"That full-sail voyage": Travel Narratives and Astronomical Discovery in Kepler and Galileo

In the prefatory epistle to his Astronomia nova (1609), Johannes Kepler uses a series of related allegorical images to celebrate his discovery of the elliptical orbit of the planet Mars. He begins by announcing to his Imperial master, Rudolf II: "I am now at last exhibiting for the view of the public a most Noble Captive, who has been taken for a long time now through a difficult and strenuous war waged by me under the auspices of Your Majesty."1 Kepler’s description figures his topic as a triumph in which, "riding in the triumphal car," he "will display the remaining glories of our captive that are particularly known to [him], as well as all the aspects of the war, both in its waging and in its conclusion."2 Kepler goes on to describe how Mars was brought to bay:whenever he [i.e. Mars] was driven or fled from one castle, he repaired to another, all of which required different means to be conquered, and none of which was connected to the rest by an easy path—either rivers lay in the way, or brambles impeded the attack, but most of the time the route was unknown.3

While the sites of difficulty in his calculations are described as castles that must be besieged and overcome, and Mars, the hunt’s quarry, provides an objective for the chase, the unknowability of the paths between these sites presents a problem that must be addressed.

Kepler’s imagery provides an important comparison to William Eamon’s work on the venatio, or hunt, as a scientific metaphor in the early-modern period. For Eamon, the venatio embodied a new, objective attempt to uncover the secrets of nature.4 Eamon connects this new epistemological attitude to early-modern narratives of travel and exploration. Yet the venatio and the travel narrative— implied by Kepler’s dedication to Rudolph (as cited above)—would seem to suggest quite distinct tropes for seeing the world. The venatio is primarily goal-oriented, deliberately seeking out the traces of its quarry (the facts). On exactly that basis, however, the venatio is vulnerable to the epistemological paradox of pre-cognition, or foreknowledge. Only if one knows, to some extent, what facts are out there can one know how, and where, to hunt for them. The travel narrative, by contrast, entails no such paradox. Navigational exploration can function randomly or haphazardly, being no more interested in its putative destination than in the places, peoples, and objects that it encounters along the way. Precisely by enabling a mode of accidental discovery, in other words, travel and exploration are superior to the hunt as tropes for scientific objectivity.

In this topic, I will examine the use of travel narrative (as opposed to venatio) in Kepler’s Astronomia nova (1609) and Galileo’s Sidereus nuncius (1610). I will argue that the trope offers not only an organizational frame for historical accounts of exploration, but also an hermeneutics of discovery that focuses on error as beneficial precisely because of the accidental discoveries it produces. To this end, I will discuss the importance of travel narratives as a form of early-modern knowledge-making; examine Kepler’s description of travel narrative as a system for historical narrative in his account of the mathematical exploration of Mars’s orbit; and consider Kepler’s insistence on the importance of difficulty as a vital component of the process of discovery. Finally, I will turn to the Sidereus nuncius and discuss its narrative of accidental discovery in the context of Kepler’s travel metaphor.

"Although we by no means become Argonauts": Narrative Organization and Mathematical Exploration in Kepler’s Astronomia nova During the European age of expansion, travel produced not only new trade goods and accounts of foreign places and peoples, but also a paradigmatic image of the acquisition of knowledge. Old forms and ways of knowledge shifted and transformed in response to the influx of new geographical and anthropological information.5 Francis Bacon signals the importance of long-distance networks of trade to early-modern knowledge production in his depiction of the idealized scientific community in the Utopian New Atlantis (1625). A significant component of this research community are the "Merchants of Light": scientific intelligencers who travel incognito, seeking out and gathering together information on technological developments and natural particulars from all corners of the world:

For the several employments and offices of our fellows; we have twelve that sail into foreign countries, under the names of other nations (for our own we conceal); who bring us the topics, and abstracts, and patterns of experiments of all other parts. These we call the Merchants of Light.6

Travel narratives were an important early-modern method of transmitting knowledge gained during the process of exploration. As Ann Blair has pointed out, the order of a work posed a serious problem for natural philosophy in the sixteenth and seventeenth centuries.7 While earlier genres, such as the navigatio, were comparatively disorganized, the late sixteenth century saw the development of the "relation"—a broad tradition that included the Relazioni of Venetian ambassadors, and the Jesuit relations—along with a formal theory of travel writing, the Ars apodemica.s As a result, the genre of the travel narrative came to provide a framework for gathering "facts" into natural histories.9 This framework also proved to be strikingly useful for other presentations of scientific knowledge.

