Pythagoras, Euclid and Ptolemy thought that light moved in straight lines. They also believed the eye emitted visual rays, like feelers, that touched the object and created the sensation of sight.
Leonardo da Vinci thought the eye is a camera obscura into which light rays penetrate through the pupil and project an inverted image on the back of the eye.
This idea became the dominant model of human vision in the 17th Century.
Huygens proposed the undulatory theory in 1678: light transmitted as waves. Light waves spread in different directions from a light source, and the retina detected their vibrations.
In contrast, Isaac Newton favoured the corpuscular theory: Light as particles. Light rays spread from a light source in a stream of tiny particles or 'corpuscles', shooting through space, and were detected by their impact on the retina.
Light does not appear to bend. Sound can go through crooked pipes, but light is not known to follow crooked bends. However, when light passes through water, the angels of incidence and refraction differ.
Diffraction was first seen by Francesco Grimaldi in the mid-17 Century. When he shined a light through a small aperture, then passed it through a second aperture onto a screen, the spot of light on the screen was a bit bigger than the second aperture and had coloured fringes. That meant light could be bent.
Michael Faraday showed the inter-relationship of electric and magnetic fields of force. James Clerk Maxwell took Faraday's fields and combined them mathematically into a single concept: an electromagnetic wave with transverse electric and magnetic components that would move through the empty space at a speed similar to the measured speed of light.
Different colours of light was found to have different wavelengths and frequencies. In the 1880s, Heinrich Hertz proved these wave's existence experimentally.
Physicists today have to accept that light behaves as both a particle and a wave. But its underlying physical nature is still mysterious.
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