6

Gulliver’s Worlds

But the most hateful sight of all, was the lice crawling on their clothes. I could see distinctly the limbs of these vermin with my naked eye, much better than those of a European louse through a microscope, and their snouts with which they rooted like swine. They were the first I had ever beheld, and I should have been curious enough to dissect one of them, if I had had proper instruments, which I unluckily left behind me in the ship, although, indeed, the sight was so nauseous, that it perfectly turned my stomach.

– Jonathan Swift, ‘A Voyage to Brobdingnag’, Gulliver’s Travels (1726)

§ 1

One day towards the beginning of 1610 Johannes Kepler was walking across a bridge in Prague when a few snowflakes settled upon his coat.1 He was feeling guilty, because he had failed to give his friend Mathias Wacker a New Year’s present. He had given him nichts, nothing. On his coat the snowflakes melted and turned into nothing. Watching them, Kepler evidently grasped two things more or less simultaneously. Each snowflake was unique, but they were all alike in that they were all six-cornered. This got Kepler thinking about two-dimensional six-cornered shapes and how they form a lattice: the cells of a honeycomb, or the seeds of a pomegranate. And about how the only shapes that one can use to tile a floor, if all the tiles are the same, are triangles, squares and hexagons. And about the patterns you can make if you pile cannon balls. Kepler thought he could work out the most space-saving way of piling spheres: his claim has become known as the Kepler conjecture (that the best arrangements are ones in which the centres of the spheres in each layer are above the centres of the spaces between the balls in the layer below) and was finally proved true for any regular lattice in 1831, and for any possible arrangement of spheres in 1998. For Kepler, this was applied mathematics: Thomas Harriot had been asked by Sir Walter Raleigh in 1591 how cannon balls should be piled on the decks of ships in order to get as many on board as possible, and Harriot had passed the problem on to Kepler.

Kepler was the first person we know of to imagine that snowflakes might be worth close inspection, and the little pamphlet he wrote about them (On the Six-cornered Snowflake, 1611) is now hailed as the founding text of crystallography. But he wrote it because he had also thought of a pun that he could not resist making. The Latin for snowflake is nix, almost the same as the German for nothing. If you give someone a snowflake, you are giving them nothing, for soon it will melt; he could give his friend a little book about snowflakes and it would be both something and nothing. He would no longer have to feel embarrassed about having given him nothing; now he could take pride in it.

Like Galileo, Kepler believed that the book of nature is written in the language of geometry. In his first major work, The Cosmographic Mystery (1596), he had argued that the spacing between the planets in the Copernican system was the spacing you would get if the five Platonic solids had been nested within each other in a certain order (working from the inside out: octahedron, icosahedron, dodecahedron, tetrahedron, cube). If God was a mathematician (and who could doubt it), then one must expect to find a mathematical logic in the most unexpected places, for example in the organization of the solar system or in a snowflake.

Kepler was thus conceptually prepared to find a mathematical order in the snowflake. But he was surprised to find himself looking for it there, of all places, and to find the same order at work in the great and the little. Indeed, he found himself considering the possibility that diamonds and snowflakes are formed by the same shaping agency, which could be neither cold nor vapour, but must be the Earth itself:

But I am getting carried away foolishly, and in attempting to give a gift of almost Nothing, I almost made Nothing of it all. For from this almost Nothing I have very nearly recreated the entire universe, which contains everything! And having before shied away from discussing the tiny soul of the most diminutive animal [the chigger], am I now to present the soul of that thrice greatest animal, the orb of the earth, in a tiny atom of snow?2

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Kepler’s representation of the five Platonic solids (cube, dodecahedron, icosahedron, octahedron and tetrahedron) nested within each other, from the Mysterium cosmographicum (1596). Kepler argued that the size of the planetary orbs corresponded to the size of an orb which would just fit within each of the solids if the solids were nested inside each other in the right order. He saw this as proof of God’s pleasure in mathematical symmetry showing in his design of the universe.

Kepler enjoys his joke about nothing. He even imagines a local doctor dissecting the chigger, the smallest creature visible to the human eye – and thus of course impossible to dissect.3

A couple of months later, on 15 March, Kepler’s world was transformed. His friend Wacker came racing round in his carriage, so excited that he was shouting out his news without even bothering to get out of the carriage and go indoors. Word had arrived that in Venice someone called Galileo, using some sort of new instrument, had discovered four planets circling a distant star. Bruno was right – the universe was infinite and there were other earths; and Kepler, who had always insisted that the sun and the Earth were unique, was plain wrong. Kepler describes them shouting at each other and laughing, Wacker delighting in his triumph and Kepler laughing off being in the wrong, and laughing, too, with delight at the thought of such an extraordinary discovery.4

Galileo’s book (dedicated to Cosimo II de’ Medici, the ruler of Florence; Galileo would soon move from Venice to Florence) had been published on 13 March; on 8 April a copy reached Prague in the diplomatic post and was presented by the Florentine ambassador to the emperor, who passed it straight on to Kepler.5 It turned out that the rumour Wacker had picked up was wrong.ii In fact, Galileo had discovered moons circling Jupiter, not planets circling a distant star. Bruno was not necessarily right after all, although the new discovery certainly proved that Copernicus had been entitled to claim that the Earth could be a planet and at the same time have a moon going around it, which had seemed deeply implausible to the defenders of Ptolemy (for whom the moon was one of the planets) and of Brahe.

§ 2

The story of Galileo’s discoveries is, it seems, straightforward. In 1608 the telescope was invented in the Netherlands. It was a chance discovery made, perhaps, by Hans Lippershey, a spectacle maker (two other spectacle makers disputed Lippeshey’s priority claim). In 1609 Galileo, who had never seen a telescope, worked out how to make one.6 It had an obvious application in warfare, both on land and sea, and so he persuaded the Venetian government to reward him for his invention. They were somewhat irritated to discover within a few days that telescopes were becoming widely available and that Galileo had taken them for a ride. Galileo’s first telescope had a usable magnification of 8x; by the beginning of 1610 he had managed to produce one that had a magnification of 30x and he had begun to explore the heavens.7

There is a standard phrase that is used over and over again in the literature: ‘Galileo turned his telescope to the heavens.’ Of course he did, in the autumn of 1609. Harriot did the same thing in England four months before Galileo (his first telescope had a magnification of 6x).8 The puzzle lies in the enormous effort that Galileo put into improving his telescope, grinding on his own equipment two hundred lenses in order to end up with ten telescopes with a magnification of 20x or better. For what is strange about these ten telescopes is that they were too good for their obvious, military, use. Their field of view was tiny – Galileo could see only part of the moon at a time. Held with two hands, they shook and wobbled so anything you were looking at kept slipping out of the field of view: some sort of tripod or mount was essential.

