A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Review: "The Naked Nautical Sextant"
From: Frank Reed
Date: 2009 Mar 9, 14:41 -0700
From: Frank Reed
Date: 2009 Mar 9, 14:41 -0700
Review: "The Naked Nautical Sextant and its Intimate Anatomy" Last week, the President of the Florida Senate opened the latest session of that legislative body with a symbolic gift for every member: a sextant in a wooden case. He expected Florida state senators to look to this symbol for guidance in tough times, to remember that in the darkness, they can still find their way... Is that all that sextants are today? Symbols? Echos of a bygone era? Bill Morris, a retired engineer living in Pukenui, New Zealand, has recently written a book entitled "The Naked Nautical Sextant and its Intimate Anatomy," and for Bill sextants are anything but symbols. They are intricate devices to be dis-assembled and re-assembled and brought back to life. They are not just old navigators' tools, but scientific instruments capable of amazing accuracy in the measurement of angles when properly cleaned, restored, adjusted, and calibrated. Sextants are a bit obsolescent, yes, and Bill admits that in his preface, but they are far more than symbols. Bill's "book" is an electronic book, delivered by download from his web site at www.sextantbook.com for $24.95 (USD) or $32.95 when shipped on CDROM, well worth the money in my opinion. This is certainly a book in terms of the scale of the content within it. There are over 250 pages in fifteen chapters and four appendices and over 200 color photographs as well as diagrams. Like computer software, electronic books can be updated regularly if errors are found with little or no cost to the end user. While reading Bill's book I did spot a few little typos here and there, inconsequential things (for example, the table of contents labels appendix 5 as appendix 4 and in the caption for the frontispiece, a sextant is labeled as "unamed"), but by and large the book has been carefully edited, and I would assume that any updates would add content rather than correcting the few flaws in it. Fundamentally, this is a "how-to" book. It is the summation of Bill's many years of practical experience tearing down and restoring nautical sextants. Read it and you will learn how to disassemble and re-assemble every component of a standard nautical sextant. In addition, though he makes no claims of detailed scholarship, the book necessarily includes extensive information on the history of sextants and their basic optical principles, too. And as an aside, there's an interesting section on the history and construction of Ramsden's Dividing Engine which made accurate sextants possible. There's next to nothing, of course, on wooden quadrants or more recent plastic sextants. The book covers standard metal sextants, such as were made from the early 19th century through the latter half of the 20th century. "The Naked Nautical Sextant" offers excellent advice on tools and techniques. Naturally, the author details the standard tools required: various sizes of screwdrivers, non-magnetic forceps, vices, etc. and perhaps a pin-wrench (for removing those little notched rings that secure lenses in telescopes), but he also advises the would-be sextant restorer on inexpensive aids like small sandbags to support the sextant on a work table. A great idea! According to the author "Using just a few hand tools, the average person with the aid of this book should be able to strip down a sextant to its component parts, clean and lubricate them, put them together again correctly and adjust the instrument." This stretches the concept of an "average person" a little bit, but I think it would be fair to say that the "average person who might actually pick up this book" would be abl e to follow the directions and advice and accomplish most of the claimed goals. There are a few little curiosities of style in the book. For example, Bill writes in his preface (briefly commenting on modern electronic systems that have largely replaced the sextant in practical navigation) that it is possible "for several times the cost of a sextant, to buy a system that provides the user in real time with her position on a chart of the area through which she is passing." and then says in a footnote "I do not of course intend to imply that there are no male navigators." I suppose that this is an inside joke. There are over 200 diagrams and photographic illustrations in the book. A few could use some revision. For example, there's a numbered diagram of the sextant components that would be clearer if the numbers ran in a consistent order. All of the photographs are professional in quality and illustrate the intended point beautifully. There's an excellent section in the book describing the various sextant frames, their composition (brass versus aluminum) and design. The photographs here are a real pleasure: there's something delightful about seeing all of these familiar instruments torn down to just the frame. It is indeed a collection of "naked nautical sextants". Though there is plenty of information in the book for the beginner, much of the advice here will also be interesting to those with significant mechanical skill or engineering background. For example, with respect to severely damaged screws, he notes that "taps and dies" are available "if you have to make a new screw from scratch." The book occasionally assumes some knowledge of tools and the language of tools that may not be present. For example, we read, "This is a common engineering solution when an accurate, shake-free fit is required between a plug and a socket, seen most commonly in the Morse tapers of drill shanks. It is not generally appreciated that the rectangular tang of such a drill plays no part in transmitting torque." I was left scratching my head over that one. Likewise, regarding certain shades, "The mountings are often not easily dismantled as