The city of Delft: a node of optical knowledge?

As early as the end of the sixteenth century Delft had witnessed inside its walls the activities of some mathematicians and scholarly liefhebbers. Well known, for instance, are the involvements of the mathematician and engineer Simon Stevin of Bruges with Delft windmills in the 1580s. One of his Delft acquaintances was Jan Cornets de Groot, the father of the famous legal scholar Hugo Grotius. In 1575 De Groot had been one of the first students of Leiden University, and with a degree in philosophy he excelled in many scholarly subjects. Professionally Jan de Groot would become one of Delft's mayors, but in the history of science he is better known as the person who, together with Stevin, performed experiments on falling bodies, pre-dating the similar – but better-known – experiments by Galileo Galilei.Footnote ¹⁸ In 1585 Stevin dedicated his book L'Arithmetique to De Groot. From this dedication we know that De Groot had also carried out optical experiments, especially with mirrors.Footnote ¹⁹ Stevin himself was also engaged in this subject. Already in 1595 he was working on a book on optics, which was eventually published in 1605 as a volume of his Wisconstige Gedachtenissen (Mathematical Thoughts).Footnote ²⁰ Another young man with an interest in optics was Petrus Vosmer, member of one of Delft's leading families. In 1599 he owned a copy of Giambattista della Porta's De Refractione Optices (1593),Footnote ²¹ in which image formation and location in concave mirrors and convex lenses is discussed.Footnote ²² Vosmer's inscription at the beginning of his book reveals that he evidently appreciated its content.

Also active in Delft were the mathematical practitioners Simon van der Eycke and Ludolph van Ceulen, who in the 1580s fought a fierce printed battle against each other over the value of π. Van Ceulen was a protégé of Jan de Groot. In the 1580s and early 1590s he taught both mathematics and the art of fencing. With this he acquired such fame that the Leiden professor in mathematics, Rudolph Snel (Latin Snellius) sent his own son (and later successor), Willebrord Snel, to Delft for instruction by Van Ceulen. Indeed, when, in 1600, the Dutch stadtholder Count Maurits of Nassau founded a new division at Leiden University devoted to mathematical instruction in the vernacular for surveyors and military engineers, the curators of that university (among whom were Jan de Groot) appointed Van Ceulen its first professor.Footnote ²³

After graduation, many military engineers trained at this Duytsche Mathematique found employment in Delft. From a military perspective, Delft was one of the most important cities in the Dutch Republic. In 1572 the States General, the supreme political organ of the young republic, had selected Delft as the central place to store its gunpowder and weaponry. A former Catholic chapel, sequestered by the government after the Protestant Reformation, was equipped as their arsenal. This Generaliteits Magazijn stood along the Oude Delft, one of the main canals of Delft. The provincial government, the States of Holland, followed this example. In 1602 they, too, constructed a large arsenal at the end of the Oude Delft.Footnote ²⁴ Opposite and next to this Armentarium were the offices and warehouses of the Delft branch of the Dutch East India Company (VOC), founded in the same year. Over the next two decades Delft also obtained participation in the Noordsche Compagnie, as well as in the West India Company (GWC), founded respectively for whale hunting and trade with the Americas. This robust military and nautical presence in Delft meant that during the entire seventeenth century basic mathematical knowledge was abundantly present within its walls.

The emergence of the telescope 1: an early spyglass from Delft at Leiden University

As a starting point for our investigation of the optical interest in Delft we take the itinerary of telescope lenses produced in Delft in the first half of the seventeenth century. The impact of the telescope, invented in 1608, on new cosmology and natural philosophy is well documented. The influence of this instrument on the shaping of theory and other optical devices developed later is well known and can hardly be underestimated. Optical instruments of the seventeenth century embodied ‘the intersection of mathematical, physical and technical sciences’.Footnote ²⁵ However, far less is known about the local production and use of optical instruments, although the artisanal knowledge of lens grinders was indispensable for the building of these theoretical frameworks.

After the demonstration of the telescope at an international peace conference in The Hague in 1608, the device rapidly spread all over Europe.Footnote ²⁶ Already in 1609 – that is, within a year of its invention – such a spyglass made by an unnamed Delft spectacle-maker was shown at Leiden University. In one of the lectures of the mathematics professor Rudolph Snel, an ‘ordinary telescope which had only one tube’ was demonstrated. According to the recollection of one of Snel's students, Théodore Deschamps, this instrument had been made by a Lunetier de Delft. The maker had constructed the telescope by ‘putting the glasses at due distance, and to cover the parts of the convex glass where the rays coming from the object did cross each other too much’.Footnote ²⁷ Deschamps probably indicates here the diaphragm that was needed at the objective end of the instrument, to cut off the outer light rays which would blur the image as a result of imperfect curvature near the circumference of the objective lens.Footnote ²⁸

At that time the only spectacle-maker in Delft was a certain Evert Harmansz, who in the mid-1630s would adopt the family name ‘Steenwijck’.Footnote ²⁹ Around 1610 he was one of few opticians of the Dutch Republic and the only one in Delft.Footnote ³⁰ Bearing this in mind, we can confidently identify him as the constructor of this early Leiden telescope.Footnote ³¹ A bill, dated 1628, proves that he did indeed make telescopes. It documents Evert Harmansz's delivery of a versich (a ‘far-see-er’; that is, a telescope) to the Delft citizen Floeris Gijsbertsen Castel.Footnote ³² Circumstantial evidence further supports the conclusion that Evert Harmansz was the constructor of Rudolph Snel's telescope. Evert was very close to several persons with connections to the mathematical branch of Leiden University. In 1607, in Leiden, he had married Annetgen Pietersdr, the daughter of Pieter Bailly.Footnote ³³ Evert's father-in-law not only was the former macebearer (Dutch pedel) of Leiden University, he also had worked at this university as an assistant at the mathematics and fencing school, directed by the former Delft mathematician Ludolf van Ceulen.Footnote ³⁴ Since the year 1600 Van Ceulen was also mathematics professor at the Duytsche Mathematique. This made Van Ceulen a direct colleague of Rudolph Snel. So, through his father-in-law, and perhaps also via Van Ceulen or Jan de Groot (then one of the curators of Leiden University), Evert Harmansz had a direct link to this institution.