How do we know that Galileo’s telescope was too good for naval and military use? If you are looking for ships at sea, the curvature of the globe means that the limit of how far you can see is determined by the horizon. From a height of 24 feet the horizon is only 6 miles away: the maximum distance from which a lookout on one galley could see another is about 12 miles. The practical range of cannon fire was about a mile, so in a battle on land that was the crucial range for improving vision. In 1636, towards the end of his life, Galileo entered into negotiations with the Dutch. He had a cherished scheme for working out the longitude of a ship by using the moons of Jupiter as a clock (a reliable sea-going chronometer was not invented until 1761). At that time there was not a single telescope in the whole of the Netherlands capable of 20x magnification – and yet the Dutch had plenty of fine telescopes perfectly adequate for military and naval use.9 If telescopes with a magnification of 20x had had a practical application, they would have had them.iiii It is clear then that Galileo had turned his telescope into an instrument that was good for only one purpose – looking at the heavens. He had turned it into a scientific instrument. Others, including Harriot, raced to catch up with him.

It is important here to distinguish between the impact of the telescope and that of the microscope. The two are basically the same thing, so as soon as Galileo had a telescope he could use it to study flies, for example. He later devised a better, table-top instrument and studied how flies could climb up glass. But the first publication to represent what could be seen through a microscope, a single broadsheet entitled ‘The Apiarium’ (about bees, in honour of Pope Urban VIII, the symbol of whose family, the Barberini, was the bee) did not appear until 1625, and the first major publication was Hooke’s Micrographia of 1665.10 The telescope, on the other hand, transformed astronomy almost overnight, while the microscope was slow to be adopted (and, towards the end of the century, quick to be abandoned).11 The reason for this is simple: there was an established body of astronomical theory, and what was seen with the telescope was at odds with it. Astronomers could scarcely dispute the relevance of the telescope to their studies. But the microscope brought into vision a world previously unknown; it was hard to establish how the new information it produced related to established knowledge. The telescope addressed directly issues that were already under discussion; the microscope opened up new lines of enquiry whose relevance to current concerns was not obvious. That the telescope flourished and the microscope languished is one of the signs that the Scientific Revolution can properly be understood as a revolution – that is, a revolt against a previous order. Both telescope and microscope produced new knowledge, but in the seventeenth century only the telescope directly endangered the existing order.

In 1609, however, it was far from obvious that the telescope was going to transform astronomy: if it had been, there would have been large numbers of astronomers trying to make high-powered telescopes (as there were as soon as Galileo published his discoveries). Why did Galileo take it seriously as a scientific instrument? It would seem evident that he thought there was something that he would be able to see if his telescope was powerful enough. What? There is only one possible answer to this question: he was looking for mountains on the moon. Orthodox teaching was that the moon, being a heavenly body, was a perfectly smooth, round sphere. The variations in its colouring, however they were to be explained, were certainly not due to any surface irregularity. But Galileo was familiar with Plutarch, who had claimed that the moon had a landscape of mountains and valleys.12 Kepler was so taken with this idea that in 1609, as part of his exchanges with Wacker, he had begun to write a story – the first work of science fiction – about a voyage to the moon (it was eventually published posthumously, in 1634).13 From the moon, he argued, one would have the illusion that the moon was stationary and that the Earth floated through the sky. Kepler was not alone in imagining a moon with features like the earth. In 1604 someone close to Galileo (perhaps Galileo himself) had published an anonymous tract in Florence which claimed that there were mountains on the moon:

There are also on the moon mountains of gigantic size, just as on earth; or rather, much greater, since they are [even] sensible to us. For from these, and from nothing else, there arise in the moon scabby little darknesses, because greatly curved mountains (as Perspectivists teach) cannot receive and reflect the light of the sun as does the rest of the moon, flat and smooth.14

When Galileo pointed his improved telescope at the moon in 1609 he was able to pick out something much more striking and unambiguous than ‘scabby little darknesses’ (which were presumably what we now call craters). He was able to show that along the terminator – the boundary between the light and the dark parts of the moon – which would be a smooth, unbroken line if the moon was a perfect sphere, one could see dark marks where there should be light, and light patches where there should be dark. These, he argued, were shadows and highlights such as you would find on a mountain range as it caught the rising sun. He had confirmed Plutarch’s theory and, whether he liked it or not, he had reopened the question of the existence of other habitable worlds.15 As John Donne put it in 1624 (with perhaps a backward look to Nicholas of Cusa, or Bruno):iiiiii

Men that inhere upon Nature only, are so far from thinking, that there is anything singular in this world, as that they will scarce thinke, that the world it selfe is singular, but that every Planet, and every Starre, is another World like this. They find reason to conceive, not only a pluralitie in every Species in the world, but a pluralitie of worlds.16

In The Starry Messenger (1610) Galileo acknowledged no debts, except to Copernicus; Plutarch, Nicholas of Cusa, Bruno and della Porta do not rate a mention, which seemed unfair to Kepler (who evidently thought some of his own contributions to the field were, for that matter, neither irrelevant nor insignificant).17 Telescopic astronomy was presented as a brand-new beginning – which indeed it was.

It so happens that Harriot had already seen exactly what Galileo had seen. We have a sketch he drew on 26 July 1609. Looking at it, it is perfectly clear that the terminator is irregular, but this irregularity is what information scientists call ‘noise’: it makes no sense and conveys no information. We have another sketch by Harriot, dated 17 July 1610.18 This difference this time is that Harriot had now read Galileo’s Starry Messenger, which had been published in the spring. Now what he saw was exactly what Galileo had seen. Indeed, it seems clear that what he was doing was comparing Galileo’s illustration with what he could see through his telescope, for both Galileo’s illustration and Harriot’s feature a large circular boss. In fact, there is no such prominent object on the moon, and scholars have suggested that Galileo deliberately enlarged a crater to enable the viewer to, as it were, zoom in on a tell-tale feature.19 Harriot, looking at the moon, saw the irregular terminator, the highlights and shadows, the mountain ranges and valleys that Galileo had described – and he also convinced himself that he saw Galileo’s imaginary crater. Once Galileo had described what he had seen, once he had trained viewers in how to look, it was almost impossible to dispute that the moon had mountains and valleys; but Galileo could only understand what he was looking at because he had a better telescope than Harriot, and because he (unlike Harriot) was accustomed to looking at perspective paintings. The anonymous author of 1604 had been quite right to insist that the theory of perspective would provide the key to interpreting the image of the moon.

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One of Galileo’s illustrations of the moon, from The Starry Messenger (1610). Galileo’s purpose is to show how the terminator (the line between the light and the dark sides of the moon) is not smooth but jagged, proof that the moon is not a perfect sphere. On either side of the terminator one can see shadows (on the light side) and highlights (on the dark side), just as when the sun rises or sets over a mountain range the peaks are illuminated before the valleys.

