Elevator

Lifting loads by mechanical means goes back at least to the Romans who used primitive hoists operated by human, animal, or water power during their ambitious building projects. An elevator employing a counter-weight is said to have been built in the seventeenth century by a Frenchman named Velayer, and it was also in that country that a passenger elevator was built in 1743 at the Versailles Palace for King Louis XV. By 1800, steam power was used to power such lift devices, and in 1830, several European factories were operating with hydraulic elevators that were pushed up and down by a plunger that worked in and out of a cylinder.

All of these lifting systems were based on the principle of the counterweight, by which the weight of one object is used to balance the weight of another object. For example, while it may be very difficult to pull up a heavy object using only a rope tied to it, this job can be made very easy if a weight is attached to the other end of the rope and hung over a pulley. This other weight, or counterweight, balances the first and makes it easy to pull up. Thus an elevator, which uses the counterweight system, never has to pull up the total weight of its load, but only the difference between the load-weight and that of the counterweight. Counterweights are also found inside the sash of old-style windows, in grandfather clocks, and in dumbwaiters.

Until the mid-nineteenth century, the prevailing elevator systems had two problems. The plunger system was very safe but also extremely slow, and it had obvious height limitations. If the plunger system was scrapped and the elevator car was hung from a rope to achieve higher speeds, the risk of the rope or cable breaking was an ever-present and very real danger. Safety was the main technical problem that the American inventor, Elisha Graves Otis (1811–1861) solved when he invented the first modern, fail-safe passenger elevator in 1853. In that year, Otis demonstrated his fail-safe mechanism at the Crystal Palace Exposition in London. In front of an astonished audience, he rode his invention high above the crowd and ordered that the cable holding the car be severed. When it was, instead of crashing to the ground, his fail-safe mechanism worked automatically and stopped the car dead.

The secret of Otis's success was a bow-shaped wagon spring device that would flex and jam its ends into the guide rails if tension on the rope or cable was released. What he had invented was a type of speed governor that translated an elevator's downward motion into a sideways, braking action. On March 23, 1857, Otis installed the first commercial passenger elevator in the Haughwout Department Store in New York, and the age of the skyscraper was begun. Until then, large city buildings were limited to five or six stories which was the maximum number of stairs people were willing to climb. When the iron-frame building was developed by architects in the 1880s, the elevator was ready to service them. By then, electric power had replaced the old steam-driven elevator, and the first commercial passenger elevator to be powered by electricity was installed in 1889 in the Desmarest Building in New York. In 1904, a "gearless" feature was added to the electric motor, making elevator speed virtually limitless. By 1915, automatic leveling had been introduced and cars would now stop precisely where they should.