Why does not the weight o remain in its place? It does not remain because it has no resistance. Where will it move to? It will move towards the centre [of gravity]. And why by no other line? Because a weight which has no support falls by the shortest road to the lowest point which is the centre of the world. And why does the weight know how to find it by so short a line? Because it is not independant and does not move about in various directions.
[Footnote: This text and the sketch belonging to it, are reproduced on Pl. CXXI.]
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.