Having observed the moon, Galileo turned his telescope to Jupiter and discovered that Jupiter had moons. According to conventional Ptolemaic astronomy, all heavenly bodies revolved around the Earth; a difficulty with Copernicanism was that it not only put the Earth in motion and the sun at the centre of the universe, but it required the moon to revolve around the Earth at the same time as the Earth revolved around the sun. Jupiter’s moons made this arrangement rather less implausible than it had seemed. Galileo now rushed to publish his discoveries, which transformed astronomy in the space of a few months – the time it took for others to acquire telescopes with which they could corroborate his findings.

But there is something more to this story than at first meets the eye. Galileo had not only made a remarkable discovery; using his telescope, he had seen something where, before, there was apparently nothing at all to see. In the winter of 1609–10 he had transformed what seemed to be nothing into something. The idea that out of almost nothing you could re-create the entire universe was plainly ridiculous, yet that was what Galileo was now doing. The idea that one might dissect a chigger was also ridiculous in 1610 – but, thanks to the microscope, that too would soon be possible.

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Harriot’s first drawing of the moon as seen through his telescope, before he had read Galileo: Harriot has not grasped that the pattern of light and dark can be interpreted as showing that the moon has mountains and valleys, so that it is for him meaningless.

Nobody, not even Galileo, was better prepared for this new world where nothings became somethings than Kepler. He rapidly wrote a letter to Galileo (which was soon published in Prague, in Florence and in Frankfurt as the Dissertatio cum Nuncio sidereo) praising Galileo’s discoveries, even though others suspected Galileo of telling lies, and Kepler had not yet confirmed the discoveries with his own eyes. Perhaps, he said, if, as Galileo claimed, there were mountains on the moon, Bruno had been partly right – maybe the moon was inhabited, and life was not confined to the Earth. Kepler tried making his own telescope, but it wasn’t good enough to see the moons of Jupiter. On 5 September he managed to get hold of a telescope Galileo had sent to the elector of Cologne, and finally he saw for himself. Kepler had described his snowflakes as like little stars; now, everywhere he turned his telescope he found them, thick enough to make a snowstorm.

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Harriot’s drawing of the moon after he had read Galileo’s Starry Messenger: under the influence of Galileo, Harriot draws a large circular object which appears in Galileo’s illustration but which is not actually to be seen on the moon. One suggestion is that Galileo deliberately magnified a typical crater in order to bring out its structure as shown by the shadows and highlights to be seen on it; Harriot may have been doing the same thing, or he may have been genuinely persuaded that the structure was there, since with a good telescope he would have been able to see only a part of the moon’s disc at a time.

§ 3

It is easy to assume that the discoveries reported in The Starry Messenger are the most important that Galileo made with the telescope. This is not the case. It would seem that soon after its publication Galileo first observed sunspots, which could be regarded as definitive proof that there is change in the heavens, but at first he did not know what to make of them: it was not until April 1611 that he started to draw other people’s attention to them.

In October 1611 Galileo, who had now moved to Florence, began to observe Venus through his telescope. His motivation was simple: Venus was a problem for both the Ptolemaic and Copernican systems because, according to both theories, its distance from the Earth varied greatly. According to the Ptolemaic system, it travelled on a large epicycle, which brought it sometimes closer to and sometimes further from the Earth. According to the Copernican system, as both Venus and the Earth travelled around the sun, the distance between them must alter radically: sometimes they must be on opposite sides of the sun, and sometimes Venus must come between the Earth and the Sun and be, relatively speaking, very close to the Earth. Yet, although Venus is sometimes brighter and sometimes less bright in the sky, it was difficult to see the variation that either theory must predict. Galileo had a further motive for looking at Venus. He had argued that the moon was an opaque body, shining solely by reflecting the light of the sun. He had explained the fact that the dark side of the moon seems sometimes to shine by its own ghostly light by claiming that the moon was being illuminated by light reflected from the Earth; that just as we on Earth see moonshine, so on the moon there is earthshine, and it is much brighter there than moonshine is here. If Venus was, similarly, an opaque body, it would, like the moon, have phases. So Galileo wanted to see if Venus had phases.

He must have realized from the beginning that if Venus did have phases, the nature of them would establish whether Ptolemaic astronomy was well founded or not. Ptolemaic astronomers were unable to agree on whether Venus was closer to the Earth than the sun. If Venus was closer to the Earth than the sun, its phases would range from crescent to half and never pass the half-illuminated point. However, if Venus was further from the Earth than the sun, its size would vary considerably over time, but it would nearly always be a full circle, and never be much less than that.20

Before 1611 the competition between the three alternative accounts of the cosmos – the Ptolemaic, the Copernican and the Tychonic – represents a genuine case of under-determination. In the Ptolemaic, or geocentric, system, which had been in existence for many centuries, the stars, sun, planets and moon all circle the Earth, but the planets and sun also move on other circles (epicycles). In the Copernican, or heliocentric, system, effectively new in 1543, the planets (of which the Earth is now one) circle the sun, but the moon circles the Earth. In the Tychonic, or geoheliocentric, system, invented as an alternative to Copernicanism in 1588, the planets circle the sun, and the sun and moon circle the Earth. These three systems are, when fully articulated, geometrically equivalent, which is to say that, although they combine circles in different ways, they produce identical predictions of the apparent locations of bodies in the heavens when viewed with the naked eye from the Earth.iviv A Ptolemaic combination of a circle and an epicycle to predict the movement of a planet produces exactly the same result as the Copernican combination of the orbit of the planet with the orbit of the Earth, and that produces exactly the same effect as Brahe’s combination of the orbit of the sun with the orbit of the Earth (just as taking one step forward and then two steps to the left is equivalent to taking two steps to the left and then one step forward) – which is why it was impossible to choose between them on the basis solely of information relating to the position of the planets in the sky.vv

There was a widespread view that it ought to be possible to construct a fourth system which would better meet the requirements of Aristotelian philosophy: a homocentric system in which all the circles shared a common centre, ideally the Earth. Despite the efforts of major intellectual figures, such as Regiomontanus (1436–76), Alessandro Achillini and Girolamo Fracastoro (1478–1553), no one managed to construct a successful version of this system: it could not be made (as we would say) to fit the facts.vivi21 (Even the Copernican system did not achieve homocentrism, as the moon circled the Earth, rather than the sun.)

After Galileo discovered the phases of Venus in 1610 and thus proved that Venus orbited the sun, the Ptolemaic system ceased to be viable, although it was still possible to argue that some planets (Mercury, Venus, Mars) orbited the sun, and others (Saturn, Jupiter) orbited the Earth; this was the conclusion of Riccioli’s New Almagest of 1651. Now there were only two (or two and a half) surviving systems, and intelligent and well-informed people had difficulty choosing between them for another half-century or so. So between 1610 and 1710 (say) cosmological theories were under-determined, in that there were at least two systems for which a strong case could be made, but not undetermined, in that everyone agreed that the Ptolemaic and homocentric systems were clearly not viable.

Galileo began to observe Venus in June 1610, as soon as it distanced itself enough from the sun to be visible. At first there was nothing interesting to see, as Venus was a full circle in his telescope; it was evidently on the far side of the sun. But at the beginning of October it became apparent that Venus was changing shape: slowly, it was moving towards being a half-circle. Day by day, Galileo watched this change carefully. On 11 December he sent Kepler a cipher which, when decoded, said, ‘The mother of love [i.e. Venus] imitates the shapes of Cynthia [the moon].’22 By this point Galileo knew both that Venus had phases (which meant that it was an opaque body shining by reflected light) and that the range of phases it displayed were incompatible with Ptolemaic astronomy, which required Venus always to be either further from the Earth than the sun or closer to the Earth than the sun. He waited a while longer until he was absolutely sure, and then on 30 December he wrote to his pupil Castelli (who had asked him in a letter Galileo will have received on 11 December – a letter which evidently provoked him to register his discovery with Kepler – whether Venus might not have phases) and to the leading mathematician in Rome, Christoph Clavius, announcing his discovery. On 1 January 1611 he wrote to Kepler, deciphering his earlier message, and Kepler went on to publish his correspondence with Galileo in his Dioptrice (1611).23

Clavius and Kepler will have had no difficulty confirming immediately that Venus had phases: all they had to do was point a decent telescope in the right direction. But a Venus with phases is perfectly compatible with Ptolemaic astronomy; what isn’t is a Venus whose phases go from crescent to full: such a Venus must be in orbit around the sun. You do not need to observe the whole sequence of phases. All you need to do is either see Venus move from nearly full to half (as Galileo had in December), or see her move from crescent to nearly half.

When Galileo announced his discovery Venus was moving towards the sun: conjunction occurred on 1 March. There was nothing interesting to be seen, because all the phases that occurred between 1 January and 1 March would be repeated in reverse order as Venus emerged from the conjunction. On 5 March Galileo announced his intention to leave for Rome; on the nineteenth he was still impatiently waiting for a litter to carry him and complaining that he had a deadline to meet.viivii Within a day or two he had left; Galileo was thus in Rome as the Jesuit astronomers turned their telescopes on Venus and watched it move towards a half-circle. It was probably during March that Clavius made revisions to a new edition of his Sphere: he records with care Galileo’s discoveries to date (he makes no mention of sunspots, which Galileo had not yet drawn to his attention); he mentions the phases of Venus, and he says that astronomers are going to have to revise their theories in the light of these new findings.24 What he does not say is as important as what he does: he does not say that Venus orbits the sun. Similarly, in April, Cardinal Bellarmine asked the Jesuit astronomers whether Galileo’s discoveries had been confirmed. They said they had (though they reported that Clavius thought it might be possible to regard the moon’s mountains as internal, not external, structures), and included the phases of Venus; they make no mention of Venus orbiting the sun.25

On 18 May, however, the Jesuit astronomers threw a party for Galileo. Odo van Maelcote delivered a lecture in which he announced that, although they had not yet seen Venus as a full circle (this would not happen for another few months, as Venus approached the sun and passed behind it in December 1611), they had seen enough to be sure that Venus did not revolve around the Earth. The philosophers in the audience were scandalized by this claim; Galileo was naturally thrilled to have been vindicated and feted. Clavius by this time was very ill, and we do not know what he made of this new evidence.26

It is essential to understand that what Maelcote announced was a killer fact: the Ptolemaic model in which all the planets (including the sun and the moon) revolve around the Earth had been proved to be wrong. It was evident that Venus travelled around the sun (and this would become clearer and clearer as the months advanced towards the next conjunction) and, presumably, Mercury did too. After 18 May the Ptolemaic system, which had survived for more than 1,400 years, was fatally wounded. The choice was now between Copernicanism (all the planets, including the Earth, going around the sun); Brahe’s system (all the planets going around the sun, and the sun going around the Earth, which remains stationary at the centre of the universe); or a compromise between Brahe and Ptolemy, in which the inner planets go round the sun and the outer planets go round the Earth. No competent astronomer defended the traditional Ptolemaic system once they had heard that Venus had a full set of phases; you had to be an ill-informed philosopher to do so. Moreover, it was generally acknowledged that the Tychonic system was incompatible with belief in solid heavenly spheres. Now, anyone who wanted to believe in solid spheres would have to imagine the sun going round the Earth, an epicycle on a deferent, and then Mercury and Venus going round the sun, of necessity cutting through the sphere of the sun. It is not surprising that this was regarded as further evidence against solid spheres (which Clavius had defended up until the last).27

According to contemporary history and philosophy of science, there are no such things as killer facts. We have seen already that the two-spheres theory could not survive the discovery of America; now we find that traditional Ptolemaic astronomy could not survive the discovery of the phases of Venus. Thus in August 1611 the anti-Copernican mathematician Margherita Sarrocchi described the phases of Venus as a ‘geometrical demonstration that Venus goes round the sun’. The Jesuit astronomer Christoph Grienberger wrote to Galileo from Rome on 5 February 1612 confirming that the annual changes of Venus, ‘just like the monthly changes of the Moon, very clearly demonstrate that it goes around the Sun’.28 Galileo, in his first letter to Mark Welser about sunspots, which was written on 4 May 1612 (and published in 1613), says of the phases of Venus: ‘These … will not leave room for anyone to be in any doubt … that its revolution is about the Sun.’29 On 25 July 1612 Galileo’s opponent on the issue of sunspots, the Jesuit astronomer Christoph Scheiner, wrote to Welser, describing the phases of Venus as an ‘ineluctable argument’: ‘Venus goes around the Sun: the prudent man will scarcely dare to doubt it in the future.’30 And Galileo writes in his third letter on sunspots, dated 1 December 1612, that the phases of Venus ‘serve as a single, solid, and strong argument to establish its revolution around the Sun, such that no room whatsoever remains for doubt’.31 No one was so foolish as to dispute these claims.viiiviii

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The frontispiece to Giovanni Battista Riccioli’s New Almagest (1651). Hanging in the balance being held by Astraea, the goddess of justice, are the competing world systems of Tycho Brahe and Copernicus; Riccioli is one of the last major astronomers to insist on the superiority of the Tychonic system. Discarded on the floor is the Ptolemaic system, which became indefensible when Galileo discovered the phases of Venus, and Ptolemy himself lies slumped in the background. In Riccioli’s version of the Tychonic system Jupiter and Saturn orbit around the Earth, not the sun.

It is easy to show that conventional Ptolemaic astronomy was thriving until 1610 and went into crisis immediately afterwards: one only has to look at publications of the standard textbook, Sacrobosco’s Sphere, and of the more advanced textbook, Peuerbach’s Theoricae novae planetarum. Included in the figures for Sacrobosco are, for example, editions of Clavius’s Commentary, which went through fifteen editions between 1570 and 1611, with a solitary final edition in 1618. (By comparison, there are only two editions of Kepler’s Epitome of Copernican Astronomy, the first part of which was first published in 1618.) Clavius was published in Rome, Venice, Cologne, Lyons and Saint-Gervais. No textbook emerged capable of replacing Sacrobosco, Peuerbach and Clavius for the simple reason that no new consensus was established on the question of how the universe was organized until the eventual triumph of Newtonianism well into the eighteenth century – by which point the vernacular languages had replaced Latin, so no textbook could hope to have the international presence that they had had.