The emergence of the telescope 2: other early telescopes at Leiden University

Willebrord Snel, Rudolph's son and later his successor in the Leiden chair of mathematics, was also very interested in optics. Snel Junior discovered the law of refraction, later named after him. From his correspondence we know that in 1610 he, too, owned a telescope, this one having a drawtube.Footnote ³⁵ He discussed this instrument with his ‘honoured uncle and friend’ Aemilius van Rosendael in The Hague, who also possessed a crude spyglass, made by a local spectacle-maker.Footnote ³⁶ Rosendael was evidently dissatisfied with the quality of his instrument.Footnote ³⁷ Therefore he requested Snel to order two lenses, similar to those in his telescope. In a following letter Willebrord confirmed that his lens grinder had made these glasses. Again, the name of the glasslijper is not mentioned. As the Snels lived in the same house,Footnote ³⁸ it is therefore not unlikely that Willebrord ordered his instrument from the same spectacle-maker as the earlier specimen, but of course we will never know this for certain.

Interestingly, in the years 1609–1610 spyglasses were also delivered to students of Leiden University. First, in the summer of 1609, ‘a fairly good’ telescope from the Netherlands was delivered to the German nobleman Johan Philip Fuchs von Bimbach. Recently, Arjen Dijkstra has convincingly argued that this telescope was acquired by von Bimbach's relative, Adamus Valentinus Fuchs von Bimbach, who matriculated at Leiden University in June 1609.Footnote ³⁹ After its arrival in Germany, von Bimbach lent the instrument to the astronomer Simon Marius, who started astronomical observations with this Dutch spyglass as early as November 1609.Footnote ⁴⁰ Shortly thereafter, Johannes Fabricius from East Friesia, who matriculated at Leiden University in December 1609, also brought a few telescopes home. Together with his father David Fabricius, he used these instruments in March 1611 in the discovery of sunspots, on which Johannes published a small tract in the summer or autumn of 1611.Footnote ⁴¹ Having heard of these new phenomena, Fabricius's Leiden teacher, Willebrord Snel, immediately devoted a booklet to these new celestial phenomena. But remarkably he ‘preferred in this matter to lean on reasoning, rather than to be informed by observations’.Footnote ⁴²

Snel obviously did not have much faith in the instrument, which at the time provided an observer with only a very small field of view. This dislike is also evident in Snel's letters. For although Snel's spyglass was evidently better than Van Rosendael's, Willebrord complained that he had the impression that his telescope performed less well than when he had first acquired it, but he admitted to Van Rosendael that this could not be true.Footnote ⁴³ However, seen in retrospect, Snel's observation can indeed have been correct. The early handmade lenses were far from homogeneous, so the mutual positions of the lenses were rather critical for correct image formation. A small displacement or rotation could blur the image. Only a proper combination of lenses resulted in a working telescope. In fact, in 1628 an optician from Dordrecht told Isaac Beeckman that in order to get a good spyglass, it was required to test many sets of lenses.Footnote ⁴⁴

The emergence of the telescope 3: Delft telescopes of Isaac Beeckman and Jacob Spoors

The next time a Delft telescope-maker is mentioned is around 1622. That year the astronomer Philippus Lansbergen advised Isaac Beeckman to obtain ‘a telescope like the one it seemed that Galilei had in his Sidereus Nuncius’.Footnote ⁴⁵ At first Beeckman tried to order suitable lenses from spectacle-makers in Middelburg and The Hague, but he was not satisfied with the results. He desired a lens with – in modern terms – a larger focal length. In 1624 he asked a grinder (den slyper) in The Hague to make such a glass, but this artisan answered him that ‘no one in the world’ would be able to produce a glass with these specifications.Footnote ⁴⁶ Nevertheless Beeckman believed that somewhere there must be an artisan capable of doing this job. Eventually he obtained his first proper telescope from ‘the man in Delft’.Footnote ⁴⁷ Again this ‘man’ can be identified as Evert Harmansz Steenwijck, for in the first half of the seventeenth century he was the only optician in this city.Footnote ⁴⁸ About this Delft telescope Beeckman noted in his Journal that the maker had made some scratches on the lenses, so one could verify the correct position of the glasses. This remark testifies that Evert Harmansz was aware of the importance of a reproducible positioning of the lenses.

Why Beeckman turned to this Delft artisan to obtain his desired telescope is not known. He could have been tipped off by his acquaintance Jacob Spoors, with whom he performed the optical experiment mentioned earlier, and with whom Beeckman had kept up a correspondence.Footnote ⁴⁹ Spoors had been born and raised in Delft, and although in the 1620s he had moved to Oud-Beijerland (near Dordrecht), he always kept close ties with Delft, where his family lived. Originally Spoors was educated as a surgeon. He worked in that capacity in the years 1614–1621.Footnote ⁵⁰ But then he made a remarkable career change. Spoors went to Leiden, where he was trained in mathematics by Willebrord Snel (probably at the Duytsche Mathematique). Snel was also the examiner of the surveyors at the time of Spoors's admission on 24 September 1622.Footnote ⁵¹ The next year Spoors also qualified as a notary public. In 1623 he was admitted to this profession in the city of Dordrecht, although Oud-Beijerland remained his residence until 1636, when Spoors settled in Delft again. In that city Spoors worked for the rest of his life as a surveyor, notary public and solicitor at the municipal court of justice.Footnote ⁵²

