Abstract
In a work of popular history published in 2009, Gavin Menzies claims that maps and other knowledge passed to Europe in 1434 inspired the exploration of a route to Asia by travelling westward across the Atlantic, and that, together with the wealth brought from the New World, this knowledge sparked the Renaissance in Europe. Stripped of any claims that are entirely unnecessary to believe that the Chinese had an important role in kickstarting the Renaissance, the plausibility rests in the claim that the Chinese had the knowledge, and instruments of sufficient accuracy, to produce maps that could have been useful to explorers such as Columbus and Magellan. This paper explores that question, and concludes that the Chinese probably did have the ability to produce maps that indicated longitude by the end of the thirteenth century, but had probably lost it by the sixteenth century. It is therefore impossible to be certain whether they could have produced useful navigational aids in the early fifteenth century.
Introduction
I happened across the book, 1434, by Gavin Menzies (2009), quite by accident. I picked it up in a second-hand bookshop in London. The basic argument that Menzies puts forward is that a Chinese fleet sailed to Italy in 1434, bringing knowledge from the orient that ignited the Renaissance. Most importantly, that knowledge included maps of the Americas, which acted as a stimulus and guide to the voyages of discovery that followed at the end of the fifteenth century. The book has been the focus of considerable controversy since its publication.
Among the stories that Menzies relies upon is the claim, supposedly made by Magellan, that he knew that what are now called the Magellan Straits opened into the Pacific Ocean, because he had seen the map.
Professional historians have ridiculed Menzies account and have put forward two main arguments. In the first place, Menzies is no historian. He does have relevant expertise, however, as a navigator, and he claims this gives him privileged insights into the material he is presenting. I shall come back to this question of the ad hominem argument later. But the second, and most damning argument is that nobody else seems to have noticed the arrival of a Chinese fleet in Italy in 1434, and there is no independent evidence that such a fleet ever existed. And that would appear to be the end of Menzies’ central argument.
And that probably would be the end, if the interest of the story depended on a map being carried by a fleet to Italy. But what there is no dispute about is that the Silk Road had been functioning for centuries before these supposed events, and that Marco Polo had brought news and artefacts from China to Europe much earlier. Take away the physical fleet arriving in Italy in 1434, and there still remains the tantalising possibility that a map might have been carried from China to Europe along the Silk Road, and that such a map, or maps, could have been a stimulus to exploration in the Western Hemisphere.
The main obstacle to that interpretation of events is that, to be useful to Columbus and Magellan, such maps would need to have been marked clearly with lines of longitude, and the problem of longitude was not solved until the eighteenth century. So the plausibility of this less demanding interpretation of a map arriving in Europe hinges on the simple question: Could the Chinese have solved the problem of measuring longitude at least three hundred years before the Europeans?
The Problem of Longitude
In the eighteenth century, the problem of measuring longitude was such an obstacle to trade and the safe passage of Royal Navy vessels that the British government, in 1714, offered a substantial prize of twenty thousand pounds for the discovery of a method that would result in the accurate measurement of longitude in a way that was repeatable and could be performed on a ship (Sobel, 1996). This led to a race to find a solution as quickly as possible.
In marine navigation at that time, there was no major difficulty in measuring latitude; a simple sighting of the elevation of the sun at midday would tell a ship's navigator how far north or south of the equator the ship was. There was no correspondingly simple way of measuring longitude, or how far east or west of a fixed line a ship was. It was therefore common practice to sail to a particular latitude, and then sail east or west until one met with land, at which point it would hopefully be possible to identify the land in question. This was not only wasteful in terms of being able to sail following the most direct route, it was also dangerous when the conditions of the wind and sea meant that arriving at land could come with considerable peril. It was the loss of a number of Royal Navy ships with considerable loss of life that prompted the government to institute a prize for solving the problem of longitude. Although the prize was never officially awarded to anybody, the problem was eventually solved by the ingenious John Harrison, who developed an accurate ship's chronometer, or clock. His ingenuity was shown in the many inventions that he made in developing a clock mechanism that could function accurately in conditions of varying temperature and humidity on board a rocking ship. In 1773, Harrison eventually proved that he had made a chronometer that met the criteria for the longitude prize and was awarded a sum of money in recompense for his work by the English parliament.
