While reading the article I couldn't help noticing a few errors which I would like to bring up.

You stated that "the circumference of the Earth was first determined by the Greek cosmographer Eratosthenes". If I'm not mistaken it was probably Aristotle who recorded the first mathematical estimate of the size of the Earth, some 400,000 stadia along the equator. There are some who even postulate that Eudoxus of Cnidos actually determined it through astronomical observation.

You stated that "Ptolemy, himself, under-exaggerated the circumference of (sic) the Earth, by calculating each degree of longitude as 500 stadia, instead of a more accurate 700 stadia". Actually, Ptolemy probable "accepted" Posidonius' calculations of 500 stadia to a degree.

You stated "another of Ptolemy's errors was a belief that a southern continent existed, which counter-balanced the weight of the land masses in the northern hemisphere, to keep the Earth stable on its axis". Actually this belief can be traced to Crates of Mallos who constructed a terrestrial globe showing four symmetrically arranged continents separated by two great oceans that balanced the Earth.

You stated "Yet, Ptolemy's maps depicted the World as it was known nearly fourteen hundred years earlier". This statement is highly debatable. Were maps themselves ever present in his work? And if so, might not they have been changed in any way from the time of his residence on this planet to the time they were "rediscovered" in Europe in the early 15th century? 

You stated that Berlinghieri's Geographia was " augmented with more modern writings". These more modern writings would better be stated as Italian verse.

Finally, you stated about the Zeno map of the North, "while now considered to be faked by that ancestor, the map is still a remarkably good depiction of southern Greenland and Iceland". Ib Kjelbo presented convincing evidence of its forgery in "Zenokortet - dets kilder of dets betydning for den kartografiske udforming af det nordlige atlanterhav" (in Danish). Basically what he states is that Zeno copies place names in Greenland from Cladius Clavus who himself used an old Danish poem to represent the various parts of Greenland. The depiction of Greenland and Iceland can also be traced back to Clavius. Zeno had no talent other than being able to copy others' works and get away with it!

As a further note, I believe one can also argue that the last two editions of Ptolemy with maps were pubished in 1596 and 1597 without further qualification about your intent. The last Ptolemy which Stevens lists is the 1730 edition.

With best regards,
Mark Cohagen

The Editor:  So far as I am aware - and I have looked through my reference library again - Eratosthenes was the first to accurately determine the circumference of the world, although there had clearly been earlier attempts, for example Anaximander is said to have made a globe of the world in the sixth century, and Dicaearchus, a pupil of Aristotle's, worked on establishing the extent of the known world (and is supposed, by some, to have made a series of maps).  I would be very interested in any reference to Aristotle's works in this area. Ptolemy's work clearly served as a synthesis of the thoughts and theories of numbers of earlier astronomers and mathematicians.  I did not mean to attribute the origin of particular theories to Ptolemy, but only to note that he believed certain things to be true, and these beliefs - which contained the mistakes I highlighted - were reflected in his text.  After all, it was Ptolemy's text that fifteenth and sixteenth century geographers were concerned with, rather than reconstructing the origins of his material. I personally believe that Ptolemy did compile maps for inclusion in his text.  However, it would seem that maps were not associated with the text when the text was re-discovered by the Byzantine Greeks in the thirteenth century, and there may be some merit to the suggestion that Maximos Planudes was responsible for creating a set of maps to go with a text that he had, circa 1300 A.D., which served, either as a source, or an impetus, for the creation of subsequent sets of maps.  As to your question whether the maps (if they did originally exist), changed, I do not think they did.  I think it more likely that the importance of Ptolemy's text was sufficient to ensure that his materials were preserved, even in the face of evidence of his errors, and transmitted unchanged, with the exception of scribal error. Book I and parts of Book VIII of Berlinghieri's 'Geographia' are a paraphrase of Ptolemy's text.  The rest of the book is an amalgam of various classical sources, including Ptolemy, Strabo, Mela and Pliny), augmented by the inclusion of material from more modern prose sources, such as Christoforo Buondelmonte (and, incidentally, also from modern maps).  The text was then written in Italian verse. As for the Zeno map, that is my fault.  I meant descendant and wrote ancestor.   While, there is some toponymic connection to Clavus (and how could there not be), I think there is probably an intermediate source.  Clearly, the Zeno map is not based on the Clavus' first map of Scandinavia, as copied in the Nancy Codex of 1427 for example.  If Clavus' second version is the source for the map of Scandinavia in the Zamoiski codex of 1568, illustrated by Nordenskiold (Facsimile-Atlas, reprint edition, New York: Dover Press, 1973, fig.34) one may be closer to Caterino Zeno's source. However there are still important differences, for example the presence of the imaginary island of Frisland.   The illustrated maps are from the Ulm Ptolemy of 1482, which reflects Clavus's first map, and the Ruscelli copy of the Zeno map, published in 1561)  As you rightly point out, the last edition of Ptolemy's text with maps was published in 1730. I was thinking in terms of editions to commission a new sets of map plates, and the text has been altered accordingly.

Thanks again for a great resource.

Mike Rainwater

The Editor: Thank you for your kind words.  We're planning to cover the Seventeenth Century Dutch map trade later in the year, and hope that you find the article worth waiting for.

I liked the Speed stuff - are you going to include that he and Susannah had 18 children, that he was given a room in Custom's House in 1598 by Queen Elizabeth, that he went blind and suffered from gall stones in later life and allegedly did all the placename corrections himself ? And that he wrote a theological treatise? Interesting men these early mapmakers!

Paula Dryburgh

Librarian, Todhunter-Allen Collection, Bodleian Map Section. Oxford.

The Editor: Thanks - a timely reminder that biography is also about the chaps, not just their maps!

Mark Babinski