“The centre of gravity of a parallelogram is the point of intersection of its diagonals.”

Book 1, Proposition 14.
On the Equilibrium of Planes

Book 1, Proposition 4.
On the Equilibrium of Planes

of the portion adjacent to the base
Proposition presumed from previous work.
The Method of Mechanical Theorems

Proposition presumed from previous work.
The Method of Mechanical Theorems

Book 1, Proposition 13.
On the Equilibrium of Planes

Source: Mathematics as an Educational Task (1973), p. 133

Vol. 2 "Further Psychological Observations" as translated in Essays and Aphorisms (1970), as translated by R. J. Hollingdale
Parerga and Paralipomena (1851), Counsels and Maxims

This is how it has been understood by the great philosophers from Plato, the poet, to Nicolas of Cusa and other representatives of frigid scholasticism. Once this definition has been accepted, it gives rise to a series of important consequences. Love is power of producing inter-centric relationship. It is present, therefore (at least in a rudimentary state), in all the natural centres, living and pre-living, which make up the world; and it represents, too, the most profound, most direct, and most creative form of inter-action that it is possible to conceive between those centres. Love, in fact, is the expression and the agent of universal synthesis. <br class="br"> pp. 70–71 https://archive.org/stream/ActivationOfEnergy/Activation_of_Energy#page/n65/mode/2up <br class="br">Activation of Energy (1976)

Proposition 6.
The Method of Mechanical Theorems