1861-1939 united States electrical engineer noted for his work on the theory of alternating currents; independently of Oliver Heaviside he discovered the existence of an atmospheric layer that reflects radio waves back to earth
1889-1953as the universe expands united States astronomer who discovered that the speed with which nebulae recede increases with their distance from the observer
1889-1953as the universe expands united States astronomer who discovered that the speed with which nebulae recede increases with their distance from the observer
(1909-91) a US scientist who invented POLAROID (= a special substance that is put on glass to make the sun seem less bright), which is used on SUNGLASSES and car windows. He also invented the Polaroid camera, which uses a special film to produce photographs as soon as they have been taken.