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This chart shows the number of distinct editions of Sacrobosco’s Sphere (folio, quarto and octavo editions are shown separately) and of Georg von Peuerbach’s Theoricae novae planetarum – the two standard textbooks, one elementary and one advanced, for the study of astronomy in Renaissance universities. The figures at the base of columns are the first year of the decade, so 1470 refers to the decade 1470–1479. It is apparent that the publication of Copernicus (1543) had no effect on sales of these books, but there does seem to have been a dip following the comet of 1577 and the publication of Tycho’s new system in 1588. However, demand was fully re-established in the decade 1600–1609, and not just for the new more complex commentaries such as that of Clavius, published in fat quartos, but also for cheap octavo editions. Demand collapsed, however, immediately after Galileo’s telescopic discoveries. From this evidence it would appear that it was the telescope that killed off Ptolemaic astronomy. Publications of Sacrobosco are taken from the list in Jürgen Hamel, Studien zur ‘Sphaera’ des Johannes de Sacrobosco (2014) and of Peuerbach from Worldcat. I am indebted to Owen Gingerich (as always) for discussing this chart with me, and for suggesting breaking down the publications of Sacrobosco by format.

§ 4

Thus by 1611 not only was it generally accepted that the moon was a body rather like the Earth, in that it had mountains, but also, Venus had become an opaque body like the Earth and the moon. It followed that, if the Earth was inhabited, so other heavenly bodies might be; and if Venus shone brightly in the sky above the Earth, so the Earth must shine brightly in the sky above Venus. Scholastic philosophers had fertile imaginations and had often imagined looking at the Earth from far away, even from the stars; but they had not imagined that the Earth would shine like the brightest stars.

The telescope itself provides a form of space travel; as Hooke put it, a ‘transmigration into heaven, even whil’st we remain here upon earth in the flesh’.32 Everyone now began to imagine looking at the Earth from deep space. Milton would imagine the Earth as a ‘pendent World, in bigness as a star’, and Pascal would go further, imagining what it would be like to look at the Earth from deepest space only to lose sight of it: ‘an imperceptible point on the vast bosom of nature’. This became a new commonplace. For Locke, the Earth is not a point but a spot: ‘our little spot of Earth’, ‘this spot of the Universe’.33 The idea that the Earth was tiny compared to the universe, or that one might imagine looking at it from far away, was not new; what was new was the expansion of scale that came with the new astronomy, so that the Earth could be simultaneously held to be a bright star if seen from another planet and invisible if seen from deep space, and the hold that this idea of seeing the Earth from a vast distance had over the imaginations of the educated.ixix

Galileo’s telescope made two ideas that had previously seemed abstract and theoretical suddenly seem plausible and perfectly realistic: there might indeed be other inhabited worlds, and space might indeed be infinite. A whole literature was soon dedicated to these notions.34 As early as 1612–13, John Webster in The Duchess of Malfi refers to Galileo’s telescope as making visible ‘another spacious world i’ th’ moon’.35 In England, Francis Godwin’s fictional The Man in the Moone appeared posthumously in 1638 – it had been written some time after 1628 – and was translated into French and German. Its account of a voyage to the moon marks the beginning of science fiction in English.36 Godwin was a bishop and a crackpot; he seems to have believed that he had invented the radio.37 John Wilkins, also a bishop and later a founder of the Royal Society, published his non-fiction The Discovery of a World in the Moon the same year (in which he argues that it may one day be possible to travel to the moon and suggests that the moon may be inhabited) and A Discourse Concerning a New World and Another Planet in 1640 (the first part is a reprint of the Discovery and the second an account of how our world is now, thanks to Copernicus, known to be a planet).38 But by far the most important of such works was Cyrano de Bergerac’s posthumous The States and Empires of the Moon (1657), an account of a journey to the moon, followed shortly by The States and Empires of the Sun.39 Cyrano was later turned into a fictional character by Edmond Rostand, but the real Cyrano has little (apart from a large nose) in common with the fictional character. A lover of men, not women, and an atheist, he used the device of space travel to criticize everything he disliked about the real world. His work, inevitably, had to be toned down for publication and did not appear unbowdlerized until 1921. Even so, his moon book went through at least nineteen editions in French and two in English before the end of the century.

image

Frontispiece to Francis Godwin’s posthumous and anonymous The Man in the Moone (1638), arguably the first work of science fiction. The hero flies to the moon in a vehicle powered by gansas (swans).

Fiction provided a useful disguise for dangerous ideas such as the atheism and materialism of Cyrano. But as the century went on it became less necessary to adopt such a disguise. Pierre Borel published A New Treatise Proving a Multiplicity of Worlds: That the Planets are Regions Inhabited and the Earth a Star (French, 1657; English, 1658), the first work since Bruno to argue that the planets were inhabited worlds. Borel believed that visitors from outer space had already arrived; not little green men, but birds of paradise. No one has ever found their nests, he claims, so it is evident that they visit us from another planet.40 Influenced by Borel, John Flamsteed, the future first Astronomer Royal, concluded that all the stars were accompanied by ‘systemes of planets, like our earth inhabitable & fild with creatures, perhaps more obedient to the lawes of their maker, then its [our Earth’s] inhabitants’.41 Borel was followed by two other works of popularizing science. Fontenelle’s Conversations on the Plurality of Worlds sought to promulgate the cosmology of Descartes: it appeared in at least twenty-five French editions between 1686 and Fontenelle’s death in 1757; in the same period there were ten editions of two English translations.xx42 It was followed by Christiaan Huygens’ Kosmotheoros (1698), yet another posthumous work, which appeared in Latin, French and English.43

image

The frontispiece to John Wilkins, A Discourse Concerning a New World (1640; reprinted 1684): Copernicus and Galileo discuss the Copernican system, which is illustrated behind them; like Digges, Wilkins assumes the stars are spread out through an unbounded space. Copernicus presents his ideas hypothetically; Galileo says he has confirmed them with his telescope; and Kepler whispers in his ear, saying, ‘If only you could confirm it by flying there!’

