...they have never affirm'd any thing, concerning the Cause, till the Trial was past: whereas, to do it before, is a most venomous thing in the making of Sciences; for whoever has fix'd on his Cause, before he experimented; can hardly avoid fitting his Experiment to his Observations, to his own Cause, which he had before imagin'd; rather than the Cause to the Truth of the Experiment itself.
Referring to experiments of the Aristotelian mode, whereby a preconceived truth would be illustrated merely to convince people of the validity of the original thought.

[L]et us not overlook the further great fact, that not only does science underlie sculpture, painting, music, poetry, but that science is itself poetic. The current opinion that science and poetry are opposed is a delusion. … On the contrary science opens up realms of poetry where to the unscientific all is a blank. Those engaged in scientific researches constantly show us that they realize not less vividly, but more vividly, than others, the poetry of their subjects. Whoever will dip into Hugh Miller’s works on geology, or read Mr. Lewes's “Seaside Studies,” will perceive that science excites poetry rather than extinguishes it. And whoever will contemplate the life of Goethe will see that the poet and the man of science can co-exist in equal activity. Is it not, indeed, an absurd and almost a sacrilegious belief that the more a man studies Nature the less he reveres it? Think you that a drop of water, which to the vulgar eye is but a drop of water, loses anything in the eye of the physicist who knows that its elements are held together by a force which, if suddenly liberated, would produce a flash of lightning? Think you that what is carelessly looked upon by the uninitiated as a mere snow-flake, does not suggest higher associations to one who has seen through a microscope the wondrously varied and elegant forms of snow-crystals? Think you that the rounded rock marked with parallel scratches calls up as much poetry in an ignorant mind as in the mind of a geologist, who knows that over this rock a glacier slid a million years ago? The truth is, that those who have never entered upon scientific pursuits know not a tithe of the poetry by which they are surrounded. Whoever has not in youth collected plants and insects, knows not half the halo of interest which lanes and hedge-rows can assume. Whoever has not sought for fossils, has little idea of the poetical associations that surround the places where imbedded treasures were found. Whoever at the seaside has not had a microscope and aquarium, has yet to learn what the highest pleasures of the seaside are. Sad, indeed, is it to see how men occupy themselves with trivialities, and are indifferent to the grandest phenomena—care not to understand the architecture of the Heavens, but are deeply interested in some contemptible controversy about the intrigues of Mary Queen of Scots!—are learnedly critical over a Greek ode, and pass by without a glance that grand epic written by the finger of God upon the strata of the Earth!

Any opinion as to the form in which the energy of gravitation exists in space is of great importance, and whoever can make his opinion probable will have, made an enormous stride in physical speculation. The apparent universality of gravitation, and the equality of its effects on matter of all kinds are most remarkable facts, hitherto without exception; but they are purely experimental facts, liable to be corrected by a single observed exception. We cannot conceive of matter with negative inertia or mass; but we see no way of accounting for the proportionality of gravitation to mass by any legitimate method of demonstration. If we can see the tails of comets fly off in the direction opposed to the sun with an accelerated velocity, and if we believe these tails to be matter and not optical illusions or mere tracks of vibrating disturbance, then we must admit a force in that direction, and we may establish that it is caused by the sun if it always depends upon his position and distance.

As pure truth is the polar star of our science [mathematics], so it is the great advantage of our science over others that it awakens more easily the love of truth in our pupils. … If Hegel justly said, “Whoever does not know the works of the ancients, has lived without knowing beauty,” Schellbach responds with equal right, “Who does not know mathematics, and the results of recent scientific investigation, dies without knowing truth.”

Do the day’s work. If it be to protect the rights of the weak, whoever objects, do it. If it be to help a powerful corporation better to serve the people, whatever the opposition, do that. Expect to be called a stand-patter, but don’t be a stand-patter. Expect to be called a demagogue, but don’t be a demagogue. Don’t hesitate to be as revolutionary as science. Don’t hesitate to be as reactionary as the multiplication table. Don’t expect to build up the weak by pulling down the strong. Don’t hurry to legislate. Give administration a chance to catch up with legislation.

Histology is an exotic meal, but can be as repulsive as a dose of medicine for students who are obliged to study it, and little loved by doctors who have finished their study of it all too hastily. Taken compulsorily in large doses it is impossible to digest, but after repeated tastings in small draughts it becomes completely agreeable and even addictive. Whoever possesses a refined sensitivity for artistic manifestations will appreciate that, in the science of histology, there exists an inherent focus of aesthetic emotions.

