The Forster Notebook II

Every weight that is suspended
freely original: "sopeso liberamēte" pulls
along the line of its
natural center toward the
center of the world Leonardo uses "center of the world" to refer to the center of the Earth, following the Aristotelian view that the Earth is the center of the universe.

M H
The question is whether a bird weighs
as much in the air
when it is above the air on a balance
as it does below the balance.

A bird weighs in an air
that is entirely enclosed in a vessel
exactly as much as the weight of that bird. Leonardo correctly deduces that in a closed system, the bird's weight is transferred to the container via the air it displaces and pushes against.