From a book that Spoors published in 1638 we know that he, too, possessed a telescope. As usual, it is not stated who made this instrument. We only know that at that time Spoors lived only a few steps away from the workshop of the optician Evert Harmansz Steenwijck. With his ghesicht-gereetschap (‘tool for the eye’) Spoors made several astronomical observations. He witnessed the phases of Venus and the ‘mountains’ on the Moon. He had also projected the Sun's image on a screen to observe its ‘wonderful spots’. By recording the configuration of these sunspots, Spoors had confirmed Galileo's discovery that the Sun rotated on its axis, according to Spoors in about twenty days. He had also observed Galileo's major discovery: Jupiter's four satellites.Footnote ⁵³ This optical performance of a telescope is not as obvious as it would seem, for around the same time the Amsterdam professor Martinus Hortensius begged Galileo in Florence to send him a set of his Italian lenses, because – according to Hortensius – ‘in Venice, Paris, or Amsterdam no telescope could be acquired, capable of performing satisfactory astronomical observations’.Footnote ⁵⁴ In general, lens grinders capable of making good-quality lenses seem to have been very scarce in the 1630s.Footnote ⁵⁵

Spoors's new wonders of the world (1638) 1: the genre of the ‘books of wonders’

Spoors mentions his telescope in a remarkable booklet on the new natural philosophy that he published in April 1638: the Oratie van de nieuwe wonderen des wereldts, de nuttigheyd, de waerdigheyd, der wis- ende meet-konsten (Oration on the New Wonders of the World, and on the Use and Dignity of Mathematics and Geometry).Footnote ⁵⁶ The title indicates that we are dealing with a tract written in the tradition of the so-called ‘books of wonders’.Footnote ⁵⁷ Books of wonders were primarily books about nature, wherein authors demonstrated the wonders of God's Creation with references to both the Bible and natural phenomena. They were widespread in the seventeenth-century Dutch Republic. Both rarity and regularity in nature could be seen as examples of the almighty power of God. The study of nature thus became a moral obligation and a religious activity. Dutch orthodox Calvinists embraced this view. In this context, the metaphor of the ‘Book of Nature’ was often used: nature was like a second God-given Bible that could be studied to give testimony to or to contemplate the greatness of his creation.

Books of wonders published in the Dutch Republic followed this line of reasoning, combining the miracles of nature with popular theological ideas. Eric Jorink has assigned four distinguishing features to these books of wonders: first, they serve a pious, often apologetic goal, in which nature was presented as a book, a theatre or a mirror. These metaphors focused attention on the non-biblical sources of knowledge about God, which were in principle visible to all mortals. Second, the works are based on a wide range of sources, varying from the Bible to autonomous observations. Third, the works offer a survey of the most ‘wondrous’ facets of the whole of nature, giving examples of monstrous creatures, magical stones and giants, phenomena that were usually given a supernatural meaning. Finally, these works were published in the vernacular, because the authors were aiming at a wide popular audience.Footnote ⁵⁸

Shortly before Spoors's Oratie was printed, the Delft minister Dionysius Spranckhuysen had published two such ‘books of wonders’: the Macro-cosmus, ofte aenmerckinghen over de scheppinghe vande groote werelt (1634) (Macrocosm, or Remarks on the Creation of the Great World), and the Micro-cosmus, dat is aenmerckingen over de scheppinghe vanden menschen, ofte de kleyne werelt (1636) (Microcosm, That Is, Remarks on the Creation of Humankind or the Small World). Both books follow the story of the Creation as told in Genesis, without any reference to the natural-philosophical developments of the day. As Jorink has noted, these new scientific currents appear to have entirely bypassed this Delft minister.Footnote ⁵⁹

Spoors's new wonders of the world (1638) 2: nature as a source of new knowledge

In his own book ‘on the new wonders’, Spoors presents a completely different message, although he uses a rhetoric similar to Spranckhuysen's. By doing so, Spoors positions himself in the familiar discourse understood by his audience and the city governors to whom he dedicated his book. Yet he simultaneously stresses the importance of nature as a source of new knowledge. Thus while Spoors refers to his observations as ‘wondrous’ (wonderlijck), a ‘novelty’ (nieuwigheyd) or an ‘oddity’ (vreemdigheyd), he also emphasizes the truth lying in mathematics and optics. In contrast to Spranckhuysen, Spoors considers observing with his eyes and with his ‘tool for the eye’ (ghesicht-gereetschap) as the ultimate proof of these new oddities. In fact, the telescope is conceptualized as a wondrous new instrument that makes visible what was invisible before.

Spoors thus maintains the style and vocabulary of Van Spranckhuysen's two books of wonders, but adds other dramatic content to it. In a way it looks as though Spoors tries to complement Spranckhuysen's two volumes. He discusses several topics on which Spranckhuysen had written, such as the heavenly bodies, the proportion of the human body and the ancient Olympic Games.Footnote ⁶⁰ But where Spranckhuysen gives the primacy of authority to the Bible and considers this God-given book a compendium of all knowledge, including nature, Spoors prefers the observation of nature itself as the most reliable source of information and authority. Studying nature in its own right, for instance by observing the heavens, is for Spoors the ultimate way to experience and honour God's almighty powers. Both Spranckhuysen and Spoors refer to the Bible and to several classical authors. But where Spranckhuysen cites ancient philosophers such as Plato, Anaxagoras, Thales of Miletus, Diogenes, Empedocles and, primarily, the biblical Moses, Spoors refers mostly to ancient mathematicians, such as Euclid, Ptolemy, Anaxagoras, Pythagoras and Aristarchus of Samos.Footnote ⁶¹ In this choice Spoors underpins the importance of ‘the touchstone’ of mathematics.Footnote ⁶²

Spoors opens his book with his own translation of a few lines from the Latin poem Octavia, which he attributed to the stoic Seneca (this poem is nowadays considered to stem from a later period), wherein the poet praises observation of the heavens, the sun and the moon as a way to achieve peace of mind. This opening statement provides an important clue to Spoors's ideas regarding natural philosophy and optical instruments. Like the assumed Seneca, Spoors supposes a direct correlation between the cosmic order and the moral order. This moral and natural order is universal and can be seen everywhere around us. Observations demonstrate this order and lead us to God. Spoors explains how, through his ‘knowledge of measuring the earth’ (kennisse van het meeten der Aerde), he rose to his knowledge of the heavens. He paraphrases Psalm 19:2, by saying that ‘the heavenly creatures’ preach the great power of God, ‘day and night’.Footnote ⁶³