In the Astronomia nova, Kepler uses specifically geographical, not cosmological, thinking to explain the very organization of his astronomical work. He compares his account to a travel narrative, in which the incidents of the voyage, as much as the destination, are likely to be of interest to the reader:

Here it is a question not only of leading the reader to an understanding of the subject matter in the easiest way, but also, chiefly, of the arguments, meanderings [ambagibus], or even chance occurrences by which I the author first came upon that understanding. Thus, in telling of Christopher Columbus, Magellan, and of the Portuguese, we do not simply ignore the errors [errores] by which the first opened up America, the second, the China Sea, and the last, the coast of Africa; rather, we would not wish them omitted, which would indeed be to deprive ourselves of an enormous pleasure in reading. So likewise, I would not have it ascribed to me as a fault that with the same concern for the reader I have followed this same course in the present work. For although we by no means become Argonauts by reading of their exploits, the difficulties and thorns of my discoveries infest the very reading—a fate common to all mathematical topics. Nevertheless, since we are human beings who take delight in various things, there will appear some who, having overcome the difficulties of perception, and having placed before their eyes all at once this entire sequence of discoveries, will be inundated with a very great sense of pleasure.10

Kepler’s comparison of his work with travel narratives draws attention to the genre’s effectiveness as a narrative and organizational form. He suggests that the Astronomia nova, like the accounts of Christopher Columbus, Magellan, and the Portuguese—even the Argonauts—will hold the attention of its readers because of the surprises of its meandering form and the pleasures of vicarious discovery. Only once the work has been read fully will its whole shape be understood, laid out "all at once" as if in an idealized theater of knowledge.11 Yet this description of the errant narrative of the Astronomia nova directly prefaces, and purports to explain, the topic summaries by which Kepler lays out the contents of his topic.

During the early-modern period, knowledge of the structure of the universe— the earth and the heavens—was, of course, subsumed under the discipline of cosmology. In this context, it might seem straightforward to map geographical travel narratives onto the astronomical exploration of the heavens, by metaphorically applying one to the other. However, formally speaking, astronomy was not part of cosmology, but instead preserved a separate character as a mathematical discipline intent on prediction. As such, astronomy’s mathematical descriptions "saved the appearances," while abdicating to cosmology the responsibility for describing the form of the heavens. Only after Copernicus’s claims to discover the heavens by astronomical calculation could a connection be made between active geographical exploration and seemingly-passive astronomical observation. This is consistent with the rhetorical and imaginative problem that Kepler confronts.

At issue here is Kepler’s problem of how to organize the discussion of his astronomical discoveries, given the new methodological approach of his work. The extent of his difficulties is apparent in his battery of prefatory material. The main body of the work is preceded by a series of different introductions: the triumphal dedicatory letter to his patron, the Emperor Rudolf II (which I have already described); a series of dedicatory poems; an introduction for the "physicists," in which he presents arguments in favor of the heliocentric system specifically directed at natural philosophers; and, finally, an "elucidating introduction" offering a series of synoptic tables, topic summaries, and an index of terms and authors.12 This elaborate apparatus is necessary because, as Kepler complains, "it is extremely hard these days to write mathematical topics, especially astronomical ones."13 His intention is contrary to the conventions of astronomical writing: it "is not chiefly to explain the celestial motions. Nor yet is it to teach the reader, to lead him from self-evident beginnings to conclusions, as Ptolemy did as much as he could."14 In other words, astronomical descriptions are usually organized either in terms of physics—based on the form of the thing described; or mathematics— built up from axioms like Euclidean geometry. While the first method is obviously not appropriate, because the subject of Kepler’s topic is not primarily physics, the second poses a problem: "For unless one maintains the truly rigorous sequence of proposition, construction, demonstration, and conclusion, the topic will not be mathematical; but," he warns, "maintaining that sequence makes the reading tiresome."15

