a pupil of Verkolje’s. A member of the guild with Vermeer, Van der Wilt was particularly known for his talents in perspective. He painted The Anatomy Lesson of Abraham van Bleyswijk, among other works. His son, Willem, born in 1691, was said to be an exceptional draftsman, and Boitet says that Willem van der Wilt was Van Leeuwenhoek’s schilder. “Nearly all the plates in the celebrated work of Mr. Leeuwenhoek were marvellously drawn from life by him through magnifying-glasses.… But he died in the flower of his life on 24 January 1727, at the age of 35.” As Boitet was writing only two years after Willem’s death, he is probably correct that he had done illustrations for Van Leeuwenhoek. But there must have been one or more illustrators before Willem, since his letters contained images from the 1670s, before Willem was even born. It is possible that Van Leeuwenhoek’s first draftsman was Willem’s father, Tomas van der Wilt.
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But there was more to Van Leeuwenhoek’s success than just his skill at making microscopes, his creativity in using light to make observations, and his willingness to deploy artists. His vision may also have been particularly suited for the task. In several of his letters, Van
Leeuwenhoek mentions needing his spectacles to see something. If Van Leeuwenhoek was nearsighted, that condition would have made it easier for him to make observations through his kind of microscope. In the eye of a nearsighted person, the image of something seen focuses in front of the retina, and a lens is needed to move it farther back onto the retina; that is why the nearsighted person wears glasses. But if the lens is instead provided by a microscope held quite close to the eye, the nearsighted observer would be able to focus closer, and for a longer period of time, on something held quite close to the eye, than could someone who was not nearsighted. The microscope would, in a sense, play the role of spectacles or contact lenses. For someone who has normal vision, an image seen without a lens would hit the retina as it should, and so spectacles are not needed to push the image farther back. For this person, using a single-lens microscope brought close to the eye would cause the image to be pushed behind the retina, making it appear blurry. It would be as if someone with perfect vision put on a pair of glasses made for a nearsighted person—it would be hard to see, and the effort of focusing correctly would cause eyestrain. That may be one reason why others using Leeuwenhoek-type microscopes could not spend the hours looking through them that he did.
Not only was his vision particularly suited to observing with his microscopes, but Van Leeuwenhoek was also immensely skilled at preparing and fixing his specimens so that he could see more structures within them. Tiny, solid objects could often be simply glued to the pin of the microscope, but even this took much work; in the course of several days Van Leeuwenhoek had to kill more than one hundred mosquitoes in order to display the mouth properly. Other specimens, such as sperm and insect muscle fibers, were allowed to dry on a piece of mica or thin glass and then fixed to the pin. Liquids such as his infusions, semen, and blood were viewed in thin glass tubes—so thin they sometimes measured only the width of a hair. Van Leeuwenhoek may have been the first person to stain microscopic specimens, a common practice today. Van Leeuwenhoek used a bright yellow infusion of saffron to stain cross sections of muscle fiber; because the stain is absorbed at different rates by various structures in the specimen, each one stands out clearly and is easier to see. With his shaving razor, he was somehow able to slice sections thin as a hair; a rival microscopist later expressed amazement at his incredible dexterity, even when Van Leeuwenhoek was seventy-eight years old. After reviewing the specimens that Van Leeuwenhoek sent to the Royal Society, Brian Ford concluded in 2003 that they are “technically excellent,” meeting modern-day standards of specimen preparation.
Van Leeuwenhoek was exceedingly talented at measurement. Since he was the first one to observe such tiny organisms, he had to devise new ways to determine and describe just how small they were. He developed a method for measuring microscopic structures and organisms by means of macroscopic (and common) objects like grains of sand, millet seeds, and hair. Sometimes he placed a brass ruler near the microscope in order to measure the width of a hair seen under the microscope. He could then employ the hair as a measuring device when he wanted to determine the size of microscopic objects. Eventually, he would deploy microscopic objects—red blood “globules,” the “smallest animalcules in pepper-water”—as units of measure for the most minuscule organisms. Today’s microscopists are amazed at how accurate his measurements were, given the lack of modern micrometers and other instruments now used for measuring microscopic objects.
In fact, Van Leeuwenhoek’s measurements were so accurate that some confusion was caused by his reference to “a hair on my head” as a measuring device. By assuming that his measurements were correct, as were all of his others, it worked out that the hair he was using must have measured only about 43 microns (thousandths of a millimeter) in thickness. But actually, human hair is closer to 70 microns. After some bewilderment on the part of researchers, it was realized that the hair from Van Leeuwenhoek’s head was actually a hair from his wig. In the Netherlands at the time, wigs were generally made of Angora goat hair, which are 43 microns in thickness. Once the proper hair was taken as his measuring device, the dimensions he had given were correct.
