12
SCIENCE DURING WARTIME
In The Hague, Christiaan Huygens had his portrait done by Caspar Netscher, a leading society painter and an artist he personally admired. It is a sumptuous painting, but there is nevertheless something cold and impersonal about it. Huygens is wearing a bronze-and-blue padded silk robe in a fashionable Japanese style and resting his arm on a velvet cushion positioned on a socle with a carved relief. He is extravagantly laced at his collar and his sleeves, which are tied with ribbon knots. The golden curls of his wig tumble heavily around his face.
Ignore, if you can, all this disguise. What do you see? His wide, dark eyes look straight out of the canvas with disarming directness. There is a little colour on his lips. If anything, he looks younger than his forty-two years, that girlish look from his childhood still present, despite the faint line of a moustache on his lip. You would not think he was ill.
You certainly would not know he was a scientist. There is no telescope or clock resting casually next to him to remind the viewer of his achievements, no chart of the heavens on the wall to hint at the scope of his thoughts. Even books and papers are banished from the scene. It could have been otherwise: Netscher painted the astronomer Nicolaas Hartsoeker in 1682 with a globe, telescope and geometry instruments crammed onto the plinth next to him, and he painted himself holding his palette and brushes. Clearly, Netscher was following Huygens’s wish to be shown above all as a man of the world. As portrait painter to the Huygens family, he was perhaps also acting on the father’s instructions; the picture has a strong formal resemblance to the portrait he produced of Christiaan’s sister Susanna a couple of years earlier.
Is Huygens trying to suggest that he is not a scientist at all, or telling us that he is so much more than a scientist? He may have felt, in 1671, that his great discoveries and inventions lay in the past. Perhaps he no longer had any need for the tools of the trade. He was as secure in his position as he had ever been; he felt needed by Colbert and the king. He was an officer of the state, all but, a senior functionary of the French court just arrived from Paris.
In the late spring Huygens passed what must have been a pleasant reacquaintance with his native land, sailing up and down the IJssel and Lower Rhine rivers near Arnhem, engaged in a survey of the vital waterway with Johannes Hudde, who had been his fellow student with Frans van Schooten. The project was on commission from the States General, in which Johan de Witt, another graduate of Schooten’s classes, had for many years held the position of the States of Holland Grand Pensionary. In the past, the three men had occasionally worked together on mathematical problems of national relevance, such as the calculation of state annuities based on life expectancy. The hydrological survey involved measuring the river depths, channel widths and the stream gradient in order to establish whether works were necessary to avoid excessive silting. Hudde and Huygens made a few recommendations of where to dredge and where to cut new channels, but decided that major interventions were not needed.
The rivers also possessed strategic significance as a forward defensive line against attack from the south. However, the next year, during what the Dutch came to know as the rampjaar, the year of disaster, Louis XIV and an army more than 100,000 strong was to cross them without difficulty, taking advantage of the weakened political and military situation in the republic.
By then, Huygens had already been back in Paris for several months. He returned to find an enlarged apartment waiting for him, and the unpleasant surprise that in his absence Carcavi’s son had taken out his carriage without permission and wrecked it in an accident. This strained relations with his neighbour for a time, but there were new friends to see him, among them the remarkable Perrault brothers, the architect Claude, Charles the renowned writer of fairy tales, and Pierre, who would shortly be the first to describe the hydrological cycle.
There was also a brilliant young polymath eager to make his acquaintance. In November 1670 Oldenburg had written to Huygens to make him aware of ‘a certain Doctor Leibnitzius of Mainz, who is advisor to the Elector there, but is also involved in philosophy, principally in speculations on the nature and properties of motion. He claims to have found the very principles of the laws of motion, which others, says he, have stated only simply, without proofs a priori.’ The twenty-six-year-old Gottfried Wilhelm Leibniz had come to Paris with the Elector’s backing to put forward an elaborate plan for peace, but, overtaken by events, he stayed on and began to study mathematics with Huygens. Leibniz would eventually surpass his tutor by developing differential and integral calculus.
