The Motion of Air and Water; Optics of the Pinhole
The daily cycle of dew and frost; a swollen candle-flame and inverted pinhole images
Opening under the heading "On the motion of air and water," this folio gives Leonardo's account of the daily cycle of atmospheric moisture, vapour drawn aloft by the sun's heat and falling back as dew in summer and frost in winter. Two optical demonstrations follow: a distant candle-flame that appears greatly enlarged yet can be hidden by a slender stick, and a small aperture through which rays cross so that things are received inverted though understood upright. Marginal ray-sketches and a labelled aperture figure accompany the text.
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The moisture of the air becomes dew and frost
The air moving over the terrestrial machine is mixed with humidity like the earth's. Once in 24 hours its excess falls to the earth, then rises again drawn by the sun's heat and is held aloft while the sun stays in our hemisphere; abandoned at the sun's departure, being heavy it falls back. In summer this humidity is called dew, and in winter, frozen by cold, frost.
A distant candle-flame swells, yet a stick blots it out
A candle 400 braccia away appears to the eye enlarged 100 times its true size; yet a stick a little thicker than the flame will hide a light that seemed 2 braccia wide. The error comes from the eye, which takes the luminous species not only by the point of the light but with all its light.
Images through a small aperture arrive inverted
All things the eye sees beyond small apertures are seen upside down and known upright. Let a-d be the light that through the aperture n sees the line e-h: e is seen from the lower part of the eye d, and h from a, the upper part of the eye.