According to Spoors, mathematics provides mankind with a divine tool, with which the order and regularity of God's Creation can be understood. Through mathematics one can read the true new wonders of the world. Spoors's ideas about nature, like those of Beeckman, are coloured by the practical techniques of craftsmen, as well as by the sixteenth-century philosophical concepts of Petrus Ramus. Ramus underpinned the significance of mathematics in reasoning and emphasized the importance of a connection between theory and practice. Ramus's philosophy was very influential in the early seventeenth-century Netherlands. Both Rudolph Snellius and Isaac Beeckman have been identified as adherents of Ramism.Footnote ⁶⁴ Spoors, too, refers to Ramus in his discussion on the analogies between God and the geometrical figure of the circle, both perfect of form, with neither beginning nor end.Footnote ⁶⁵

Spoors's new wonders of the world (1638) 3: ‘maintaining the right proportions’

In accordance with this mathematical approach, Spoors discusses in his Oratie ideal proportions. According to the Bible, the human body is the crown of God's Creation and ‘the measure of all things’.Footnote ⁶⁶ Therefore its geometrical forms must be considered perfect. For that reason the proportions of both Noah's Ark and the Jerusalem Temple were based on those of the human body – that is, the proportions of healthy humans, Spoors hastens to add. There are also human ‘mutts and monsters’, sick people, who lack the right proportions.Footnote ⁶⁷ Spoors emphasizes the defining importance of proportion and measure to ‘all arts and professions’ (alle Consten ende Ampten), such as music, medicine, rhetoric, shipbuilding, furniture design, architecture and, of course, painting.Footnote ⁶⁸ Especially in painting, ‘mirroring’ the right proportions is of the utmost importance; it determines whether a picture gives an ‘ideal’ or a ‘monstrous’ image. The painting technique of an artisan and his use of colour can be as neat as one can imagine, but the resulting product, the painting, can only be truly beautiful if the right proportions are applied.Footnote ⁶⁹ Therefore it is crucial to apply a correct use of perspective. This determines whether or not an image attains the right proportions. By saying this, Spoors more or less puts into words a way of thinking that in due time became mainstream thought among Delft painters.

Spoors's new wonders of the world (1638) 4: man-made machines providing ‘irrefutable demonstrations’

Spoors's devotion to perfect proportions is also the reason why he unhesitatingly accepts the Copernican planetary system. As Rienk Vermij has noted, in those years – around 1640 – this world view was far from generally accepted in the Dutch Republic.Footnote ⁷⁰ According to Spoors, the ultimate proof of Copernicanism is that this theory is more ‘orderly, appropriate, better and perfect’ in the sense that it comes closer to the ‘true form of the Heavens’.Footnote ⁷¹ God is the perfect architect, wise and careful, whose works are faultless, better than anything that can ever be created by mankind.Footnote ⁷² Nevertheless Spoors praised man-made visual tools which represented the Copernican system, such as a planetarium by Cornelis Drebbel in the cabinet of the English king, or a sphaera designed by the Amsterdam instrument-maker and publisher Willem Jansz Blaeu, and a planisphere recently made by the Haarlem citizen Roelof Jansz.Footnote ⁷³ In their ability to visualize abstract reasoning, such objects were of vital importance, as people could ‘witness with their eyes the truth, instead of delusion’.Footnote ⁷⁴ Spoors admired Drebbel's ability to ‘copycat nature’ (de natuyr weten near te apen) and thus ‘prove by act’ (metter daedt bewesen) the Copernican world view.Footnote ⁷⁵ In this manner, man-made objects could confirm in a directly visible way by ‘irrefutable demonstrations’ (onweder-leggelijcke demonstratien) the underlying moral and Godly order of nature.Footnote ⁷⁶

Spoors's new wonders of the world (1638) 5: experiments, observations and the importance of optics

Spoors was evidently impressed by the work of learned contemporaries such as Galileo Galilei, Tycho Brahe, Johannes Kepler and their Dutch counterparts Simon Stevin, Philippus Lansbergen, Isaac Beeckman, Martinus Hortensius and Cornelis Drebbel. He praised ‘these superb scholars of the whole world’, who by their observations had displayed the new world system with ‘concise incontestable reasoning’.Footnote ⁷⁷ With the remark neffens ons (‘like myself’) Spoors placed himself on the same footing as these renowned scholars. After all, he too had performed experiments and had ‘mirrored’ nature with his own visual tool. Spoors refers here also to the experiment mentioned at the beginning of this paper. With some other equipment Spoors had investigated the ‘thickness of the air’ and ‘our vision from the eye to the stars’ (onse ghesicht-strael tot aen de vaste sterren). In this experiment Spoors used the light of a candle as an analogy for the light of the stars. It is a nice example of the use of simple tangible objects in a demonstration of a rather abstract phenomenon.Footnote ⁷⁸ This experiment, which Spoors had performed at the request of ‘some learned persons’ (that is to say, Beeckman), had proven that the stars were ‘not as large’ as had hitherto been assumed.Footnote ⁷⁹ According to Spoors, this result could also be achieved by mathematical reasoning, but he does not explain further. Beeckman, however, expresses himself more clearly about this experiment in his Journal. Because starlight travels continuously through a vacuum, while the candlelight travels through air (experiencing absorption during its whole trajectory), comparatively speaking, starlight diminishes less than candlelight. So Beeckman concluded that the amount of light emitted by the stars must be less than originally expected, or, as he put it, ‘Consequently the apparent diameters of the fixed stars are much smaller than one thinks’.Footnote ⁸⁰

All in all, it is evident that Spoors valued optics as one of the most important elements of mathematics. Thanks to the light of the stars, the wonders of the universe are revealed to mankind. The title page of Spoors's book signals his emphasis on optics as one of the main keys to the study of God's Creation (see Figure 1). Not only does he refer to the well-known Psalm 8, but the vignettes on this page are four optical representations, demonstrating various roles played by sun- and starlight. These roles are: (1) the Sun illuminating the Moon, (2) the Sun indicating time on a sundial, (3) the Sun igniting fire using spectacles as a burning glasses and (4) the light of the Pole Star showing north. The metaphor of light informed Spoors's body of thought: light is the moral counterpart of shadow. It is therefore only appropriate that Spoors dedicates his book to the city's magistrates, expressing his wish that they will shine their light upon the city of Delft, just as God the father will shed his light upon them.Footnote ⁸¹

Figure 1.

