[time-nuts] establishing your position w/o gps

David davidwhess at gmail.com
Tue Jan 24 12:16:47 EST 2012


I think James Burke discussed these clocks in one of his documentary
series.  Besides not using a pendulum, they were temperature
compensated by using materials with opposite temperature coefficients
of expansion and then gimbaled for use on a rolling and pitching ship.

Oddly enough, the phase locked loop came significantly earlier when a
clock maker used it to regulate pendulum clocks overnight to quickly
calibrate a new clock to a reference clock.

On Tue, 24 Jan 2012 17:50:54 +0100, Azelio Boriani
<azelio.boriani at screen.it> wrote:

>Yes, the first real push was the Longitude Act (1714) and the Harrison's
>clocks.
>
>On Tue, Jan 24, 2012 at 5:36 PM, Chris Albertson
><albertson.chris at gmail.com>wrote:
>
>> On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali <attila at kinali.ch> wrote:
>> > On Tue, 24 Jan 2012 11:04:08 +0000
>> > "Poul-Henning Kamp" <phk at phk.freebsd.dk> wrote:
>> >
>> >> In message <20120124115848.312d60bd4fccce4f3e71c136 at kinali.ch>, Attila
>> Kinali w
>> >> rites:
>> >>
>> >> >All this talk about telling the time using stars or the sun made me
>> wonder
>> >> >how did people tell what position their telescopes had back in the days
>> >> >before GPS?
>>
>> Sailingships and trade was what pushed this.   At the time of Columbus
>> he was able to know his latitude within a few 10s of miles but even
>> after returning to Europe he did no know how far around the world he
>> had sailed.  Was it 1/3rd or 2/3rds?  They had no way to know.    The
>> problem was that on one had a clock that should keep time well enough.
>>  They used hour glasses on board ship for short duration time keeping
>> but those were of no use on a longer ocean crossing.
>>
>> Later they discovered the idea of common view of the moons of Jupiter
>> and they could measure the time from local noon some even on Jupitor
>> while a person back home did the same thing.  Later when he got back
>> home they compare notes and then know the difference in longitude.
>>  Good ocean going clocks were still centuries away.    But in the
>> 1500's they could only know the location after the fact when they
>> returned




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