The origins of the Royal Society lie in a so-called invisible college of natural philosophers who began meeting in the mid-1640s for discussions of the new methods of seeking knowledge of the natural world through observation and experiment. On November 28, 1660, twelve men met at Gresham College after a lecture by Christopher Wren, then the Gresham Professor of Astronomy, and decided to found “a Colledge for the Promoting of Physico-Mathematicall Experimentall Learning.” The gathering included Wren, Robert Boyle, John Wilkins, Sir Robert Moray, and William, Viscount Brouncker. One of the first acts of Charles II when he was restored to the throne was to bestow a charter on the group, from then known as The Royal Society of London for Improving Natural Knowledge. The society planned to meet weekly, on Wednesdays “after the lecture of the Astronomy Professor,” to witness experiments and discuss scientific topics.

The earliest meetings of the Royal Society demonstrated the wide-ranging nature of its members’ interests. The men discussed the petrification of wood, properties of the lodestone (natural magnet), parts of the anatomy of various creatures, the transfusion of blood of one animal into another, the ebb and flow of the sea, the kinds and feeding of oysters, the “wonders and curiosities” observable in the deepest mines. They sent emissaries to try to answer questions about a strange poison believed to be in the possession of the king of Macasser, about whether master craftsmen in Peru used a method to intensify the color of their native rubies, and whether the bones of a certain fish were able to stop the flow of blood from a wound (only this last question was answered definitively, with samples of the fish sent to England on Dutch ships).

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Early meetings of the Royal Society were devoted to the methods and processes of artists. On April 10, 1660, the society appointed a committee “to consider about all sorts of tooles and instruments for glasses for [making] perspectives.” On January 16, 1660/61, the fellows heard Dr. Goddard read a paper titled “A Brief Experimental Account of the production of some colours by mixtures of several liquors, either having little or no colour, or being of different colours from those produced.” At the same meeting Mr. Eveleyn was asked to “bring in a history of engraving and etching.” In April of 1666 the fellows heard about a method of making a nonglossy paint glaze by the addition to the paint of either an egg or the sap of the fig tree. No less a member than Sir Robert Moray, one of the society’s founders, went along with Hooke to see the method in action at the artist’s studio; afterward it was reported that Moray himself had “broken eggs into two little vessels.” (Around this time Van Hoogstraten complained that the glossiness of paintings was one reason why they could never fully deceive the eye into believing it was viewing anything other than a picture.) The following year, Thomas Povey produced a letter by an artist, Alex Marshall, reporting his methods for producing different colors of paint. Povey tried to get the Royal Society’s support for a large-scale “History of the Art of Painting,” which he would facilitate by bringing together Royal Society fellows and the “best masters of that art living in London,” including Peter Lely. Sounding much like Van Hoogstraten’s call to artists, published a few years later, Povey described painting as “this almost divine art, which not only imitates but approacheth very deceivably, even to the giving of life itself.”

The Royal Society fellows had a particular interest in devices to aid the artist, befitting its original charter “to improve the knowledge of natural things, and all useful Arts Manufactures, Mechanic practices, Engines and Inventions, by Experiments.” In 1668 Hooke demonstrated to the group Della Porta’s method of projecting with a mirror and lens a scene from another room—without mentioning Della Porta’s description in his book, which had been translated into English ten years earlier. In Della Porta’s discussion, the experiment had appeared as “how in a Chamber you may see Hunting, Battles of Enemies, and other delusions,” while at the Royal Society the demonstration received a more mundanely descriptive title: “A contrivance to make the picture of anything appear on a wall, cupboard, or within a picture frame, etc. in the midst of a light room in the daytime, or in the night time in any room which is enlightened with a considerable number of candles.” Boyle had demonstrated his box-type camera obscura sometime before this, and Wren showed his “machine for drawing in perspective” to the fellows in 1669.

What tied together all these different areas of inquiry was the importance placed upon experimentation. It was not enough to read reports of travelers extolling the Macasser king’s poison or the blood-clotting fish; the fellows wanted to see for themselves. They did not just read a paper on the egg-glaze method for making paintings appear with less of a glare in the noontime sun—they went and saw (and mixed in the egg) for themselves. As the first historian of the Royal Society, Thomas Sprat, put it in 1667, they believed the “Seat of Learning” should be in “Laboratories” not “Schools.” This emphasis was codified in the society’s motto, a saying from Horace: “Nullius in verba,” roughly translated as “Take no one’s word for it,” expressing the determination of the fellows to reject the domination of authority of past texts and experts and instead to verify all statements by an appeal to experiment. The Royal Society endeavored, in Sprat’s words, “to separate the knowledge of Nature, from the colours of Rhetorick, the devices of Fancy, or the delightful deceit of Fables.”

