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.

Movement will fail sooner than usefulness.

Fix your course on a star and you'll navigate any storm.

Nothing can be loved or hated unless it is first known.

In the days of thy youth seek to obtain that which shall compensate the losses of thy old age.

It vexes me greatly that having to earn my living has forced me to interrupt the work and to attend to small matters.

Those who become enamoured of the art, without having previously applied to the diligent study of the scientific part of it, may be compared to mariners who put to the sea in a ship without rudder or compass and therefore cannot be certain of arriving at the wished for port.