Huygens busied himself with the grand waterworks that were under way at Versailles, proposing modifications to the windmills erected to pump water to its ornamental lakes and fountains, and introducing design details familiar from the Netherlands, such as small holes in the bottom of the water buckets, which help the wheel restart after a lull in the wind. The major embellishment to the Academy of Sciences in his absence was Perrault’s observatory on the Left Bank of the Seine, which was nearing completion. It looked, said Huygens, ‘most handsome and magnificent’.
Cassini was appointed as the first director of the Paris Observatory, and given a salary of 9,000 livres, which peeved Huygens, on his 6,000. However, Cassini adopted French citizenship, became thoroughly naturalized in France and ensconced himself deeply at the observatory. He died in Paris in 1712 after more than forty years at the helm, the first of a dynasty of Cassinis who would lead the institution right up until the French Revolution. He was industrious in cartography as well as astronomy, and published numerous astronomical tables and almanacs, which were popular at court. Cassini was always a more systematic watcher of the skies than Huygens, and a herald of the growing professionalization of scientific work. He was rewarded in 1671 and 1672 with the discovery of two new satellites of Saturn in addition to Titan, which Huygens had found more than fifteen years earlier. (He found two more in 1684.) ‘He . . . does not miss a clear night to contemplate the Sky,’ Huygens complained to Lodewijk, ‘to which I would not wish to subject myself, being content with my old discoveries, which are worth more than all those made since.’
Cassini’s discovery was assisted by the disappearance of the planet’s thin ring that Huygens had expected to occur as it fell edge-on to the sun’s light as seen from Earth. On 5 November 1671 Huygens wrote to his brother Constantijn: ‘I observed yesterday in the evening Saturn which I had not seen for 10 or 12 days, and I found its arms so greatly diminished that it was all I could do to perceive them, so much so that I said goodbye to them this time. And there is my prediction verified . . .’ He was doubtful that Cassini had identified a true satellite, however, thinking it might be simply a passing comet, but Cassini was quickly shown to be correct.
In 1669, Huygens had written ‘EUREKA’ in his notes, thinking he had finally found a practical alternative to the supposedly ideal, but apparently unmakeable, hyperbolic lens. Now, three years on, he went back and deleted the word in a series of angry looping slashes. The reason was that Huygens had just learned, from the ever-reliable Oldenburg, that an Englishman by the name of Isaac Newton had designed a reflecting telescope and devised a convincing new theory of colours, which together instantly rendered obsolete much of his work on optical aberration.
Newton’s theory of colours based on his famous experiments with a prism explained the coloured fringes that were seen when looking through many lenses, and which Huygens had been unable to explain or get rid of in his own. These unwanted artefacts were now revealed as an intrinsic property of light itself refracted through the thickness of the glass. Oldenburg sent Huygens a brief description of the reflecting telescope, along with a promise to enclose fuller details and a diagram in his next letter. The instrument worked by transmitting the image from the objective to the eyepiece by means of two mirror surfaces, one concave and one planar, and thus completely avoided the separation of the light into colours that would have occurred with glass lenses. When the Royal Society’s telescope-maker had become aware of the invention, Oldenburg added, he had ceased his own lens-grinding on the spot.
Huygens greatly admired Newton’s innovation when he saw the detailed design, and passed on the exciting news to his friends in the French academy, calling the instrument ‘beautiful & ingenious’. As well as obviating the need for a thick lens ground to the shape of a complex curve, he pointed out, the polished mirror required its metal to be perfect only on the surface and not through its entire depth like glass. Liaising with Constantijn in The Hague, he immediately set about trying to replicate Newton’s achievement. But the brothers struggled to a find a metal that could be formed into shape and polished to the necessary high degree. Then, as the political crisis in the Dutch Republic deepened, Constantijn was called away to pressing duties for William III of Orange, in which capacity he had largely succeeded to his father’s historic function from before the Stadholderless Period.
Encouraged by Oldenburg, Christiaan Huygens offered some suggestions for improvements that Newton might consider making to his design. Newton at this stage was very much the junior partner in the exchange, while Huygens was acknowledged as the most able optical physicist in Europe, and he was pleased to hear that Huygens ‘who hath done so much in Dioptricks hath been pleased to undertake the improvement of Telescopes by Reflexions also’. A positive reaction to constructive criticism was somewhat unusual coming from Newton, and the fact that he responded warmly may be taken as a sign that Huygens’s scientific opinion was one of few he felt he could truly respect.
