The measured rule of diminution; bodies enlarged by fog
Size halves at equal intervals up to 20 braccia; fog makes near objects read as distant giants
A text page of the Treatise on Painting giving a quantified rule of perspectival diminution. Objects of equal size, spaced at equal intervals, halve in apparent size step by step provided the interval stays within twenty braccia; Leonardo then tabulates the losses (two quarters within 20 braccia, four-fifths within 40, nine-tenths, then nineteen-twentieths at 60). Two further chapters explain that bodies seen in fog appear larger than their true size because the fog reads as horizon-distance, and that the higher parts of a building show more confused than its base.
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A measured rule: apparent size halving at equal intervals to 20 braccia
A third object equal to the first two, set as far beyond the second as the second is beyond the first, appears half the second's size, and so on by halves at equal intervals up to twenty braccia. Leonardo tabulates the loss of a figure's size: two quarters within 20 braccia, four-fifths within 40, nine-tenths, then nineteen-twentieths at 60.
Bodies in fog appear larger than their true size
The perspective of the misty medium fails to match its colour to the object's magnitude, so fog behaves like the confused air lying between eye and horizon in clear weather. A body near the eye but seen behind near fog therefore reads as if at the horizon, where even a huge tower would look smaller than a man standing close by.