Rays converging on a lit surface, a balance and arithmetic
Optical diagrams of converging rays with calculations and a balance schema
This mount carries two once-separate sheets. The visible recto is filled with double-cone and converging-line diagrams: a note explains that an illuminated area is brightest where the rays meet at a wider angle. Nearby are columns of arithmetical operations, a small balance schema marked 3, and a faint show-through of the ornamental drawing on the verso. The second sheet (988b recto) was invisible before restoration and bears no writing or drawings.
On this page
Brightness where rays converge
An inverted diagram labelled p, a and n carries the rule that the part of an illuminated place is brightest where the rays converge at a wider angle. It is drawn among many bowtie-shaped ray diagrams whose lines cross at a point.
Columns of calculation
A block of arithmetical operations runs down the right side, working with figures such as 73, 5, 365, 12, 30 and 29. The numbers are set out in short columns for addition or division.
Balance schema
A small schematic balance is sketched and marked with the figure 3. It sits among the optical and arithmetical notes.