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Re: 7 ways to determine longitude
From: George Huxtable
Date: 2003 Dec 24, 17:31 +0000
From: George Huxtable
Date: 2003 Dec 24, 17:31 +0000
Dan Allen said- >I have just started to read an old book called "Spherical and Nautical >Astronomy", a two volume set by William Chauvenet who was a professor >at Washington University in St. Louis. My copy was printed in 1903 but >it appears that it is just a reprint of an 1863 edition. > >Chapter 7 is "Finding Longitude by Astronomical Observation" where it >lists seven different methods, which are: > >"1st method - by portable chronometers > 2nd method - by signals > 3rd method - by the electric telegraph > 4th method - by moon culminations > 5th method - by azimuths of the moon, or transits of the moon > and a star over the same vertical circle > 6th method - by altitudes of the moon > 7th method - by lunar distances" > >By chronometers it means chronometric expeditions: taking a chronometer >from Greenwich to Boston and comparing mean noon times. By signals it >includes eclipses, occultations of Jupiter's moons, and terrestrial >signals. =============== Chauvenet (presumably, from his name, of French extraction) was one of the important names in early American science. (In astronomy, Simon Newcomb was the next, to establish the American lead over the rest of the world in astronomical matters). Chauvenet's great two-volume work was intended for astronomers and surveyors, rather than for the more simple-minded navigator, I suspect. It is remarkably thorough and comprehensive. Lots of detailed drawings of survey instruments and telescope mounts. It's the only published work that I have seen, which assesses the (small) effect of the elliptical shape of the Earth on the AZIMUTH of the Moon. That doesn't affect any observations involving just the Moon's altitude, but it does, of course, affect the oblique lunar distance to another body; an effect that's usually neglected. I have never seen any note, in a subsequent work, drawing attention to an error in Chauvenet, so I conclude he got it all right. The chronometer expeditions that Dan mentions were big business before the telegraph came in. Literally dozens of chronometers were shipped bachwards and forwards between Greenwich and Dublin, time and again, to establish their longitude difference. Also between German observatories and Pulkovo (St Petersburg). Does anyone know whether chronometers were ever shipped up the Mississippi for that purpose, before the days of the telegraph? Or sent by pony express, even, if they could withstand the rigours of that journey? My own copy of Chauvenet has a text-date on the preface of 1863, like Dan's, but otherwise says nothing about its date other than "5th edition". Does Dan have an edition-number with his 1903 printing, that might help to fix the date of my own copy better? George. ================================================================ contact George Huxtable by email at george@huxtable.u-net.com, by phone at 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ================================================================