I did not have much time to study the list recently and coming back from short vacations I noticed that as usual subjects are fascinating.
Yes, longitude was the biggest problem in navigation and the working solution to it was the invention of chronometer in late 1700s. Cook used chronometers during his late voyages. They were already prooven solution to the longitude problem or more generally to the problem of conservation of time which is of essence for precise navigation. You seldom determine latitude and longitude separately, you rather find lines of position and hopefully are at the point of their crossing. The rival method was of Lunar Distances developed in parallel with chronometers and used till the beginnings of XX century. Due to fast apparent motion of the Moon against the "constant" stars it is possible to determine time by measuring angular distance of the Moon from selected stars along its orbits. The sextant allows measurements of angle up to 0.1' of arc which roughly corresponds to 0.4 second of time. The problem with Lunar Distances was to prepare special tables that could be practical for navigators at sea who do not have much time to work on their observations. Such tables were published in Nautical Almanachs till the beginning of our century. Mathematics was not beyond reach of navigators. Joshua Slocum, one of the first yachtsmen and the first solo circum-navigator, used Lunar Distances thanks to which he had only simple alarm clock instead of chronometer which he could not afford. Lunar Distances were inferior to chronometer. They worked only when the Moon was visible, calculations took longer and were more complex introducing more chances for errors. So as usual technology prevailed, and chronometer was masterpiece of technology. The rivalry between promoters of chronometers and Lunar Distances was fierce and many dirty tricks were played, especially by astronomers involved in Lunar Distances method who sometimes were in charge of testing chronometers and judging their usability for navigation. In this respect our world does not change much. As for Columbus, yes certainly he was lucky. He was good navigator too and there is no doubt about it. Like every navigator he made mistakes. In his earlier voyages he visited Iceland where memories about the land in the West were still fresh. Yet when he discovered new land he did not associate it with Vinland which was far to the North. During vacations I was in Yosemite in Tuolomne Meadows about 2,400m (8,000 feet) above sea level. Of course you drive there by car and the highest point you drive trough is Tioga Pass 3,031 m (9,945 feet) above sea level. In spite of altitude forests are growing there allright. There is lots of rocks too. Tuolomne Meadows is of absolute beauty and I recommemd visiting it to everyone. We try to be there every year. This time I had my wonderful marine sextant and was able to correct my earlier position greatly by a series of careful sightings. Possibly I was the first and the only visitor taking sextant to the mountains of Yosemite, but who knows, maybe there were other cranks. At home I checked my navigation using Microsoft Terraserver (I do not have GPS) maintaining the data base of sattelite photos of good resolution (up to 1 m detail) giving precise coordinates of each photo. Few of my lines went through the sattelite position, other were not far away. Terraserver may be of interest to you http://terraserver.microsoft.com I easily found my old house in Poland and new house in America and could distinguish conspicuous places elsewhere. Not yet the whole Earth is covered by the data base. And you need fast Internet connection to use the Terraserver because locating the place by zooming in requires many steps during which images have to be transferred to your computer. You may however find the place in one step provided that you know geographical coordinates and the photos are in the data base. Good to be back on the list Slawek At 10:16 PM 8/3/99 -0600, you wrote: >Commenting on Arthur's question and responses by Patrick and Fernando,I >agree with the comments and recommendation for the book "Longitude: The >True Story of a Lone Genius Who Solved the Greatest Scientific Problem of >His Time" by Dava Sobel (Penguin Books ISBN 0 14 02-5879 5). It >demonstrates difficulty of the problem and teaches that the phrase used by >lawyers also applies to navigators solving the problem of longitude. "Time >is of the essence". > >A personal hero of mine who solved the longitude problem is David Thompson, >a fur trader, explorer and cartographer who explored and mapped my part of >the world from 1797 to 1812. He taught himself celestial navigation and >surveying while working for the Hudsons Bay Company. On his travels and >trading missions in Western Canada, he took sextant sights reflected in a >small pool of mercury and determined the time by observing the eclipse of >moons of Jupiter. His map >accurately fixed the position (Latitude and Longitude) of the major >features of western Canada. This formed the basis for the later suryeying >for the railroads and farm settlement. His original map hung in the meeting >room of the North West Company. A 16" x 20" photo reproduction now hangs in >my den. > >Roger Bailey >Walking Shadow Designs >51 N 115 W > > > > > Slawek Grzechnik 32 57.4'N 117 08.8'W http://home.san.rr.com/slawek
