Leveling the bronze: a water-channel test for the cast
Doubt about uneven pouring onto croup and head, tested by pouring from mouths m and n meeting at r
Under the heading 'Leveling bronze, for a test,' Leonardo worries that bronze raining from different furnaces will pool unevenly — much on the croup, little on the head — so that the head cannot be relieved in time, threatening the perfection of the cast. To settle the doubt he proposes a level channel with pouring mouths m and n set two braccia apart, asking where the two streams will meet at r and whether they will knit. A cluster of circles and a labelled channel figure (a m r n) work through the experiment, treated frankly as a problem of water finding its level.
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Doubt: bronze pooling unevenly on croup and head
Leonardo doubts whether bronze raining with greater force in one place than another will level at the surface. If much falls on the croup and little on the head, the croup's bronze would have a long crosswise way to relieve the head, casting doubt on the perfection of the cast.
The channel test: streams m and n meeting at r
He will make a level channel, three braccia long, with two mouths pouring at m at one end and one at n at the other, two braccia apart, all unstopped at once. Where will the streams meet? The water at m rises more than twice as high as at n, so the double amount runs farther and passes r.