Eccentric cam-wheel and the flaws of machine motion
A book titled 'On Quantity and Power', plus a note on Tadeo, a nine-year-old lute player (1497)
The central figure is a lobed or 'imperfect' cam-wheel whose flexible, globular outline drives the member f to varying distances from its centre, illustrating how such a wheel produces unequal motion. Leonardo warns that mechanisms fail when a part is made too long or short to pass through its mortises and channels — 'like putting 8 into 7' — leaving their makers 'dismayed and spellbound', and notes that a wider bar runs more smoothly in its channel. The leaf also carries two jotted headings, 'On the posing of the figure' and a 'Book titled On Quantity and Power', and a personal memorandum that Tadeo, son of Nicolaio del Turco, turned nine on 28 September 1497 and played the lute at Milan among the finest in Italy.
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A lobed cam-wheel and unequal motion (a, f, b, c)
The 'imperfect', globular or flexible circle drawn here generates all the unequal motions Leonardo means to study: as it turns, it pushes the front of the member f to various distances from its centre. The wheel's non-circular profile is what makes the driven part advance and retreat unevenly.
A bar too large for its channel jams the motion
If a bar running through a channel does not touch at every point along it, it 'grows' and would try to enter with its full diameter, so its lines increase until the space can no longer hold it. Leonardo adds that the wider the bar, the better its motion — a lesson on clearances in mortises and channels.
Tadeo, the nine-year-old lute player (1497)
A memorandum records that Tadeo, son of Nicolaio del Turco, completed nine years on the vigil of St Michael, 28 September 1497. On that day the boy was at Milan, played the lute, and was judged among the good players of Italy.