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Lewis (lifting appliance)
A lewis (sometimes called a lewisson) is one of a category of lifting devices used by stonemasons to lift large stones into place with a crane, chain block, or winch. It is inserted into a specially prepared hole, or ''seating'', in the top of a stone, directly above its centre of mass. It works by applying principles of the lever and utilises the weight of the stone to act on the long lever-arms which in turn results in a very high reaction force and friction where the short lever-arms make contact with the stone inside the hole and thereby prevents slipping.
==Etymology==
The name ''lewis'' may come from the Latin ''levo -avi, -atum'' meaning ''to levitate or lift'',〔http://www.perseus.tufts.edu〕 but the ''Oxford English Dictionary Online''〔()〕 states, "the formation and the phonology are not easily explained on this hypothesis", preferring "origin obscure", and speculating that the term may derive from a personal name. The Romans used the lewis. The specially shaped hole that is shaped to fit the device is known as a ''lewis hole''. Lewis holes in the uppermost masonry coursings are neatly repaired with matching indented plugs after the stone has been set in place.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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