Flow in a long narrow-mouthed ditch; light, distance and vision
A candle dims but keeps its size; sunlight reflected from water; visual rays at varying distances
The page joins a hydraulic problem to a set of optical notes. At the top Leonardo poses the proportion of water pouring from a very long ditch whose outlet is a hundred times narrower than its width and depth, asking how much slower the upper water moves; the ditch is drawn as a box labelled o, b a, b, c and S t. The optical notes explain that a candle removed to a distance dims but does not shrink in apparent size, that a diminished light keeps its former reach so long as it does not move, and that sunlight on water reflects outward like material light. Marginal figures show waves from round obstacles, visual rays to objects at different distances (a, c, b d e), and a semicircle labelled q, a n o p, L, with the full proof deferred to folio 40.
On this page
Flow from a long ditch with a narrow mouth
Leonardo poses the proportion of the water pouring from the bottom of a very long ditch whose outlet is a hundred times narrower than the ditch's width and depth, asking how much slower the upper water moves than water in a channel matching the mouth. The ditch is drawn as a box at upper right with points o, b a, b, c and S t.
A distant candle dims but keeps its size
As the candle's image diminishes with distance from the eye, the apparent size of the flame does not shrink; only the power and brightness of its splendor is lessened.
A diminished light keeps its former reach
A light reduced in quantity loses illuminating power, yet, so long as it does not move, it still lights all the places it lit before. As proof, sunlight striking the water's surface reflects back and shoots out like material light, illuminating both outward and within; the full definition is deferred to folio 40 for want of paper. The margin bears a semicircle labelled q, a n o p and L.
Visual rays to objects at different distances
A marginal figure, labelled a, c and b d e, sets out visual rays reaching objects placed at varying distances.