Traite de la lumiere
Christiaan Huygens(1629-1695)
 In this treatise, Huygens evolved the mechanistic theory of light and established the theory of wave-propagation which is known under his name. Huygens considered light to be a series of shock waves or impulses which propagate through the ether. He defined ether as a uniform medium which is tightly permeated with minute elastic corpuscles. The luminous body gives impact to the corpuscle, and the impulse is transmitted to all the adjoining corpuscles, that is, the light is the propagated disturbance of the medium. He further theorized that the wave of light is a spherical wave front which consists of spherical wavelets of each pulsating corpuscle. Each corpuscle at this wave front generates secondary waves. Thus Huygens was able to explain the rectilinear propagation of light, reflection and refraction in a way that is still in use in our textbooks.
 Huygens also explicated the double-refraction of Island Spar by means of a supposition in which two spherical wave fronts proceed with different velocities. Although he was aware of the phenomena of polarization and diffraction, he could not explain them. His concept of the wave indicated merely pulsation, which did not imply vibration with frequency, wave-length or periodic movement in any sense.
 Huygens first announced this treatise before the French Academie des Sciences in 1678. At that time he had already been informed of Newton’s theory of light which was reported at the Royal Society in 1671. Therefore it is believed that Huygens’s wave-theory of light was his criticism against Newton’s corpuscular theory of light. Huygens’s theory was ignored for over one hundred years out of blind deference for Newton, who dominated eighteenth century optics, until Young and Fresnel employed it to explicate optical interference and polarization.