Huygens found greater difficulty with Newton’s theoretical work. He wrote back cautiously at first to Oldenburg when he read the Englishman’s paper on the generation of colours from white light, calling the work ‘ingenious’ and ‘very likely’, but demanding experimental confirmation, not of the separation and recombination of white light by prisms, which he accepted, but in regard to how chromatic aberration arose in lenses, where he justifiably felt himself to be an expert. This time Newton responded abruptly to Huygens, and accused him of seeking an explanation that was entirely superfluous to the working of the theory.
Newton was doubtless exasperated by the fact that Huygens was far from his only critic. Hooke, too, had misgivings about his colour theory, and Newton had huffily offered to resign from the Royal Society in the face of his attacks. His disappointment with Huygens, though, was perhaps all the more intense because the Hollander was assuredly his learned equal. The nub of the problem was that Huygens was still enough of a Cartesian to wish to see a mechanical explanation for colour. He wanted an answer to the question: what motion causes colour? This question did not interest the more empirical Newton in the least. Furthermore, Huygens’s own ideas about colour were highly unsatisfactory – he believed that a hypothesis able to explain ‘the most saturated colours’, which he held were blue and yellow, would be sufficient to explain them all. As the spat developed, Oldenburg forwarded Newton’s response to this notion directly to Huygens, with a cover note to warn him: ‘I can assure you that Monsieur Newton is a person of great candour . . .’ Newton advised Huygens how to separate and recombine the colours of the rainbow as he himself had done, ‘a tedious and difficult task’, before repeating: ‘But to examine how Colors may be explain’d hypothetically, is besides my purpose.’
After more than a year – and thanks in large part no doubt to Oldenburg’s careful handling of the affair – both men finally agreed to let the matter rest, holding fast to their original positions. Somewhat gracelessly, given how wrong he was, Huygens wrote of Newton: ‘seeing that he holds his opinion so hotly it removes the wish to argue’. Wisely, as it turned out, Huygens never discussed colours in any of his works on light. However, as a Cartesian, he could not remain satisfied, as Newton was, by the evidence of experiment alone, and the question of the original cause of colours continued to exercise him for the rest of his life.
All this time, Huygens remained sharply aware of the deteriorating relations between France and the Dutch Republic. Louis XIV, his patron, declared war on 6 April 1672, with England joining in on the French side soon after. The French army marched into the country the following month. The republic that had grown and prospered through trade, and built up sufficient military power to eject the Spanish and to contain the separate threats from England and France, proved unable to counter their forces combined. Financial collapse and poor efforts by the authorities to defend the country led to riots in many cities. On 21 June Johan de Witt was wounded in a knife attack in The Hague – in Paris the rumour was that he had been killed. Huygens wrote to Lodewijk wishing to know at first-hand ‘everything that is happening in our miserable country’. He was worried for his family as well as for the safety of the Dutch forces and The Hague and other cities. He revealed his split loyalties and ambivalence about the war in a pointed further remark to Lodewijk: ‘I see that you are not very well informed about the dead and injured on the French side.’
Huygens struggled to separate fact from rumour in Paris, the task made more difficult still when the brothers did not always receive each other’s weekly letters. He feared his communications were being intercepted, although he was careful to write ‘nothing which could do me ill; so that I regret only the loss of a letter’. Even at this time, his news typically included snippets about his latest experiments in Paris, and he continued to ship scientific equipment when necessary, although some of these items too were seized by doubtless mystified border officials.
Huygens feared his homeland would be brought to ruin by the conditions imposed by its enemies. As control was ceded of many provinces, and Catholic worship reintroduced elsewhere, de Witt resigned his office and other civic officials were purged. The Orangists, who had always opposed Johan de Witt, now promised the reforms necessary to bring peace. William III was appointed as Stadholder of the largest provinces, the first to hold that office since his father William II had died in 1650. But Christiaan could at least welcome Constantijn’s appointment as William’s secretary, succeeding his father in this role to the preceding two stadholders. ‘If the State is saved from this bad situation, the brother is certainly in a good position,’ he observed.
