Balance-arm mechanics, an axle-pin recipe, and a lune figure
Weight, friction and effort in the two arms of a balance; preparing a pin for compass or cart.
The main sheet treats the lines n e and n m as the two arms of a balance whose fulcrum is n, and works out how friction and the direction of pull change the resistance and the effort demanded of the mover. A separate note gives a practical recipe for a pivot-pin (polo): well dried, then boiled in wax for a compass or in tallow or linseed oil for a cart, so it neither swells nor shrinks. A small crescent (lunula) at lower right is annotated with the numbers 17, 7 and 34.
On this page
The two arms n e and n m of a balance about fulcrum n
Leonardo supposes the lines n e and n m to be the two arms of a balance whose fulcrum is n. A body weighing 6 develops, by his cited proposition, 3 of frictional resistance in the straight line, so that 3 of power stands equal to a body of 9 pounds. Drawing the body 9 along the oblique line b e shortens the line r n against n m, forcing the effort at the mover b to grow at every degree of motion; if instead S f is the mover it makes no friction but bends downward with an effort of 1 and 1/2.
Preparing a pivot-pin for a compass or a cart
A pin (polo) must be thoroughly dry. For a compass it should be boiled in wax so that it may never swell or shrink; for a cart it should be boiled in tallow or in linseed oil.
Figure of a lune with the numbers 17, 7, 34
A small crescent-shaped figure (lunula) is drawn and annotated with the numbers 17, 7 and 34.