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Reference.org
Lewis (lifting appliance)
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<p>A lewis (sometimes called a lewisson) is one of a category of <a href="/facts/Lifting_equipment/WxSrel02">lifting devices</a> used by <a href="/facts/Stonemason/kzvdRB4A">stonemasons</a> to lift large stones into place with a <a href="/facts/Crane_(machine)/Q5axXY0l">crane</a>, <a href="/facts/Hoist_(device)/Bq7wudq4">chain block</a>, or <a href="/facts/Winch/zUI7eqt0">winch</a>. It is inserted into a specially prepared hole, or <i>seating</i>, in the top of a stone, preferably above its <a href="/facts/Centre_of_mass/n4Lr9GAz">centre of mass</a>. It works by applying principles of the <a href="/facts/Lever/HYDtMuAq">lever</a> 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 <a href="/facts/Friction/d0108Rpu">friction</a> where the short lever-arms make contact with the stone inside the hole and thereby prevents slipping. </p>