Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    Name or NavList Code:
    Email:
       
    Reply
    Re: How Worsley Navigated [Was Navigation and Whaling]
    From: Brad Morris
    Date: 2009 Feb 23, 19:31 -0800

    Hi George
    
    The type of sextant (Heath Hezzanith) and its use for the journey cannot be 
    disputed.  The exact sextant used by Worsley tours with the James Caird and 
    can be seen (but not handled)by visitors.  Who originally used it or owned 
    that sextant prior to the journey, while technically correct, is IMHO kind of 
    irrelevant.  It is the sextant that Worsley used on that journey, for his 
    reasons.  I can see why Worsley chose this sextant, it has every feature you 
    could ever dream of.
    
    So I went the additional step.  I took the photographic evidence of the 
    sextant and tracked it down.  I found the same make and model sextant with 
    all of the options as shown in the image.  It clearly is a high end sextant 
    as can be seen by all of the features and the arc accuracy presented herein.  
    
    
    Fantastically, all of those lines in the telescope tubes are present, just as 
    Bowditch calls for and they are unbroken.  There are eyepiece shades in 
    addition to the normal shades, as well as every other bit of kit (including 
    the key and screw driver).  Paid an outrageous price for it and giggled all 
    the way home.  It was mine!  Spent the next few months getting the mirrors 
    re-silvered and then adjusting all of the optics per Bowditch's 1849 
    description.  The index and horizon mirrors are perpendicular to the arc and 
    parallel to each other when the nonius is very close to zero.  The rising 
    telescope feature is present and the telescopes are parallel to the arc, 
    using Bowditch's method. I am thrilled, to say the least.
    
    There is a sight tube, two inverting scopes (4 & 11 powers) and two erect 
    scopes (3.5 and 4 powers), one of which is a large aperture star scope.  It 
    also has the binoculars which attach to the rising telescope feature.  I have 
    shot lunars with it (you don't realize how heavy it is until you hold it at 
    those weird angles for minutes at a time!) as well as the standard altitude 
    shots.  
    
    The patent "greatest angle clamp" is there as well as the patented box clip 
    that holds the sextant in place.
    
    The arc is divided to 150 degrees, yet the useful range is only to 125 
    degrees, as it is a vernier type.  The final divisions yield measurements to 
    to 10".
    
    At this juncture, I would like to have the arc calibrated but as we all know, 
    those services just don't exist anymore.  I keep hoping Frank will determine 
    the economic feasibility of his calibration methodology alluded to in earlier 
    posts. But until then, I am forced to use the National Physical Laboratory 
    record of 1921 of my sextant, which shows ZERO minutes and ZERO seconds for 
    every reading from 15 degrees to 120 degrees. Naturally, the device should 
    have worn over the years.  Maybe Bill Morris can comment on the evenness of 
    wear over the years.  Uneven wear would contribute to an eccentricity and may 
    throw that unbelievable calibration certificate out.
    
    The National Physical Laboratory certificate claims it is a "CLASS A", does 
    anyone know the classifications at the NPL?
    
    At this point, you have to ask yourself if Worsley chose poorly.  Given the 
    feature set and the fact that the expedition would have obtained the greatest 
    accuracy possible (zero point zero error) then this sextant is an obvious 
    choice.
    
    Best Regards
    Brad
    
    
    
    
    --~--~---------~--~----~------------~-------~--~----~
    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
    To , email NavList-@fer3.com
    -~----------~----~----~----~------~----~------~--~---
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Get a NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

    Enter the email address associated with your NavList messages. Your NavList code will be emailed to you immediately.
    Email:

    Email Settings

    NavList ID Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site