How to start on my adventure—how to become a forester—was not so simple. There were no schools of Forestry in America. … Whoever turned his mind toward Forestry in those days thought little about the forest itself and more about its influences, and about its influence on rainfall first of all. So I took a course in meteorology, which has to do with weather and climate. and another in botany, which has to do with the vegetable kingdom—trees are unquestionably vegetable. And another in geology, for forests grow out of the earth. Also I took a course in astronomy, for it is the sun which makes trees grow. All of which is as it should be, because science underlies the forester’s knowledge of the woods. So far I was headed right. But as for Forestry itself, there wasn’t even a suspicion of it at Yale. The time for teaching Forestry as a profession was years away.

If you are young, then I say: Learn something about statistics as soon as you can. Don’t dismiss it through ignorance or because it calls for thought. … If you are older and already crowned with the laurels of success, see to it that those under your wing who look to you for advice are encouraged to look into this subject. In this way you will show that your arteries are not yet hardened, and you will be able to reap the benefits without doing overmuch work yourself. Whoever you are, if your work calls for the interpretation of data, you may be able to do without statistics, but you won’t do as well.

In science, each of us knows that what he has accomplished will be antiquated in ten, twenty, fifty years. That is the fate to which science is subjected; it is the very meaning of scientific work, to which it is devoted in a quite specific sense, as compared with other spheres of culture for which in general the same holds. Every scientific “fulfilment” raises new “questions”; it asks to be “surpassed” and outdated. Whoever wishes to serve science has to resign himself to this fact. Scientific works certainly can last as “gratifications” because of their artistic quality, or they may remain important as a means of training. Yet they will be surpassed scientifically—let that be repeated—for it is our common fate and, more our common goal. We cannot work without hoping that others will advance further than we have. In principle, this progress goes on ad infinitum.

It is indeed an Opinion strangely prevailing amongst Men, that Houses, Mountains, Rivers, and in a word all sensible Objects have an Existence Natural or Real, distinct from their being perceived by the Understanding. But with how great an Assurance and Acquiescence soever this Principle may be entertained in the World; yet whoever shall find in his Heart to call it in Question, may, if I mistake not, perceive it to involve a manifest Contradiction. For what are the forementioned Objects but the things we perceive by Sense, and what do we perceive besides our own Ideas or Sensations; and is it not plainly repugnant that anyone of these or any Combination of them should exist unperceived?

It is requisite that we should here say something of Magick, which is so linked to Astrology, as being her near Kinswoman, that whoever professes Magick without Astrology, does nothing, but is altogether out of the way.

It seems to me that every phenomenon, every fact, itself is the really interesting object. Whoever explains it, or connects it with other events, usually only amuses himself or makes sport of us, as, for instance, the naturalist or historian. But a single action or event is interesting, not because it is explainable, but because it is true.

Man is an imitative creature, and whoever is the foremost leads the herd.

Nothing is really small; whoever is open to the deep penetration of nature knows this.

One should not wrongly reify “cause” and “effect,” as the natural scientists do (and whoever, like them, now “naturalizes” in his thinking), according to the prevailing mechanical doltishness which makes the cause press and push until it “effects” its end; one should use “cause” and “effect” only as pure concepts, that is to say, as conventional fictions for the purpose of designation and communication—not for explanation.

People give ear to an upstart astrologer [Copernicus] who strove to show that the earth revolves, not the heavens or the firmament, the sun and the moon. Whoever wishes to appear clever must devise some new system, which of all systems is of course the very best. This fool wishes to reverse the entire science of astronomy.

Science and technology, like all original creations of the human spirit, are unpredictable. If we had a reliable way to label our toys good and bad, it would be easy to regulate technology wisely. But we can rarely see far enough ahead to know which road leads to damnation. Whoever concerns himself with big technology, either to push it forward or to stop it, is gambling in human lives.

Scientific truth is marvellous, but moral truth is divine; and whoever breathes its air and walks by its light has found the lost paradise.

Society is a republic. When an individual endeavors to lift himself above his fellows, he is dragged down by the mass, either by means of ridicule or of calumny. No one shall be more virtuous or more intellectually gifted than others. Whoever, by the irresistible force of genius, rises above the common herd is certain to be ostracized by society, which will pursue him with such merciless derision and detraction that at last he will be compelled to retreat into the solitude of his thoughts.

The future … [is] something which everyone reaches at the rate of sixty minutes an hour, whatever he does, whoever he is.

The masses have never thirsted after truth. Whoever can supply them with illusions is easily their master; whoever attempts to destroy their illusions is always their victim.

The sweetest and most inoffensive path of life leads through the avenues of science and learning; and whoever can either remove any obstruction in this way, or open up any new prospect, ought, so far, to be esteemed a benefactor to mankind.