Accordingly, Kepler turns to the genre of historia, in which matter is organized in a chronological rather than a logical fashion.16 Mathematically, the Astronomia nova is a series of iterative approximations and refutations based upon Tycho Brahe’s data, by which Kepler eventually produces the conclusion that Mars’s orbit of the Sun is elliptical in shape.17 But "along with the former methods," Kepler "mingle[s] the third, familiar to the orators; that is, an historical presentation of my discoveries."18 The Astronomia nova is, Kepler suggests, more a journal of his work than a typical methodized text. Yet despite Kepler’s claims, the Astronomia nova was not a strictly or minutely historical account of his investigations.19 As William Donahue notes, Kepler does not "claim to present such a history: he says only that he is mingling some history with the theoretical and didactic matter of the topic."20 Kepler "describe[s] only so much of that labour of four years as will pertain to [his] methodical enquiry."21 The resulting mixed form aimed to provide both a rigorous geometrical argument and a persuasive explanatory method.

However, the combination of the two ran the risk of confusing the reader. It is for this reason that travel narrative is used to explain the synoptic table and its accompanying topic summaries. Kepler explains that the synopsis will not be of equal assistance to all. There will be those to whom this table (which I present as a thread leading through the labyrinth of the work) will appear more tangled than the Gordian Knot. For their sake, therefore, there are many points that should be brought together here at the beginning which are present bit by bit throughout the work, and are not so easy to attend to in 22 passing.22

Although he claims that the reader will find his work to be "well ordered through this method," that order comes out of the very wandering path of his investigations.23 Although earth-bound astronomy was limited to observation, as the topic summaries show, Kepler’s process of mathematical approximation functions as a metaphorical "exploration" of the orbit of the planet Mars, in which he attempts to trace the movement of the planet, to follow its path through the stars precisely. The narrative structure of the work follows Kepler’s attempts to determine its course as they go off track, each part of the work returning to a new starting point with new assumptions. For instance:

When I was on this same path and was confronted with this equivocal fork in the road, and the observations (most faithful guides) were seen to be at war with observations, the thought occurred to me to alter completely the way the path was set out, using the method which follows.24

Kepler’s investigation is a process of exploration that turns back on itself, going through similar attempts to approximate as successive hypotheses break down. Each of the five parts of the main narrative begins again, based upon new premises discovered in the previous stage. This approach transforms dead ends, encountered during attempts to fit different mathematical models to observations, into new points of departure.

Kepler’s interest in historical narrative and its accidents is apparent throughout the Astronomia nova. Thus, for instance, in topic seven, Kepler presents an account of the circumstances by which he first came to study astronomy, joining together his interest in the structure of the cosmos and the "invisible agency" of fate:

It is true that a divine voice, which enjoins humans to study astronomy, is expressed in the world itself, not in words or syllables, but in things themselves and in the conformity of the human intellect and senses with the sequence of celestial bodies and their dispositions. Nevertheless, there is also a kind of fate, by whose invisible agency various individuals are given to take up various arts, which makes them certain that, just as they are part of the work of creation, they likewise also partake to some extent in divine providence.25

Kepler goes on to explain that, while he was seduced by "the sweetness of philosophy," he had "no special interest in astronomy." It merely so happened that the first job "to offer itself was an astronomical position."26 As a result of his work on astronomy, he wrote the Mysterium cosmographicum (1599) and was driven by his "own ardour to seek, through a reworking of astronomy, whether my discovery [the speculations in the Mysterium] would stand comparison with observations made with perfect accuracy."27 It was because of this interest in observations that he wrote to Brahe and went on to work with him. Moreover, his interest in the planet Mars came about because it "happened by divine arrangement, that I arrived at the same time in which he [Brahe] was intent upon Mars," when he otherwise might have become interested in another of the planets.28