Vignette on the title page of Spoors's Oratie (1638) (Amsterdam University Library).

The optical commodities of the military engineer Johan van der Wyck

In March 1650 a Delft optician emerges again in the historical sources. Lieuwe van Aitzema, a well-known Dutch diplomat and author, asked this Delft artisan if he could make a special telescope for his patron, the German Duke August of Braunschweig-Lüneburg.Footnote ⁸² This duke was a great collector of books as well as objects, and the library he founded (the Herzog August Bibliothek in Wolfenbüttel) is still renowned for its collections. To obtain his commodities the duke had agents on the lookout all over Europe. In Holland, Aitzema was such an agent, delivering information, books and objects to the Wolfenbüttel Kunstkammer.Footnote ⁸³ Apparently he had spotted a novelty in Delft: a walking cane with a hidden spyglass: a real desideratum.Footnote ⁸⁴ But things were not going as expected: ‘The man who makes telescopes in Delft is old and a bad liar, because he has repeatedly promised to deliver such a tube, but he does not keep his word’, a disappointed Aitzema wrote to his patron.Footnote ⁸⁵ This complaint was repeated several times, so it is unclear whether the desired optical walking cane was ever delivered.Footnote ⁸⁶ At that time (1650) the optician Evert Harmansz Steenwijck was in his seventies. His wife had passed away not long before, and perhaps he was ailing himself, for he died in April 1654.Footnote ⁸⁷

But to Aitzema's good fortune, another person emerged in Delft who could do the same trick, and much more.Footnote ⁸⁸ This was the young military engineer Johan van der Wyck, our third Delft practitioner. Until now he has been overlooked completely in the vast literature on Delft painting or scholarship. Whether or not Van der Wyck learned his lens-making skills from Steenwijck is not known. But it is quite possible that Steenwijk's optical tools were bought by Van der Wyck, for since Steenwijck's death his heirs had been looking for a buyer of all his goods, which must have included his workshop.Footnote ⁸⁹

Van der Wyck was born in 1623 near Osnabrück as the second son of a German nobleman. He had left his parents when still young, probably for reasons of faith.Footnote ⁹⁰ After his arrival in the Calvinist Dutch Republic, he had chosen to enlist in the army, a rather typical career for a younger son of noble descent. As a military engineer Van der Wyck was assigned to Delft, at some point between 1646 and 1654.Footnote ⁹¹ He stayed there until the spring of 1657, when he left for Sweden. In the Baltic he had a glorious military career, ending as general in the Swedish army, returning to the Netherlands after his retirement.Footnote ⁹²

During his sojourn in Delft, Van der Wyck made several optical instruments (telescopes, microscopes and other ‘rare works’), which attracted attention from all over Europe. In the fall of 1654 his skills as an optician were noticed by the young Christiaan Huygens in The Hague, who just at that time was learning the art of telescope-making. In October 1654, only two weeks after the huge explosion of the Delft gunpowder repository, an event known as the Delftse Donderslag, a parcel with two telescope lenses made by Van der Wyck was delivered to Huygens in The Hague.Footnote ⁹³ During the next year Huygens would discuss Van der Wyck's work on several occasions with both his father and his brother Constantijn. And although Christiaan was sceptical about Van der Wyck's abilities, he still urged his brother to investigate the microscopes of this Delft ‘polisher’ which showed ‘worms in the cream of milk, in flour and in the flesh of a hare’.Footnote ⁹⁴

In August 1655 Van der Wyck's optical skills had also been noticed across the North Sea. The reason was a remarkable demonstration Van der Wyck had given before an audience in The Hague. This event is recorded in the papers of Samuel Hartlib in London, one of the important ‘intellectual brokers of seventeenth-century Europe’.Footnote ⁹⁵ Hartlib had a wide-ranging interest in science-related subjects of all kinds, especially technological innovation in optics. In August 1655 he wrote in his ephemerides – a personal diary – about ‘an excellent Man at Delph in Optics and glass-grinding, who begins now to make some rare works’.Footnote ⁹⁶ Later he gives more details:

It is evident that Hartlib's note describes some kind of projection device. More details of the optical devices made by this ‘most rare workeman’ from Delft are revealed in the papers of Duke August. In the winter of 1654–1655 Van der Wyck had boasted to Lieuwe van Aitzema that he had already delivered some optical playthings with rhombic glasses to ‘a foreign king’, as well as to an Amsterdam merchant. But now he could offer to Duke August something very special: a device that he recently had invented, which had never been seen before. It was an optical show-box, a kind of peepshow, in which the viewer could witness the alteration of the architectural setting of an Italian castello with a background of mountains, into a naval piece revealing ships and mast. Van der Wyck's muddled Latin description does not mention the working mechanism of the device, but it probably involved a kind of perspective box with a semi-transparent mirror and alternating lighting.Footnote ⁹⁹ This description is a most interesting document, for the better-known perspective box emerged in the Netherlands in the late 1650s (see Figure 2).Footnote ¹⁰⁰ Van der Wyck's device evidently was a variant of such an apparatus, indicating that in building this device he must have cooperated with at least one of the contemporary Delft painters.

Figure 2.

