The pupil, the blowpipe, and a divided quadrilateral
In dim light the pupil widens, so the eye at the blowpipe sees the object larger and clearer
A cross-hatched square lettered LV and BE heads the sheet, followed by repeated LV/BE letter groups, which the caption calls a divided quadrilateral. Below it a small diagram of two crossed tubes accompanies Leonardo's optical rule that as light diminishes the pupil of the observing eye enlarges. He concludes that the eye looking through a blowpipe, having the wider pupil, sees the object larger and clearer than the other eye, with the demonstration marked a and b.
On this page
Pupil dilation and the blowpipe eye
As the light diminishes, the pupil of the eye that regards that light grows larger. Therefore the eye that sees through the blowpipe has a bigger pupil than the other, and sees the object larger and clearer than the other eye does. The two viewing conditions are lettered a and b.
A divided quadrilateral labelled LV, BE
A hatched rectangular figure at the top of the page is set out as a divided (compartimented) quadrilateral, its corners tied to the letters LV and BE. Beneath it the same LV and BE groupings are repeated in rows as a running key.