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This demand for experimental verification was explicitly linked to the new philosophy proposed by Francis Bacon. Bacon had called for a fresh start to knowledge of the physical world; the natural philosopher must “vex” nature, as he vividly put it, learning her secrets by observation and rigorous experimentation. This was a requirement that resonated with the natural philosophers of the time, who had already begun to practice what Bacon was preaching.

Bacon’s inductive method was explicitly opposed to that of the Aristotelians. Bacon respected Aristotle himself, but disdained the views of many medieval followers of Aristotle, who slavishly believed whatever their master had said so many centuries before. Bacon knew that Aristotle himself would have changed his mind on some of his conclusions had he had access to modern knowledge and ways of investigating nature. In the year that Leeuwenhoek and Vermeer were born, Galileo had expressed Bacon’s point with a sly story he recounted in a book promoting the Copernican view against the old Aristotelian astronomy. He told of a man attending a dissection at the home of a famous anatomist. Aristotelians believed that all the nerves originated in the heart, while their opponents held they began in the brain. “The anatomist showed that the great trunk of nerves leaving the brain and passing through the nape, extended down the spine and then branched out through the whole body, and that only a single strand as fine as a thread arrived at the heart,” Galileo wrote. The anatomist then turned to an observer who was an Aristotelian and asked whether he was now convinced that the nerves originate in the brain and not the heart. “The philosopher, considering for awhile, answered: You have made me see this matter so plainly and palpably that if Aristotle’s text were not contrary to it, stating clearly that the nerves originate in the heart, I should be forced to admit it to be true.”

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Kepler, too, criticized the slavish allegiance to ancient wisdom, referring to it as nothing but a “world on paper.” William Harvey, who discovered the circulation of blood by the pumping of the heart, claimed, “I profess both to learn and to teach anatomy, not from books but from dissections, not from the positions of philosophers but from the fabric of nature.” Leeuwenhoek would later similarly chide those who drew conclusions about salt particles in the body without ever having seen them.

Bacon rejected as well the claims of those who thought that all knowledge, even knowledge of the physical world, came primarily through human reason and not the senses. He considered these philosophies to be like the method of the spider, which spins a web entirely out of its own body, not using anything outside of itself. In Leeuwenhoek’s time the most prominent “spider” was René Descartes, who had lived in Amsterdam for twenty years until leaving for Sweden to tutor Queen Christina in 1649 (there he died, partly from the cold climate, soon afterward). Descartes espoused an epistemology, or method of knowledge acquisition, that expressed mistrust in the senses, and placed primary value on reasoning from ideas found in the mind rather than from observations of nature.

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For example, in determining his three laws of motion, Descartes began from a “clear and distinct” idea found in his mind: the idea of God. His idea of God included, by definition, that God is omnipotent, immutable, and eternal (that is what we mean by “God,” Descartes believed). From this “first principle” Descartes derived his three laws of physics, what we would call his laws of motion, as well as a general law, the law of conservation of motion—that the total amount of motion in the world remains constant. Descartes’s proof of this law is logical, rather than empirical, following necessarily from God’s properties. When God created the universe, he endowed its material bodies with a finite quantity of motion. At each moment subsequently, God acts to preserve this same amount of motion.

It is obvious that when God first created the world, He not only moved its parts in various ways, but also simultaneously caused some of the parts to push others and to transfer their motion to these others. So in now maintaining the world by the same action and with the same laws with which He created it, He conserves motion; not always contained in the same parts of matter, but transferred from some parts to others depending on the ways in which they come in contact.

In his treatise on scientific method, Descartes employed the same logic to prove all sorts of laws of nature. By the end of the book he concluded—optimistically and erroneously—“no phenomena of nature have been omitted. . . . There is nothing visible or perceptible in this world that I have not explained.”

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As the Royal Society’s historian Sprat put it, “I confess the excellent Monsieur des Cartes recommends to us another way in his Philosophical Method. . . . He at once rejected all the Impressions, which he had before receiv’d . . . and wholly gave himself over to a reflexion on the naked Ideas of his own mind.” Sprat allows that this might be appropriate for the “Contemplation” of a gentleman, but emphatically not for a philosopher’s “Inquiry” into the natural world. In Amsterdam, the microscopist Swammerdam criticized Descartes’s scientific method on similar grounds, noting that many a natural philosopher had made egregious errors by relying on reasoning while neglecting to observe the phenomena for himself.

Not only did Descartes invent his theories solely from his mind; he also erred, according to the method of the new philosophy, by not carefully testing and retesting his theories. For Bacon, experimentation was required in order to make a proper induction to a scientific law in the first place. Most of his seventeenth-century followers required additional experimental confirmation of a scientific law. While Descartes did claim to have conducted experiments to confirm his conservation law, many writers today agree with Sprat, who pointed out that his so-called experiments were merely “grosse trials” based on “conjecture.” Descartes envisioned experiments based on the assumption that the law was correct, and in this way “proved” what he already “knew” to be true—not only true, but self-evidently true, obvious just by definition. Indeed, echoing Galileo’s Aristotelian anatomist, Descartes insisted that “the demonstrations are so certain that, even if experience seemed to show us the contrary, we would nevertheless be obliged to place more faith in our reason than in our senses.”