By 1700 every educated person was familiar with the idea that the universe might be infinite and that there were probably other inhabited worlds. Indeed, the idea had become entirely respectable, so that we find it being given forceful expression in Richard Bentley’s Boyle Lectures against atheism (1692):

[W]ho will deny, but that there are great multitudes of lucid Stars even beyond the reach of the best Telescopes; and that every visible Star may have opake Planets revolve about them, which we cannot discover? Now if they were not created for Our sakes; it is certain and evident, that they were not made for their own. For Matter hath no life nor perception, is not conscious of its own existence, nor capable of happiness, nor gives the Sacrifice of Praise and Worship to the Author of its Being. It remains therefore, that all Bodies were formed for the sake of Intelligent Minds: and as the Earth was principally designed for the Being and Service and Contemplation of Men; why may not all other Planets be created for the like Uses, each for their own Inhabitants which have Life and Understanding? If any man will indulge himself in this Speculation, he need not quarrel with revealed Religion upon such an account. The Holy Scriptures do not forbid him to suppose as great a Multitude of Systems and as much inhabited, as he pleases.44

The result was a quite new sense of the insignificance of human beings.xixi ‘Man is the measure of all things,’ Protagoras (c.490–420 BCE) had said, and, once, this was literally true. The foot as a unit of measurement is based, naturally, on the foot. An ell (Italian, braccio; French, aulne) is the length of the forearm. A mile is a thousand Roman paces. Galen defines hot or cold in the patient in simple terms: a hot patient is one who is hotter than the physician’s hand. In Galen’s view the hand of a healthy person was designed to be the proper measure of hot and cold, damp and dry, soft and hard. As late as 1701 Newton wanted to take blood heat as one of the two fixed points for a temperature scale (the lower point being freezing water); it was one of three fixed points in Daniel Gabriel Fahrenheit’s scheme, still widely used, of 1720, while a few years later John Fowler thought the upper fixed point should be the hottest water that can be endured by a hand held still.45 Time was measured against a day divided into twenty-four hours, but in ordinary life short periods of time were measured subjectively, in Ave Marias or Paternosters: the time it took to say the Hail Mary or the Lord’s Prayer. Only where weight was concerned was man not the measure. Man ceased to be the measure of all else only with the adoption of the metric system in France in 1799.46 The basic unit of measurement (from which volumes and weights were derived) became the metre, originally defined as one ten millionth of the distance from the equator to the North Pole. The metric system merely completed a process that had begun with the invention of the telescope, which definitively destroyed the idea that the universe was made on the same scale as man.

§ 5

According to orthodox Christian thinking (at least until Pascal), the universe had been made to provide a home for humankind. The sun was there to provide light and heat by day, the moon and stars light by night. There was a perfect correspondence between the macrocosm (the universe as a whole) and the microcosm (the little world of the human body). The two were made for each other. The Fall had partly disrupted this perfect arrangement, forcing human beings to labour to survive; but the original architecture of the universe was still visible for all to see. Platonism, with its account of the universe’s creation by a divine craftsman, the Demiurge, could be invoked to support this view – indeed, the idea of microcosm and macrocosm derived from neo-Platonism; but even Aristotelian philosophy, which held the universe to be eternal, assumed that human beings have all the faculties required to understand the universe.

For human-centredness had not been confined to measurement. Magnifying glasses were known to the ancient Greeks, and spectacles were in use from the thirteenth century. But lenses were used to correct imperfect vision, not to see things which could not be seen by someone with good eyesight. Again, the assumption was that God had given us eyes that were, when healthy, quite good enough for our purposes.xiixii Moreover, human beings were made in the image of God: a view hardly compatible with the notion that their senses were defective.

In the half-century or so between 1610 and 1665 this delightful picture of the universe as a home for humankind, an extension of Eden, was fatally undermined, and with it the notion that man is the proper measure of all things. This transformation has three distinct but interlocking components: first, humanity was displaced from the centre of the universe, which implied the possibility of intelligent life elsewhere; second, the correspondence between microcosm and macrocosm was shattered, so that the universe was no longer made to fit around us; and third, size became relative and scale became arbitrary – stars became snowflakes and snowflakes became stars.47 This great transformation has escaped proper attention because it does not have a label, and it does not have a label primarily because it is three transformations rolled into one.

In fact, all three had a single cause: the telescope, whose impact was the same for anyone who looked through it. Here, for example, is one of the first uses of the word ‘telescope’ in English, in a religious tract from the English Civil War:

This sober honest Mercury [i.e. news-sheet] coming to my hands, I thought it no great Error if I gave it that entertainment which I sometimes give even the Phrantick Bedlam Pamphlets: I must confesse it was to me a kind of Eye-salve, for I looked formerly at the wrong end of the Perspective [i.e. telescope], and the transgressions of our Welsh Itinerants, palliated with the name of Saints, seemed but small Atoms in a large Sun-shine. This Book is a new Telescope; it discovers what we could not see before; and the Spots in this Spiritual Moon, are Mountains.48

The telescope and the microscope do exactly the same thing: they turn atoms into mountains, and, if you look through the other end, mountains into atoms. This is the Scaling Revolution, as we might call it, by which, as William Blake put it in ‘Auguries of Innocence’, you can ‘see a world in a grain of sand’ or, alternatively, see a world as a grain of sand. The classic reflection on this revolution is Voltaire’s story Micromégas (1752; the name combines the Greek words for ‘small’ and ‘large)’, which describes the visit to Earth of a 20,000-foot-tall giant from one of the planets of Sirius, accompanied by an inhabitant of Saturn one third his size. For them, human beings are barely visible to the naked eye.49

The Scaling Revolution was not entirely without precedent. Lucretian atomism presented a picture of a universe which is frequently dissolved and remade, where the processes of nature are interactions between atoms which are invisible to us, and where sensations such as smell and taste are dismissed as subjective interpretations caused by the shape and movement of atoms. It was his familiarity with atomism which made it possible for Bacon, exceptionally and presciently, to dismiss human sensory organs as inherently defective and often misleading.50 But if atomism suggested the existence of an invisible world of micro-mechanisms, it did not imply the existence of an invisible world of micro-organisms. That world was discovered by the Dutchman Antonie van Leeuwenhoek when, in 1676, he was the first to see living creatures invisible to the naked eye. Van Leeuwenhoek’s discovery was met with initial scepticism: Hooke, in England, could see nothing comparable through his own microscope: but then he was using a compound microscope, not the tiny glass bead (a simple microscope) with which Leeuwenhoek achieved astonishing levels of magnification. It took four years for Leeuwenhoek’s discovery to be confirmed. Galileo’s discovery of the moons of Jupiter had been confirmed within a few months.

The first microscopists thought there was no limit to what they might see. Henry Power, who published just before Hooke, but whose book had little impact because there were only three illustrations, and those of poor quality, thought that eventually the microscope might reveal ‘the Magnetical Effluviums of the Loadstone, the Solar Atoms of light (or globuli aetherii of the renowned Des-Cartes), the springy particles of air …’51 Hooke may actually have hoped to see the physical basis of memory, the ‘continued Chain of Ideas coyled in the Repository of the Brain’.52 Instead, the microscope hit a limit with Leeuwenhoek’s single-celled organisms (1676). Hooke had shown that the louse was every bit as complicated a creature as a lizard. Leeuwenhoek dissected them, exploring their genitalia and discovering their sperm. Such experiences created the assumption that the very smallest creatures were as complex as the largest, and had the same sorts of organs. Far from recognizing that protozoa were different in character from larger organisms, Leeuwenhoek’s work seemed to imply that they were the same. Size appeared to be irrelevant.

