Necessity is a guardian in Nature.

Nothing is more apt to deceive us than our own judgment of our work. We derive more benefit from having our faults pointed out by our enemies than from hearing the opinions of friends.

Every obstacle is destroyed through rigor.

Obstacles cannot bend me. Every obstacle yields to effort.

Drawing is based upon perspective, which is nothing else than a thorough knowledge of the function of the eye.

To speak well of a base man is much the same as speaking ill of a good man.

The Bactrian have two humps; the Arabian one only. They are swift in battle and most useful to carry burdens. This animal is extremely observant of rule and measure, for it will not move if it has a greater weight than it is used to, and if it is taken too far it does the same, and suddenly stops and so the merchants are obliged to lodge there.