However, the spectacular achievements of Harrison can blind us to the fact that he was in competition with other methods of solving the longitude problem. In fact, not long after the development of accurate chronometers, a practical solution to the problem of longitude by astronomical means was found. The essence of the measurement of longitude is a calculation of local time, and a comparison of local time with a standard time at a known location. If the standard time was taken at Greenwich, as it was for British ships, then moving fifteen degrees to the east would mean that noon (locally) occurred an hour early in comparison with the reference time in Greenwich. Noon locally could be found by measuring the height of the sun above the horizon, while Harrison's accurate chronometers meant that the reference time in Greenwich could be carried on board the ship. If a different, astronomical, way could be found for measuring the time at Greenwich (or any other fixed reference point), then that would also be a solution to the longitude problem.
The method of measuring longitude by lunar distance was perfected at the end of the eighteenth century. It depends upon the comparison of accurate measurements of the moon's position against the fixed stars, and calculations of where the moon would be expected, as observed from, say, Greenwich, at a particular time on a particular date. The calculations were complex, and the necessary observations of the moon's position accurate, but the process could be somewhat simplified by the production of tables of lunar positions on different dates and at different times throughout the year. Such tables were first published in 1766, containing the data for 1767, by Nevil Maskelyne, the fifth Astronomer Royal (Royal Museums, 2022).
The problem of measuring longitude can be conceived as consisting of two parts: there is the question of measuring longitude while at sea, and there is the question of measuring longitude from a position on land at the end of a sea voyage. In one sense, thinking of Harrison's chronometer as the solution to the problem of measuring longitude makes it harder to see this distinction, since, to be effective, a chronometer must function continuously whether at sea or on land. There can be no question of restarting the chronometer once one has arrived at the end of the journey, as that would defeat the whole purpose of using measurements of time to gauge longitude.
In contrast with this, measuring longitude by lunar distance does not face a similar obstacle. Although the calculation of longitude from the observation of the position of the moon involves a complex calculation, it does not place any constraint on the instruments used in terms of their performance between observations.
Thus, if we see the chronometer as being in direct competition with the astronomical method of measuring longitude, we can see that the chronometer has the advantage that the calculation needed to move from an observation to a measurement of longitude is simple, the process quick, and the measurement must be possible at any time when it is possible to make a clear observation of the sun at noon, whether on land or sea. It has the disadvantage, however, that any inaccuracy in the measurement of time must aggregate over time, and the accuracy of the measurement of longitude deteriorate, unless the chronometer can periodically return to its point of reference to be checked and recalibrated.
In contrast with the chronometer, the astronomical method requires an accurate observation of the position of the moon, astronomical tables that tabulate the expected position of the moon at different times, and a complex calculation that takes considerable time to perform. This combination of features makes the astronomical method less suitable for use at sea. However, it has the advantage over the chronometer in the fact that its accuracy does not deteriorate over time, and it does not need recalibrating, except in so far as new tables are needed for each day in the future. But there is, in principle, no obstacle to producing tables that will be valid for any arbitrary date in the future. Thus, while the chronometer was more suitable for measuring longitude while at sea, the strength of the astronomical method means that it may be more practical for observers who wish to measure longitude on land.
Part of the difficulty of perfecting the lunar method for measuring longitude was the complexity of the calculations necessary for computing the position of the moon. But there was also a difficulty of making measurements with sufficient accuracy on board a moving ship. But that latter source of error was not necessarily a problem for astronomers or cartographers who could leave the ship and, while on land, make accurate lunar observations.
