Counterweight for a lever's friction, with a dissection note
A numerical rule for balancing friction on a lever, and a margin memo for an anatomical drawing
A crowded computational sheet developing a rule for the counterweight (contra peso) needed to overcome the friction (confregazione) of a loaded lever, on the principle that friction resists at one quarter of the rubbed weight. Leonardo works the rule through repeatedly with fulcrum weights and fractional results, surrounding the prose with dozens of small balance diagrams and columns of figures. A short note by an octagonal figure and, in the right margin, a memorandum for an anatomical study of the veins, intestines and spine appear among the mechanical work.
On this page
Rule for the counterweight of a lever's friction
Multiply the counterweight's arm by 4 as often as it contains the friction's arm, subtract one, divide the friction by the remainder, multiply the result by 4, and divide by the number of the lever's arms. The one is subtracted so an even number becomes odd and, restored later, returns even, since a quarter of the rubbed weight equals its friction.
Worked example: the friction of 8 resolved into thirds
The friction of the eight is 2, divided by 3 giving 2/3; added to 2 this makes 8/3. Resolving the fulcrum's 8 into thirds gives 24/3, and adding the counterweight's 8/3 gives 32/3; the quarter of 32 thirds is those 8 thirds, which divided by the number of the lever's arms yields the true counterweight.
Memo for an anatomical drawing
A margin instruction to himself for a dissection study: to draw first all the veins, then the intestines, and to remove the spine. The note accompanies a small anatomical sketch.
