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A ladder is a vertical or inclined set of rungs or steps. There are two types: rigid ladders that can be leaned against a vertical surface such as a wall, and rope ladders that are hung from the top. The vertical members of a rigid ladder are called stringers or rails (US) or stiles (UK). Rigid ladders are usually portable, but some types are permanently fixed to buildings. They are commonly made of metal, wood, or fiberglass, but they have been known to be made of tough plastic. ==Variations== Rigid ladders are available in many forms, such as: * Assault ladder, used in siege warfare to assist in climbing walls * Attic ladder, pulled down from the ceiling to allow access to an attic or loft * Bridge ladder, a ladder laid horizontally to act as a passage between two points separated by a drop * Cat ladder (US chicken ladder), a lightweight ladder frame used on steep roofs to prevent workers from sliding * Christmas tree ladder, a type of boarding ladder for divers which has a single central rail and is open at the sides to allow the diver to climb the ladder while wearing swimfins * Counterbalanced ladder, a fixed ladder with a lower sliding part. A system of counterweights is used to let the lower sliding part descend gently when released * Extension ladder or "telescopic ladder", a fixed ladder divided into two or more lengths for more convenient storage; the lengths can be slid together for storage or slid apart to expand the length of the ladder; a pulley system may be fitted so that the ladder can be easily extended by an operator on the ground then locked in place using the dogs and pawls. 65 ft., 50 ft. and some 35 ft. extension ladders for fire service use "bangor poles", "tormentor poles" or "stay poles" to assist "raise, pivot, steady, extend, place, retract and lower" them due to the heavy weight. * Fixed ladder, two side members joined by several rungs; affixed to structure with no moving parts * Folding ladder, a ladder in the step ladder style with one or more (usually no more than three) one-way hinges. Ideal for use on uneven ground (i.e. stairs), as a trestle or when fully extended a Fixed ladder. Some variations feature a central one-way hinge with extensible locking legs * Hook ladder or pompier ladder, a rigid ladder with a hook at the top to grip a windowsill; used by firefighters * Mobile Safety Steps or Platform Steps are self-supporting structures that have wheels or castors making them easy to move. They sometimes have a small upper platform and a hand rail to assist in moving up and down the steps. * Orchard ladder, a three legged step ladder with the third leg made so that it can be inserted between tree branches for fruit picking * Retractable ladder, a ladder that looks like a drainpipe but can be deployed instantly when required (for example in case of emergency) * Roof ladder, a rigid ladder with a large hook at the top to grip the ridge of a pitched roof * Sectional ladder, also known as a builder's ladder, has sections that come apart and are interchangeable so that any number of sections can be connected * Step ladder, hinged in the middle to form an inverted V, with stays to keep the two halves at a fixed angle * Telescoping ladder, commonly used to refer to a hybrid between a step ladder and an extension ladder with 360-degree hinges; has three parts and can be taken apart to form two step ladders; i.e. Little Giant * Trestle ladder, an "A-Frame"-style ladder with a telescoping center section * Turntable ladder, an extension ladder fitted to rotating platform on top of a fire truck * Vertically rising ladder, designed to climb high points and facilitate suspending there * X-deck ladder, a US patented ladder design that is a combination ladder and scaffold Rigid ladders were originally made of wood, but in the 20th century aluminium became more common because of its lighter weight. Ladders with fiberglass stiles are used for working on or near overhead electrical wires, because fiberglass is an electrical insulator. Henry Quackenbush patented the extension ladder in 1867.〔(【引用サイトリンク】url=http://www.google.com/patents/US70016.pdf )〕 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「ladder」の詳細全文を読む スポンサード リンク
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