>> The clock would then only have to remain within spec for 24 hour Not really. The only useful clock is a VERY accurate one. You cannot stay linked with Greenwich by using an inaccurate clock and "correcting" it for local time. For one thing, when you are actually moving east west, local time "noon to noon" is no longer exactly 24 hours. In fact, it is the discrepancy that you are trying to detect to see how far east west you have gone. If you are not moving, then correcting your clock every 24 hours does you no good. Part of the engineering problem was creating a clock that remained accurate under the varying conditions of temperature, humidity and motion that are inherent on a sailing vessel. >> On Jul 30, 2010, at 9:20 AM, Craig Jungers wrote: >> The clock would then only have to remain within spec for 24 hours AND >> MEASURE LOCAL TIME and not for months or years to maintain >> synchronism with >> Greenwich. Presumably there were enough stars visible in both the >> southern >> and northern hemispheres so that Cook in Australia could use the >> tables >> developed at Greenwich TO TRY OUT THE LUNAR METHOD........... >> >> Thinking this over, the ancient Pacific navigators could have used >> very > much the same system using a sand-clock calibrated for 24 hours. > Accuracy > would not have been so great but then they would at least have had > some > measure of local time. What does local time have to do with figuring out longitude? You need a clock accurate enough to detect that if you sail 100 miles west the day is longer than if you travel 100 miles east. That is not a sand clock. And they did not have sand clocks anyway. They had no glass. You try and make a even vaguely accurate sand clock out of the materials that they had and sell it to your tribe as something that was useful. It is implausible that the natives were aware that the day was shorter when they sailed east than when they sailed west. This is awfully sophisticated stuff and would require a lot of formal experimentation -- the earth is round, it rotates on its axis etc. What would even impel them to want to make an accurate sand clock? They were not trying to run a train system. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Sun Aug 08 2010 - 17:48:36 PDT
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