The balance: friction at the fulcrum and the limits of weighing
Levers, pulley-weights and the science of the balance, with impossibility aphorisms
Leonardo investigates why, in nature, one weight (n) resists another (m) in the balance, and challenges himself to prove it with a precise rule. Diagrams of two poles on a support and of loaded balances, labelled with letters (f, b, n, S, r, c, m) and numbers, work out how friction at the fulcrum (confregazione) consumes a quarter of each added weight, a loss that recurs 'infinitely.' Aphorisms conclude that it is impossible to state precisely the proportion by which one weight exceeds another in the balance, in theory or by experiment. A marginal note at top-left refers to 'the mill with its water.'
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Why n resists m — a rule demanded to prove it
Leonardo poses the problem directly: why in nature does n resist m precisely, and he sets himself to make his rule demonstrate it with precision. The question introduces the friction analysis that follows.
Friction at the pole apportioned across the levers
Working through a figure of two poles on a support labelled f, b, n, S, r, c, m, he tallies how weights of 4 return in friction as fractions (1, 1/4, 1/16, 35/64). He distinguishes the two pounds shown only through motion from the two supported at the point f, shown both with and without motion.
It is impossible to name the excess of one weight over another
Three aphorisms declare that one cannot precisely give the proportion by which one weight exceeds the other in the balance; that although mathematics demonstrates the powers and resistances of weights, practical makers remain confused; and that no experiment can precisely give a weight that moves its opposite in the other arm.
The more weight, the more friction — a quarter given endlessly
Reasoning on a balance marked 8-64-64, he shows 4 standing against 6: the eight pounds bearing on the support give 1/4, that is 2; but that 2 in turn gives its fourth in friction (1/2), and each added half again gives a quarter of itself, so the correction continues infinitely in nature and in theory.
"The mill with its water"
A short label in the upper-left margin names 'the mill with its water,' set beside a small circular sketch. It stands apart from the statics notes that fill the rest of the sheet.
