On motion: air resistance and the fall of weights of 16 and 1
A falling-body experiment dropping two iron pieces into uniform liquid mud
Under the heading "De moto," Leonardo argues that the resistance of the air will not let a body sixteen times heavier (a = 16) move sixteen times faster than a lighter one (b = 1). He proposes testing this by dropping two pieces of drawn iron weighing 16 and 1 into poured mud of uniform consistency. A measured vertical scale keyed a b runs down the left margin.
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Air resistance and the fall of unequal weights
Leonardo denies that a weight sixteen times greater will fall in sixteenfold proportion, because the resistance of the air prevents it. He designs an experiment in poured mud of uniform liquidity, letting two pieces of drawn iron of 16 and of 1 fall into it to observe the difference.
The 16-to-1 proportion of the weights
The two measured vertical lines a b are labelled 16 and 1, fixing the ratio at the heart of the argument. Leonardo terms the expected fall a motion of "sixteenfold proportion" that the air will not permit.