This account, with its emphasis on coincidence and happenstance, also bears a strong resemblance to the fortuitous arrival of Duracotus at Brahe’s observatory on Hven in Kepler’s Somnium, which itself takes the form of a series of voyages. Duracotus is sold to a sea captain by his mother, but because of his sea-sickness is left on the island of Hven, where he comes into the service of Brahe. Here, he is driven by his particular circumstances—including his own mother’s magical communions—to investigate not Mars, but rather the moon.29 It is the very circumstantiality of these stories and their unexpected turns in response to difficulties that Kepler hoped would produce pleasure in the reader.

"The thorns in my discoveries": Difficulty and the Accidents of Discovery

The deliberately haphazard chronological argument of the Astronomia nova seems, at first glance, to contradict Fernand Hallyn’s account of the poetics of Kepler’s astronomy.30 Hallyn draws attention to the importance of "mannerist aesthetics" in Kepler’s works, particularly the geometrical and musical speculations of the Mysterium cosmographicum (1596) and the Harmonicae mundi (1619). However, the wandering path of Kepler’s argument, and the emphasis on order and harmony in his conception of God’s order, are not contradictory; but rather meet in his focus on the perplexing difficulties that he encountered during his investigations.

The dedicatory epistle to the Astronomia nova emphasizes the strangeness of Mars’s orbit as an incitement to astronomical exploration: the eternal Architect of this world, and the Father of the Heavens and Humans in common, Jupiter located [Mars] in the front lines of the visible bodies … so that he might raise human minds, lulled to sleep by a deep somnolence, from the slanderous reproach of idleness and ignorance, arouse them to venture forth, and provoke them forcefully to carry out investigations in the heavens for the praise of their Creator.31

Kepler’s description of this incitement to investigation aligns with a widespread understanding of the importance of wonder and curiosity to early-modern knowledge-making.32 These passions were aroused by encounters with strange objects, places, and peoples—what Bacon would call the "heteroclites or irregvlars of nature"—that both attracted attention and impeded understanding.33 These "diversions" and "digressions" from the course of nature draw attention in the same way as the errores, the wanderings and mistakes, of Kepler’s narrative. These accidents, as Donahue has suggested, were a crucial part of Kepler’s innovative approach to discovery.34 In his introduction, Kepler notes that following the path of Mars was not easy: "either rivers lay in the way, or brambles [sentibus] impeded the attack, but most of the time the route was unknown."35 In the explanation of the synopsis, he complains that in his mathematical work, "the difficulties and thorns [spinae] of my discoveries infest the very reading."36 These thorny difficulties suggest a further connection with travel narratives. The "thorns" which infest his work not only suggest the difficulties of the process of exploration, but also the discoveries made on those voyages—the foreign plants that might be brought back from the new world and subsequently domesticated.37

The interest of the work, then, is not just in its conclusions, but also in the use that can be made of its difficulties in later work. Mathematical difficulties, like the plants encountered by explorers of the new world, could become objects of study in their own right. Thus Kepler emphasizes this orientation metaphorically, as in his deployment of an image of winnowing to describe the process of separating out useful results from his work:

How small a heap of grain we have gathered from this threshing! But you also see what a huge cloud of husks there is now. They ought to have been hauled back to the beginning of ch. 48, since before I investigated the arcs of the oval path I would have dealt with them. But for the sake of bringing light, they ought to be winnowed. Besides, we might end up finding a few useful grains.38

Plants that seem to be obstacles are found to produce valuable seeds, bark or roots. Similarly, Kepler’s mathematical discoveries might, like the facts in real travel narratives, be plucked out of the topic and reused in other settings. As such, there is a sense in which we can see his text as a resource for further astronomical or mathematical work.

