LIGHT.

The apparent linear propagation of light was known since antiquity, and the ancient Greeks believed that light consisted of copuscules; aview held by Newton. The English scientist Robert Hooke and Dutch astronomer, mathematician and physicist Christian Huygens proposed a wave theory of light , which was confirmed by the demonstration of interference in the early 19thcentury by British physicist Thomas young. However, the particular nature of light had to be assumed by Max Planck in 1900(he called it quantas) to explain the blackbody radiation and by Albert Einstein to explain photoelectric effect in 1905(photons). The speed of light was first measured by the Danish astronomer Olaus Roemer in 1676. His measurements as fair agreement with the improved 19th-century observations of Armand fizeau, and with the work of the American Albert Abraham Michelson and co-workers, which extended into the 20th century. Maxwell showed that light is electromagnetic waves are known to cover from gamma rays, through x-rays, visible light, microwaves and radio waves. Maxwell's work, however, could not provide insight into mysterious medium called ether, a hypothetical substance that was thought to transmit electromagnetic radiation, including light , and was thought to permeat all space. In 1887, the Michelson and the American chemist adwars Williams Morley, was performed, to measure the motion kf the Earth through the ether. The result of the experiment was unexpected and inexplicable. It was not until the arrival of the theory of relativity in 1905 that an explanation was obtained. Many substances have been catalogued. Duscrute line spectra originate from gaseous substances, while a heated solid has a continuous spectrum over the full visible range and into the infrared and ultraviolet region. Attempts to explain these radiation characteristics using the tools of theoretical physics available at the end of the 19th century led a wrong conclusion.