In view of these reflections on the methods of measuring longitude, as they developed in the late eighteenth century in Europe, the question of whether Chinese cartographers could have measured longitude while on land can be reduced to the question of whether the mathematical skills and astronomical instruments were available that would make it possible for cartographers on land to use of the lunar distance method, or something like it, to compile maps of land masses showing lines of longitude.
There is no great difficulty in imagining that the Chinese could have sailed to the Americas and developed charts of the coasts of the continents, as contended by Menzies (2008) in his book 1421. Even supposing that they did not wish to venture out into the open Pacific, they could have followed the coast, the Bering Straits not representing a very major obstacle to staying in contact with the coast. Nor is there any great difficulty in believing that, if the Chinese had such maps, they could have passed relatively easily to Europe along the Silk Road. Thus, it would be relatively easy to accept the central tenet of Menzies hypothesis, while discounting his more flamboyant accounts of an actual Chinese fleet arriving in Italy in 1434. But for such Chinese maps to be useful, it would be essential that the Chinese should have the ability to measure longitude, so that Columbus and Magellan could understand where on their journey the maps would be useful to them.
Since the ancient Greeks had reasonable estimates of the size of the Earth, we have to dismiss from our minds the traditional ideas that the explorers who set off looking for an alternative route to the East Indies could really mistake a journey of 5,000 miles with one of 20,000 miles, and believe that they were in Asia when they arrived in the Americas. Nor can we believe that they imagined, as some of their uneducated sailors might, that they were in danger of falling off the edge of the world. We must instead imagine that, when they encountered land only 5,000 miles west of Europe, that they knew they had encountered some previously unknown continent, or some continent that the Chinese had mapped in a position where they could, more or less, expect it to be. But for that part of Menzies hypothesis to be credible, it is necessary that the Chinese should be able, by the year 1400 or thereabouts, to measure longitude and represent it on their maps. And it was that question that first aroused my interest.
Enter Guo Shoujing
One day when I was looking for a peaceful spot to sit and contemplate near Beijing Normal University, I happened upon the Memorial Hall of Guo Shoujing. This charming little museum is on the edge of the lake, Xihai, close to the Second Ring Road of Beijing, and tucked away behind Jishuitan Metro Station. The museum, which has few visitors, and which has exhibits that are labelled only in Chinese, was able to convey to me only the shadiest of ideas about the achievements of the great man. However, it was clear to me, even only being able to look at the physical objects on display, and the panoramas depicted on the walls, that Guo Shoujing was an engineer who had constructed canals, and who had an interest in astronomical instruments. It was extremely difficult, from such impressions alone, to form a precise opinion as to how accurate Guo Shoujing might have been in his observations.
Actually, most of the exhibition is devoted to the construction of canals, which does seem to have been a very major part of Guo Shoujing's accomplishments. But that is partly because it is rather easier to depict, and for the layman to interpret, achievements in structural engineering than achievements in astronomy. Some of Guo Shoujing's earliest achievements were in the development of water clocks, which, it should be noted, would have been unsuitable for measuring longitude, as they could not have maintained their accuracy when being transported (Wikipedia, 2022).
Over the years I have returned to the museum that is Guo Shoujing's Memorial Hall on several occasions, sometimes on my own, and sometimes in the company of Chinese friends who have been willing to translate the labels on exhibits. And over the same time, the exhibits have been ‘improved’, which has mainly meant labelling and displaying artefacts better, and increasing the focus on canal building rather than astronomy. (During a visit to the China Science and Technology Museum in Beijing, in 2024, I discovered that Guo Shoujing's astronomical achievements and inventions are more fully recorded there than in his own Memorial Hall, presumably on the grounds that the audience in a science museum are more likely to value his scientific achievements more.) But it became clear to me that the question I had posed, ‘Could the Chinese have measured longitude by around 1400?’, could be simplified rather dramatically to the question, ‘Could Guo Shoujing measure longitude using astronomical methods?’
