jock123 Moderator
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#9 · Posted: 19 Mar 2005 22:23
yamilah the meridian in use at the time of the Unicorn (1698) was neither Greenwich's nor Paris' one...
Err, there was no global standard for the meridian established for any map until 1884, and that was really for the purposes of time-keeping (and hence the improvement of naval navigation, which relied on accurate chronometry); so the notion of “the meridian in use at the time†is a false one. Any meridian could be used.
Maps were made to both, the Paris Meridian from 1671 (the meridian had been established before the French Royal Observatory was laid out in 1667, through which it runs), and the first Greenwich Meridian from 1675, when Sir John Flamsteed, Astronomer Royal to Charles II established it, so an English chart of 1698 would have used the Flamsteed Meridian.
As Ferro’s Meridian (the one that the article is referring to in the Canary Isles) was thought to be exactly 20º West of the Paris one, the French maps of the period were often dual-standard, and had the degrees marked to Paris across the top, and Ferro’s along the bottom - but the Paris meridian was certainly in use before 1698.
Without accurate clocks however, all navigation was by dead reckoning, so anybody could establish their own meridian if they wished to, as it was as good as any other.
There are actually four Greenwich meridians - Flamsteed’s, Halley’s (1725), Bradley’s (1784, I think) and Airy’s (1851), all slightly different. Although Airy’s is the 0º used for the time signal, Bradley is, for some reason, the preferred meridian for map-making in Britain.
Anyway, more disturbing is the fact the globe shown in the vaults beneath Marlinspike is completely wrong - the U.K. is missing entirely for one thing...
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