Perspective box by the Dordrecht painter Samuel van Hoogstraten (c.1670) (National Gallery, London).

Today only six of these mid-seventeenth-century perspective boxes have survived, but none with an illusionistic arrangement as described by Van der Wyck.Footnote ¹⁰¹ Due to the lack of surviving documents we can only speculate which painter the then thirty-two-year-old Van der Wyck might have engaged in his project. Walter Liedtke has rather convincingly demonstrated that the View of Delft, painted in 1652 by Carel Fabritius, once had been part of a perspective box, but as Fabritius died in the Delftse Donderslag in October 1654 his involvement in Van der Wyck's project of 1655 can be ruled out.Footnote ¹⁰² It is tempting to suppose that the two eldest sons of Evert Steenwijck were involved in Van der Wyck's optical project (both were educated as painters), but given their oeuvre – still-life paintings with a so-called vanitas or memento mori bias and some kitchen interiors – this seems quite improbable.Footnote ¹⁰³ Other Delft painters more likely to have contributed to a perspective box are Leonaert Bramer (fifty-nine years of age in 1655), the then forty-four-year-old Hendrick Cornelis van Vliet, or the twenty-six-year-old Pieter de Hooch, who had settled in Delft in 1652.Footnote ¹⁰⁴ Especially the latter is renowned for his ‘box-like chamber views’ and his experimenting with optical effects in his paintings.Footnote ¹⁰⁵

In either case, in June 1655 the Nobilis optici zu Delfft was paid a total sum of 310 ‘reichsthaler’ for a complete set of this optical equipment, on which he had worked for twelve weeks.Footnote ¹⁰⁶ This delivery included two telescopes with five lenses each, indicating that Van der Wyck followed the newly invented scheme for an eyepiece tube with multiple lenses, proposed in 1645 in a publication by Antonius Maria Schryrl de Rheita.Footnote ¹⁰⁷ Compared to the earlier Dutch telescope, such a multiple lens arrangement widens the field of view, as is confirmed by Van der Wyck's statement that with his telescopes one could observe at one hour distance ‘two cohorts of soldiers’ instead of ‘only half a man’, as with the older Dutch telescopes.Footnote ¹⁰⁸

This commission for Duke August was one of Van der Wyck's last optical projects in Delft, as he would enter the service of the Swedish crown, leaving Delft in the spring of 1657. In the summer of 1663 Van der Wyck returned to Delft for a short visit. His presence there was noted by Christiaan Huygens, as well as by Isaac Vossius, another Dutch scholar with a great interest in optics.Footnote ¹⁰⁹ In a meeting with the well-known French traveller Balthasar de Monconys, Vossius praised the Delft telescopes, with which ‘one could see the mountains on the moon’.Footnote ¹¹⁰ However, at that time Van der Wyck had already returned to his military service, with a commission as governor of Stralsund, one of the Baltic ports in German territory conquered by the Swedish army. But even there Van der Wyck continued to make telescopes. The astronomer Caspar March informs his colleague Johannes Hevelius in Danzig about Van der Wyck's activity in Stralsund:

Jacob Spoors as the nexus of a Delft network of ‘like-minded thinkers’?

Johan van der Wyck and Jacob Spoors evidently were well acquainted. This is clear from the fact that in 1675, after his retirement from the rank of general in the Swedish army, Van der Wyck and his wife travelled to Delft specifically to have Spoors draw up a new will.Footnote ¹¹² The couple had settled in a mansion in Noordwijk (near Leiden), so their choice of Spoors as their notary can only be explained as a gesture ‘for old times’ sake’.

Thus, when Van Aitzema, Huygens, Hartlib and Vossius heard of the remarkable optical products of der Perspectivmacher zu Delfft, it can hardly be conceived that a liefhebber such as Spoors, living only a few yards away, should have been unaware of Van der Wyck's optical achievements.Footnote ¹¹³ On the contrary, given his contacts and interests, one can imagine that Spoors was fully aware of what was happening on his own doorstep. Moreover, when we realize that Van der Wyck emerged as a skilled optician in the very first years of Johannes Vermeer's career as a painter (he was inscribed at the St Luke Guild on 29 December 1653), it is tempting to think that Vermeer, too, witnessed a demonstration of Van der Wyck's optical devices, of the kind mentioned by Hartlib. At such an optical performance, Vermeer could even have had the company of the then still unknown Antoni van Leeuwenhoek, who had returned to Delft that very year. Was Spoors perhaps their go-between? The notary records suggest that Spoors was on good terms with Vermeer and his mother-in-law Maria Thins.Footnote ¹¹⁴ It was also Spoors who, in the years 1674–1677, probably in the process of surveying the city for the a new bird's-eye-view map of Delft (the Kaart Figuratief), was assisted by Van Leeuwenhoek in measuring the height of one of the Delft church towers.Footnote ¹¹⁵ In making this map Spoors worked closely with Jacob Verkolje, the same artisan who later painted Van Leeuwenhoek's magnificent portrait.Footnote ¹¹⁶

From the sources it is evident that Spoors was connected with artisans and practitioners of different sorts. Spoors indeed can be called a key figure in a Delft ‘network of like-minded thinkers’. Originally trained as a surgeon, he knew the basics of anatomy and medicine; as a surveyor he mastered practical mathematics, as a liefhebber he performed observations and experiments, as a botanist he had a tulip named after him, as an author he wrote about natural philosophy, as an editor he doubled the text of a judicial textbook (in 1642 and 1658), and as a poet he mourned the death of the famous Delft legal scholar Hugo Grotius (in 1645).Footnote ¹¹⁷ Put together these facts confirm that Spoors was one of Delft's prominent liefhebbers: a man well respected for his practical skills and theoretical knowledge. As such he acted in 1640 as the representative of Reynier Janssen de Witte, engineer of the king of France (ordinaris ingenieur des Conings van Francrijck) in Calais.Footnote ¹¹⁸ Similarly, in 1667 he mediated between the Delft surgeons' guild and two Amsterdam merchants in the sale of a stuffed rhinoceros and a large armadillo.Footnote ¹¹⁹ Spoors was also the notary of the mathematical instrument-maker Antony Sneewins, probably indicating that the men were on good footing with each other; not surprising when we realize that Spoors worked as a surveyor until an advanced age.Footnote ¹²⁰

