rique ", ▁" Opt ics ", ▁or ▁" D io ptr ics "), ▁is ▁a ▁short ▁treat ise ▁published ▁in ▁ 1 6 3 7 ▁included ▁in ▁one ▁of ▁the ▁Ess ays ▁written ▁with ▁Disc ourse ▁on ▁the ▁Method ▁by ▁R ene ▁Des cart es . ▁In ▁this ▁ess ay ▁Des cart es ▁uses ▁various ▁models ▁to ▁understand ▁the ▁properties ▁of ▁light . ▁This ▁ess ay ▁is ▁known ▁as ▁Des cart es ' ▁greatest ▁contribution ▁to ▁opt ics , ▁as ▁it ▁is ▁the ▁first ▁publication ▁of ▁the ▁Law ▁of ▁Ref raction . ▁ ▁First ▁Disc ourse : ▁On ▁Light ▁ ▁The ▁first ▁disc ourse ▁capt ures ▁Des cart es ' ▁theories ▁on ▁the ▁nature ▁of ▁light . ▁In ▁the ▁first ▁model , ▁he ▁comp ares ▁light ▁to ▁a ▁stick ▁that ▁allows ▁a ▁blind ▁person ▁to ▁disc ern ▁his ▁environment ▁through ▁touch . ▁Des cart es ▁says : ▁You ▁have ▁only ▁to ▁consider ▁that ▁the ▁differences ▁which ▁a ▁blind ▁man ▁notes ▁among ▁trees , ▁rocks , ▁water , ▁and ▁similar ▁things ▁through ▁the ▁medium ▁of ▁his ▁stick ▁do ▁not ▁seem ▁less ▁to ▁him ▁than ▁those ▁among ▁red , ▁yellow , ▁green , ▁and ▁all ▁the ▁other ▁colors ▁seem ▁to ▁us ; ▁and ▁that ▁never theless ▁these ▁differences ▁are ▁nothing ▁other , ▁in ▁all ▁these ▁bodies , ▁than ▁the ▁diverse ▁ways ▁of ▁moving , ▁or ▁of ▁resist ing ▁the ▁movements ▁of , ▁this ▁stick . ▁▁ ▁Des cart es ' ▁second ▁model ▁on ▁light ▁uses ▁his ▁theory ▁of ▁the ▁elements ▁to ▁demonstrate ▁the ▁rect il