This assumption was crucially important when it came to trying to understand reproduction. The general view was that all life came from an egg (or at least all life visible to the naked eye; microscopic life was thought to generate spontaneously), even though no one had actually seen a mammalian egg. A contemporary of Leeuwenhoek’s, Jan Swammerdam, showed that butterflies, which had been regarded as new creatures born out of the pupa, were already present within the caterpillar: their organs could be identified by dissection. Marcello Malpighi showed that the parts of the full-grown tree were present in the seed.53 This led to the doctrine of preformationism: the adult existed fully formed within the egg. It followed logically that the egg already included the eggs of the next generation, that preformation implied pre-existence, and indeed that Eve had contained within her all future human beings to the end of time, each one fully formed within an egg within an egg within an egg, and so on. Thus Pascal’s dream of worlds within worlds became a serious theory that every human individual was already present in Eve’s ovaries (to which one might want to add all the humans who never happened to be born – the children nuns might have had if they had married, for example).54

Ovism, as this was called, seems to us the most fantastical of theories. It had obvious defects: it could not, for example, explain the inheritance of characteristics from the father; in 1752 Maupertuis showed that polydactylism could be inherited in the male as well as the female line. Preformationism assumed that new life was never created, yet in 1741 Abraham Trembley showed that you could cut a polyp into a dozen pieces and it would turn into a dozen polyps. Above all, ovism seems to us utterly impossible: how could every human being that ever existed or ever will exist be contained, fully formed, within Eve’s ovaries? Yet this was not seen as a serious problem at all. The idea that there might be worlds within worlds had become entirely respectable. Only when cell theory established itself in the 1830s was preformationism abandoned. Only at this point did it become clear that the Scaling Revolution had its limits, that the idea of worlds within worlds was fantastical, not real.

Jonathan Swift knew all about Leeuwenhoek’s discoveries when he wrote in 1733:

So, Nat’ralists observe, a Flea

Hath smaller Fleas that on him prey,

And these have smaller Fleas to bite ’em;

And so proceed ad infinitum.xiiixiii

Yet long before Leeuwenhoek such creatures had existed in the imagination of those who had grasped the full implications of the Scaling Revolution. Cyrano writes of them, and Pascal (d.1662), who as far as we know never looked through a microscope, and certainly never saw Hooke’s famous image of a flea (published in 1665), imagined someone inspecting a scabies mite:

Let a mite be given him, with its minute body and parts incomparably more minute, limbs with their joints, veins in the limbs, blood in the veins, humours in the blood, drops in the humours, vapours in the drops. Dividing these last things again, let him exhaust his powers of conception, and let the last object at which he can arrive be now that of our discourse. Perhaps he will think that here is the smallest point in nature. I will let him see therein a new abyss. I will paint for him not only the visible universe, but all that he can conceive of nature’s immensity in the womb of this abridged atom. Let him see therein an infinity of universes, each of which has its firmament, its planets, its earth, in the same proportion as in the visible world; in each earth animals, and in the last mites, in which he will find again all that the first had, finding still in these others the same thing without end and without cessation.55

Borges summarizes Pascal thus: ‘There is no atom in space which does not contain universes; no universe that is not also an atom. It is logical to think (although he does not say it) that he saw himself multiplied in them, endlessly.’56

But which then, in all these endless universes, nested within one another, would be the real Pascal? The answer is that we could not possibly tell. This is quite different from the world of Rabelais. Pantagruel (1532) and Gargantua (1534) play with size-shifting: a whole army, for example, lives within a giant’s mouth. But these are pre-telescopic texts and there are always clues as to who is normally sized and who is miniaturized or gigantized. Giants eat, drink and defecate against the backdrop of a normally sized word. In Gulliver’s Travels, on the other hand, Swift creates a (more modest) version of Pascal’s world. When Gulliver finds himself among the Brobdingnagians the wasps are the size of partridges, and the lice correspond exactly to Hooke’s illustration:

image

Hooke’s representation of a flea, from his Micrographia (1665), the first major work of microscopy.

I could distinctly see the Limbs of these Vermin with my naked Eye, much better than those of an European Louse through a Microscope; and their Snouts with which they rooted like Swine. They were the first I had ever beheld, and I should have been curious enough to dissect one of them, if I had proper Instruments (which I unluckily left behind me in the Ship) although indeed the Sight was so nauseous, that it perfectly turned my Stomach.57

Is it Gulliver or the Brobdingnagians who are the wrong size? The Brobdingnagians, we would say, but that is only because we know that Gulliver’s size is our size. Swift had read Cyrano, and Gulliver is a cunning variation on the by then conventional themes of science fiction, one in which islands are substituted for planets.

The central message that readers were bound to take away from such texts is that human beings have a mistaken sense of their own importance. Cyrano was absolutely explicit, attacking

the unsupportable Pride of Mankind, who perswade themselves, that Nature hath only been made for them; as if it were likely that the Sun, a vast Body, Four hundred and thirty four times bigger than the Earth, had only been kindled to ripen their Medlars, and plumpen their Cabbages. For my part, I am so far from complying with their Insolence, that I believe the Planets are Worlds about the Sun, and that the fixed Stars are also Suns, which have Planets about them, that’s to say, Worlds, which because of their smallness, and that their borrowed light cannot reach us, are not discernible by Men in this World: For in good earnest, how can it be imagined, that such spacious Globes are no more but vast Desarts; and that ours, because we live in it, hath been framed for the habitation of a dozen of proud Dandyprats? How, must it be said, because the Sun measures our Days and Years, that it hath only been made, to keep us from running our Heads against the Walls? No, no, if that visible Deity shine upon Man, it’s by accident, as the King’s Flamboy by accident lightens a Porter that walks along the Street …58

So even before the microscope had been put to serious use, the telescope created a vertiginous sense of the infinite vastness of the universe and the insignificance of human beings when viewed, in the mind’s eye, from outer space. In the Lucretian universe the gods are indifferent to human beings, and human beings are an accidental consequence of the random jostling together of atoms. The Scaling Revolution had the effect of forcing even those who continued to believe in a divine architect to recognize the coherence of this view. Even Kepler and Pascal, who wanted to think of themselves as inhabiting a universe made by God for man’s salvation, found that they had no choice but to recognize that the universe was so vast, and the tiniest creatures within it were so exquisitely detailed, that it was either infinite, or might as well be. ‘The eternal silence of these infinite spaces frightens me,’ wrote Pascal.59 Like it or not, even those who insisted that Bruno was wrong when he described an infinite universe were forced to imagine what it would be like if he were right.

