Friday, 5 April 2013

Moving islands

Following on from my post about Sandy Island, I found another example of a cartographic blunder. Not as dramatic, but still quite peculiar.

In the 1700s, Great Britain was a proud, sea-faring nation. It rose in influence until it could rightfully call itself a world power by the end of the century.

So it must have been with some surprise when Joseph Huddart travelled to the Scilly Isles of the coast of Cornwall, with a watch made by Arnold to help him measure longitude, he found that the previous co-ordinates for the islands were off by almost twenty minutes. Namely, the Scilly Lights were thought to be 49° 56' 0" N, 6° 46' 0" W but, in fact, turned out to be 49° 53' 36" N, 6° 19' 23" W.

Joseph Huddart
His discovery was confirmed two years later when angles to points in the Scilly Isles were measured from Land's End. It was not uncommon in those days for the co-ordinates of islands to be incorrect. The book “Tables of Positions...” by Purdy, published in 1816 contains many entries which are updated from previous erroneous figures, or are even an estimate given the available data, but those were mostly for isolated islands. As Mudge (quoted in Hudddart, 1821) wrote

“How in a maritime country like our own, where chronometers are in such constant use, so great an error as 26'37” in the longitude, should have remained undetected, excepting by one person, is surprising.”

Google maps showing the old location of the Scilly Isles

Huddart, J. (the younger) (1821), "Memoir of the late Captain Joseph Huddart", W. Phillips, London.
Purdy, J. (1816) “Tables of the Positions, or of the latitudes and longitudes, of places, composed to accompany the 'Oriental Navigator,' or Sailing directions for the East-Indies, China, Australia, &c.”
Purdy, J. (1825) “Memoir, Descriptive and Explanatory, to accompany The New Chart of the Atlantic Ocean”

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