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.

Mechanics is the paradise of the mathematical sciences because by means of it one comes to the fruits of mathematics.

He turns not back who is bound to a star.

Just as iron rusts from disuse... even so does inaction spoil the intellect.

O Time! consumer of all things; O envious age! thou dost destroy all things and devour all things with the relentless teeth of years, little by little in a slow death. Helen, when she looked in her mirror, seeing the withered wrinkles made in her face by old age, wept and wondered why she had twice been carried away.

He who does not understand the supreme certainty of mathematics is wallowing in confusion.

Just as iron rusts from disuse, and stagnant water putrefies, or when cold turns to ice, so our intellect wastes unless it is kept in use.