The new stadholder quickly mustered support and was able to retake the territory lost to France within a couple of years. But worse was to come for Holland before that. On 20 August 1672, an angry mob set upon Johan de Witt as he visited his brother Cornelis in prison in The Hague. Both men were beaten, stabbed and shot to death. Their bodies were dragged to the gibbet nearby on the Vijverberg, where they were hanged by the ankles and disembowelled, their clothes ripped off, and their body parts auctioned to the frenzied crowd. According to one eyewitness account, pieces of the entrails were cooked and eaten by some of the bystanders. ‘The story of Monsieur the Pensionary and his Brother is horrible,’ Huygens wrote to Lodewijk when he heard the news.
I had known it since Friday, but not with the details that you relate. When one sees things like that, one would surely say that the Epicurians were not wrong to say Versari in Republicâ non est Sapientis.* There was much imprudence on the part of the Pensionary in going out into the open to the angry people, but I strongly remain of the opinion that he had not committed any crimes that would merit death.
De Witt’s republican regime had endured for nearly twenty years, the logical outcome as he saw it of the struggle of the Eighty Years War. During that time, his government had stood for a high degree of sovereignty of the individual provinces, for toleration, freedom of thought and a Cartesian separation of theology and philosophy, ideals with which Christiaan – despite his family’s allegiance to the House of Orange and his own to the very different regime in France – could say he was broadly in accord.
Huygens escaped from reality not by surveying the heavens but by peering into the microcosm. He had received an early copy of Robert Hooke’s groundbreaking illustrated book on optics and microscopy, Micrographia, in April 1665. Some of the optical theory contained in the work gave him pause for thought, but he was astounded by the images he saw there. ‘Good figures. Flea and louse as big as a cat. Writes much about Refraction, Coloures &c. but in English,’ he summarized to Johannes Hudde, for whom he would later translate parts of the work into Dutch.
Huygens’s own interest in the microscope sprang from his personal experience of lens-making, and no doubt also from his awareness of his father’s poetic raptures at the new worlds revealed by Drebbel’s instrument when he had visited him in London. Christiaan favoured a design modified from a telescope like Drebbel’s, based on two lenses, rather than the more recent innovation based on a single glass bead for the lens, which he had tried and found hard to focus.
It was the father, too, who first became acquainted with Anthoni Leeuwenhoek of Delft, not far from The Hague, and encouraged him in the work he was doing with the microscope. Apprenticed as a cloth merchant, but lately employed as a sheriff’s clerk in the city, Leeuwenhoek’s duties left him ample time to pursue his unusual obsession. Largely self-taught, he may have acquired the technique of making bead lenses from Hudde or from seeing Micrographia. To construct a microscope, Leeuwenhoek mounted a good specimen from among the many beads he made in a hole drilled through a simple oblong plate of brass about the size of a folded letter of the time. The object to be viewed would then be fastened to a threaded pin which could be gradually brought up close to the lens. Leeuwenhoek made hundreds of such microscopes for his own use. The best lens that survives today is no bigger than a mustard seed and has a focal length of less than one millimetre, but gives an impressive magnification of 270 times.
Scepticism about bead lenses from reputed scientists such as Christiaan Huygens and Hooke was understandable. The very first microscopes, such as those made by Drebbel and the lens-grinders of Middelburg, likely employed optics developed from spectacle lenses. At a time when optical ray diagrams were rudimentary at best, it was not at all obvious that in fact smaller lenses might produce much greater magnification. Both Huygens and Hooke had tried making very small lenses, but exceptionally tiny, clear beads – far simpler than any ground lens – were the innovation of Leeuwenhoek in the 1670s.