Guo Shoujing was born in 1231 and died in 1316. He fits quite well into the time sequence necessary for believing that the Chinese had mapped the Americas in a way that could be useful to Columbus and Magellan. It is more difficult to evaluate the level of his skill and the extent of his achievements in astronomy. But Guo Shoujing has been referred to as ‘the Chinese Tycho Brahe’ (Wikipedia, 2022), and knowing that Tycho Brahe had played a prominent role in the development of astronomy in the West, and contributed to the line of research that eventually led to Newton's exposition of the Universal Law of Gravitation, it seemed probable that if anybody could achieve the necessary feat, it would be Guo Shoujing. There is, of course, an irony in referring to Guo Shoujing (1231–1316) as the Chinese Tycho Brahe (1546–1601); he lived three centuries too early to have really been the Chinese Tycho Brahe.
It eventually dawned on me, after several visits to Guo Shoujing's Memorial Hall, that if I was going to form a reasonable idea about what Guo Shoujing was capable of, I was going to need the help of somebody who combined knowledge of Chinese, knowledge of English, and technical knowledge of astronomy. And it took me longer than it should have done to realise that that particular combination of knowledge could be found in the work of Joseph Needham and Wang Ling (Needham & Ling, 1959). And, sure enough, Guo Shoujing (Kuo Shou-Ching in Needham's transliteration) makes many appearances in that volume.
Needham is better known for his less technical and more general work on the transfer of technology from China to Europe along the Silk Road, The Grand Titration (Needham, 1969). That work chronicles the transfer of paper and printing, the magnetic compass, gunpowder, and an effective horse harness from China to Europe. These Chinese inventions were revolutionary in Europe and led to the developments that became the Renaissance and eventually the Industrial Revolution. These alone could have had the effect, as suggested by Menzies, of stimulating rapid development in Europe. But Needham and his colleagues did not suggest a single historical event, such as the arrival of a Chinese fleet in the Mediterranean, as being necessary. They supposed the less dramatic possibility that these technologies had percolated from east to west along the Silk Road through the normal process of trade.
But forming a clear idea of Guo Shoujing's abilities is complicated by the loss of all of the written works of Guo Shoujing, and the fact that after the twelfth century, Chinese astronomy went into decline. Needham and Ling (1959, pp. 368–9) offer the evidence of one notable witness, Matteo Ricci, that by the end of the sixteenth century the Chinese were not capable of sophisticated astronomical observations. Ricci was an Italian Jesuit who arrived in China in 1582 and remained in China until his death in 1610. Needham and Ling (1959, p. 369) state that, Ricci was greatly impressed by the astronomical instruments of the Yuan dynasty, though holding a poor opinion of those Chinese contemporaries whom it was his strategy to supplant, and venturing a particularly erroneous guess about the origin of the instruments.
Needham and Ling (1959, p. 374) point to one very practical difference between the instruments of Guo Shoujing and the practice of astronomy elsewhere in the world. European and Islamic scholars divided the circle into 360 degrees, a system that they inherited from the Babylonians, via the ancient Greeks. In contrast, the circles of the instruments designed by Guo Shoujing divided the circle into 365¼ degrees, reflecting more the number of days in the year. The difference, and the fact that neither system adopted the other method of measurement, probably reflects the different interests of the Chinese and the Western scholars. Chinese astronomers were primarily concerned with the preparation of the most accurate calendar, with which the Emperor and his government could manage the empire. Consequently, adopting a circle of 360 degrees would have represented a loss of accuracy. On the other hand, Western astronomers were primarily concerned with developing theoretical models of the movements of heavenly bodies, and adopting a circle of 365¼ degrees would have rendered their calculations impossibly complex.
