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航海
Crystal gazing
水晶球觀海術
A mineral found in a shipwreck was an ancient form of compass
在沉船里發現的礦石是古代的一種指南針
THIS may look like a nondescript lump of rock, but it is, in fact, a sunstone.
很難形容這塊石頭的外觀，其實它是一塊日長石，至少法國法國雷恩大學的Guy Ropars和他的同事是這么看的。
That, at least, is the opinion of Guy Ropars of Rennes University, in France, and his colleagues.
磁羅盤出現之前，維京水手使用這種被視為神物的石頭。
Sunstones are legendary items supposed to have been used by Viking sailors in the days before magnetic compasses.
據說即使陰天或者那個熾熱的星球還沒有高出地平線的時候，
Looking at the sky through one, it is said, would reveal the sun's direction even on a cloudy day or when that fiery orb was below the horizon.
透過日長石觀看天空，就能顯示太陽的方向。
Dr Ropars thinks sunstones were real, and were actually crystals of Iceland spar, a form of calcite that polarises light.
博士Ropars認為日長石真的有這種作用，它實際上是冰洲石的晶體，是可以將光極化的一種方解石。
Light from the sky is polarised and, as he discovered in 2011, looking through a piece of Iceland spar reveals the direction of polarisation, and thus the direction of the sun, to within 5.
來自天空的光線被極化，他在2011年發現，透過冰洲石能觀察到偏振方向，太陽方向和這個方向的夾角小于5度。
Dr Ropars also believes the use of sunstones persisted until at least the 16th century.
Ropars博士還相信直到16世紀，人們還在使用日長石。
Their existence is mentioned in church records, and they would have been useful because although magnetic compasses were known by then, they were unreliable for reasons not then understood, such as proximity to the large amounts of iron in ships' cannons.
教會檔案中有使用日長石的記錄，盡管磁羅盤已經出現，但有些原因當時的人們還不了解，比如接近船上鐵鑄加農炮，羅盤會失靈，所以大家認為它靠不住，就繼續使用日長石。
He thinks this block of mineral is such a stone.
他認為這塊礦石就有這些用途。
It was found in a wreck believed to be that of an unnamed English warship which an admiral's report from November 29th 1592 says was lost off the coast of Alderney, in the English Channel.
1592年11月29日，一位海軍上將報告說有一艘未命名的英國戰艦在英吉利海峽里靠近奧爾德尼島海岸的地方沉沒，這塊石頭就是在失事船只里面發現的。
Four centuries underwater have rendered it opaque, but it is the right shape and density to be Iceland spar, and it was discovered within a metre of a pair of navigational dividers of the sort used to measure distances on charts.
四百年的水下歲月磨滅了它的透光性，但是它的形狀和密度和冰洲石不差分毫。在冰洲石一米之內還發現了一副兩腳規，用它可以在海圖上測量距離。
Dr Ropars's latest research, just published in the Proceedings of the Royal Society, used spectroscopy to confirm the stone's composition as calcite.
Ropars博士的最新研究成果剛剛發表于《英國皇家學會學報》，他使用光譜學分析了這塊石頭的成分，確認這是一塊方解石。
He also did further experiments with a recently mined Iceland-spar crystal of the same size.
他還用最近開采的冰洲石晶體做進一步的試驗，試驗用的石頭和原來那塊大小一樣。
He and his colleagues found they could locate the direction of the sun even more accurately than before: to within 1°.
他和同事們發現用這塊石頭更能準確定位太陽的方向，偏差不到1°。
The Alderney crystal, as it is known, is thus almost certainly a sunstone.
幾乎可以確定這塊所謂的奧爾德尼水晶是日長石。
It didn't save the ship, though.
盡管它沒能挽救這艘船的命運。