Constantijn Huygens had supposed that the microscope would be of interest mainly to artists, craftsmen and traders – a cloth merchant already accustomed to using a thread-counter might want one to inspect the fabric he was buying, for example. Leeuwenhoek, though, was the first to use one to make a systematic study of nature. He observed red corpuscles in his own blood, and discovered diertgens – little animals – swarming in a drop of water from a lake. ‘The motion of most of these diertgens in the water was so swift, and with such varied movements, up as well as down and around, that it was truly astonishing to see,’ he wrote.
We do not know what Mevrouw Leeuwenhoek thought when one day in 1677 her husband dashed from the conjugal bed and, ‘before six beats of the pulse had intervened’, placed his own semen under the microscope for examination. He announced the discovery of human spermatozoa with some circumspection, although it made him famous and gave him a fruitful topic for much further research. He revelled in his success, and later added ‘van’ to his name. His election to the Royal Society occasioned him ‘some small vanity’, Constantijn reported to Christiaan, as he wondered whether he would now no longer need to bow and scrape before a doctor of medicine. Based on his discovery, Leeuwenhoek rejected the concept of the mammalian egg, believing instead that ‘the seed of plants and animals contain animals which in their seed contain still others in infinitum, and that no new creatures are made in the world but those which are made already merely enlarge and grow, which would be a wonderful thing’.
A little later, Johannes Swammerdam, a physician in Amsterdam, began to make bead lenses too – forty an hour, he boasted, though not all of optical quality. He made further pioneering microscopical observations before turning to the priesthood. His work included an attempt to introduce a classification of insects based on their varied and intricate anatomies, which showed, he said, that they should not be regarded as inferior, but were as miraculous as any of God’s creatures.
For a brief moment, it seemed that microscopy was an exclusively Dutch art. Though they were more powerful than the two-lens alternative, bead lenses were prized as much for their clarity of image as for high magnification. Their main use was to reveal the surface of things in greater glory, with perhaps little conception that, if you kept zooming in, there would be further new levels of detail to be seen. Instead, the unfamiliar scenes that people were able to glimpse fed a growing hunger for visual richness and novelty. Visible complexity had grown to be a matter of curiosity in its own right, offering something new to admire beyond simple form and colour. Patterned shells and minerals were coveted for collectors’ cabinets, and tulips were bred with ever more outlandish variegated flowers. Even before the instruments were invented, Dutch paintings seemed to require the eye to operate simultaneously as telescope and microscope, bringing the distant close and rendering the minuscule large. We see the entire city in Vermeer’s View of Delft, but we draw close to inspect the glittering drops on the roofs after the rain. In the numerous paintings that show a terrestrial globe – de Keyser’s portrait of Constantijn Huygens, for instance, or Vermeer’s The Geographer – we see the Earth as if from a distance across space even as we crane forward to inspect the detail of its coastal outlines.
Now, however, Leeuwenhoek and Swammerdam had gone much further. They had revealed things that were utterly new, and which demanded to be understood and described accurately for what they were, just as the mysterious form around Saturn had once demanded to be decoded as a planetary ring. Neither man had any pretensions as a philosopher, yet the primacy that their work afforded to what was simply being seen for the first time, with no theory a priori ready to receive it, represented a major challenge to the Cartesians’ lofty lack of interest in the observable world.*
Christiaan first became aware of Leeuwenhoek’s work in June 1673, presumably through his father, when he was sent some of his observations and a description of his microscope. He was sceptical of both the instrument, which, he told Oldenburg, ‘seemed to convert everything into little balls’, and of Leeuwenhoek’s observations, which he thought might be ‘deceptions of his sight’. When he tried to replicate some of the observations made in aqueous media in Paris, he was unable to see what Leeuwenhoek claimed to have seen, and asked Oldenburg what credence was being given to his observations in England. Eventually, Leeuwenhoek told Huygens’s father that he was using fine glass capillary tubes to draw up the liquid to be viewed under the lens, and sent him some tubes to try for himself. Even using these aids, Christiaan still struggled to get results, but after persistent effort he was rewarded, and in July 1676, when he returned to The Hague, he began to take a more serious interest in this form of microscope.
