Chapter II: Preface (2)

But it must be noted, that in this our organ, we treat of logic, and not of philosophy. Seeing, however, that our logic instructs and informs the understanding, in order that it may not, with the small hooks, as it were, of the mind, catch at, and grasp mere abstractions, but rather actually penetrate nature, and discover the properties and effects of bodies, and the determinate laws of their substance (so that this science of ours springs from the nature of things, as well as from that of the mind); it is not to be wondered at, if it have been continually interspersed and illustrated with natural observations and experiments, as instances of our method. The prerogative instances are, as appears from what has preceded, twenty-seven in number, and are termed: solitary instances, migrating instances, conspicuous instances, clandestine instances, constitutive, instances, similar instances, singular instances, deviating instances, bordering instances, instances of power, accompanying and hostile instances, subjunctive instances, instances of alliance, instances of the cross, instances of divorce, instances of the gate, citing instances, instances of the road, supplementary instances, lancing instances, instances of the rod, instances of the course, doses of nature, wrestling instances, suggesting instances, generally useful instances, and magical instances. The advantage, by which these instances excel the more ordinary, regards specifically either theory or practice, or both. With regard to theory, they assist either the senses or the understanding; the senses, as in the five instances of the lamp; the understanding, either by expediting the exclusive mode of arriving at the form, as in solitary instances, or by confining, and more immediately indicating the affirmative, as in the migrating, conspicuous, accompanying, and subjunctive instances; or by elevating the understanding, and leading it to general and common natures, and that either immediately, as in the clandestine and singular instances, and those of alliance; or very nearly so, as in the constitutive; or still less so, as in the similar instances; or by correcting the understanding of its habits, as in the deviating instances; or by leading to the grand form or fabric of the universe, as in the bordering instances; or by guarding it from false forms and causes, as in those of the cross and of divorce. With regard to practice, they either point it out, or measure, or elevate it. They point it out, either by showing where we must commence in order not to repeat the labors of others, as in the instances of power; or by inducing us to aspire to that which may be possible, as in the suggesting instances; the four mathematical instances measure it. The generally useful and the magical elevate it.

Again, out of these twenty-seven instances, some must be collected immediately, without waiting for a particular investigation of properties. Such are the similar, singular, deviating, and bordering instances, those of power, and of the gate, and suggesting, generally useful, and magical instances; for these either assist and cure the understanding and senses, or furnish our general practice. The remainder are to be collected when we furnish our synoptical tables for the work of the interpreter, upon any particular nature; for these instances, honored and gifted with such prerogatives, are like the soul amid the vulgar crowd of instances, and (as we from the first observed) a few of them are worth a multitude of the others. When, therefore, we are forming our tables they must be searched out with the greatest zeal, and placed in the table. And, since mention must be made of them in what follows, a treatise upon their nature has necessarily been prefixed. We must next, however, proceed to the supports and corrections of induction, and thence to concretes, the latent process, and latent conformations, and the other matters, which we have enumerated in their order in the twenty-first aphorism, in order that, like good and faithful guardians, we may yield up their fortune to mankind upon the emancipation and majority of their understanding; from which must necessarily follow an improvement of their estate, and an increase of their power over nature. For man, by the fall, lost at once his state of innocence, and his empire over creation, both of which can be partially recovered even in this life, the first by religion and faith, the second by the arts and sciences. For creation did not become entirely and utterly rebellious by the curse, but in consequence of the Divine decree, “in the sweat of thy brow shalt thou eat bread,” she is compelled by our labors (not assuredly by our disputes or magical ceremonies), at length, to afford mankind in some degree his bread, that is to say, to supply man’s daily wants.

FOOTNOTES:

[Footnote 2: Selection from the Preface to the _Novum Organum_.]

[Footnote 3: Part II, Conclusion of the _Novum Organum_.]

II

NICOLAUS COPERNICUS

1473-1543

_One of the first and most striking contributions to modern science was the substitution of the Copernican for the Ptolemaic conception of the universe._

_Nicolaus Copernicus was born in the Prussian village of Thorn, located on the Vistula River, February 19, 1473. Although destined for the Church, he became interested in medicine, which he studied at the University of Cracow. Later, he turned to mathematics and continued his studies at the Universities of Vienna, Bologna, Padua, Ferrara, and Rome. Although he settled down as canon at Frauenberg, Poland, and gratuitously practised medicine in conjunction with his ecclesiastical duties, he found considerable time for other intellectual pursuits. Reading widely in the Greek philosophers, he came across a statement that the earth moved in its own orbit. This idea deeply appealed to him. “Occasioned by this,” he wrote, “I also began to think of a motion of the earth, and although the idea seemed absurd, still, as others before me had been permitted to assume certain circles in order to explain the motions of the stars, I believed it would be readily permitted me to try whether on the assumption of some motion of the earth better explanations of the revolutions of the heavenly bodies might not be found. And thus I have, assuming the motions which I in the following work attribute to the earth, after long and careful investigation, finally found that when the motions of the other planets are referred to the circulation of the earth and are computed for the revolution of each star, not only do the phenomena necessarily follow therefrom, but the order and magnitude of the stars and all their orbs and the heaven itself are so connected that in no part can anything be transposed without confusion to the rest and to the whole universe.”_

