On Motion: a Weight Dropped through the Centre of the World
A thought-experiment on falling, the indivisible centre, and oscillation about it
Under 'De moto', Leonardo argues that the centre of the world is indivisible and, since only nothingness is indivisible, the centre is equal to nothing. He imagines a shaft bored along the world's diameter through its centre: a weight thrown in gains weight the farther it falls, yet on reaching the centre — which is a name only and in its being equal to nothing — it meets no resistance, passes through, and then returns. The passage is one of his gravitational thought-experiments about motion toward and oscillation about the earth's centre.
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A weight falling to the centre of the world
Leonardo imagines a shaft whose diameter is the diameter of the world; a weight thrown into it grows heavier the more it moves, but at the centre finds no resistance, so it passes beyond and then returns. He describes the fall and rebound of a body oscillating about the earth's centre.
The indivisible centre of the world equal to nothing
He reasons that the centre of the world is indivisible, and since only nothingness is indivisible, the centre is equal to nothing — a point that has only the name and no being. The cosmological centre is treated as a dimensionless point.