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A fathom = 6 feet or 1.8288 metres, is a unit of length in the old imperial and the U.S. customary systems, used especially for measuring the depth of water. There are two yards (6 feet) in an imperial fathom.〔''Encyclopædia Britannica'' eleventh edition 1911.〕 Originally based on the distance between a man's outstretched arms, the size of a fathom has varied slightly depending on whether it was defined as a thousandth of an (Admiralty) nautical mile or as a multiple of the imperial yard. Formerly, the term was used for any of several units of length varying around . The name derives from the Old English word ''fæðm'', corresponding to the old Frisian word "fadem" meaning embracing arms or a pair of outstretched arms.〔''Oxford English Dictionary'', second edition, 1989;〕〔(Fathom - Definition from the Merriam-Webster Online Dictionary. )〕 In Middle English it was ''fathme''. A ''cable length'', based on the length of a ship's cable, has been variously reckoned as equal to 100 or 120 fathoms. At one time, a ''quarter'' meant one-fourth of a fathom. == International fathom == One fathom is equal to: * 1.8288 metres exactly (1 metre is about 0.5468 fathoms) * 2 yards (1 yard is exactly 1/2 of a fathom) * 6 feet (1 foot is exactly 1/6 of a fathom) * 18 hands * 72 inches In the international yard and pound agreement of 1959 the United States, Australia, Canada, New Zealand, South Africa, and the United Kingdom defined the length of the international yard to be exactly 0.9144 metre. With the adoption of the metric SI system the use of fathoms declined. 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「fathom」の詳細全文を読む スポンサード リンク
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