Although Kepler mentions these thorny impediments only in a couple of places in the Astronomia nova, they reappear in his illustrations: many of the complex diagrams illustrating the hypothetical relationships between the planets are surrounded by printed woodcut ornaments of flowers and plants. Decorative ornaments, particularly vines and plants, were in fact sometimes used in the period to protect delicate woodcuts of geometrical diagrams.39 However, in the Astronomia nova the practice thematically connects itself with Kepler’s metaphor and, as a result, draws attention to the complexity of the diagrams as sites in his work. In this context, Kepler’s mathematical thorns can also be read as a counterpart to the poetic and rhetorical flowers that humanists gathered during their reading, often marked in the margins with a trefoil symbol. Ann Blair has suggested that the juxtaposition of different material in the commonplace topic acted as a stimulus to early-modern natural philosophy.40 In Kepler’s work we see both the results of this practice of poetic gathering, and the use of poetic allusion to draw attention to cruxes in his argument.

These different modes come together in next topic, Kepler’s account of the via buccosia or puff-cheeked orbit. He begins the topic with a quotation from Virgil (Eclogues, 3.64):

Galatea seeks me mischievously [malum], the lusty wench:

She flees the willows, but hopes I’ll see her first.

It is perfectly fitting that I borrow Vergil’s voice to sing this about Nature. For the closer the approach to her, the more petulant her games become, and the more she again and again sneaks out of the seeker’s grasp just when he is about to seize her through some circuitous route. Nevertheless, she never ceases to invite me to seize her, as though delighting in my mistakes.41

As Donahue points out, Virgil’s malum is also the Latin for "apple," implicitly suggesting the hypothesis of a puff-cheeked orbit. As Voelkel has argued, this passage, perhaps more than any other, shows that Kepler’s organization of the text is both persuasive and explanatory. Voelkel suggests that Kepler included the example of the puff-cheeked path in the Astronomia nova specifically because, when discussing his investigations with David Fabricius, the omission of this erroneous step had confused his correspondent and led to disagreements.42 Kepler’s decision to allude to this particular fruit of his investigations by means of poetic quotation draws yet more attention to the passage. Moreover, it raises the possibility of reading the image allegorically, connecting its mischievousness with the false knowledge that Eve gained by eating the apple in the Garden of Eden (a context in which the pun on malum was very common). The reader could connect this episode with other botanical imagery in Kepler’s text, as well as with its explicit imagery of pursuit.

Sea Voyages and the Movement of the Earth

Kepler marks the significant transition between parts three and four of his text with a quotation from Ovid: "Part of what has been begun, part of the work is finished: The anchor is cast; here let the craft lie."43 By marking the pause between arguments by a shift into the poetic register, Kepler reminds his readers of his organizational metaphor of the travel narrative, as they rest for a moment in preparation for the next stage. In doing so, however, he also returns to the theme of the voyage, which plays an important role in Kepler’s attempts to address concerns about the instability of a moving earth.

Although the Astronomia nova substitutes elliptical orbits for the regular circuits of Copernicus, it is based on Copernican foundations. Therefore, Kepler was confronted by the need to address scriptural authority, with its accounts of the centrality and immobility of the earth.44 Kepler responds to these "objections concerning the dissent of holy scriptures, and its authority" by distinguishing between literal and accommodationist views of scripture. He argues that since we acquire most of our information, both in quality and quantity, through the sense of sight, it is impossible for us to abstract our speech from this ocular sense. Thus, many times each day we speak in accordance with the sense of sight, although we are quite certain that the truth of the matter is otherwise. This verse of Vergil furnishes an example: "We are carried from the port, and the land and cities recede." Thus, when we emerge from the narrow part of some valley, we say that a great plain is opening itself out before us.45

In this passage, Kepler reuses a poetic description from Virgil that Copernicus used to explain the same problem of the apparent motion of the heavens. Both invoke poetry to show the validity of metaphorical language, in contrast to literal readings of scripture. As with the quotation from Virgil discussed above, Kepler’s poetic quotation draws attention to his point. It also suggests the importance of voyages as a metaphor for the new conception of the earth’s place in the heavens.

