The 'Ounce' of Water and How Its Flow Can Vary
Seventeen conditions that change the quantity delivered through a single outlet
A full page of text defines the measure ('ounce') of water passing through a fixed outlet and then enumerates seventeen conditions under which the same-sized mouth delivers more or less water. These include the height of the water surface above the mouth, the velocity of approach at the bank, the obliquity and thickness of the mouth's sides and lips, its shape (round, square, triangular, or long), its placement on concave or convex banks, and whether the falling water takes in air or falls enclosed. No diagram accompanies the list; it reads as a systematic checklist of the variables governing discharge.
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Seventeen ways one outlet varies its discharge
Leonardo asks how water pouring through a mouth of one size can nonetheless deliver differing quantities. He lists seventeen causes, beginning with the height of the water surface above the mouth and the velocity of the current arriving at the bank.
Shape and lips of the mouth
Among the conditions he singles out the shape of the mouth itself, whether round, square, triangular, or long, together with the thickness of its lips and the obliquity of its sides, as factors that alter how much water passes.
Whether the falling water is enclosed or takes in air
The later conditions concern the fall of the water beyond the mouth: whether it draws in air, whether it falls freely through the air or is enclosed on one or all sides, and whether that enclosed fall is thick or thin, long or brief.