He made a French translation of Leeuwenhoek’s account of his major achievements for communication to the French Academy of Sciences. (An English translation appeared in Philosophical Transactions.) The paper described in vivid tones how Leeuwenhoek had seen in rainwater ‘little animals which appeared to me more than ten thousand times smaller than those of which M. Swammerdam has described the form, which he calls flea or water lice’, including organisms with bodies comprising clusters of transparent balls, some with little horns ‘like horses’ ears’, and tails three times longer than the body with another ball at the end. Other results concerned well water taken from his courtyard, sea water and Delft canal water (which was used to make beer), as well as peppered water and waters infused with ginger, cloves and nutmeg. All these revealed animal life teeming in such profusion that ‘there could be several thousand in a drop of water’; only water melted from three-year-old snow revealed no living creatures. Leeuwenhoek wrote delightedly to Christiaan when he heard that news of his discoveries had been well received in France, and hoped he would repeat the favour for some ‘trifling observations’ he had made since.
Christiaan Huygens probably learned of Leeuwenhoek’s discovery of human spermatozoa from him directly when he was back in Holland. This work in particular seems to have kindled a wish to take up experimental microscopy for himself. In addition to his exchanges with Leeuwenhoek, he also visited Swammerdam. A young Rotterdam lens-maker, Nicolaas Hartsoeker, who had seen Leeuwenhoek’s public demonstrations of the microscope, schooled Christiaan and his brother Constantijn in a new way of making the bead lenses, and devised a better means of controlling the illumination of the object to be viewed. Christiaan may have improved or altered Hartsoeker’s setup sufficiently to satisfy his conscience in claiming it as his own when he took one of these microscopes with him back to Paris in 1678. Constantijn even had one of the highly portable devices with him at the bloody battle of Saint-Denis in August 1678, the last major engagement of the Franco-Dutch War. Huygens made his own observations of the spermatozoa of various animals, and experimented by heat-treating various waters and then counting the animalcules that appeared under the microscope. He found that the microorganisms reappeared both in water that had been frozen and in water that had been boiled, but they multiplied much more slowly in the latter.
As he had hoped he might, Hartsoeker accompanied Huygens back to Paris, where he was able to take advantage of the senior man’s introductions to French scholars. Their work together, along with the Dane Rømer, culminated in the development of a microscope with a rotating stage capable of holding six different lenses. With renewed patriotic consciousness after the war (and briefly forgetful of where his funding came from), Huygens reminded his French colleagues that spermatozoa were a Dutch discovery, and that for this new invention ‘none of the honour is to be attributed to the French nation, for it played no part in it’.
After just a year in Paris, Hartsoeker was disappointed to find the novelty of the instrument already wearing off. In September 1679 he reported to Huygens: ‘I doubt not that the French interest in microscopy has already evaporated . . . people will have to persist with it for longer ere they become much wiser.’ But Huygens, too, soon set aside the microscope in favour of other activities. Hartsoeker departed for Holland; he would return to settle in Paris in 1684, but this time it would be to build a series of ever larger telescopes for the observatory. Microscopy fell from fashion, limited by the difficulties of seeing and of knowing what one was seeing, and scholars’ interest turned back to the venerable science of astronomy.
‘Cursed and banned from the people of Israel’ in Amsterdam, Baruch Spinoza was earning his living by grinding lenses in the small village of Voorburg outside The Hague when he wrote one of the greatest of all works of modern philosophy. Ethics was published in 1677, a few months after Spinoza’s death at the age of forty-four.
He had known it would cause controversy. Using mathematical rigour, he sought to disprove the existence of a sentient god. For good measure, he declared that good and evil did not exist in any absolute sense, but were to be regarded objectively as forces leading to individual human betterment or impairment. He reasoned that emotional investment in past traumas and in future hopes or fears is irrational because they are only products of our artificial conception of time. His greatest influence had been Descartes, but now he argued contrary to the Frenchman that the body and mind are not mutually independent like a machine and its controller. Instead, they are metaphysically identical, so inextricably bound up with one another that there are forms of knowledge that can be said to be embodied – held within the body, not only by the mind. This is credible when one considers sporting prowess or the physical aspect of creativity displayed by a painter or a sculptor, but in Spinoza’s conception it extended to more quotidian areas of expertise, such as writing or sewing or washing down the stoop. These ideas have taken their place in the philosophical canon. But what was the background that encouraged Spinoza to nurture these so humane, and at the time so revolutionary, thoughts?