As one would expect from a philosopher emphasizing the use of the senses, Bacon praised microscopes for extending the reach of the sense of sight. (Descartes, too, had praised the invention, as a means to rectify some of the infirmities of the senses, but he still emphasized that the mind had precedence over the senses in science.) The microscope, “lately invented,” said Bacon, enables us to “perceive objects not naturally seen.” These instruments “exhibit the latent and invisible minutiae of substances, and their hidden formation and motion.” With the assistance of a microscope “we behold with astonishment the accurate form and outline of a flea, moss, and animalculae [little animals], as well as their previously invisible color and motion.” Indeed, microscopes and telescopes satisfied the “true and lawful goal of the sciences”: to ensure that “human life be endowed with new discoveries and powers.” These new instruments gave natural philosophers the power to make thrilling discoveries.

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Instruments themselves cannot transform science, Bacon was careful to add—experimentation was necessary in conjunction with aids to the senses. Merely looking at the world, even with a microscope, is not enough. But Bacon believed that science fundamentally involved the investigation of “hidden schematisms” and unobservable structures, and the “true textures” of physical bodies; and this was where the microscope would later prove invaluable. One of the problems with the followers of the Scholastics, according to Bacon, had been their readiness to rely on the naked senses; he criticized them for ending their investigations “where sight ceases.” The new investigators of nature would have to go beyond naked sight itself.

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Even before his reputation grew in his native England, Bacon’s works were appreciated in the Dutch Republic. One of his earliest and most prominent Dutch readers was Constantijn Huygens, who became interested in Bacon’s writings after meeting him in London in 1622. But Bacon’s reputation in the Dutch Republic had preceded him; the year prior to Huygens’s trip to London, he had solicited the poet and classics professor Daniel Heinsius’s opinion of Bacon’s Instauratio magna, which had just been published in England. While Huygens did not care for Bacon personally, he admired his writings on scientific method and his efforts to spark a new era in science. Huygens saluted Bacon, along with Drebbel, as his time’s leading thinkers, saying, “I have looked up in awe at these two men who have offered in my time the most excellent criticism of the useless ideas, theorems, and axioms which . . . the ancients possessed.” Indeed, at times Huygens seemed to revere Bacon as an intellectual saint, admitting that he had a sort of “sacred respect” for him. Huygens agreed with Bacon’s view that the natural philosopher must reject ancient learning and start anew to discover knowledge through observations and experiments.

In 1648 Bacon’s Sylva sylvarum was translated from English into Latin by a Dutchman, Jacob Gruter, allowing the book to become more accessible to Dutch readers accustomed to books written in the scientific language of Latin. Gruter’s brother Isaac later published a number of important manuscripts of Bacon’s he had inherited from the British diplomat Sir William Boswell. Isaac also put out a second edition of his brother’s translation of the Sylva, asking Huygens whether any corrections were needed. The botanist and physician Herman Boerhaave, who would be appointed a lecturer in medicine at Leiden in 1701, expressed a view widespread among his countrymen when he called Bacon “the father of Experimental Philosophy.”

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The philosophical outlook of Bacon particularly appealed to the Dutch, with their emphasis on practical innovation and invention, as much as to the English. Indeed the English natural philosophers, who favored the Baconian approach to that of Descartes—partly for patriotic reasons—saw the Dutch as their compatriots in Baconianism. In his defense of the Baconian philosophy against the attack of the Cambridge Platonist Henry More, William Petty (one of the founders of the Royal Society) contrasted the useful activity of the Dutch inventor Cornelis Drebbel with the worthless endeavors of the speculative philosophers such as the Frenchman Descartes. Philosophical systems, Petty argued, were premature and vacuous, metaphysical speculations unproductive; only practical inventions based on observations, experiments, and trials were worth the natural philosopher’s time and energy. The “hub” of Dutch scientific activity was known to be Constantijn Huygens’s hometown, The Hague (in large part because Huygens lived there), which Sprat compared to Bacon’s ideal of a scientific nation, the “New Atlantis” (described in Bacon’s book by that name): “They have one place (I mean the Hague) which may be soon made the very Copy of a Town in New Atlantis; which for its pleasantness, and for the concourse of men of all conditions to it, may be counted above all others (except London) the most advantageously seated for this service.”

Another reason Bacon’s empirical philosophy appealed to the Dutch was a religious one. While Bacon did not place scientific inquiry squarely upon the shoulders of God, as Descartes had done, he nevertheless expressed a religious, as well as scientific, motivation for studying nature.

