What detail is lost first; the rule of linear perspective
Outlines and thin limbs vanish before the mass; perspective measures diminution by degrees
A text page of the Treatise on Painting continuing the discussion of recognition at a distance. It first concludes that a man a crossbow-shot away is too small to reveal nose, mouth or limbs and so cannot be known, then explains which parts of a body are lost first: the highlights of round and columnar forms, the thinner limbs (as a stag's legs and antlers before its trunk), and above all the outlines that bound surfaces. A third chapter opens the definition of linear perspective as the measured proof, by visual lines, of how much each successive object shrinks with distance.
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Outlines vanish first; thin limbs go before the mass
The parts of smallest figure least preserve their evidence with distance: the highlights of spherical or columnar bodies, and slender members such as a stag's legs and antlers, which fail before its thicker trunk. But the very first thing lost at distance are the lineaments that terminate the surfaces and figures of bodies.
Linear perspective measures diminution degree by degree
Linear perspective employs the visual lines to prove by measure how much the second object is smaller than the first, the third than the second, and so on to the limit of sight. By experience, when the second object lies as far from the first as the first lies from the eye, then although equal in true size...