‘[A] good-looking young man, with an unmistakably Mediterranean appearance’, according to the monk who left us the best contemporary description of him, Spinoza was small in stature, with black eyes, black hair, and a ‘beautiful face’. Sephardic Jews, his ancestors had fled from Spain to Portugal and then, when the Inquisition pursued them, to the Dutch Republic, where Baruch was born in 1632 and spent the entirety of his quiet life. By his virtuous conduct and work, he became the man whom Bertrand Russell called ‘the noblest and most lovable of the great philosophers’.
In Amsterdam, he gained the education – absorbing ideas from literature, dissenting Protestant thought and even the theatre – that ultimately caused the elders of his synagogue to exile him for the ‘abominable heresies which he practised and taught’. It was probably after this that he learned to grind lenses. This practical skill stood him in good stead when he moved away, initially to Rijnsburg outside Leiden and then to Voorburg, where he sustained himself by making lenses for the new optical instruments – the telescopes and microscopes of gentleman scientists, camera obscuras for artists – as well as lenses for spectacles. Lens-grinding, though it might seem like an antiquated handicraft, was also a wholly modern activity, and Spinoza became very good at it. His lenses were sought out by leading astronomers, including Christiaan and Constantijn Huygens. Even though they ground their own lenses, they prized Spinoza’s above those of other makers. The Huygens brothers regarded Spinoza both as an occasional associate and as a competitor. They swapped calculations and books, and compared methods of bringing lenses to a high polish, but did not share everything, especially not the ‘Huygens eyepiece’, an arrangement of two lenses which Christiaan had found would overcome chromatic aberration.
Spinoza was greatly interested in the new sciences, especially optics, and was aware of the work of the Huygenses early on through his correspondence with Henry Oldenburg, who had visited Spinoza in Rijnsburg. When Spinoza moved to Voorburg in 1663, his little house in the town was only yards from the Huygenses’ Hofwijck estate. There, in the spring of 1665, Christiaan was able to show Spinoza the shadow cast by Saturn’s ring onto the planet’s surface. We may picture them. The telescope is set up in the garden, perhaps on the gravel forecourt across the moat bridge from the house, where it would not be too shaded by trees. The night is moonless and clear, for to see Saturn at all it requires optimal conditions, and the air is not yet warm. The two men, both in their early thirties, huddle before the telescope in their heavy clothes, shapeless in the dark. Equals in some respects, both were free spirits without the ties of family life, both comfortable in their chosen pursuits. But there may have been some awkwardness. Christiaan might have been patronizing, even a little bumptious, eager to show off his planet. Spinoza, necessarily, would have been deferential, hesitant to follow his host’s lead, as well as captivated and enthralled not only by what he was able to see, but also by the marvellous apparatus by which he could view it.
This unlikely companionship between a banished Jewish tradesman and an aristocrat with links to the highest levels of Dutch society was strictly scientific. The practical empiricist in Christiaan found Spinoza’s tendency to abstract thinking hard to take, and their relationship remained cordial but distant, with Huygens referring to ‘the Jew of Voorburg’ and ‘the Israelite’ in correspondence with his brother rather than using any familiar name.
Spinoza had found an occupation that would maintain him, and one that made good use of his scientific acumen. Perhaps he had found something more, too. ‘Grinding and polishing lenses, in Spinoza’s day, was a quiet, intense, and solitary occupation, demanding discipline and patience – in a word, an occupation perfectly suited to Spinoza’s temperament,’ according to his biographer Steven Nadler. What connection might there be then between this work and Spinoza’s philosophical output?
Spinoza believed that lenses were best ground by hand: ‘a spherical surface is more safely and better polished freehand, rather than by any machine,’ he told Oldenburg. It was tedious and hazardous work for those not fully attuned to its rhythms and demands. Understandably, efforts were made, not least by the Huygens brothers themselves, to mechanize the process in order to lessen the drudgery and reduce the risk of making a slip. But Spinoza felt it was better to use his sense of touch to adjust the pressure and friction of the glass against the dish with minute precision, and resisted the use of machinery.