It should, perhaps, be emphasised that Ricci was in some ways an unreliable witness. His purpose was to impress upon the emperor the value of western science to China. That is to say, Ricci had a vested interest in deprecating any knowledge that he found in China, and in exaggerating the claims of European science. He may not have needed to simulate this belief, as it is likely that he was himself convinced that knowledge should flow from west to east. He was, after all, in China primarily as a missionary and evangelist. On several points Needham and Wang found Ricci to be in error, but most particularly in his claim that the Chinese must have developed their astronomy under the influence of western scholars.
Needham and Wang also point out that the system of astronomy developed in the tradition of Europe and the Middle East was markedly different from that developed in China. They argue that this difference related to the way in which observations were made, and that this made interpretation of the Chinese system by Europeans particularly difficult (Needham & Ling, 1959, pp. 172–3): Chinese astronomy was essentially polar and equatorial, depending largely on observations of the circumpolar stars, while Greek and medieval European astronomy had been essentially ecliptic, depending largely on heliacal risings and settings of zodiacal constellations and their paranatellons. The Jesuits were naturally quite unprepared for the possibility that another entire system of astronomy might have existed, equal in scope and value, but different in method from that of the Greeks.
In more general terms, there is a serious difficulty here for those who wish to maintain that we should respect indigenous knowledge; it can be extremely difficult, when it comes to concrete cases, to determine the origins of any specific piece of knowledge. For, while it is fairly clear that the astronomy of both the ancient Greeks and the Chinese have a common ancestry in the astronomy of the Babylonians, the edifices that they built on those foundations are quite distinct. This may, in part be traced to a divergence of interests. The ancient Greeks favoured abstraction and theorising, and pursued their astronomy into the epicycles of Ptolemy, the Chinese pursued astronomy for the practical purpose of developing the most accurate calendar possible. And it should perhaps be remembered that the Chinese to this day use a lunar calendar, so we might suppose that the Chinese paid particular attention to the position of the moon, and would therefore have been very likely to have been capable of making the necessary measurements of the moon's position to calculate longitude.
In passing, it is interesting to note that Needham and Ling (1959, p. 184) speak highly of Leopold de Saussure, who possessed the knowledge of a sailor and navigator as well as considerable sinological knowledge. Saussure was, therefore, the first European scholar, apart from the eighteenth century Jesuits, to bring practical knowledge of astronomy to bear on the interpretation of Chinese texts. Needham and Wang argue that earlier scholars made many mistakes in translating and interpreting early Chinese texts, because they looked upon the problem merely as one of language, and not one of technology. By combining a knowledge of the technology with the question of interpretation, Saussure was able to correct some of the interpretations made by earlier scholars. This casts an interesting light on two aspects of this story. It suggests that I was by no means the first to identify the need for a combination of language skills and scientific knowledge in interpreting the work of Guo Shoujing; Needham and Wang had certainly come to that conclusion earlier, and attributed a number of flaws in the nineteenth century history of astronomy to its lack. The other point, of course, is that when Menzies claims that his experience as a navigator gave him a unique advantage over professional historians, his claim may not be entirely without foundation.
Indigenous Knowledge and Decolonising Knowledge
This story offers some interesting sidelights on current debates about indigenous knowledge and epistemic colonialism. While there are clearly some actors in this story who have a vested interest in promoting the science of western Europe, and using that science to extend their influence, as is the case of Matteo Ricci, there are also scholars working in the global north, such as Joseph Needham and Wang Ling, who are determined to assert that the influence has been in the opposite direction.
Indeed, the puzzle that seems to have preoccupied Needham most was the question of why, when such inventions as gunpowder, the compass, and printing had such explosive results in the west (no pun intended), they left Chinese society largely unaffected. The most interesting effects seem to have been produced through a process of hybridisation. And that is to say that very peculiar combinations of scientific and technological knowledge within social contexts have the ability to produce unexpected change. And often times knowledge is so hybridised as to make it very difficult to know where a particular idea originated.
