[ISHMap-List] New Tetrabiblos Edition and Finding Longitude
dougsims1945 at yahoo.com
Mon Nov 7 06:18:30 CET 2016
Dear ISHMappers, It has just come to my attention that a book has been recently published, which might be of considerable interest to cartohistorians, although it is not likely to have been noticed by many in our field. Its relevance to map historians might at first seem questionable. It might take me a while to explain this book's value to us, but I think that anyone with an interest in the history of finding longitude, a little studied area, will find the read worth his while. The book is : Vuillen-Diem, Gudrun, ed., Steel, Carlos G, ed., with the assistance of Pieter de Leemans (Ptolemy). 'Ptolemy's Tetrabiblos in the Translation of William of Moerbeke' (Ancient and Medieval Philosophy, Series 1, 19). Leuven, 2015. (xi, 443 pp.; facsimiles/25 cm. Includes bibliography and indexes). We all know that Ptolemy wrote a number of works. But there are three works between which we may say there is a loose unity (though not, to be sure, to the point of being able to speak of a trilogy), that is, the 'Geographia (geography and cartography), the Almagest (astronomy), and the 'Tetrabiblos' (astrology, taken, incidentally, quite seriously by Ptolemy, as well as many others before and after him; sometimes called the 'Quadripartitum'). There have been a number of editions of the 'Tetrabiblos' over the centuries, most in Latin, but sometimes in other languages, including English, and other languages. The problem with all translations up to now is that they all ultimately stem from Arabic texts. Vuillem-Diem and company have, for the first time, translated the work from a Greek manuscript text, that of William of Moerbeke. Their translation is into Latin, which may discourage many readers who can plod their way through Latin only at a prohibitavely slow pace, and with much uncertainty (as with the present writer). Fortunately, this presents no problem here, for the great majority of the work consists of extensive commentary and notes by the authors, all of it in English, and it is this material which interests us. In any case, , if one should wish to consult the 'Tetrabiblos''s text itself other than in Latin, the editions hailing back to Arabic texts cannot be hopelessly unreliable. So this is no problem. Some readers may object (as I do) to the edition's use sometimes of the phrase "astrological science", but this too presents no problem to us. So, why would a book on astrology be of such interest to a historian of cartography? Before answering this, I should make some observations on my activities in the course of several years, from 2007-2012, for which I beg the reader's patience, for this will take a couple of paragraphs. During, and before and after, these years 2007-2012, I was avidly researching a certain 16th century cartographer and his work. The question of astronomical determination of terrestrial coordinates, and especially the question of getting longitude on land, kept hitting me in the face during this work, but I couldn't deal with it, because I knew so very little about it. I began to attack this monster with all the pertinacity I could summon. In these five years I consulted, not hundreds, but a couple of thousand works, both of recent authors, and ancient authors, many times more of the latter than of the former, because it became clear that my minuscular knowledge was not less than other modern scholars, though there did not lack at times pretenders to knowledge. There is, in fact, considerable good work on the arduous labor, necessary, of slowly improving the tables, ephemerides as well as others, and on the equally slow, but vital, work of improving instruments, and a few less important topics. But how do use these tables and instruments to find your longitude? On this, essentially nothing solid. Very few even knew how to find local mean solar time. Indeed, few really knew what that was. But if you don't understand this, and know it as well as you know the palm of your hand, you may as well give up and go play a game of tennis as try to find longitude. The same goes for understanding parallax, through and through, this being a demon, probably the most difficult of all problems with astronomical determination of longitude, though there are a number of other essentials as well. The literature was virtually a tabula rasa. As to the older texts, there was very little help, either. They were still worse. As to these old texts, it is essential to ascertain which of these invariably and horrendously elliptical treatments of the question are (often slyly written, to conceal ignorance) poppycock and pseudo-mathematics. I think it an understatement to say that over 90% of these treatments belong to the latter category. This goes on from some indeterminate time before the 15th century, right up to the 17th, and probably, 19th century! When all this clutter is swept away, the problem becomes approachable to the point that it is possible to make real progress, albeit with much difficulty. But if it is not swept away (and one must know a bit to do this selective sweeping), it is not difficult, but absolutely impossible. You might as well try to drive from Boston to New York with a blindfold on, Though no one will tell you so, the fact is that the majority, practically the entirety of present cartohistorians consider in their hearts that a true resolution to the historical question of longitude is a hopeless morass, best avoided, for it will never be brought into the light of full understanding. This is wrong, and it is my hope and dream to demonstrate that the question of the history of longitude can be understood just as clearly, though not just as easily, as how to water one's garden. As to the work I did in 2007-2012, it was brought to halt by events of force majeur (a hurricane and others), and furthermore, not long after these events, I realized that it would not in any event be possible, as I had wished, to include my longitude findings in the work on my cartographer. It would simply have made the book too long. So there sits my project, in a large set of folders in four large Staples boxes, and six lengthy card files, each with over 1000 cards. They sit there, largely ignored for over four years because of other obligations and problems, and I have grown a little distant from them. But with a little push, I will be able to set afire once again my familiarity with this work, and my love for it. I have not made the comments above to boast, and I hope they shall not be taken that way. I have made them simply to make it clear that the observations I will now make about the importance of the 2015 'Tetrabiblos' edition have behind them knowledge obtained from many years of digging in books. That is, I wish to gain the reader's confidence as