Sound waves can reflect off surfaces. We hear reflected sound waves as echoes. Hard, smooth surfaces are particularly good at reflecting sound. This is why empty rooms produce lots of echoes. Soft, ...

To investigate the reflection of light by a plane mirror.

IN GREEK mythology, Echo was a mountain nymph who lost her voice and was condemned to repeat only the words of others. Now science is poised to silence the sprite completely. A group of physicists, ...