Welcome to the NavList Message Boards.


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

Compose Your Message

Add Images & Files
    Bissaker Sliderule
    From: Nicolàs de Hilster
    Date: 2008 Mar 31, 16:05 +0200

    Dear Group,
    I cross-post this message to Rete and NavList, so some of you will get 
    this message twice.
    Last January I was contacted by Werner Rudowski with questions about the 
    Bissaker sliderule. Rudowski is currently writing an article about the 
    Bissaker sliderule. Robert Bissaker was a Mathematical Instrument Maker 
    who worked between 1642 and 1664 and created this sliderule, which is on 
    display at the Science Museum in London, in 1654.
    Rudowski contacted me with several questions, one of which concerned one 
    of the scales: This scale, the so called 'm-scale' (after a description 
    by Baxandall from 1914), has a, yet unknown, purpose. The divisions have 
    been measured using a modern metric ruler (which I post here with his 
    degrees on m-scale
        90  85  80  75  70  65  60  55  50  45  40  35  30  28  26  24  22
    mm  0   10  20  32.5    46  61.5    80  99  124     154     189.5   -
        331     366     406     454
    The origin (90 degree mark) is located at 111mm from the start of the 
     From these values I was able to reconstruct the following two formulae:
    1) 154/(TAN(degrees)^1.2)
    2) 154/SQRT(2) * ((1/TAN(degrees/2))-1)
    I attached an image with both formulae in a more clearer notation. The 
    constant 154 was taken from the 45 degree measurement and might be 
    slightly different.
    Although the first formula gives a better fit, it seems to me that the 
    second is more likely as I am not sure whether or not they were able to 
    solve the power 1.2 in those days.
    Would any of you be able to explain the purpose of this scale based on 
    the figures and formulae given? The part 1/TAN(degrees/2) of the second 
    formula is known from stereographic projections, so perhaps there is a 
    on behalf of Werner Rudowski
    best regards,
    Nicolàs de Hilster
    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
    To unsubscribe, email NavList-unsubscribe@fer3.com


    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    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 Settings

    Posting Code:

    Custom Index

    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