Design for a rectangular crystal reading lens
With notes on intersecting jets of falling water and a wave breaking on a rock
The page opens with brief propositions on waters falling through the air and intersecting with different thicknesses, lengths of motion and forces, and on how a wave's reflected motion never rises as high as the incident motion unless it strikes as a wave does against a sea-rock, illustrated by the small sketch of water breaking beside a tree at the upper right. The main text specifies a rectangular reading lens of clear, spotless crystal, thick at the edges (one ounce of an ounce, i.e. 1/144 braccio) and thin in the middle, ground in the same mould as the user's own spectacles and measuring about three ounces by two. Used a third of a braccio from both eye and page, it magnifies ordinary print to look like the large lettering on apothecaries' boxes; a compass-drawn diagram of visual rays in a double semicircle and a right-margin note give a smaller size for outdoor use.
On this page
Intersecting jets of falling water
On waters falling through the air that intersect one another with various thicknesses, lengths of motion and powers.
Reflected motion of a breaking wave
The reflected motion will never reach the height of the beginning of the incident motion, unless it strikes as the wave does against a sea-rock. The idea is echoed by the sketch of water breaking beside a tree.
Diagram of visual rays in a double semicircle
A compass-drawn figure of a double semicircle traces visual rays. It sits beside the discussion of the lens and vision.
Specifications for the crystal reading lens
A crystal eyeglass thick at the sides one ounce of an ounce (1/144 braccio) and thin in the middle, clean of spots and very clear, worked in the same mould as the spectacles that suit the user. The plate is 1/6 braccio wide and 1/4 long, i.e. three ounces by two, a square and a half; used a third of a braccio from eye and page it makes common print look like apothecary-box letters.
Alternative pocket size for outdoor use
This lens is good to keep in a writing-desk, but if you want to carry it outdoors, make it 1/8 braccio long and 1/12 wide.