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: Troughton and Simms sextant
    From: Brad Morris
    Date: 2013 Jan 10, 07:22 -0500

    Hi Norm

    The nonius is between 50 deg 10 minutes and 50 deg 20 min.  So our base angle is 50 deg 10 minutes.  The vernier aligns at 1 minute 30 seconds. 

    Add 50 deg 10 minutes to 1 minute 30 seconds and yes, we get 50 deg 11 min 30 seconds.  I agree with you.

    I try to shift the light source around as I inspect the vernier (not possible in a photo) so that the reflections off of the graduations change.  This permits a closer estimation of which is the closest line.

    As to the vernier vs micrometer argument?  Its not so hard to read a vernier with a little practice and there is never any wear.  The micrometer is easier to read but suffers from wear and backlash.  It also depends on precisely hobbed gears and clean gears at that.  I prefer the vernier myself.  I'm sure that there are strong advocates for the micrometer as well.

    Kind Regards
    Brad

    On Jan 10, 2013 1:09 AM, "Norm Goldblatt" <ngold---.net> wrote:

    What a wonderful group. I'm absolutely thrilled to meet you all. Thanks so much for all your suggestions. I cut and paste here a note to Brendan Kinch for all to comment upon.

    Ah- I just looked more closely at the second photo of your pillar frame sextant. It also has the bifrucated magnifier arm. And it too, is rectangular as opposed to mine, which is tapered. I'll take some more photos. I'm having fun trying to read the angles. In principle, seems as though you can read down to 10 sec, but it's difficult to tell the vernier line which lines up the best. I'm guessing plus or minus 20 sec is the about the accuracy to be attained. Right now, I think I'm looking at 50 deg 11 minutes 30 sec. Really? That's amazing. Or did I slip a decimal. We don't need no stinkin' micrometer! How in the world, though, would a mariner be able to read this on deck at night with the rolling seas, the spray, the wind. I'll post this on navlist, as well for comments
    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]fer3.com
    ----------------------------------------------------------------

    Linked File: http://www.fer3.com/arc/imgx/vernier-.JPG

       
    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