Central lines of motion, percussion and the rebound of blows
A quarter-circle diagram measures rebound heights; every heavy body has three centres
Folio 226v develops Leonardo's theory of percussion by defining a set of "central lines": of the weight, of any motion, of the body, and of the blow and its rebound. The central line of the blow, he says, is rigorously kept throughout the motion and ends at the point of percussion, and every heavy body has three centres, of natural gravity, of accidental gravity, and of magnitude. A second block, keyed to a lettered figure, states that the height of the rebounds is measured on the line c m in the degrees d, c and m, and argues that the power of a percussion is variable to infinity and generates a rebound proportional to it. The facing folio 229r is blank on this opening.
On this page
The central lines and the three centres of a heavy body
Leonardo defines the central line of a heavy body as the diameter passing through its centre of gravity, and the central line of the blow as that rigorously maintained through the whole motion and ending at the point of percussion. He concludes that every heavy body has three centres: of natural gravity, of accidental gravity, and of magnitude.
Measuring rebound heights; power of percussion
The height of the rebounds is measured on the line c m, in the degrees d, c and m. Percussion is an impediment of motion, the end of the incident motion and the beginning of the rebounding motion, and its power is variable to infinity; a percussion of lesser power generates a rebound of lesser length.
Quarter-circle diagram of rebound heights
Below the text a graduated quarter-circle, like a protractor, sits above a curve that sweeps down to a baseline, illustrating how rebound height is plotted against the degrees c, d and m. The construction accompanies the measurement described in the text.