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The contradiction is in the statement:-

"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".

It is simply not true. Perhaps the posting was made in haste, as I often do, 
and one makes inaccuracies which are then picked up by others.  It is no big 
deal - but is actually incorrect and worth correcting as it is so interesting 
a subject.
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It is very clear, in that Harrison's contribution was so immense that before 
Harrison - no accurate chronometers:  and after Harrison there were.

It was also the case that science and technology was dramatically increasing 
exponentially by the end of Harrison's life, compared to when he first 
started his quest for an accurate chronometer as a young man.  

It is hard for us to understand from our perspective that he spent his _whole 
life_  with this one project ( and his son helped for a great part of that 
too),  and the results of a whole man's life's work can be seen at the 
Greenwich Observatory in one single room - where mostly ignorant rubber-necks 
wander around for a couple of minutes (if that) and wander out again without 
the slightest thought for what went on to produce those wonderful clocks.

Science was moving so fast by then (something still happening to day) that 
Harrison's chronometers were not the design used by the British government 
that they had spent a lot of money in paying for the Longitude prize: it was 
the Arnold and Earnshaw spring detent escapement (both very similar in 
principle)  which became the 'gold' standard, and, remained unchanged in 
design right up to when mechanical chronometers were abandoned for quartz 
clocks.
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For those not familiar with the time-line of the use of quartz clocks - it is 
astonishing to think that quartz clocks only became possible out of the 
laboratory and into practical use with mass production in the 1960's when the 
general use of transistors became possible as the latter became cheaper - 
again with mass production and new techniques of large scale manufacture.

Quartz watches were only possible in 1970's when integrated circuits made 
possible the use of many transistors on a small enough chip of silicon.  The 
first was the Seiko 'Astron' in 1969.

I still have an intermediate technology watch of the late 1960's which uses a 
single transistor to maintain a tuning fork:  i.e. the  'Accutron' movement 
(but a Swiss version in a diver's case)  given to me as a 21st birthday 
anniversary present. I am now 61 years old, so quartz technology for watches 
has only become possible in my working lifetime. 

It is easy to forget the quartz watch has only been around in mass production 
for about forty years, and hence chronometers were still important for 
navigation up to around the mid 1960's or later.

Douglas Denny.
Chichester.  England.


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