There are certain general Laws that run through the whole Chain of natural Effects: these are learned by the Observation and Study of Nature, and are by Men applied as well to the framing artificial things for the Use and Ornament of Life, as to the explaining the various Phænomena: Which Explication consists only in shewing the Conformity any particular Phænomenon hath to the general Laws of Nature, or, which is the same thing, in discovering the Uniformity there is in the production of natural Effects; as will be evident to whoever shall attend to the several Instances, wherin Philosophers pretend to account for Appearances.

There prevails among men of letters, an opinion, that all appearance of science is particularly hateful to Women; and that therefore whoever desires to be well received in female assemblies, 'must qualify himself by a total rejection of all that is serious, rational, or important; must consider argument or criticism as perpetually interdicted; and devote all his attention to trifles, and all his eloquence to compliment.

Whoever … proves his point and demonstrates the prime truth geometrically should be believed by all the world, for there we are captured.

Whoever ceases to be a student has never been a student.

Whoever could make two ears of corn or two blades of grass to grow upon a spot of ground where only one grew before, would deserve better of mankind, and do more essential service to his country, than the whole race of politicians put together.

Whoever despises the high wisdom of mathematics nourishes himself on delusion.

Whoever does not try, does not learn.

Whoever has undergone the intense experience of successful advances made in [science], is moved by profound reverence for the rationality made manifest in existence.

Whoever is to acquire a competent knowledge of medicine, ought to be possessed of the following advantages: a natural disposition; instructionl a favorable place for the study; early tuition, love of labor; leisure.

Whoever it was who searched the heavens with a telescope and found no God would not have found the human mind if he had searched the brain with a microscope.

Whoever limits his exertions to the gratification of others, whether by personal exhibition, as in the case of the actor and of the mimic, or by those kinds of literary composition which are calculated for no end but to please or to entertain, renders himself, in some measure, dependent on their caprices and humours. The diversity among men, in their judgments concerning the objects of taste, is incomparably greater than in their speculative conclusions; and accordingly, a mathematician will publish to the world a geometrical demonstration, or a philosopher, a process of abstract reasoning, with a confidence very different from what a poet would feel, in communicating one of his productions even to a friend.

Whoever looks at the insect world, at flies, aphides, gnats and innumerable parasites, and even at the infant mammals, must have remarked the extreme content they take in suction, which constitutes the main business of their life. If we go into a library or newsroom, we see the same function on a higher plane, performed with like ardor, with equal impatience of interruption, indicating the sweetness of the act. In the highest civilization the book is still the highest delight.

Whoever undertakes to set himself up as a judge of Truth and knowledge is shipwrecked by the laughter of the gods.

Whoever wins to a great scientific truth will find a poet before him in the quest.

Whoever wishes to acquire a deep acquaintance with Nature must observe that there are analogies which connect whole branches of science in a parallel manner, and enable us to infer of one class of phenomena what we know of another. It has thus happened on several occasions that the discovery of an unsuspected analogy between two branches of knowledge has been the starting point for a rapid course of discovery.

Whoever would not remain in complete ignorance of the resources which cause him to act; whoever would seize, at a single philosophical glance, the nature of man and animals, and their relations to external objects; whoever would establish, on the intellectual and moral functions, a solid doctrine of mental diseases, of the general and governing influence of the brain in the states of health and disease, should know, that it is indispensable, that the study of the organization of the brain should march side by side with that of its functions.

Whoever, in the pursuit of science, seeks after immediate practical utility, may generally rest assured that he will seek in vain.

With science fiction I think we are preparing ourselves for contact with them, whoever they may be.

With whom [do] the adherents of historicism actually empathize[?] The answer is inevitable: with the victor. And all rulers are the heirs of those who conquered before them. Hence, empathy with the victor invariably benefits the rulers. Historical materialists know what that means. Whoever has emerged victorious participates to this day in the triumphal procession in which the present rulers step over those who are lying prostrate. According to traditional practice, the spoils are carried along in the procession. They are called cultural treasures, and a historical materialist views them with cautious detachment. For without exception the cultural treasures he surveys have an origin which he cannot contemplate without horror. They owe their existence not only to the efforts of the great minds and talents who have created them, but also to the anonymous toil of their contemporaries. There is no document of civilization which is not at the same time a document of barbarism.

Ye daring ones! Ye venturers and adventurers, and whoever of you have embarked with cunning sails on unexplored seas! Ye enjoyers of enigmas! Solve unto me the enigma that I then beheld, interpret for me the vision of the loneliest one. ... O my brethren, I heard a laughter which was no human laughter.