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    Re: Nevil Maskelyne.
    From: Frank Reed CT
    Date: 2004 Jul 16, 18:36 EDT
    Of Sobel's "Longitude", George H wrote:
    "It attempts to explain a highly-technical subject to the lay reader without the aid of explanatory diagrams. As a result, that reader is likely to emerge without really understanding much more about the determination of longitude than when he went in. "

    That's only a speculation. I have had the opportunity over the past few years to speak with a great many people who have read "Longitude". Those "lay readers" do indeed understand what they have read. I think you're exaggerating a bit when you refer to this as a "highly technical subject". Sure, there are technicalities in the details --as in any subject-- but the basic concepts are easy enough for a child to understand. Navigation is not "rocket science", and Sobel did an excellent job explaining the concepts. Would diagrams have helped? I don't think that there are many places where they would have helped a lot, though I've met a few readers who would have liked some further explanation of the inner workings of a chronometer. On the other hand, animations are tremendously helpful with these concepts and a significant number of television documentaries followed on the heels of Longitude's success --and they were filled with delightful, occasionally educational animations.

    By the way, I've just browsed the chapters on longitude and lunars in Bowditch, Norie, Lecky, and Dunraven. They contain almost no "explanatory diagrams". Does that mean they're bad books? Dunraven has the most diagrams (four, I think), and wow are they ever confusing!

    And George H wrote:
    " Sobel attributes the destruction of Shovell's fleet on the Scillies to a failure in longitude.
    Nothing could be further from the facts. "

    Perhaps. Old legends die hard. For over 250 years, those shipwrecks were widely blamed on a failure in longitude, and many professional navigation historians still routinely describe them that way today. Certainly when I first heard the tale of the wrecks in the late 1970s, it was told almost exactly the way Sobel relates it in "Longitude". The Board of Longitude and the Longitude Prize themselves were a direct response to the Shovell disaster. For a recent example, Alan Stimson, former Curator of Navigation at the National Maritime Museum (Greenwich, UK) in "The Quest for Longitude" wrote: "Flamsteed ... was directed to 'apply himself with the utmost care and diligence to rectifying the tables of the motions of the heavens and the places of the fixed stars so as to find out the so much to be desired longitude of places for perfecting the art of navigation'. A series of maritime disasters, culminating in the wrecking of part of a returning squadron of naval ships under the command of Sir Cloudesley Shovel (ca. 1650-1707) on the Scilly Islands in 1707, eventually led to the British Parliament setting up a committee to examine the problem. This, in turn, resulted in..." the Board of Longitude, the prize, and so on.

    Elsewhere in the same volume, William J.H. Andrewes, Curator of the Collection of Historical Scientific Instruments at Harvard University mentions the irony of testing Harrison's H1 at a location "not too far from where Sir Clowdisley Shovell had been shipwrecked 29 years earlier". In a footnote to that comment, he adds "This disaster took the lives of 800 men, including that of the admiral. Although possibly not directly related to an ignorance of solving the longitude problem, this event emphasized the importance of solving the longitude problem and served to stimulate the British government's decision to offer a large reward for a solution."

    That statement 'possibly not related' is fair. The point is clear; experts in navigational history still routinely refer to the Shovell disaster in the context of the longitude problem. A footnote about the ironic likelihood that it was a case of an error in latitude would have been very appropriate in Sobel's book, but your assertion that this is evidence of the book's failings goes too far.

    And wrote:
    "On page 98, Sobel refers to parallax in terms of the height of the observer above sea level, and appears not to appreciate the difference between parallax and dip."

    She wrote that the tables were set up for a geocentric observer while a ship is at sea level [and that is a correct account of parallax]. In the same sentence she adds that the navigator may be standing twenty feet higher than that which could cause some confusion between parallax and dip, but it is --at worst-- somewhat misleading. I wouldn't call it definitively an error, and it certainly would not lead a "lay reader" of this book into any serious misunderstanding. Nonetheless, this is the very section of the book where her one big mistake is at its worst. She mocks those who were suspicious of Harrison's "little ticking thing in a box". Of course, they were suspicious! Failing to see that placing one's trust in a "black box" was a radical idea in the 18th century is the number one failing of this otherwise excellent book.

    And concluded:
    "So my conclusion is that Sobel didn't really understand what she was
    writing about. "

    Bah. There is not an author on Earth who understands everything that he or she writes about, and that makes Sobel no worse than millions of other authors. But Sobel unquestionably --beyond any shadow of doubt-- understood the great majority of her subject matter, and her skillful prose makes her work far better than that of many other authors.

    Dava Sobel's "Longitude" is an EXCELLENT book, and if you want to motivate interest in celestial navigation among students, or learn the basic historical background of the longitude problem, this book is invaluable.

    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
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