Reflection in curved mirrors; a note on Roger Bacon in print
Locating the image of a point in a convex mirror, with a reminder that Roger Bacon is in print.
The recto leaf (70r) works out a construction in catoptrics under the heading 'Of mirrors': how the image (simulacrum) of a point c seen by an eye n on one mirror can be located on a lower curved mirror by drawing the tangent line n c, marking the point of contact b, and running a line from b through the mirror's centre f. A companion note observes that the straight line n c makes no angle of contingence at b even where it touches the convex mirror a b m. The verso leaf (71v) carries only a brief reminder that Roger Bacon has been put into print, together with untranscribed columns of numbers and a cluster of intersecting circles not covered by the transcription.
On this page
Locating a point's image on a lower curved mirror
Of mirrors: if the image of c is seen at b by the eye n on mirror n b m1, the same image appears at o on mirror g o h. To find it, set the imagined mirror a b m in contact with the straight line n c, which always touches at b; draw b through the mirror's centre f, and where line b f cuts mirror g o h at o the image of c is seen by eye n.
The tangent makes no angle of contingence
The straight line n c makes no angle of contingence at the point b, although it is in contact with the convex mirror a b m. The remark supports the tangent construction used to place the reflected image.
Reminder: Roger Bacon is in print
A single line at the head of the verso records that Roger Bacon has been put into print — a bibliographic memorandum to himself, unrelated to the optics on the facing leaf.
Semicircular mirrors with reflected rays
The recto is drawn with semicircular (curved) mirror profiles crossed by rays and tangent lines, the diagrams for the reflection construction. A cluster of overlapping circles on the facing leaf is not part of the transcription.