Types of pivots and a vane that catches the air
Kinds of pivot for an oscillating axle, and questions on the air-resistance of vanes of varied size and blade shape
A row of small figures (b, c, d, e and a) classifies the ways an axle can pivot on one of its ends: b to e are of equal worth except e, whose sleeve fouls with grease and iron-dust, while a is worst because it cannot keep a single line; other poles turn on themselves like a millstone pole. At the foot a four-armed vane raises air problems — which vane resists the striking air more, one of 2, 4 or 8 braccia, and which turns faster according to the number, length, breadth, thickness and weight of its arms, or whether they are perforated like a sieve, woven like a strainer, or of membrane. A line at the top continues the optical rule relating lights to the bases of composite pyramids.
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Modes of an axle pivoting on one end (b c d e; a the worst)
The axle can move on one extremity in several modes; b c d e are of equal nature save e, whose sleeve gathers grease and iron-dust into a viscous drag. a is the worst, having more motions and unable to keep a single line; other poles instead turn on themselves upon their face, like the pole of the millstones.
Air-resistance of a vane of 2, 4 or 8 braccia
A vane that catches the air is drawn, and Leonardo asks which offers more resistance in turning against the air that strikes it: the vane of 2 braccia, of 4, or of 8.
Which vane turns faster: arms, breadth and material
He asks whether a vane with many or few arms, longer or shorter, wider or narrower, thicker or thinner, lighter or heavier turns the faster, and weighs arms of unequal length but equal weight, or arms perforated like a sieve, woven like a strainer, slashed like a comb, of cartilage or membrane, smooth or taut.
Proportion of lights and the composite pyramids
The lights enclosed between the axis of the luminous ray and the plane it illuminates stand in the same proportion as the bases of the composite pyramids have among themselves.