390 - AS IV.151. Notes and sketches by Wren relating to the trigonometry of refraction in a sphere. Brown ink. 308 x 199 mm. No watermark. Inscription: Sin b e s (ang: Refractionis): bs (Rad.):: Sin bse (compt: gdf = ang Inc – ang Ref:): be / hoc est gb: Rad:: gx: de / hoc est gb: gx:: ad: de / a: b: c; a: b:: c: d:: e: f / rad: Sin Ref:: Sin Ref [(gb) over]: R:: Sin e & d [(gx) over]: de.
Note to 390: Wren produced a theory of refraction before 1667 (Bennett 1982, 33–34). This drawing may be connected with this. The values a, b, c, etc. are not related to the sketches.