Air blown under water; two rivers compared by length
A long-tube bellows drives air to the riverbed; equal channels' speeds vary inversely with length
Under the heading 'On motion' Leonardo argues that if a long-tubed bellows forces air to the bottom of water, the power the compressed air exerts as it rushes back to its element equals the weight or force pressing the bellows, and that an excessive weight makes the escaping air more violent and able to lift more. A second note compares two rivers of equal width, depth, slope and volume running from one start to one end: the ratio of their velocities matches the ratio of their lengths, so that if the short course is six times faster, the long course is six times longer. A faint wavy pen line at the right accompanies the lower note, standing for the winding versus straight watercourse.
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Compressed air forced to the bottom of water
A bellows with a long tube pushes air down to the bottom of a body of water. The power the compressed air produces as it returns upward to its own element equals the weight pressing the bellows, and a disproportionately great weight makes the air's fury stronger, lifting more.
Two watercourses, one straight and one winding
For two rivers of equal width, depth, slope and total water running from a common start to a common end, the ratio of their speeds equals the ratio of their lengths. Thus if the short one is six times the speed of the long one, the long one is six times the length of the shorter.