Lifting Things the Hard Way
The idea is ancient. The Roman architect Vitruvius wrote that Archimedes built a lifting device around 236 BC. The Colosseum, finished in 80 AD, had roughly 25 of them. Each could carry about 270 kilograms, roughly the weight of two lions, up some seven metres, worked by as many as eight men.
Around the year 1000, the Book of Secrets by Ibn Khalaf al-Muradi in Islamic Spain described a lifting device used to raise a heavy battering ram against a fortress. By the 17th century, palaces in England and France had early versions installed. Louis XV had a so called flying chair built at Versailles in 1743.
All of these ran on hoists and windlasses, turned by people or animals. Steam power arrived in the mid-19th century, first in coal mines and factories. In 1823 two London architects even charged visitors to ride an ascending room for the view over the city.
The Brake That Let Cities Grow Up
Machines that lifted goods were one thing. Lifting people meant convincing them that a snapped rope would not kill them.
Elisha Otis solved that in 1852 with the safety elevator, which locked the car in place if the cable failed. Two years later he sold the idea with a stunt at the New York exposition in the Crystal Palace, riding a platform while an assistant cut the rope. The first passenger elevator of this kind went into 488 Broadway in New York on 23 March 1857.
One building was ready before the machine was. Work on Peter Cooper's Cooper Union building began in 1853 with a shaft already built in, because Cooper was sure a safe passenger elevator was coming. He made the shaft round, thinking that shape was the most efficient. Otis later designed a special elevator to fit it. By 1870, the Equitable Life Building became what is thought to be the first office building with passenger elevators.
What Is Actually Holding You Up
Most passenger lifts today are traction machines. Steel or kevlar ropes run from the top of the car, over a grooved wheel called a sheave, and down to a counterweight on the other side. That weight usually equals the car plus 40 to 50 percent of its rated load, so the motor mostly handles the difference rather than the whole cabin.
Safety is layered. A car hangs from two to six ropes, and in tall buildings up to a dozen, each one strong enough on its own to hold the rated load plus another quarter. If the car starts descending faster than its design speed, a device called the governor, also an Otis invention, clamps brake shoes onto the vertical rails. Buffers sit at the bottom of the shaft to soften any impact.
The other common design is hydraulic, pumping fluid to push a piston up like a jack.
Buttons, Music and Clever Scheduling
Fully automatic elevators were available by 1900, but passengers did not want them. Riders were used to a human operator and were reluctant to step into an empty car. A 1945 operator strike in New York pushed people to get over it, helped along by an emergency stop button, an emergency telephone and a calm recorded voice. Radios and piped music arrived around the same time to fill the silence.
Deciding where to stop is a real problem. The classic elevator algorithm is simple: keep going the same way while there are requests ahead, then stop or turn around. Computer engineers borrowed it for scheduling reads on hard disks.
Tall, busy buildings use something smarter. A destination dispatch system asks where you are going before you board and groups riders heading to nearby floors, which can raise how much a lift carries by up to 25 percent.