Kepler pursues the metaphor in the same section of the Astronomia nova, in response to objections concerning the immensity of the heavens:

In the same place, you will find that full-sail voyage [plenis velis nauigatum] along the world’s immense orbit, which is usually held to be unnatural, in objection to Copernicus. There it is demonstrated to be well-proportioned, and that, on the contrary, the speed of the heavens would become ill-proportioned and unnatural were the earth ordered to remain quite motionless in its place.46

Here, an apparent difficulty, once resolved, itself offers a solution to other problems. Copernicus’s reconception of the universe as sun-centered is expressed by the image of earth as a ship and its orbit as a "full-sail voyage of discovery." Not only can the apparent motion of the heavens be seen as the result of the earth’s triple motion, but the problem of the vast speed of the heavens is also resolved. This freeing up of the earth leads to speculation about the possibilities inherent in the observation of the universe from a mobile, as opposed to a static, vantage point.

In his response to Galileo’s Sidereus nuncius (1610), the Dissertatio cum nuntio sidereo (1611), Kepler suggests that conceiving of the moving earth as a boat allows the observer to understand it as a mobile platform from which the processes of surveying and triangulation can be undertaken:as I said in the "Optics," in the interests of that contemplation for which man was created, and adorned and equipped with eyes, he could not remain at rest in the center. On the contrary, he must make an annual journey on this boat, which is our earth, to perform his observations. So surveyors, in measuring inaccessible objects, move from place to place for the purpose of obtaining from the distance between their positions an accurate base line for the triangulation.47

Kepler’s description of astronomical observation in terms of surveying suggests how Copernicus’s hypothesis offers a powerful new way of understanding man’s place in the universe. In this vision, it is precisely the movement of the earth that provides new sights, transforming astronomy from a static process of observation into a voyage of cosmographical exploration. The very compilation of celestial observations becomes a travel narrative—a series of sights, seen in different places, that may reconfigure themselves in surprising ways when read in order.

Starry Messages: Galileo’s Journal of His Observations

In conclusion, I want to turn to an even more famous publication than Kepler’s, from the year following the Astronomia nova: Galileo’s account of his observations with the telescope, the Sidereus nuncius (1610). Galileo, like Kepler, emphasizes the accidental character of his discoveries. He enhances the credibility of his observations by portraying them as discovery-driven rather than goal-driven. The heavens that he describes seeing through the telescope are filled with unexpected phenomena that attract his interest. This rhetoric of exploration and surprise is clearest in Galileo’s discovery of the Medicean stars, as he calls the moons of Jupiter. He reports that, on the seventh of January, 1610, he observed Jupiter for the first time with his improved telescope and saw that three little stars were positioned near him—small but yet very bright. Although I believed them to be among the number of fixed stars, they nevertheless intrigued me because they appeared to be arranged along a straight line and parallel to the ecliptic, and to be brighter than others of equal size.48

Galileo’s curiosity about these stars was rewarded, "when on the eighth, I returned to the same observation, guided by I know not what fate, [and] found a very different arrangement. For all three little stars were to the west of Jupiter."49 He moved "from doubt to astonishment,"50 and was impelled to complete a long series of observations, presented in his topic, after which he concluded that the "little stars" must be planets orbiting Jupiter. The sequence represents, in miniature, an equivalent to Kepler’s far more complicated discovery of the orbit of Mars.

The connection between the new astronomy and the European age of exploration is an established critical trope. William Shea, for instance, has argued that the reconceptualization of the universe central to the Copernican hypothesis, which transformed the planets from wandering stars into alternative worlds, enabled metaphorical connections to be made between the new exploration of the heavens and Columbus’s discovery, and the subsequent exploration and colonization, of the new world.51 Such arguments, however, place an emphasis on the ability to identify seas, coastlines, or other geographical features; rather than on the organizational form and emphasis on accidental discovery that Kepler and Galileo associate with travel narratives in their work. Both Kepler and Galileo place an epistemological value on the delights of accidence, precisely as opening up new modes of mathematical investigation, and new observational habits. The rhetorical use of the travel report by these two giants of early-modern astronomy suggests a surprising construction, via pleasure and happenstance, of the factual sensibility that would be central to the natural philosophy of the scientific revolution.

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