Tracing either the origin or the effects of a specific idea or technology can be extremely difficult and / or speculative. Anderson (1983) highlights the role of ‘print capitalism’ in the development of national identities in western Europe in the seventeenth and eighteenth centuries. Although even here I falsify by simplifying, as Anderson actually argues that nationalism first attained its modern form in the colonies of America, and that it was the creole creation of nationalism that was eventually imported to Europe. But what is clear is that paper, printing, and gunpowder, all imports from China, had a huge but indeterminate influence on the shaping of European culture. If we now have to add into the mix the printing of some specific documents, the maps that made colonisation of the Americas more likely, then the web of influences becomes indescribably more complex.
Clearly, one claim that indigenous knowledge has is that it is more specific, less abstract, than the science of western Europe. That claim seems to be borne out in the case of astronomy / geometry, with the Chinese circle of 365¼ degrees, in contrast with the circle of 360 degrees employed by the Greeks. But that rather begs the question as to why one of what must once have been two competing indigenous knowledges became the foundation of western science. It seems that, indeed it is almost tautological that, abstraction is necessary for knowledge to be applicable beyond a limited realm. Rather than ask why one was better than the other, however, we should probably focus attention on what each was better for. Chinese angular measurements were more accurate for measuring days in the year and constructing calendars, although that knowledge is only ‘local’ and ‘non-generalisable’ in the sense that it applies anywhere on our planet. Greek angular measurement could be extended into a more abstract field of geometry, which found application outside astronomy. And again, what it means for knowledge to be ‘local’ is problematic, in this case seeming to imply attachment to an intellectual field rather than a territory.
And then there is the question of the contrasting approaches to astronomy, with the Chinese viewing the heavens, as Needham and Wang note, ‘essentially polar and equatorial’, while the Greeks viewed the heavens as ‘essentially ecliptic’. It is unclear whether geography could have produced such a difference, and whether viewing the skies from Denmark Tycho Brahe might have been more inclined to one construction and Guo Shoujing in China more inclined to another. But rather than struggling to find out which approach was better, and better for what, it is perhaps simplest merely to note that the greatest developments occurred through hybridisation and cross-fertilisation between different approaches.
Conclusion
I started this quest with the chance finding of two sources: a book by Gavin Menzies that argued that knowledge passed from China, and in particular a map of the Americas, had arrived in Europe in the early fifteenth century, and had been available to the explorers who subsequently sailed west to the Americas, and the Memorial Hall of Guo Shoujing.
If we take Occam's razor to the tale spun by Menzies and remove everything that is not essential to the story, we can imagine the passage of knowledge and documents from China to Europe along the Silk Road, without any need to believe in the physical transfer of documents directly from China to Italy by means of a single fleet, unrecorded by any historian apart from Menzies. Similarly, since it is now generally accepted that the prehistoric inhabitants of the Americas arrived there from Asia by passing across the Bering Straits, it does not seem to be too much of a stretch to believe that Chinese explorers of the fifteenth century could have taken a similar route and mapped the continents. But if such maps were to be of any use to Magellan and Columbus in their journeys, they would have to have included some reference to either distance or, more likely, longitude, since otherwise they would have had no idea when the maps were likely to be useful in their passage.
This means that if there is to be any kernel of truth in Menzies’ tales, the question can be simply stated; were the Chinese able to measure longitude before the fifteenth century? And I come to the conclusion that this question should be answered in the affirmative. Guo Shoujing was probably in possession of the knowledge and necessary instruments to measure longitude in the thirteenth century. However, much of that knowledge had been lost by the sixteenth century, and it is doubtful whether Chinese cartographers in the sixteenth century could have measured longitude. It therefore remains an open question as to whether that knowledge could have been incorporated into charts that were available in the early fifteenth century.
Footnotes
Funding
The author received no financial support for the research, authorship, and/or publication of this article.
Ethical Consideration
There is no need to have ehtical approval for this research.
Declaration of Conflicting Interests
The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.