Moreover, by expanding our range of vision, the telescope and microscope made it easier to recognize the limitations of our sensory apparatus when deprived of artificial aids. Pascal’s friend Roberval suggested that human beings perceive light, but they simply lack the senses that they would need to discover what light is;60 when he goes to the moon Cyrano is told:

[T]here are a Million of things, perhaps, in the Universe, that would require a Million of different Organs in you, to understand them. For instance, I by my Senses know the cause of the Sympathy, that is betwixt the Loadstone and the Pole, of the ebbing and flowing of the Sea, and what becomes of the Animal after Death; you cannot reach these high Conceptions but by Faith, because they are Secrets above the power of your Intellects; no more than a Blind-man can judge of the beauties of a Land-skip, the Colours of a Picture, or the streaks of a Rain-bow …61

Locke agreed: other creatures on other planets may have senses that we lack, but we cannot even begin to imagine what they are like:

He that will not set himself proudly at the top of all things; but will consider the Immensity of this Fabrick, and the great variety, that is to be found in this little and inconsiderable part of it, which he has to do with, may be apt to think, that in other Mansions of it, there may be other, and different intelligent Beings, of whose Faculties, he has as little Knowledge or Apprehension, as a worm shut up in one drawer of a Cabinet, hath of the Senses or Understanding of a Man.62

What is the poor worm doing shut up in a drawer? Presumably he is a woodworm, not an earthworm, and Locke’s furniture was crawling with them.xivxiv

§ 6

It might be thought that Copernicus was responsible for the destruction of the correspondence between microcosm and macrocosm. But this would be a mistake. There was only one major scale shift in Copernicus’s universe: the stars were required to be at a vast distance from the solar system, given that there was no measurable change in their relationship to each other in the sky while the Earth orbited the sun in the course of a year, and so consequently they must be very big if they were not to be invisible. But the sun and the planets remained the same size, and Copernicus still continued (it seems) to believe that the universe consisted of nested spheres. Copernicus’s universe was no longer Earth-centred, but it was still Earth-friendly, and there was no reason to think it was not the product of benevolent design. There was nothing in his argument which might imply that the Earth was just another planet, or that the universe had not been created for the benefit of human beings. The universe still had a centre, and the sun and the Earth were still unique objects.

The key change occurred in 1608 with the invention of the telescope and the microscope. Instruments are prostheses for thinking, and act as agents of change. Before 1608 the standard scientific instruments – cross-staffs, astrolabes, and so forth – were all designed to make naked-eye measurements of degrees of a circle. Even the vast sextants and quadrants built by Tycho Brahe were simply enlarged sighting devices. These instruments were no different in principle from those used by Ptolemy, and although, by making parallax investigations of comets and novae, they could be used to undermine the traditional belief in the translucent spheres that supported the planets (as had still been accepted by Copernicus), they reinforced the assumption that human beings were the perfect observers of the cosmos, and the cosmos itself was designed to support human life.xvxv

These were not the only specialist instruments: alchemists had a specialized equipment of stills, crucibles and retorts, but these were simply a variety of containers to which heat could be applied (alchemy was frequently defined as trial by fire). They provided no new information about humanity’s place in the universe. The printing press not only transformed the dissemination of knowledge but also, by making exact visual information widely available, brought about a revision in the traditional conception of what knowledge is.

After 1608 a new range of instruments made the invisible visible. The thermometer (c.1611) and the barometer (1643) made it possible to see temperature and air pressure, the first of which had previously been a subjective sensation, while the second is, under normal circumstances, something of which human beings are completely unaware. The barometer and Boyle’s air pump (1660) made it possible to see what happened when living creatures or flames were subjected to a vacuum. We might add to these Newton’s prisms, which visually demonstrated the fact that white light is made of light of different colours for the first time (1672). So by the end of the century there was quite an array of new instruments, but none of the others had an impact comparable to that of the telescope: originally intended to serve as a simple tool in warfare and navigation, it transformed not only astronomy but also how human beings envisaged their own significance.63

§ 7

In these last two chapters we have been looking at the ways in which intellectual change has knock-on consequences. The discovery of America killed off the two-spheres theory of the Earth. Copernicanism led to the idea that the planets shine by reflected light, which was confirmed by the discovery of the phases of Venus; and this killed off the Ptolemaic system. There was nothing arbitrary or contingent about these changes; they were as inevitable as the discovery of America once Columbus had set sail. These were intellectual transformations of fundamental importance, yet historians of science barely discuss them. They have become dark stars themselves – effectively invisible.

Why? Since Kuhn’s Structure history of science has focused on controversy between scientists,64 the assumption has been that every major new theory is contentious, and that there is nothing inevitable about the process by which one theory supplants another. This approach has been extraordinarily illuminating. But, in shining a light on controversy, it has left in the shadows all those changes which took place almost silently and were inevitable – indeed, could be seen to be inevitable at the time. Nobody (or, rather, only a few confused and ill-informed individuals) sprang to the defence of the two-spheres system after 1511. Nobody defended the Ptolemaic account of Venus after 1611. By 1624, eleven years after he had made public his discovery that Venus had a full set of phases, Galileo could take it for granted that no competent person would defend the Ptolemaic system.xvixvi It is easy to find evidence to support the claim that it was the telescope that killed off the Ptolemaic system, despite Thomas Kuhn’s claim that Copernicanism was in the ascendant well before 1610 and the telescope made little difference.xviixvii As we have seen, editions of Sacrobosco’s Sphere, the elementary textbook for the Ptolemaic system, and of Peuerbach’s Theoricae, the more advanced textbook, dropped off sharply after 1610. The evidence is clear: Ptolemaic astronomy was unaffected by Copernicus; it went into crisis with the new star of 1572, but by the end of the sixteenth century it had fully recovered. The telescope, on the other hand, brought about its immediate and irreversible collapse.

Sometimes there are real, live, enduring controversies in science. In the seventeenth century such conflicts took place between those who believed in the possibility of a vacuum and those who did not, between those who believed in the possibility of a moving Earth and those (after 1613, supporters of Brahe rather than Ptolemy) who did not. Sometimes the outcome really does teeter and hang in the balance. But, at other times, vast, well-constructed, apparently robust intellectual edifices are swept away with barely a murmur because, to paraphrase Vadianus, experience really can be demonstrative. If you concentrate on controversy, then it begins to look as if progress in science is arbitrary and unpredictable. If you assume that there is no major change without controversy, then your central assumption is never tested. The relativist thesis appears to be confirmed because evidence that would challenge it is never even considered. The picture changes radically if you look more broadly at intellectual change; then the demise of the two-spheres theory and the dark-star theory emerge as striking examples of intellectual change that took place without any controversy at all. Yet these were not minor theories: one was held by the best philosophers of the later Middle Ages; the other by the cleverest Copernicans of the late sixteenth century. The importance of an intellectual change simply cannot be measured by the amount of controversy it generates.