swaging may be used to fix the various parts in place." What's swaging? Sure, I could look it up (and in fact, I did: see "swage" on Wikipedia), but an inline definition of some sort or a footnote would help here. The word turns up around ten times in the book. Sextants of many types and manufactures are covered. There are Husuns, Tamayas... the US Navy Mark II, Heath sextants and Plath. The book includes considerable practical detail on dis-assembling the popular Russian SNO-M and SNO-T sextants. To his credit, Bill does not use the name "SNO-T" sometimes found in accounts of Russian sextants ("CHO" consists of the Latin letters which resemble the Cyrillic letters that are properly transliterated as SNO). I found the sections on the internal anatomy of the micrometer assembly and bearings most interesting. These are components that most of us who have used sextants take as given and rarely get to see dis-assembled and analyzed from an engineering perspective. We can really see the generations of design that went into these seemingly simple devices. Even the release catch, which disengages the micrometer and lets the index arm swing smoothly, is analyzed in great detail. The book also covers the tangent screws which provided fine adjustment of the position of the arm in older vernier sextants from the 19th and early 20th centuries. There are details on small parts like the mirror frames or holders and how they were constructed in older instruments. A motto for this book might be: anything that can be taken apart WILL be taken apart. And so we learn how to dis-assemble a remarkable variety of mirror cells. This is encyclopedic information, and most readers will probably skip over some of it to get to the particular instrument that interests them. Even sextant shades are discussed at length. "All the properties of absorption, reflection, refraction and diffraction have been used by one maker or another in a variety of shades" (diffraction? Did he mean polarization?). The section on telescope optics is excellent, demonstrating a clear understanding of the optical principles and the construction of the various telescopes, monoculars, sighting tubes, as well as the various mounting hardware and rising pieces. Bill provides a comparison of the wide variety of solutions that sextant manufacturers have found over the decades. For an example of practical advice, when cleaning old lenses, Bill warns "but beware of soaking them in alcohol, as some of them are fixed with shellac, which dissolves in alcohol." --Interesting. I didn't know that. Even sextant legs and handles get a chapter full of details! And it doesn't stop there: the construction and carpentry of sextant boxes and cases is also covered. Chapter 14 feels like a change in editorial style, and if I didn't know that this was the work of one author, I would almost think that this was a second writer at work. Bill here finally addresses the philosophical issue of restoring an old instrument. Should it not perhaps be preserved in its original state? There are no simple answers to such questions, of course, and overall, I think Bill makes a good case for an acceptable level of restoration. It's in this chapter that you'll find most of the valuable tips and tricks on general cleaning and restoration including advice on re-painting the frame of an old instrument. This whole chapter feels more like a journal or a "blog" than the rest of the book. There's really nothing wrong with this by itself. It's still good reading and a goldmine of ideas, but it seems to me that most of this material could have been re-worked into other parts of the book. The last full chapter of the book describes sextant adjustment. It's a very fine account of the methods found in any good navigation manual. It might have benefited from a better discussion of the relative significance of the various errors and could have included some mathematics. For example, the author tells how to eliminate side error, but there's no mention of the fact that side error is unimportant (except in certain methods for measuring index error). Related to the general problem of adjustment and error-correction, one of the four appendices covers the measurement of arc eccentricity and error using collimators. So who's this book for? Who would buy "The Naked Nautical Sextant"? Anyone who owns a sextant today is likely to perform a little basic maintenance on it. And many modern sextant enthusiasts have yearned for the know-how to perform a complete re-construction of an old sextant. This book provides all the details you might ever want. But how about for those are "all thumbs"? If you are not able to work with small precision tools, no book will cure you of that. And yet there's vicarious pleasure here, even for those who will never attempt to dis-assemble a sextant. As you read along, you feel a bit like you're peering over Bill's shoulder as he works. For those who have already dis-assembled and restored a sextant, who might perhaps suspect that they know all this already, the most significant addition here will be the sheer variety of instruments examined in their dis-assembled glory. It's not just the intimate anatomy of one species of sextant -- "The Naked Nautical Sextant" is a comparative anatomy of a whole zoology of sextants. I highly recommend it. And incidentally, back to those "symbolic sextants" in Florida that I mentioned at the start of this review... The total price, including an engraving on the display box, was $32.50 per sextant, so I think we can safely conclude that they were not real sextants at all, but rather those gaudy display models --little better than toys-- that we see for sale on auction sites on the Internet. Those Floridian senators do NOT need this book! -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To unsubscribe, email NavListfirstname.lastname@example.org -~----------~----~----~----~------~----~------~--~---