He who cannot establish dominion over himself will have no dominion over others.

To speak of this subject you must... explain the nature of the resistance of the air, in the second the anatomy of the bird and its wings, in the third the method of working the wings in their various movements, in the fourth the power of the wings and the tail when the wings are not being moved and when the wind is favourable to serve as guide in various movements.

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.

There are many kinds of beauty as people who possess it.

Strive to preserve your health; and in this you will better succeed in proportion as you keep clear of the physicians, for their drugs are a kind of alchemy concerning which there are no fewer books than there are medicines.

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.

Those who are inspired by a model other than Nature, labor in vain.