"Since the wings are swifter to press the air than the air is to escape from beneath the wings the air becomes condensed and resists the movement of the wings; and the motive power of these wings by subduing the resistance of the air raises itself in a contrary movement to the movement of the wings."

"He who suffers time to slip away and does not grow in virtue the more one thinks about him the sadder one becomes. No man has a capacity for virtue who sacrifices honour for gain. Fortune is powerless to help one who does not exert himself. That man becomes happy who follows Christ. There is no perfect gift without great suffering. Our triumphs and our pomps pass away; gluttony and sloth and enervating luxury have banished every virtue from the world; so that as it were wandering from its course our nature is subdued by habit. Now and henceforth it is meet that you cure yourself of laziness. The Master has said that sitting on down or lying under the quilts will not bring thee to fame. He who without it has frittered life away leaves no more trace of himself upon the earth than smoke does in the air or the foam on the water."

"Wine is good, but water is preferable at table."

"Nature is full of infinite causes which were never set forth in experience."

"He who does not value life does not deserve it."

"The water which rises in the mountain is the blood which keeps the mountain in life."

"Observe the light and consider its beauty. Blink your eye and look at it. That which you see was not there at first, and that which was there is there no more."

"To enjoy—to love a thing for its own sake and for no other reason."

"Science, knowledge of the things that are possible present and past; prescience, knowledge of the things which may come to pass."

"Where there is most power of feeling, there of martyrs is the greatest martyr."

"Intellectual passion drives out sensuality."

"While I thought I have been learning how to live, I have been learning how to die."

"The mind passes in an instant from east to west; and all the great incorporeal things resemble these very closely in speed."

"Every part is disposed to unite with the whole, that it may thereby escape from its own incompleteness."

"Reserve the great matters till the end, and the small matters give at the beginning."

"If any man could have discovered the utmost powers of the cannon, in all its various forms and have given such a secret to the Romans, with what rapidity would they have conquered every country and have vanquished every army, and what reward could have been great enough for such a service! Archimedes indeed, although he had greatly damaged the Romans in the siege of Syracuse, nevertheless did not fail of being offered great rewards from these very Romans; and when Syracuse was taken, diligent search was made for Archimedes; and he being found dead greater lamentation was made for him by the Senate and people of Rome than if they had lost all their army; and they did not fail to honour him with burial and with a statue."

"I ask at what part of its curved motion the moving cause will leave the thing moved and moveable."

"Do not reveal, if liberty is precious to you; my face is the prison of love."

"Tell me if anything was ever done."

"When I did well, as a boy you used to put me in prison. Now if I do it being grown up, you will do worse to me."

"This writing distinctly about the kite seems to be my destiny, because among the first recollections of my infancy, it seemed to me that, as I was in my cradle, a kite came to me and opened my mouth with its tail, and struck me several times with its tail inside my lips."

"May it please our great Author that I may demonstrate the nature of man and his customs, in the way I describe his figure."

"If you meet with any one who is virtuous do not drive him from you; do him honour, so that he may not have to flee from you and be reduced to hiding in hermitages, or caves or other solitary places to escape from your treachery; if there is such an one among you do him honour, for these are our Saints upon earth; these are they who deserve statues from us, and images..."

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

"Like a whirling wind which rushes down a sandy and hollow valley, and which, in its hasty course, drives to its centre every thing that opposes its furious course... No otherwise does the Northern blast whirl round in its tempestuous progress..."

"I have seen motions of the air so furious that they have carried, mixed up in their course, the largest trees of the forest and whole roofs of great palaces, and I have seen the same fury bore a hole with a whirling movement digging out a gravel pit, and carrying gravel, sand and water more than half a mile through the air."

"The image of the sun where it falls appears as a thing which covers the person who attempts to cover it."

"A vase of unbaked clay, when broken, may be remoulded, but not a baked one."

"The ball of snow when, as it rolls, it descends from the snowy mountains, increases in size as it falls."

"The vine that has grown old on an old tree falls with the ruin of that tree, and through that bad companionship must perish with it."

"The bones of the Dead will be seen to govern the fortunes of him who moves them."

"Experience shows us that the air must have darkness beyond it and yet it appears blue. If you produce a small quantity of smoke from dry wood and the rays of the sun fall on this smoke, and if you then place behind the smoke a piece of black velvet on which the sun does not shine, you will see that all the smoke which is between the eye and the black stuff will appear of a beautiful blue colour. And if instead of the velvet you place a white cloth smoke, that is too thick smoke, hinders, and too thin smoke does not produce, the perfection of this blue colour. Hence a moderate amount of smoke produces the finest blue."

"The variety of colour in objects cannot be discerned at a great distance, excepting in those parts which are directly lighted up by the solar rays."

"A luminous body will appear more brilliant in proportion as it is surrounded by deeper shadow."

"I find that any luminous body when seen through a dense and thick mist diminishes in proportion to its distance from the eye. Thus it is with the sun by day, as well as the moon and the other eternal lights by night. And when the air is clear, these luminaries appear larger in proportion as they are farther from the eye."

"Of several luminous bodies of equal size and brilliancy and at an equal distance, that will look the largest which is surrounded by the darkest background."

"A luminous body when obscured by a dense atmosphere will appear smaller; as may be seen by the moon or sun veiled by fogs."

"A dark object seen against a bright background will appear smaller than it is. A light object will look larger when it is seen against a background darker than itself."

"A shadow will appear dark in proportion to the brilliancy of the light surrounding it and conversely it will be less conspicuous where it is seen against a darker background."

"When you represent in your work shadows which you can only discern with difficulty, and of which you cannot distinguish the edges so that you apprehend them confusedly, you must not make them sharp or definite lest your work should have a wooden effect."

"I ask how far away the eye can discern a non-luminous body, as, for instance, a mountain. It will be very plainly visible if the sun is behind it; and could be seen at a greater or less distance according to the sun's place in the sky."

"No small hole can so modify the convergence of rays of light as to prevent, at a long distance, the transmission of the true form of the luminous body causing them."

"If you transmit the rays of the sun through a hole in the shape of a star you will see a beautiful effect of perspective in the spot where the sun's rays fall."

"The body which is nearest to the light casts the largest shadow, and why? If an object placed in front of a single light is very close to it you will see that it casts a very large shadow on the opposite wall, and the farther you remove the object from the light the smaller will the image of the shadow become."

"A single and distinct luminous body causes stronger relief in the object 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 so illuminated only by the diffused light of the atmosphere."

"The outlines and form of any part of a body in light and shade are indistinct in the shadows and in the high lights; but in the portions between the light and the shadows they are highly conspicuous."

"The eye can best distinguish the forms of objects when it is placed between the shaded and the illuminated parts."

"Light is the chaser away of darkness. Shade is the obstruction of light. Primary light is that which falls on objects and causes light and shade. And derived lights are those portions of a body which are illuminated by the primary light. A primary shadow is that side of a body on which the light cannot fall."

"Darkness is absence of light. Shadow is diminution of light."

"Shadow partakes of the nature of universal matter. All such matters are more powerful in their beginning and grow weaker towards the end, I say at the beginning, whatever their form or condition may be and whether visible or invisible. And it is not from small beginnings that they grow to a great size in time; as it might be a great oak which has a feeble beginning from a small acorn. Yet I may say that the oak is most powerful at its beginning, that is where it springs from the earth, which is where it is largest."