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    Re: How Many Chronometers?
    From: Douglas Denny
    Date: 2009 Sep 24, 05:49 -0700

    I have to challenge this as it is incorrect:
    You say:-
    Remember, Harrison's biggest challenge was not making an accurate chronometer 
    (that had been done already) but rather making one that remained accurate 
    despite the motion and temperature changes experienced at sea.
    According to Rupert Gould:-
    The term chronometer is generally believed was first used in the modern sense 
    of a machine specifically designed for the purpose of keeping acurate time at 
    sea by John Arnold in his pamphlet " An Account of the going of a Pocket 
    Chronometer" published in 1782. Though it does appear to have been first used 
    in the same sense by Jeremy Thacker in his description of his "machine for 
    the longitude" published in 1714.
    Accurate chronometers had _not_  been made before Harrison (or otherwise they 
    would surely have made claim to the longitude prize); and even land-based 
    long-case pendulum clocks, so-called "regulators" (the most accurate 
    available) were not as accurate as Harrison's regulator - beside the general 
    fact they could not be used at sea.  There was NO accurate clock available 
    for use at sea - i.e. a chronometer,  before Harrison.
    It was considered _impossible_ for physical scientific reasons by all of the 
    leading scientists and astronomers of the early eighteenth century to produce 
    a clock accurate enough that could withstand the difficult conditions of 
    sailing ships of the time. That is the real measure of what Harrison was up 
    Harrison was the first to get to grips with the real problems of accuracy. 
    He understood the need to reduce friction and was the inventor of various 
    methods of reducing it including what we now call needle-roller bearings.
    He was the first to introduce temperature compensation successfully with 
    gridiron pendulum for regulators, and bimetallic stip compensators in his 
    chronometers.  This, along with the balanced spring opposing-pendulum 
    oscillator were the big breakthroughs.
    He was the first to understand the need for balanced mass/spring oscillators 
    that could maintain oscillation though subject to external forces - thrown 
    around by a sailing ship; and he undestood for the first time the need to 
    de-couple the oscillating elements from the rest of the mechanism as much as 
    possible and hence understood in principle what we would now call 'Q' - the 
    "goodness" of an oscillator.
    His 'grasshopper' escapement in his regulator is recognised as the most 
    friction free escapement of them all, which affects the motion of a pendulum 
    the least and increases accuracy thereby.  Not unitl the Shortt clock came 
    into being in the 1920s was his regulator improved upon.
    He understood the forces involved in his large rocking balance clocks and 
    realised that there was a fundamental underlying physical problem which could 
    not be overcome; hence his change after a lifetime of improving his designs 
    of the large clocks to small pocket-watch configuration - the one which 
    evenually won the longitude prize.
    Harrison can rightly be descibed as a genius in my opinon - someone who is so 
    advanced compared to his contemporaries they are unique and there is no 
    meaningful comparison really possible.  He started his working life as a 
    carpenter and joiner, working on a large estate in the service of Sir Rowland 
    Winn of Nostell Priory;  but became the world's leading master of horology in 
    marine chronometer development.  An astonishing achievement.
    His achievement is so huge and comprehensive; the brilliant inventiveness so 
    amazing;  and the lifelong dedication in the face of all the opposition, 
    including scientific negativity against him in the eighteenth century;  is 
    difficult to comprehend today.  It is probably the equivalent of someone 
    today converting their motor car into a spaceship capable of travelling to 
    the Moon and back!
    Douglas Denny.
    Chichester. England.
    Original Post:
    A fascinating experiment and experimental confirmation of my long-held belief 
    that even the cheapest digital watch makes a superb chronometer.
    Now a challenge for anyone wanting to repeat the experiment or extend the results:
    1.   Take the "watch board" and simulate motion.   Okay, maybe we can't take 
    it to sea but maybe drive it around town with us?
    2.   Vary the temperature.   Maybe put the board outside in direct sunlight 
    (and rain and maybe even snow).
    Remember, Harrison's biggest challenge was not making an accurate chronometer 
    (that had been done already) but rather making one that remained accurate 
    despite the motion and temperature changes experienced at sea.
    Whoops, as I write this I'm looking at my digital watch on my wrist and 
    watching it bounce around.   Maybe experiment #1 isn't required.   In fact, 
    the very nature of digital watches should make them motion-insensitive 
    (excluding relativistic effects :-P ).
    Lu Abel
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