Patrick Powers wrote: > Use of the moon's motion came later because the moon's motion is so > complex - indeed the main competition to Harrison's clocks in the 1700s > came from the lunar tables that had by then been calculated. >
Complementing Patrick Powers' comments: It took Harrison 40 years to build, demonstrate and prove that his chronometers were good (precise and robust) for determining longitude. By that time Isaac Newton, who had said that it was impossible to build so precise a chronometer, as required for longigute determination, had already died. Edmund Halley had died after spending years and years trying to build tables that would eventually allow a longitude to be established through sky observation. The fact is, only by the end of the 1700s longitude could be determined either using a chronometer (the "Harrison's") or -- eventually -- observing certain heavenly phenomena. This second way was next to impossible for seaman that didn't have the knowledge, didn't have the tools and certainly couldn't use them (if they had'em) in a ship shaking in the ocean. So the Chronometer was the first reliable, universal and fool- proof method of determining latitude. It seems Captain [James] Cook was the frist to try (and aprove) the chronometer in a systematic way. Only several years after it became generally available. The bottom-line is, only in the end of the nineteenth century engineers and seaman had a reliable way to find longitude. Dava Sobel wrote a romance-like book (Longitude : The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time ) where the search for a scientific way to find longitude in told. For sure, before the 1800 no student could find any longitude, anywhere in the earth. Only a few expert, with very expensive tools (chronometer or telescope) could do it. Nowadays you can user your wrist watch, a radio (you can do without one of them), the equation of time and a sundial (mandatory reference to sundials) to determine your longitude. Deceivingly simple, isn't it? - fernando > > As if all this isn't enough I do not think that in the sixteenth century > there were any accurate ways for measuring the time of occulation of a star > by the moon. I also believe that in the earliest days astronomy and marine > navigation were two nearly separate 'sciences' that didn't really > communicate with each other. > > All in all I think it was a combination of lots of reasons. Hope that > helps > > Patrick -- Fernando Cabral Padrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br Fone Direto: +55 61 329-0206 mailto:[EMAIL PROTECTED] PABX: +55 61 329-0206 Fax: +55 61 326-3082 15º 45' 04.9" S 47º 49' 58.6" W 19º 37' 57.0" S 45º 17' 13.6" W
