Cube and pyramid on a balance; why stars shine at night
Natural versus accidental centre of gravity, and the air-borne moisture that hides the stars by day
A red-chalk study of a cube and a pyramid hung from a balance (labels c, d, b, a, f, e) leads a mechanical argument that the pyramid's true natural centre of gravity at a cannot lie as close to the central line as the cube's centre, so its point-heavy excess discharges onto the cube. A pen note explains why stars are seen at night and not by day: the thick air is full of countless moisture particles that, struck by the sun's rays, each yield splendour and so conceal the stars. A right-margin note adds a barbed remark that many set up shop with false miracles, deceiving the crowd and punishing anyone who exposed them.
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Natural and accidental centre of gravity of a pyramid
Though b is the accidental centre of gravity of the hanging pyramid, its point counterbalancing its base, Leonardo argues the true natural centre at a cannot be as near the central line as the centre of the cube, being more remote from the pyramid's balancing point. Balanced on that natural centre, the point-side would outweigh the base-side, and the excess would discharge itself upon the cube.
Why the stars are seen by night and not by day
Leonardo holds that stars appear at night because we lie beneath the thickness of the air, which is full of infinite particles of moisture. Each such particle, struck by the sun's rays, yields splendour, and these innumerable splendours occupy and conceal the stars; without such air the sky would always show the stars in its darkness.
Deceivers who trade in feigned miracles (margin)
A pointed marginal note observes that many set up shop with deceits and feigned miracles, deceiving the foolish multitude; and if anyone revealed himself as one who knew their tricks, they punished him.