In Ethics, Spinoza identifies three ways in which we gain knowledge: by random sense experience or imagination; by the use of reason, which may include formal instruction; and by intuitively grasping the essence of a thing, by which Spinoza means gaining an appreciation of its place within God’s overall creation. It is bold enough to say that we can learn simply by grasping the essence of a thing, but it would surely be more bold for an ‘armchair’ philosopher to make this claim, than one like Spinoza, whose own hands were routinely engaged in close physical labour that transformed the appearance of matter.
Using methods of proof taken from Euclidean geometry, Spinoza asserts that God cannot stand outside nature, and so must be in nature and in all of nature. To the extent that God exists, God is nature, therefore. He observes further that our bodies are subject to the laws of nature – a fact readily appreciated from working at a grinding table or undertaking any exhausting physical task. When we remember this, Spinoza argues, we become free from evil passions and the fear of God because we understand the futility of resisting these laws.
Departing from Descartes, Spinoza believes that mind and matter are not inherently separate, but that the two are intimately connected. In particular, he thinks that expert knowledge belongs with the realm of ideas and thoughts, rather than residing in the mind, and is therefore accessible to the body as much as to the mind. ‘Thus,’ according to Aristides Baltas, a philosopher of science (and recent Greek minister of culture), ‘expert action manifests the merger of mind and body and displays how this merging works: a body-mind, that is, a person as body-mind, knows on his or her own, by his or her inseparable body and mind, what the body should do and what the mind should do and how to act with both as inseparable.’ Watching craftspeople at work, it is easy to appreciate this from the tactile feedback they obtain as they form an object. It is as if the eyes can see through the shaping fingers.
Voorburg seems an unlikely setting for revolution of any kind, and yet only yards away from where Christiaan Huygens was beginning to understand the relativity of motion, Spinoza was claiming that time itself was an unreality. This is surely another realization stimulated by the sensations of his work. In The Craftsman, the sociologist Richard Sennett describes how craft workers lose their self-awareness and in a sense merge with the object they are making: ‘We have become the thing on which we are working.’ The successful accomplishment of a task, arrived at through intent concentration and the application of expertise, is ‘invariably accompanied by a feeling of being at one both with oneself and with the world at large’, according to Baltas. Working in this way, body and mind together realize in the object or experience created a manifestation of the creator’s ‘whole and undivided nature’, and show that he or she has ‘taken in the world as it really is and hence that he or she has been in full harmony with it’.
Aside from the crafted object, the effect of this process on the maker is to bring a profound sense of satisfaction that infuses both body and mind – a ‘feeling that,’ as Baltas puts it, ‘he or she has fully lived the moment of success as a present moment, the feeling, precisely, of having experienced eternity’. It materializes the sense of a ‘job well done’, where body and mind have worked together without, as it were, thinking about it. Perhaps this sensation seeping through Spinoza’s body in his little workshop in Voorburg informed another doctrine of his, that of ‘the eternity of the mind’, or the idea that mind exists outside time.
Spinoza’s daily work of grinding lenses may not have directly inspired his specific ideas about the human mind and its place in nature, but it is clear from his own writing that there was little to separate the development of his philosophy from this practical activity. In a series of letters written during the first half of 1666, just a few months after Huygens had shown him the ring of Saturn, the philosopher recapitulated his conception of God. In the last of the three letters, he summarized his position – ‘there is nothing outside God that is’, he wrote – before moving seamlessly on to discuss aspects of refraction, complete with an optical diagram.
Despite the social distance between them, Huygens and Spinoza were more attentive to each other’s ideas and methods than they were sometimes prepared to let on. Though he found its abstract language challenging, Huygens was undoubtedly influenced by Spinoza’s philosophy as well as by his optics, as is apparent in the nature of the speculations he made late in his career about life on other planets. And, while Huygens was always eager to learn how Spinoza obtained such transcendent results with his apparently primitive technique of grinding lenses, the dedicated handcraftsman Spinoza was actually desperate to know more about Huygens’s machine for doing the same job.