<sod>Before the writing of the ''Book of Optics'' there were two types of theories of vision that were held in contention. One was the extramission or [[emission theory]]. This theory was presented by the mathematicians [[Euclid]]<ref>[http://philomatica.org/wp-content/uploads/2013/01/Optics-of-Euclid.pdf Euclid's Optics]</ref> and [[Ptolemy]]<ref>*[http://www.jstor.org/stable/233604?seq=1#page_scan_tab_contents Smith, A. Mark  (1988) "Ptolemy, Optics" Isis Vol. 79, No. 2 (Jun., 1988), pp. 188-207, via JSTOR]<eod>
<sod>Before the writing of the ''Book of Optics'' there were two types of theories of vision that were held in contention. One was the extramission or [[emission theory]]. This theory was presented by the mathematicians [[Euclid]]<ref>[http://philomatica.org/wp-content/uploads/2013/01/Optics-of-Euclid.pdf Euclid's Optics]</ref> and [[Ptolemy]]<ref>[http://www.jstor.org/stable/233604?seq=1#page_scan_tab_contents Smith, A. Mark  (1988) "Ptolemy, Optics" Isis Vol. 79, No. 2 (Jun., 1988), pp. 188-207, via JSTOR]<eod>