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: How Many Chronometers?
    From: Greg R_
    Date: 2009 May 6, 15:03 -0700

    --- On Wed, 5/6/09, George Huxtable  wrote:
    > By the way, there was a wonderful picture, a few weeks back, occupying a
    > double page in the Guardian. 
    A link would have been nice. Since George didn't provide one, here's a couple for those interested:
    --- On Wed, 5/6/09, George Huxtable  wrote:
    > From: George Huxtable 
    > Subject: [NavList 8167] Re: How Many Chronometers?
    > To: NavList@fer3.com
    > Date: Wednesday, May 6, 2009, 2:55 PM
    > Jim Wilson wrote-
    > | How about a log which keeps error and rate. John
    > Harrison's chronometer
    > | had to be accurate for three years at sea for him to win
    > the prize. And
    > | there were zero sources of time ticks then.
    > That's a common misunderstanding. But the test that was
    > applied to 
    > Harrison's chronometer H4 was between Portsmouth and
    > Barbados, a voyage of 7 
    > weeks, over which an error of 38.6 seconds had accumulated.
    > Cook took a different chronometer, a copy made by Kendall
    > (K1), around the 
    > World on "Resolution" on his second
    > circumnavigation. There is much 
    > misunderstanding about that too, partly the result of the
    > Sobel book 
    > "Longitude". A useful analysis was made of its
    > performance by Derek Howse, 
    > in a section, "Navigation and astronomy", of the
    > book "Background to 
    > Discovery", ed. Howse (1990). I attach a plot. Over
    > most of the period, it 
    > was gaining at over 10 seconds per day. Over a year, that
    > puts it an hour 
    > out, or 15� of longitude (= 900 miles in the tropics).
    > Over two years, twice 
    > that. It was only by checking the error, against lunars or
    > Jupiter 
    > satellites, at each stopping-point, where the rate could
    > also be checked by 
    > star transits, that Cook was able to keep its inaccuracy
    > within bounds. As 
    > long as that was done, it became a useful tool, and he was
    > delighted to have 
    > it aboard. The Arnold chronometer, carried on the consort
    > "Adventure", 
    > behaved much worse, as the plot shows.
    > Jim added, in another posting,
    > "I guess I thought that a chronometer was defined as a
    > clock with a constant 
    > rate of change."
    > Alas, there's no such thing. Every chronometer has some
    > temperature 
    > dependence, and the aim is to minimise that over the widest
    > possible working 
    > range. And every mechanical chronometer is subject to wear,
    > and to 
    > deterioration of its lubrication, which changes its rate
    > over time. It 
    > became standard practice, whenever a long stay in port
    > occurred, to return 
    > the instrument to an expert for cleaning and re-rating.
    > By the way, there was a wonderful picture, a few weeks
    > back, occupying a 
    > double page in the Guardian. Harrison's original
    > chronometer, the enormous 
    > H1, had failed, after all these working years. One of the
    > four coil springs, 
    > which contol the motion of its balance, had broken;
    > presumably, from metal 
    > fatigue. The picture showed from above Jonathan Betts,
    > curator of the 
    > horological gallery at the National Maritime Museum,
    > surrounded by the 
    > component parts of the clock like an enormous exploded
    > diagram. I do hope he 
    > manages to get it together, to run for a further 250 years.
    > George.
    > contact George Huxtable, at  george@hux.me.uk
    > or at +44 1865 820222 (from UK, 01865 820222)
    > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    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