Elevator
The elevator, also called a lift in Great Britain, is a device consisting of a car or platform that moves passengers and freight up and down between the floors of a building. The car, enclosed in a steel frame, glides quickly and smoothly between steel rails inside a vertical shaft. Although the earliest elevators were frustratingly slow and dangerous, today's electric elevators can transport passengers at speeds up to 1,800 feet (550 m) per minute. Such speed is especially important in the hugely-tall modern skyscrapers like New York's World Trade Center or Chicago's John Hancock Center whose elevators move tens of thousands of people to and from their offices every day. In the 1980s, glass elevators put on the outside of tall buildings were thought by architects to add elegance to their structures, in addition to giving passengers a spectacular view of the surrounding area. The elevator has had a tremendous impact on our modern urban landscape: it made the skyscraper practical. The concept of a device to raise and lower heavy loads mechanically reaches back to the earliest days of humanity, a part of the human will to stretch accomplishment past the confines of mere muscle power. The ancient Greeks and Romans knew how to hoist loads using winches and pulleys powered by human labor, animals, or water. Similar lifting devices were used in the Middle Ages. An early attempt at transporting people to the tops of buildings, the seventeenth-century "flying chair" was thwarted by the knotty problem of passenger safety. Freight elevators powered by steam or hydraulic systems were in common use in England and the United States by the early 1800s. Both types had serious drawbacks. The hydraulic elevators were very slow, and passengers wisely refused to ride in the steam elevators--the ropes used to lift their cabs quite often broke, plunging the cab and its contents to the building's basement. The passenger-safety problem, which had severely hindered elevator use and development, was solved in 1852 by Elisha Graves Otis. As a master mechanic for a New York bedstead factory, Otis invented a safety device for his employer's freight hoists that stopped the elevator cab from falling when the rope broke. Teeth along the sides of the cab were held back when the elevator's hoist rope was taut. When tension on the rope was released, the cab teeth sprang out and clamped onto the elevator's guide rails, which held the cab securely in place. Initial orders for this new "safety elevator" were slow, so Otis hit upon a dramatic way to publicize his invention. He set up an open elevator cab and shaft at New York's Crystal Palace Exhibition in 1853-54.
He repeatedly climbed aboard the cab and had himself hoisted above gathered onlookers. The crowd, gasping as Otis, with a flourish, ordered the hoisting rope cut, was amazed to see the cab lock safely into place. The first passenger elevator was installed in the five-story Haughwout department store in New York City in 1857. Hotel and office installations soon followed, and public acceptance of elevator safety grew. Building owners discovered they could rent rooms and offices on the top floor for as much as, or even more than, similar space on the lower floors. City buildings, previously limited to five stories (the extent of most people's stair-climbing ability), suddenly grew to ten or twelve stories. Structural steel had made the building of skyscrapers technically possible; elevator safety made such buildings physically and economically feasible. Improved versions of Otis's steam-powered elevator soon followed. A modified hydraulic elevator permitted safer stops at higher speeds. The electric passenger elevator did away with the furnaces and boilers required for steam operation and replaced the pipes and tanks needed for hydraulic systems. An early electric Otis installation in 1889 carried delighted visitors up the newly erected 984-foot (300 m) Eiffel Tower in Paris, France. Push-button controls appeared in 1894. The basic modern gearless-traction elevator system was introduced about 1903. After this, efforts to improve the elevator focused on such convenience and efficiency features as automatic leveling, power control of doors, automatic operation, and increased speed. Most of today's elevators are powered by electric traction systems, with an electric motor turning the sheave (pulley) around which the hoisting cables run. No doubt Elisha Otis, whose factory only employed eight or ten men at the time of his death in 1861, would be astonished to know that over 2 million elevators are now in service around the world, and that the average elevator in New York City travels about 10,000 miles each year.
Many very large buildings have elevators dedicated to certain floor levels or to odd or even-numbered floors. Newer buildings and malls often have observation elevators whose glass sides are thought to add elegance. They also allow passengers to view the surrounding areas. Some of these elevators are placed on the exterior walls of a building, offering an occasionally spectacular view.
Perhaps the ultimate modern elevator is the concept of the "space elevator." Proposed during the 1980s as a serious method of transporting people and materials into outer space, this "elevator" would essentially be a tether or cable that connected a stationary satellite to the earth's surface. The elevator itself would be some sort of cab connected to the tether that would literally go up and down the tether between the satellite and the earth. Although still only a concept, this potentially simple and inexpensive transport system has already been tested on the United States Space Shuttle which experimented with tethered satellites.
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