Iron rusts from disuse, stagnant water loses its purity, and in cold weather becomes frozen; even so does inaction sap the vigors of the mind.
Learning is the only thing the mind never exhausts, never fears, and never regrets.
The eye, the window of the soul, is the chief means whereby the understanding can most fully and abundantly appreciate the infinite works of Nature; and the ear is second.
Why are the bones of great fishes, and oysters and corals and various other shells and sea-snails, found on the high tops of mountains that border the sea, in the same way in which they are found in the depths of the sea?
The desire to know is natural to good men.
When you draw a nude, sketch the whole figure and nicely fit the members to it and to each other. Even though you may only finish one portion of the drawing, just make certain that all the parts hang together, so that the study will be useful to you in the future.
O painter skilled in anatomy, beware lest the undue prominence of the bones, sinews and muscles cause you to become a wooden painter from the desire to make your nude figures reveal all.
Supreme happiness will be the greatest cause of misery, and the perfection of wisdom the occassion of folly.
All knowledge which ends in words will die as quickly as it came to life, with the exception of the written word: which is its mechanical part.
Oh! Speculators on things, boast not of knowing the things that nature ordinarily brings about; but rejoice if you know the end of those things which you yourself device.
The merit of painting lies in the exactness of reproduction. Painting is a science and all sciences are based on mathematics. No human inquiry can be a science unless it pursues its path through mathematical exposition and demonstration.
The faculty of imagination is both the rudder and the bridle of the senses.
Everything comes from everything, and everything is made out of everything, and everything returns into everything.
The earth is moved from its position by the weight of a tiny bird resting upon it.
Good culture is born of a good disposition; and since the cause is more to be praised than the effect, I will rather praise a good disposition without culture, than good culture without the disposition.
The great man presides over all his states of consciousness with obstinate rigor.
There is nothing that deceives us more than our own judgment when used to give an opinion on our own works. It is sound in judging the work of our enemies but not that of our friends, for hate and love are two of the most powerfully motivating factors found among living things.
My works are the issue of simple and plain experience which is the true mistress.
A long life is a life well spent.
Let no man who is not a Mathematician read the elements of my work.
If the thing loved is base, the lover becomes base.