Gravity, the balance, spring-weapons and a river bridge
Three mounted fragments on the physics of descent, crossbow mechanisms, light rays and a timber bridge
This composite sheet mounts three fragments of Leonardo's notes. The uppermost carries a dense passage arguing that a heavy body freed outside its natural place descends more readily by a straight chord than by an arc, and concludes that the motion of a balance-arm is midway between the natural and the violent. The central fragment sets pen drawings of crossbow and saeppolo spring-mechanisms beside a query about why the two do not shoot alike, together with aphorisms on lifting weights and on light passing through angular apertures. The lowest fragment shows a timber bridge resting on the two banks of a river, explained by an accompanying note.
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Descent by chord versus arc; the balance between natural and violent motion
Every heavy thing left outside its natural place, when not held back, desires to descend more by a straight line than by an arc, because the chord is traversed in less time than its arc. From this Leonardo draws three consequences, concluding that the heavy motion of a balance-arm is neither simply natural nor simply violent, but midway between the two.
Why the crossbow and the saeppolo do not shoot alike
A marginal query asks why the crossbow (balestro) and the saeppolo, each shooting a ball, are not alike in their shooting. Beside it are pen sketches of spring-armed mechanisms, two of the forms marked 'bona' (good).
The eye in darkness and sunlight through angular apertures
Three aphorisms note that a weight raised slowly by the same force is easier to lift; that the eye will never see a luminous angle in darkness; and that sunlight passing through angular openings does not carry those angles into the patch it casts upon a wall.
Timber bridge resting on the two river banks
A note below the lowest drawing describes the joining of the timbers that are to form a bridge, which is to rest only on the two banks or embankments enclosing the river between them, as shown in the figure below.