These examples demonstrate Spoors's entwinement in Delft society. During his long life he was also well connected with several Delft painters. In the mid-1630s his tulip was depicted by Balthasar van der Ast (Figure 3).Footnote ¹²¹ In the late 1640s he and his wifeFootnote ¹²² were portrayed by the famous court painter Michiel Jansz van Mierevelt.Footnote ¹²³ Further, in 1655 the painter Pieter de Hooch became the godfather of a child of Suzanna de Roon and François Bo[o]gaert. Suzanna was the daughter of Spoors's sister Adrijana, and Bogaert was Spoors closest confrère, to whom he dedicated in 1658 his edition of the Corpus Juris.Footnote ¹²⁴ Spoors was also the acting notary for Justus de la Grange, a linen merchant, who employed De Hooch as his dienaer (servant).Footnote ¹²⁵ And in 1659 Spoors's son Johan married Aletta Elsevier, niece of the Delft painter Louis Elsevier, who twice became the godfather of Spoors's grandchildren.Footnote ¹²⁶

Figure 3.

Balthasar van der Ast's depiction of Spoors's tulip, painted in Delft in the mid-1630s (Paris, fondation Custodia).

Mapping the Delft practitioners

In Spoors's case this proximity of practitioners can even be mapped literally, when we look at a map of Spoors's immediate neighbourhood (Figure 4).Footnote ¹²⁷ During his stay in Delft, Spoors always lived on the same canal, called the Oude Delft. Until roughly 1650 he lived in a house on the east side (1A), and then he moved to the west side (1B).Footnote ¹²⁸ At paces away from his first residence we find the houses of notaries Cornelis Couckebacker (2) and Dirck de Haen (4), for whom Evert Harmansz brillemaecker (Steenwijck) frequently acted as a witness.Footnote ¹²⁹ This means that his workshop must have been nearby. Around the corner, in the Nieuwstraat, lived Floeris Gijesebertsz Castel, who in 1628 received a telescope from Evert Harmansz (5).Footnote ¹³⁰ Added to our earlier arguments, this proximity underscores the probability that Spoors's telescope came from Evert's workshop. We also find here the Generaliteits Magazijn, the military repository where Johan van der Wyck worked in the early 1650s (3).Footnote ¹³¹ He probably rented his lodgings on the other side of the canal from Catharina Noté, daughter of a military officer (11).Footnote ¹³² Close to the repository, in a house on the Hypolitusbuurt with a second entrance in the Nieuwstraat, Van Leeuwenhoek settled in 1653 (6) – so he was in the neighbourhood when Van der Wyck made his telescopes and microscopes, praised by Hartlib as ‘excelling those of Braband’.Footnote ¹³³ In Spoors's backyard, in the houses at the Wijnhaven or Wijnstraat (‘Wine Harbour’ or ‘Wine Street’), three other candidates for the supposed Delft network of like-minded thinkers can be identified. Spoors's direct backdoor neighbour was the apothecary In de Spiegel (‘In the Mirror’) (8). This shop was founded in 1584 by Cornelis Gerritsz de Man, a correspondent of the famous botanist Carolus Clusius.Footnote ¹³⁴ From 1617 to 1648 the business was run by his son, the apothecary Anthonis Cornelisz de Man, who retired in 1649 and was succeeded by his son Cornelis Anthonisz de Man. The latter was portrayed in his shop by his cousin, the painter Cornelis Willemsz de Man (Figure 5). The painting probably depicts a discussion of phosphorus, newly discovered in 1669, a substance related to the alchemical search for the transmutation of base metals into gold.Footnote ¹³⁵ In itself this painting presents firm pictorial evidence of a scholarly activity of which no written traces have survived. The portrayed discussion relates to the main businesses of the De Man family, which counted among its members several apothecaries and workers in precious metals.Footnote ¹³⁶ Interestingly, the painting reveals a chemical laboratory in the back of the shop. Some remains of these furnaces, the smoke of which Spoors must have smelled in his garden, were found during restoration in the last quarter of the twentieth century.Footnote ¹³⁷

Figure 4.

Fragment of the Kaart Figuratief, surveyed by Jacob Spoors in 1675–1677. 1A surgeon, notary and surveyor Jacob Spoors (1636–c.1650); 1B idem (c.1650–1677); 2 notary Couckebacker, for whom Evert Steenwijck frequently acted as a witness (1614–1616); 3 military repository Generaliteits Magazijn, where Johan van der Wyck worked (1654–1657); 4 notary De Haen, for whom Evert Steenwijck frequently acted as a witness (1618–1633); 5 Floris Gijesebertsz Castel, who ordered a telescope from Steenwijck in 1628; 6 Antoni van Leeuwenhoek (after 1653); 7 painter Johannes Verkolje (after 1670); 8 apothecary ‘In de Spiegel’ of Anthonis Cornelisz de Man (1617–1649), succeeded by his son Cornelis Anthonisz de Man (1649–1679); 9 notary and surveyor Johan van Beest (before 1648); 10 surgeon Assuerus van Moerkercken, where Evert Steenwijck went with his son in 1616; 11 Catharina Noté, the only Delft heir of the military engineer and optician Johan van der Wyck; 12 Binnenwatersloot, residence of Abraham Waelpot, publisher and Spoors's direct neighbour (c.1650–1658), as well as medical doctor Cornelis van der Heyden (d. 1637), owner of a large library (sold 1646).

Figure 5.

Painting by Cornelis Willemsz de Man of the apothecary's shop In de Spiegel (‘In the Mirror’) at the Delft Wijnhaven, probably depicting a discussion about glowing phosphorus, discovered in 1669. A chemical laboratory is in the background (National Museum, Warsaw, Poland, inv. M.0b. 22).

