Resolution of geometric fractions and a water wheel
Measuring a line by mutual subtraction, a numeric example, and a submerged paddle wheel
Two columns set out the 'resolution of geometric fractions': to find what part b c is of a b, the shorter length is laid off repeatedly and the remainders measured against one another until a common measure is found, giving b c as 11/19 of a b. A parallel worked example reduces 29 and 18 by mutual subtraction (the Euclidean algorithm) down to the common unit. At the right a hydraulic wheel is drawn with a note that its blades enter and leave the water edge-on and turn in air face-on, the wheel lowered to gain greater weight and fall of water. An inverted heading reads 'On the utility of machines'.
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Resolution of geometric fractions (b c as 11/19 of a b)
To find what part b c is of a b, Leonardo lays b c along a b, then measures each remainder into the previous length: a d into d b, e b into d e, and so on until o e enters exactly three times. This o e enters 11 times into b c and 19 times into a b, so b c is 11/19 of the whole line a b.
Finding a common measure by mutual subtraction
The left column repeats the procedure to find a measurer that enters every part without remainder, entering 29 times into the whole and 18, 11, 7, 4, 3 into successive parts. A numeric example carries it out: 18 into 29 leaves 11, 11 into 18 leaves 7, and so on down to a final unit 1 that measures every part exactly.
A submerged paddle wheel
At the right a hydraulic wheel is drawn: the water always strikes one tooth and half of the one above it. Its blades enter and leave the water edge-on and enter the air face-on, and the wheel is lowered into the water to gain greater weight and greater fall of water.
