Early studies in optics and catoptrics

University of Chicago Press, Chicago (1987). 

The next major figure in the story of light is found more than eight 

Also in Alhazen s writings we find reports of very detailed early dissection of the human eye. We also find speculations on the method of propagation of light that anticipates the seventeenth-century theory of Huygens. And we find the hints or rather the suggestion, demonstrated only in the nineteenth century, that light travels less easily (i.e., at lower velocity) when it enters a dense medium, and that this causes the ray to be bent toward the normal.  

our journey through the history of studies in light phenomena takes us to the age of Copernicus, specifically the invention of the microscope by Zacharias 

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