5th Book of Euclid. First definition: a part is a quantity of less magnitude than the greater magnitude when the less is contained a certain number of times in the greater.
A part properly speaking is that which may be multiplied, that is when, being multiplied by a certain number, it forms exactly the whole. A common aggregate part ...
Second definition. A greater magnitude is said to be a multiple of a less, when the greater is measured by the less.
By the first we define the lesser [magnitude] and by the second the greater is defined. A part is spoken
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.