The water which rises in the mountains is the blood which keeps the mountain in life.
Leonardo da VinciIn whatever system where the weight attached to the wheel should be the cause of motion of the wheel, without any doubt the center of the gravity of the weight will stop beneath the center of its axle. No instrument devised by human ingenuity, which turns with its wheel, can remedy this effect. Oh, speculators about perpetual motion, how many vain chimeras have you created in the like quest. Go and take you place with the seekers after gold.
Leonardo da VinciNothing 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.
Leonardo da Vinci