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
    Re: Sadler
    From: Nicol�s de Hilster
    Date: 2008 Dec 23, 15:53 +0100

    frankreed@HistoricalAtlas.net wrote:
    > Jeremy, you wrote:
    > "the effect of tides on dip seems very academic to me. "
    > Oh HELL yeah! It's completely academic. But it's at least worth noting that 
    folks do calculate these sorts of issues so that we can sort out trivial 
    things from important things. And this tidal business is definitely 
    trivial...  Two centuries ago, people even tried to calculate the difference 
    in dip in a north-south direction relative to an east-west direction due to 
    the oblateness of the Earth. Can you imagine?? They had no sense of scale.
    On board of a vessel the whole issue is indeed academic, but let us not 
    forget that Sadler's original idea was "...to observe the dip, 
    accurately by theodolite, from fixed locations on the seashore ... using 
    the height of the tide to give varying heights above sea-level.". Tidal 
    ranges of more than 10 metres are not uncommon and can be very useful in 
    such an experiment, as this will produce a difference in dip of more 
    than 3 arc minutes (assuming the observer stands at 3m above high water 
    and thus 13m above low water). Sadler only pointed out that it was 
    difficult to determine the relation between the tide measured near the 
    shore with the one measured at the horizon, an unknown perhaps not 
    measurable with a sextant, but surely with a theodolite.
    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