Optical Notes on How Lines, Angles and Shadows Meet the Eye

Bodies behind one outline look continuous

If a single line serves as the common outline enclosing several bodies ranged one behind another, those bodies will appear joined together, with no gap between them.

A curve that covers a straight line looks straight

A curved line will appear straight to the eye when each of its parts covers the parts of a straight line. The eye reads the whole as a single straight stroke.

An angle read as a straight line

An angle is judged to be nothing but a straight line when it covers to the eye the same length of straight line. Only the amount of straight line it subtends decides how it is seen.

A derived shadow larger than its primary

A derived shadow grows larger than its primary shadow as its acute angles differ more sharply from the obtuse angles of that same primary shadow.

Diagram of crossing cones of rays

At the upper right, where the caption marks an optical study, two slender cones meet point to point, a ray diagram accompanying the notes on vision.

In alto a destra studio di ottica. Dall’alto verso il basso, testi alternati a testi cassati, quest’ultimi non tutti forniti in trascrizione diplomatica nell’edizione qui trattata.

A fianco della crocetta, sotto una serie di testi cassati:

Sotto, cassato:

Segue altro testo cassato, non trascritto nell’edizione qui trattata, e sotto:

Sotto:

Segue altro testo cassato, non trascritto nell’edizione qui trattata, e sotto, a fianco dei diagrammi, altro testo cassato:

Top right, an optical study. From top to bottom, passages alternate with struck-out passages, the latter not all given in diplomatic transcription in the edition used here.

Beside the little cross, below a series of struck-out passages:

Below, struck out:

Another struck-out passage follows, not transcribed in the edition used here, and below:

Below:

Another struck-out passage follows, not transcribed in the edition used here, and below, beside the diagrams, another struck-out passage: