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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Iceland spar ： ウィキペディア英語版 Iceland spar Iceland spar, formerly known as Iceland crystal ((アイスランド語:silfurberg); lit. ''silver-rock''), is a transparent variety of calcite, or crystallized calcium carbonate, originally brought from Iceland, and used in demonstrating the polarization of light (see polarimetry).〔〔 It occurs in large readily cleavable crystals, easily divisible into rhombs, and is remarkable for its double refraction.〔〔 Historically, the double-refraction property of this crystal was important to understanding the nature of light as a wave. This was studied at length by Christiaan Huygens and Isaac Newton.〔 Sir George Stokes also studied the phenomenon.〔 Its complete explanation in terms of light polarization was published by Augustin-Jean Fresnel in the 1820s.〔 Mines producing Iceland spar include many mines producing related calcite and aragonite as well as those famously in Iceland,〔 productively in the greater Sonoran desert region as in Santa Eulalia, Chihuahua, Mexico〔 and New Mexico, United States,〔 as well as in the People's Republic of China.〔 ==Viking "sunstone"== (詳細はsunstone (, a different mineral from the gem-quality sunstone) mentioned in medieval Icelandic texts was Iceland spar, and that Vikings used its light-polarizing property to tell the direction of the sun on cloudy days for navigational purposes.〔〔 The polarization of sunlight in the Arctic can be detected,〔 and the direction of the sun identified to within a few degrees in both cloudy and twilight conditions using the sunstone and the naked eye.〔 The process involves moving the stone across the visual field to reveal a yellow entoptic pattern on the fovea of the eye, probably Haidinger's brush. The recovery of an Iceland spar sunstone from the Elizabethan ship ''Alderney'', which sank in 1592, suggests that this navigational technology may have persisted after the invention of the magnetic compass.〔''(First evidence of Viking-like 'sunstone' found )''. Discovery.com. Accessed 11 March 2013.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Iceland spar」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.