It is an educated guess that the apothecary In de Spiegel provided several painters in seventeenth-century Delft with the ingredients for their paint, perhaps making the apothecary's shop also a site for the exchange of pictorial knowledge. As a matter of fact, the painter Johannes Verkolje, with whom Spoors would make the Kaart Figuratief, settled in the 1670s in the house next to this apothecary (7).Footnote ¹³⁸

At the other side of the apothecary lived the surveyor and notary Johan van Beest, son-in-law of the painter Michiel Jansz van Mierevelt (9). It was through Van Beest that Spoors had ordered the (now lost) portraits of him and his wife. Van Beest, who died in 1648, owned a library with many mathematical and astronomical books (although it must be said that none of these were devoted to the new natural philosophy).Footnote ¹³⁹ Finally, more as an anecdote, but confirming the proximity of Evert Harmansz in the neighbourhood, in the house to the right of Van Beest had lived the surgeon Assuerus van Moerkercken (d. 1616), who in February 1616 treated a young son of Evert Harmansz brillemaecker for an upper-arm fracture (10).Footnote ¹⁴⁰ And of course there must have been other liefhebbers, beyond Spoors's proximity, who could have belonged to a Delft network of ‘like-minded thinkers’. A nice example is the medical doctor Cornelis van der Heyden on the Binnenwatersloot, who owned an impressive library, with several books on mathematics and astronomy, including a copy of Galileo's Sidereus Nuncius.Footnote ¹⁴¹

Jacob Spoors was thus literally surrounded by persons with a relation of some sort to mathematics, optics, chemistry or painting. In a more metaphorical sense Spoors was a pivotal figure, linking tacit knowledge of mathematical and optical practitioners such as Isaac Beeckman, Evert Harmansz Steenwijck, Johan van der Wyck and Antoni van Leeuwenhoek.

The innovative use of perspective among Delft painters

Perhaps Spoors's role goes even further. In – or shortly before – 1650 the brewer and painter Geraerd Houckgeest introduced a new kind of perspective in the paintings of his church interiors.Footnote ¹⁴² This innovative diagonal viewpoint inspired several other Delft painters. Artisans such as Emanuel de Witte and Hendrick Cornelisz van Vliet immediately followed this new direction in painting, which required good insight into geometry and optics. A short decade later, when Houckgeest and De Witte had already left Delft to seek their fortunes elsewhere,Footnote ¹⁴³ other painters continued to experiment with perspective and other optical effects in their depiction of Delft interiors. The best-known examples are Pieter de Hooch, Johannes Vermeer and Cornelis Willemsz de Man.

Why did these Delft painters bother to master such difficult topics? Who introduced them to geometry and optics? The above-mentioned painters all became members of the Delft St Luke Guild between 1632 and 1655.Footnote ¹⁴⁴ In these vital years there were only a few mathematically trained practitioners in the city, Jacob Spoors being one of them.Footnote ¹⁴⁵ Were these mathematicians involved in the training of painters? Did Spoors fulfil in Delft a role similar to that of Pieter Wils in Haarlem, a surveyor who advised the architectural painter Pieter Jansz Saenredam?Footnote ¹⁴⁶ Or were these painters self-taught in their understanding of geometry and optics, for instance by reading books such as Henricus Hondius's Grondighe onder-richtinghe in de optica, ofte perspective konste, published in 1623 and reissued in 1647?Footnote ¹⁴⁷ In later years the microscopist Van Leeuwenhoek, at his certification as a surveyor (1662), indeed claimed that he was self-taught in mathematics.Footnote ¹⁴⁸

Because sources are limited, we cannot reconstruct everything that happened in mid-seventeenth-century Delft. But, from the paintings, art historians have concluded that there was an important mutual influence between the pictorial stakeholders. Various Delft church interiors are evidently related to each other, and the citation of similar pictorial themes in the interiors of De Hooch, Vermeer and De Man are also obvious.Footnote ¹⁴⁹ This mutual influence went beyond the members of the Delft St Luke Guild. The painter Cornelis de Man, for instance, who returned from a sojourn of nine years abroad in 1653, evidently moved in the Delft circles of liefhebbers. Several paintings by De Man are known that depict traders in natural rarities or chemical activities, or that are scholarly portraits.Footnote ¹⁵⁰ The first known portrait by De Man was of his uncle, the rector of the Delft Latin School, Jacobus Crucius.Footnote ¹⁵¹ De Man also painted an anatomical lesson, given by the Delft medical doctor Cornelis 's Gravesande, featuring a large group of medical doctors and surgeons, but also the then already famous microscopist Van Leeuwenhoek. Did De Man also consult, or picture, Spoors, the backdoor neighbour of his cousin? There is no document or painting that can confirm this, but De Man's painting of a group of scholars gathering around a terrestrial globe reflects a meeting De Man could have witnessed at Spoors's house (see Figure 6). This painting, as well as De Man's A Scholar in His Study (Figure 7), demonstrates affinity with two of Johannes Vermeer's best-known paintings: The Geographer and The Astronomer. In the latter painting James Welu has identified a mathematics book by Adriaen Metius that certainly could be found in the houses of Spoors and his colleague and near neighbour Van Beest.Footnote ¹⁵² Perhaps Metius's book even could be found in the workshop of the Evert Steenwijck, who, as a telescope-maker, was a competitor of Metius's brother Jacob in Alkmaar, one of the claimants for the invention of this very instrument. It is an established fact that the son of this optician, the painter Pieter Everts Steenwijck, was acquainted with Vermeer's father Reynier Jansz Vermeer, at a time when the young Vermeer still lived with his parents.Footnote ¹⁵³

Figure 6.

Cornelis de Man, Scholars Gathered around a Globe (Kunsthalle, Hamburg).

Figure 7.

Cornelis de Man, A Scholar in His Study (Sotheby's, 2007).