[My uncle said to me…] When I read, forty years ago, that shells from Syria were found in the Alps, I say, I admit, with a slightly mocking tone, that these shells were apparently brought by pilgrims who were returning from Jerusalem. M. de Buffon reprimanded me very sharply in his Theory of the Earth, page 281. I did not want to quarrel with him over shells, but I remain of the same opinion, because the impossibility that the sea formed the mountains is evident to me. Some may tell me that porphyry is made of sea urchin spikes, I’ll believe it when I see white marble is made of ostrich feathers.

A Frenchman who arrives in London, will find Philosophy, like every Thing else, very much chang’d there. He had left the World a plenum, and he now finds it a vacuum. At Paris the Universe is seen, compos’d of Vortices of subtile Matter; but nothing like it is seen in London. In France, ‘tis the Pressure of the Moon that causes the Tides; but in England ‘tis the Sea that gravitates towards the Moon; so what when you think that the Moon should make it flood with us, those Gentlemen fancy it should be Ebb, which, very unluckily, cannot be prov’d. For to be able to do this, ‘tis necessary the Moon and the Tides should have been enquir’d into, at the very instant of the Creation.

A physician is an unfortunate gentleman who is every day required to perform a miracle; namely to reconcile health with intemperance.

Before Kepler, all men were blind, Kepler had one eye, and Newton had two eyes.

Bile makes man passionate and sick; but without bile man could not live.

But nothing is more estimable than a physician who, having studied nature from his youth, knows the properties of the human body, the diseases which assail it, the remedies which will benefit it, exercises his art with caution, and pays equal attention to the rich and the poor.

Changes That Have Occurred in the Globe: When we have seen with our own eyes a mountain progressing into a plain; that is to say, an immense boulder separating from this mountain and covering the fields; an entire castle broken into pieces over the ground; a river swallowed up which then bursts out from its abyss; clear marks of a vast amount of water having once flooded regions now inhabited, and a hundred vestiges of other transformations, then we are much more willing to believe that great changes altered the face of the earth, than a Parisian lady who knows only that the place where her house was built was once a cultivated field. However, a lady from Naples who has seen the buried ruins of Herculaneum, is much less subject to the bias which leads us to believe that everything has always been as it is today.

Descartes constructed as noble a road of science, from the point at which he found geometry to that to which he carried it, as Newton himself did after him. ... He carried this spirit of geometry and invention into optics, which under him became a completely new art.

Doctors are men who prescribe medicines of which they know little, to cure diseases of which they know less, in human beings of whom they know nothing. (1760)

He who has heard the same thing told by twelve thousand ocular [eye]witnesses, has only twelve thousand probabilities, equal to one strong one, which is not equal to certainty.

Heroes of physics, Argonauts of our time
Who leaped the mountains, who crossed the seas …
You have confirmed in uncomfortable places
What Newton knew without leaving his study.

I know of nothing more laughable than a doctor who does not die of old age.

In fact, no opinion should be with fervour. No one holds with fervour that seven times eight is fifty-six, because it can be shown to be the case. Fervour is only necessary in commending an opinion which is doubtful or demonstrably false.

In geometry, as in most sciences, it is very rare that an isolated proposition is of immediate utility. But the theories most powerful in practice are formed of propositions which curiosity alone brought to light, and which long remained useless without its being able to divine in what way they should one day cease to be so. In this sense it may be said, that in real science, no theory, no research, is in effect useless.

In medicine … beware of ambiguity.

It is in everything else as it is in colors; bad eyes can distinguish between black and white; better eyes, and eyes much exercised, can distinguish every nicer gradation.

It is not strictly demonstrated that atoms are indivisible; but it appears that they are not divided by the laws of nature.

It is not sufficient to see and to know the beauty of a work. We must feel and be affected by it.

It is said, sometimes, that common sense is very rare.

It is the flash which appears, the thunderbolt will follow.

Mathematics must subdue the flights of our reason; they are the staff of the blind; no one can take a step without them; and to them and experience is due all that is certain in physics.

Men argue, nature acts.

Men who are occupied in the restoration of health to other men, by the joint exertion of skill and humanity, are above all the great of the earth. They even partake of divinity, since to preserve and renew is almost as noble as to create.

One day in the year 1666 Newton had gone to the country, and seeing the fall of an apple, [as his niece (Mme Conduit) told me,] let himself be led into a deep meditation on the cause which thus draws every object along a line whose extension would pass almost through the center of the Earth.

Our spirit is often led astray by its own delusions; it is even frightened by its own work, believes that it sees what it fears, and in the horror of night sees at last the objects which itself has produced.

