 Wave theory, to explain the origin of colors. Robert Hooke 1635-1703 developed a pulse theory and compared the spreading of a light to that of waves in water in his 1665 work Micrographia Observation IHEX. In 1672 Hooke suggested that light's vibrations could be perpendicular to the direction of propagation. Christiane Onhegans 1629-1695 worked out a mathematical wave theory of a light in 1678, and published it in his treatise Own Light in 1690. He proposed that light was emitted in all directions as a series of waves in a medium called the luminiferous ether. As waves are not affected by gravity, it was assumed that they slowed down upon entering the densored medium. The wave theory predicted that light waves could interfere with each other like sound waves as noted around 1800 by Thomas Young. Young showed by means of a diffraction experiment that light behaved as waves. He also proposed that different colors were caused by different wavelengths of light, and explained color vision in terms of three colored receptors in the eye. Another supporter of the wave theory was Leon Tarr-Euler. He argued in Novotheorio Lucy said colorum 1746 that diffraction could more easily be explained by a wave theory. In 1816 Andrew Murray Ampere gave Augustin Jean Freinelle an idea that the polarization of a light can be explained by the wave theory if light were a transverse wave. Later, Freinelle independently worked out his own wave theory of a light, and presented it to the academia desciences in 1817. Simeon Dennis Poisson added to Freinelle's mathematical work to produce a convincing argument in favor of the wave theory, helping to overturn Newton's corpuscular theory. By the year 1821, Freinelle was able to show via mathematical methods that polarization could be explained by the wave theory of a light and only if light was entirely a transverse, with no longitudinal vibration whatsoever. The weakness of the wave theory was that light waves, like sound waves, would need a medium for transmission. The existence of the hypothetical substance Luminiferous Ether proposed by Huygens in 1678 was cast into strong doubt in the late 19th century by the Michelson Morley experiment. Newton's corpuscular theory implied that light would travel faster in the denser medium, while the wave theory of Huygens and others implied the opposite. At that time, the speed of a light could not be measured accurately enough to decide which theory was correct. The first to make a sufficiently accurate measurement was Leon Foucault, in 1850. His result supported the wave theory, and the classical particle theory was finally abandoned, only to partly re-emerge in the 20th century.