Perhaps most important to his success was the fact that Van Leeuwenhoek had an almost unlimited supply of patience for returning, again and again, to the same observations, sometimes for hours at a time. He speaks of spending long periods gazing at sights such as the circulation of blood in the capillaries of the frog, the masses of spermatozoa tangled up in animal semen, the mite that, as it lay stuck on the specimen pin behind the microscope, kept passing an egg back and forth from foot to foot. On observing the circulation of blood in the hind legs of a small frog in a glass tube, Van Leeuwenhoek said it “gave me so much pleasure that I looked at it again and again on several days.” Of the movement of the cheeks of baby eels, he wrote, “This sight gives me more pleasure than if I were to see a big cabinet of curiosities, with many different horns, shells, sea-plants, etc., however costly and curious one might call such a cabinet.” His specimen collection comprised his own cabinet of curiosities.
Van Leeuwenhoek must have needed to rest his eyes between viewings, each of which, he says, lasted for hours. The amount of patience and concentration required for this extended observation was extreme. As he explained in a letter when he was eighty-eight years old, “Nor should I ever have attained thereto, but by continual Labor in the investigation of things, which are concealed from our naked Eyes, and towards which I have a much greater inclination, than what I observe in most other Men.”
This intense concentration became more difficult as he got older, and Van Leeuwenhoek occasionally expressed fatigue. On viewing many different samples of sperm, he noted, “this multiple sight, which was contemplated by me as if I could not get enough of it, not only fatigued my eyes, but also gave me a headache.” Yet until the end of his life Van Leeuwenhoek endured headaches and other ailments for the sake of observing those things “concealed from our naked eyes.”
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Van Leeuwenhoek continued his microscopic observations right up to his death. On March 19, 1723, at the age of ninety, he wrote to the Royal Society about the size of red blood cells, and on May 31 he sent a description of the histology of the diaphragm, which he had studied in sheep and oxen, trying to support his view that his own illness involved an obstruction of that organ, and not “palpitations of the heart” as his physicians thought. Van Leeuwenhoek pointed out that when this “violent motion” in the chest lasted, he could feel no quickening of his pulse on his wrist. Yet by his dissections he determined that obstructions could “excite convulsive motions in the tendons” of the diaphragm. (The rare disorder characterized by rapid, involuntary contractions of the diaphragm is now known as Van Leeuwenhoek’s disease.) In August, Van Leeuwenhoek suffered another attack. As he lay dying, “when his limbs were already growing numb,” and with his “lips stammering and well-nigh stiff,” he summoned his friend Dr. Jan Hoogvliet to his bedside, and dictated two letters that he directed the doctor to convey to the Royal Society as a “final gift.” He died on August 26 no longer only “From the Lion’s Gate”—as the name Leeuwenhoek originally signified—but a true scientific lion.
He was buried in the Oude Kerk on August 31, 1723, “with 16 pall-bearers and with coaches and tollings of the bell at 3 intervals.” His burial notice recorded that he was “lid van de koninklijke societeijt binnen Londen”: a member of the Royal Society in London. Six weeks later his daughter Maria—who had never married, preferring to stay and take care of her father, a widower since Cornelia’s death in 1694—sent the Royal Society a bequest of her father. He had put together for them a black-and-gold cabinet, which held thirty rectangular tin cases covered with black leather. In each case lay two gleaming silver microscopes—the silver “extracted from the ore,” and the lenses ground, by Leeuwenhoek himself. Attached to each microscope was a prepared specimen, labeled in his own hand. In recognition of the gift, the Royal Society sent Maria a silver bowl engraved with the arms of the society. T
he microscopes, and their specimens, were cataloged and described by Martin Folkes in the Philosophical Transactions of the Royal Society. One hundred and twenty years later, the cabinet and its precious contents were lost, and have remained missing to this day.*3
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Already in 1662, Hooke had complained of a reaction against the microscope among natural philosphers, who were, he believed, “bored and disenchanted” by the device. Later, in 1743, the English naturalist and poet Henry Baker suggested that all the important microscopical discoveries had already been made (some by himself). With Van Leeuwenhoek’s death, the number of publications about microscopic observations sharply declined. That was, however, simply because Leeuwenhoek had been writing so many letters to the Royal Society right up to the end. It was not that there was nothing new in nature to uncover. It was, rather, that by the time he died his microscope—like the telescope—had become a routine component of a natural philosopher’s toolkit, neither more nor less exciting than other instruments, such as a ruler or a balance. Microscopes could be deployed or dispensed with, as required. In a sense this was the triumph of the new way of seeing: it became commonplace, no longer a thrilling oddity.
Among the general public, the knowledge that there was more than meets the eye led to a vogue for “toy” microscopes. Throughout the eighteenth and nineteenth centuries, manufacturers sold inexpensive microscopes prepackaged with “sliders,” a selection of specimens mounted between mica or glass slides. These premounted specimens were like Leeuwenhoek’s collection, made for ease of viewing. With these microscopes, as with the earlier flea glasses, people could see for themselves how strange the previously unseen realm was—both the microscopic world and the world of tiny insects enlarged beyond imagination.
Eye of the Beholder: Johannes Vermeer, Antoni van Leeuwenhoek, and the Reinvention of Seeing Page 34
