NavList:

   

Reply

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.navlist.net
To post, email NavList@navlist.net
To , email NavList-@navlist.net
-~----------~----~----~----~------~----~------~--~---

   

Reply