Let no man upon a weak conceit of sobriety or an ill-applied moderation think or maintain, that a man can search too far, or be too well studied in the Book of God’s Word, or in the Book of God’s Works—Divinity or [Natural] Philosophy. But rather, let men endeavour an endless progress or proficience in both.

This idea that God had created two books—the book of scripture and the book of nature—was perfectly attuned to the Calvinism of the day, in both England and the Dutch Republic. The Apostle Paul had described the universe “which is before our eyes as a most elegant book, wherein all creatures great and small, are so many characters leading us to contemplate the invisible things of God, namely his eternal power and Godhead.” Closer to home, the opening lines of the Protestant Confession of Faith as revised during the Synod of Dordrecht (1619), establishing the fundamental principles of Calvinism, had echoed the apostle’s words by noting, “We know [God] by two means. Firstly, through the Creation, preservation and government of the entire world. . . . Secondly, He reveals himself yet more clearly and perfectly through his holy and Divine word.”

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Science was esteemed as a way of learning more about God, by studying his works on earth. As Jacob Cats, the most popular poet of the Dutch Republic in the seventeenth century, put it, the first of God’s books taught his will; the second, his power. The religious justification for science that was, in a sense, “built in” to Protestant theology helps explain why England and the Dutch Republic were such bastions of scientific discovery in the early modern period, as opposed to the Catholic countries like Spain and the Papal States in Italy, where the Inquisition persecuted Galileo and spread fear throughout the scientific community. It also explains the dominance of Baconianism in Calvinist countries. In the worldview of the Puritans, according to one historian, Bacon’s writings “came to attain almost scriptural authority.” The Royal Society co-opted this “natural theology,” as it was called in England, highlighting the fact that “the Power, Wisdom, and Goodness of the Creator, is display’d in the admirable order, and workman-ship,” of his creation.

In one of his works Bacon had quoted from Proverbs, “It is the glory of God to conceal a thing, but the honor of Kings to search out a matter.” The microscope accordingly became the means of searching out what God has chosen to conceal from man’s naked sight, a way of magnifying the “Wisdome of the great Architect of Nature,” in the words of Matthew Wren, a cousin of Christopher Wren’s and a political writer and proponent of monarchy. As the microscope began to expose the surprising complexity of the smallest insects, natural philosophers and theologians alike mused that by studying these creatures we could come to understand God as never before. The Northern Brabant minister Johannes Feylingius exclaimed in a work titled De wonderen van de kleyne werelt (The wonders of the small world), “God has deposited his holiness in all things; / He can be read in the tiniest ant and stone.” The Englishman Thomas Moffett would go so far as to say that, apart from man, nothing in the universe is more divine than insects. While some wondered why God would have bothered to create structures so small that we could not see them, others were content to assume that God foresaw that man would invent devices with which such intricacy could be observed and admired.

Similar claims had been made about the structure of the heavens—with its faraway stars and moons only now visible to men and women. An admirer of Galileo’s, Thomas Seggett, had even noted that by enabling humans to behold what was until then the prerogative of heavenly dwellers, the telescope rendered mortals similar to Gods. Constantijn Huygens similarly rhapsodized, “At last mortals may, so to speak, be like gods / If they can see far and near, here and everywhere.” Swammerdam, who would later cease his scientific examinations to devote himself full-time to theology, enthused that the study of the smallest visible things, by allowing us to peruse “the book of Nature,” would be a way by which “God’s invisibility becomes visible.” Leeuwenhoek himself would proclaim that there was “no better way to glorify God than observe in amazement his omniscience and perfection in all living things no matter how small.” One of his own draftsmen, while drawing the leg of a flea, would, Leeuwenhoek reported, “often burst out with the words, ‘dear God, what wonders there are in such a small creature!’”

Constantijn Huygens ended his autobiography with an account of the emotion that overtook him when he first looked through Drebbel’s microscope.

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Nothing can compel us to honor more fully the infinite wisdom and power of God the Creator unless, satiated with the wonders of nature that up till now have been obvious to everyone . . . we are led into this second treasure-house of nature, and in the most minute and disdained of creatures meet with the same careful labor of the Great Architect, everywhere an equally indescribable majesty.

For the English and Dutch natural philosophers, nature was God’s second book, a treasure-house given to us by our Creator. Microscopes and telescopes were new instruments that would enable us to peer more deeply into this treasure-house than ever before.

Excerpted from "Eye of the Beholder: Johannes Vermeer, Antoni van Leeuwenhoek, and the Reinvention of Seeing" by Laura J. Snyder. Published by W.W. Norton and Co. Copyright © 2015 by Laura J. Snyder. Reprinted with permission of the publisher. All rights reserved.