Society is as ancient as the world.

Superstition is to religion what astrology is to astronomy; the mad daughter of a wise mother.

The art of causing intemperance and health to exist in the same body is as chimerical as the philosopher’s stone, judicial astrology, and the theology of the magi.

The art of medicine consists of amusing the patient while nature cures the disease.

The word atom signifies without parts—not to be divided. You divide it in thought; for, if you were to divide it in reality, it would no longer be an atom.

There is an astonishing imagination, even in the science of mathematics. … We repeat, there was far more imagination in the head of Archimedes than in that of Homer.

There is no sect in geometry; we never say,—An Euclidian, an Archimedian.

Truth is an abstract word which most men use indifferently in their books and judgments, for error and falsehood.

Vous avez trouve par de long ennuis
Ce que Newton trouva sans sortir de chez lui.

We must not, however, reject all discoveries of secrets and all new inventions. It is with them as with theatrical pieces, there may be one good out of a thousand.

When he to whom a person speaks does not understand, and he who speaks does not understand himself, that is metaphysics.

When I first read Plato and came upon this gradation of beings which rises from the lightest atom to the Supreme Being, I was struck with admiration. But when I looked at it more closely, the great phantom vanished. … At first the imagination takes a pleasure in seeing the imperceptible transition from inanimate to organic matter, from plants to zoophytes, from these to animals, from these to genii, … and finally angels.

Mock on, mock on, Voltaire, Rousseau!
Mock on, mock on: 'Tis all in vain!
You throw the sand against the wind,
And the wind blows it back again.
And every sand becomes a gem
Reflected in the beams divine;
Blown back they blind the mocking eye,
But still in Israel's paths they shine.
The atoms of Democritus
And Newton's particles of light
Are sands upon the Red Sea shore,
Where Israel's tents do shine so bright.

When I read an Italian letter [Saggio by Voltaire] on changes which had occurred on the surface of the earth, published in Paris this year (1746), I believed that these facts were reported by La Loubère. Indeed, they correspond perfectly with the author’s ideas. Petrified fish are according to him merely rare fish thrown away by Roman cooks because they were spoiled; and with respect to shells, he said that they were from the sea of the Levant and brought back by pilgrims from Syria at the time of the crusades. These shells are found today petrified in France, in Italy and in other Christian states. Why did he not add that monkeys transported shells on top of high mountains and to every place where humans cannot live? It would not have harmed his story but made his explanation even more plausible.

There are some men who are counted great because they represent the actuality of their own age, and mirror it as it is. Such an one was Voltaire, of whom it was epigrammatically said: “he expressed everybody's thoughts better than anyone.” But there are other men who attain greatness because they embody the potentiality of their own day and magically reflect the future. They express the thoughts which will be everybody's two or three centuries after them. Such as one was Descartes.

Hyper-selectionism has been with us for a long time in various guises; for it represents the late nineteenth century’s scientific version of the myth of natural harmony–all is for the best in the best of all possible worlds (all structures well designed for a definite purpose in this case). It is, indeed, the vision of foolish Dr. Pangloss, so vividly satirized by Voltaire in Candide–the world is not necessarily good, but it is the best we could possibly have.

“On doit etre etonné ([Abbé Raynal]says) que l'Amerique n’ait pas encore produit un bon poëte, un habile mathematicien, un homme de génie dans un seul art, ou une seule science.” …“America has not yet produced one good poet.” When we shall have existed as a people as long as the Greeks did before they produced a Homer, the Romans a Virgil, the French a Racine and Voltaire, the English a Shakespeare and Milton, should this reproach be still true, we will enquire from what unfriendly causes it has proceeded, that the other countries of Europe and quarters of the earth shall not have inscribed any name in the roll of poets. But neither has America produced “one able mathematician, one man of genius in a single art or a single science.” … In physics we have produced a [Benjamin] Franklin, than whom no one of the present age has made more important discoveries, nor has enriched philosophy with more, or more ingenious solutions of the phaenomena, of nature. … [The quadrant invented by Godfrey, an American also, and with the aid of which the European nations traverse the globe, is called Hadley’s quadrant.] … We have supposed Mr. [David] Rittenhouse second to no astronomer living: that in genius he must be the first, because he is self-taught. As an artist he has exhibited as great a proof of mechanical genius as the world has ever produced. … We therefore suppose, that this reproach is as unjust as it is unkind; and that, of the geniuses which adorn the present age, America contributes its full share. [Compared to the much larger populations of European countries.]