to my remarks on the significance of the 2015 'Tetrabiblos' edition. And so: Even in Ptolemy's time, the basic notion of longitude, the drawing on the terrestrial sphere of a scheme, in the sexagesimal system, providing an ideal partitioning of the globe, such that every place would have a unique location, was perfectly understood. This was a theoretical construct, and by its nature, it is perfect. Ptolemy had this. But he didn't have at all the means of giving correct positions of places. His approximations cannot be considered a total failure, but there was no pressing need to try to do better. Nor were the necessary mathematical tools yet available. Later, the Arabs came along, and made some desultory improvements, as with Ptolemy, perhaps not fully worthless. But their heart, too, was not into the work, and they also lacked the mathematical tools to make much improvement. Both with Ptolemy and the Arabs, the impetus to try to do better was simply lacking. Shortly after, in the 15th and 16th centuries, came the age of discovery. Suddenly, the picture changes. With the advent of navigation, and I suspect for other reasons which are still unclear to us, longitude suddenly began to take on great importance. It had almost the air of an Eldorado, or Holy Grail, about it. It was It was a coveted thing. At this point, there occurred a collision, which, in the reading I have done, appears not to have yet been discussed or even recognized. The collision was between the sudden arising of great importance to finding longitude with considerable accuracy, and two other factors: (1) the fact that the necessary means (as to mathematics and instruments) to arrive at the newly needed accuracy still did not exist, and (2) the world of astrology DID exist, and along with it, there existed a long-standing confusion between the two ideas, astronomy and astrology. That the minds of the time had great difficulty separating these two fields is common knowledge. Remember, too, that astrology was long revered as a source of secret or divine information, something which could give real answers. The confusion was made greater by the obvious fact that, indeed, both fields involved scrutinizing the stars and planets and following their movements. But the spirit of this following of movements is utterly different in the one firld as opposed to the other. Astronomical work calls for (even in the times when it could not yet achieve it) high degrees of accuracy in these movements and measurings. The magic of astrology comes from elsewhere entirely. The striving for accuracy is not there. Take a very simple example, and this will be clear, that is, the example of a conjunction, which can occur in both fields. But witness the tremendous difference between a conjunction in aastrology and astronomy. For horoscopic purposes, the moon and Mars, for example, remain in conjunction for quite some time, as they make their way through, say, Taurus. The supposed astrological implications of this conjunction remain valid throughout the period when they are together within the same zodiacal sign in the sky, which could be a period of something over two days! But an astronomical conjunction can last only for an instant, by definition. The conjunction is valid only for the instant when the center of Mars, the center of our moon, and the center of the earth, are all momentarily along one straight line in space (technically, we should say in one plane). Furthermore, complicating things still more, though the fact is not of great importance in the present discussion, the lining-up will happen twice, depending upon whether we are considering that our conjunction occurs within the milieu of the ecliptic system of coordinates, or equinoctial coordinates. Around 1500, the former would most likely have been the case, for that rare astronomer who made the distinction at all. In fact, there existed a belief that one could find longitude by comparing, in two places, the time at which such a true conjunction was occurring. (This, incidentally, would require the use of tables, based, say, on Seville, with its predicted time of the conjunction, and, when we consider that tables of the time gave tabulated positions of bodies at a period of one time a day (!), as opposed to 10 minute intervals, as eventually became the case, we needn't be surprised that errors of 20, 30, 40, etc. degrees were possible). I have found five instances of this would-be procedure in the early 16th century. It falls under the head of poppycock and pseudo-mathematics. (It would have been quite impossible to do such a thing, mainly due to quite unsolvable parallax problems' as well as the problem that theorbital speeds of heavenly bodies vary constantly, especially as to the moon, and for other reasons (bad tables, bad instruments, etc.) In reality, the purported longitude seeker simply made an estimate of some longitudinal difference, as the explorers did regularly, and then he jimmied his figures in such a way that it came out to his approximation. The "procedure" is complete nonsense. The important thing for us at the moment is the fact that around the start of the 16th century, astronomy and astrology became hopelessly conflated notions in face of the new need to find longitude with reasonable accuracy. (They had been conflated rather often before that, one should add, though the conflation was of less consequence). The confusion between astronomy and astrology, and its effects on beclouding the pursuit of longitude, is a story which permeates the early literature in many ways. Although this is "negative" information, it can help us understand why longitude could in fact not be found at the time. Almost nothing has been written on this, either mathematically or in a more general sense. But any history of longitude finding, when we finally get around to writing one, must include a section on this strange period which confused astronomy and astrology, which in turn added confusion to the search for longitude, already filled with enough difficultiues. Four or five pages would probably suffice, but it must be included. Editons of both the 'Almagest' and the 'Tetrabiblos' were available to scholars at the time ('Almagest', 1480 [Epitome], 1496, 1515, 1528, etc., and manuscript editions/'Tetrabiblos' (or 'Quadripartitum'), 1464, 1493, 1500, 1519, etc., and manuscript editions and they must have contributed to the fateful widespread confusion between astrology and astronomy at the time. The extensive commentary in the book of Vuillen-Diem, et al, , can certainly throw some much needed light on this aspect of the history of finding longitude, and no doubt lead us to still other sources. Doug Douglas W Sims3516A Bayview Ave.Brooklyn, New York, 11224 718-891-6684 dougsims1945 at yahoo.comss
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