If you throw a stone in a pond... the waves which strike against the shores are thrown back towards the spot where the stone struck; and on meeting other waves they never intercept each other's course... In a small pond one and the same stroke gives birth to many motions of advance and recoil.

Every obstacle yields to stern resolve.

Our life is made by the death of others.

Those who condemn the supreme certainty of mathematics feed on confusion, and can never silence the contradictions of the sophistical sciences which lead to eternal quackery.

Of several bodies, all equally large and equally distant, that which is most brightly illuminated will appear to the eye nearest and largest.

A single and distinct luminous body causes stronger relief in the objects than a diffused light; as may be seen by comparing one side of a landscape illuminated by the sun, and one overshadowed by clouds, and illuminated only by the diffused light of the atmosphere.

Every action needs to be prompted by a motive. To know and to will are two operations of the human mind. Discerning, judging, deliberating are acts of the human mind.