Doris Kerberg, age 9, of Cleveland, Ohio, for her question:

HOW DOES AN ESCALATOR WORK?

An escalator is a moving stairway used in stores, air terminals and bus and railroad stations. You stand on a step and the escalator carries you up or down.

The steps of an escalator are on an endless belt. The top and bottom steps fold so that two or three are level with the floor, making a moving platform that allows you to get on or off easily without tripping.

The first escalator was installed by the Otis Elevator Company at the Paris Exposition of 1900. In 1901 this machine was installed in Gimbel Brothers' department store in Philadelphia where it was in use until 1939.