Update cheatsheet.en.md

01.curriculum/01.physics-chemistry-biology/03.Niv3/02.Geometrical-optics/01.geometrical-optics-general/01.geometrical-optics-validity/02.geometrical-optics-domain-of-validity-overview/cheatsheet.en.md

@@ -26,9 +26,11 @@ Finally, it allows us to understand how light can propagate in an optical fiber,
 
 #### Geometrical optics : the oldest science of optics
 
-![](chrono_opt_geo_en_v2.jpeg)
+*Chronological vision*, brief and imperfect, *dated from the present time*
+
+![](historic-rays-optics_en_L1200.jpg)
+
 
-![](chrono_text_opt_geo_fr_v2.jpeg)
 
 
 #### Geometrical optics : position in the optical sciences