The Echo Tube is a very long tube sloping up almost to the roof of the Exploratorium. When the visitor claps his hands at the end near the floor, an echo is heard about 1/5 second later. The echo has a strange sound unlike the original clap (and much like the ricochet heard in old cowboy movies) due to the many different paths that the sound takes inside the tube. A rough estimate of the speed of sound can be made by timing the echo of the clap. You can also listen to the echo of your voice as it traverses the length of the tube. This makes speaking difficult due to the delay between saying a word and hearing it.