Weight of Balls on a Support of Varying Obliquity
The load a ball delivers to its support changes with the slope
A quarter-circle diagram — a quarter of a wheel — carries balls stepped along its arc, each marked 4, with positions labelled 4, 3, 2, 1, 0 along the top and radial threads dropping to the corner pivot. Leonardo argues that the quantity of weight each ball gives to its support varies with the obliquity of that support. He stresses that the plumb threads are drawn only to mark the perpendicularity of the weights, not to bear them, citing the ninth conclusion of his fifth book.
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Load on the support varies with obliquity
The figure shows how much weight balls give of themselves to their support, a quantity that varies as much as the obliquity of that support varies. The threads descending perpendicularly from positions 4, 3, 2, 1, 0 only mark the perpendicularity of the weights; were they made to bear the loads, the weights would not vary, as shown in the ninth conclusion of the fifth.
Quarter-wheel with balls stepped along the arc
The drawing is a quarter of a wheel: a square quadrant with a curved arc, balls set at intervals along it and each labelled 4, with radial lines running to the lower corner. Positions along the top edge are numbered 4, 3, 2, 1, 0.