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
    or...
       
    Reply
    Re: Bris Sextant
    From: Alexandre Eremenko
    Date: 2005 Oct 31, 19:10 -0500

    Dear John,
    My Bris sextant consists of 3 glass panes,
    of size 1 times 1.6 centimeters.
    One pane is dark, the other two colorless, transparent.
    The thickness of the glass is about 2mm of the dark glass
    and 1.6 to 1.7 for the clear one.
    The two angles between the three glass panes I still don't see how to
    measure, Bill says he has some devises, and I wonder what they are:-)
    As I said, I can compute the angles from the Sun altitudes
    I measured last summer, but I had no chance to do this yet.
    Hopefully, by the end of this week I will see Bill,
    and he will make good quality photos of the devise.
    which I will post on my web site.
    The external angle (between the first and the third panes)
    seems to be 22
    or 23 degrees, as measured by Chinese-made plastic ruler and
    protractor, the only things I have to measure such angles:-(
    But I promise to compute these angles by the end of the week,
    unless Bill has some wonderful devise to measure them:-)
    Alex.
    
    
    On Mon, 31 Oct 2005, John Rae wrote:
    
    > Dear Alex
    > The dimensions that would be useful to me would allow me to compute the 
    actual physical angles between the small pieces of glass.  By looking 
    sideways at the instrument, ther will be two triangles with the apex at the 
    bottom where all three touch, and two gaps at the top.  If I knew the 
    vertical distance represented by the length of glass, and the gap at the top 
    between the three glasses (two measurements) then I can compute the angles 
    between the glasses, assuming the tangent and sine of small angles is 
    approximately the same.
    >
    > Using this calculated angle (or angles) I can then adjust my test instrument 
    for further trials to simulate the instrument you have.  I thank you for the 
    information.
    
    
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

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

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

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

    Email Settings

    Posting 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