Pulley weights and the law of constant resistance
Paired figures; by the 28th of the 'Teorica' the three loads never change their nature
Two figures show weights carried on ropes over pulleys, marked n, m, r, a, b and f. Leonardo asks what load at a b will raise the weight f when m n stands level with r, then cites the twenty-eighth proposition of his 'Theory': in whatever position the three weights are raised or lowered, they always offer equal resistance to one another and never change from their first nature. In other words, no degree of rising or falling alters their relation.
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Equal resistance in every position (28th of the 'Teorica')
Once the weights n m stand level with r, Leonardo invokes the twenty-eighth proposition of his 'Theory' to argue that in any raised or lowered position the three weights keep equal resistance and never vary from their first nature. No degree of motion, up or down, changes them.
Two rope-and-pulley arrangements
At left a rope runs over a pulley in a V shape down to a central weight; at right three cords descend from pulleys to hanging weights, one line reaching a further pulley set on the ground. The load f is the weight to be raised by the weight at a b.