_In 1530 he issue a “Commentariolus” which outlined his theory, but his prudence prompted him to withhold the publication of his great work, “De Orbium Caelestium Revolutionibus,” until 1543. In May of that year the first printed copy was laid on his death-bed._

THE NEW IDEA OF THE UNIVERSE[4]

I can well believe, most holy father, that certain people, when they hear of my attributing motion to the earth in these books of mine, will at once declare that such an opinion ought to be rejected. Now, my own theories do not please me so much as not to consider what others may judge of them. Accordingly, when I began to reflect upon what those persons who accept the stability of the earth, as confirmed by the opinion of many centuries, would say when I claimed that the earth moves, I hesitated for a long time as to whether I should publish that which I have written to demonstrate its motion, or whether it would not be better to follow the example of the Pythagoreans, who used to hand down the secrets of philosophy to their relatives and friends only in oral form. As I well considered all this, I was almost impelled to put the finished work wholly aside, through the scorn I had reason to anticipate on account of the newness and apparent contrariness of my theory to reason.

My friends, however, dissuaded me from such a course and admonished me that I ought to publish my book, which had lain concealed in my possession not only nine years, but already into four times the ninth year. Not a few other distinguished and very learned men asked me to do the same thing, and told me that I ought not, on account of my anxiety, to delay any longer in consecrating my work to the general service of mathematicians.

But your holiness will perhaps not so much wonder that I have dared to bring the results of my night labors to the light of day, after having taken so much care in elaborating them, but is waiting instead to hear how it entered my mind to imagine that the earth moved, contrary to the accepted opinion of mathematicians--nay, almost contrary to ordinary human understanding. Therefore I will not conceal from your holiness that what moved me to consider another way of reckoning the motions of the heavenly bodies was nothing else than the fact that the mathematicians do not agree with one another in their investigations. In the first place, they are so uncertain about the motions of the sun and moon that they cannot find out the length of a full year. In the second place, they apply neither the same laws of cause and effect, in determining the motions of the sun and moon and of the five planets, nor the same proofs. Some employ only concentric circles, others use eccentric and epicyclic ones, with which, however, they do not fully attain the desired end. They could not even discover nor compute the main thing--namely, the form of the universe and the symmetry of its parts. It was with them as if some should, from different places, take hands, feet, head, and other parts of the body, which, although very beautiful, were not drawn in their proper relations, and, without making them in any way correspond, should construct a monster instead of a human being.

Accordingly, when I had long reflected, on this uncertainty of mathematical tradition, I took the trouble to read again the books of all the philosophers I could get hold of, to see if some one of them had not once believed that there were other motions of the heavenly bodies. First I found in Cicero that Niceties had believed in the motion of the earth. Afterwards I found in Plutarch, likewise, that some others had held the same opinion. This induced me also to begin to consider the movability of the earth, and, although the theory appeared contrary to reason, I did so because I knew that others before me had been allowed to assume rotary movements at will, in order to explain the phenomena of these celestial bodies. I was of the opinion that I, too, might be permitted to see whether, by presupposing motion in the earth, more reliable conclusions than hitherto reached could not be discovered for the rotary motions of the spheres. And thus, acting on the hypothesis of the motion which, in the following book, I ascribe to the earth, and by long and continued observations, I have finally discovered that if the motion of the other planets be carried over to the relation of the earth and this is made the basis for the rotation of every star, not only will the phenomena of the planets be explained thereby, but also the laws and the size of the stars; all their spheres and the heavens themselves will appear so harmoniously connected that nothing could be changed in any part of them without confusion in the remaining parts and in the whole universe.

THAT THE UNIVERSE IS SPHERICAL

First we must remark that the universe is spherical in form, partly because this form being a perfect whole requiring no joints, is the most complete of all, partly because it makes the most capacious form, which is best suited to contain and preserve everything; or again because all the constituent parts of the universe, that is the sun, moon, and the planets appear in this form; or because everything strives to attain this form, as appears in the case of drops of water and other fluid bodies if they attempt to define themselves. So no one will doubt that this form belongs to the heavenly bodies.

THAT THE EARTH IS ALSO SPHERICAL

That the earth is also spherical is therefore beyond question, because it presses from all sides upon its center. Although by reason of the elevations of the mountains and the depressions of the valleys a perfect circle cannot be understood, yet this does not affect the general spherical nature of the earth. This appears in the following manner. To those who journey towards the North the north pole of the daily revolution of the heavenly sphere seems gradually to rise, while the opposite seems to sink. Most of the stars in the region of the Bear seem not to set, while some of the southern stars seem not to rise at all. So Italy does not see Canopes which is visible to the Egyptians. And Italy sees the outermost star of the Stream, which our region of a colder zone does not know. On the other hand to those who go towards the South the others seem to rise and those to sink which are high in our region. Moreover, the inclination of the Poles to the diameter of the earth bears always the same relation, which could happen only in the case of a sphere. So it is evident that the earth is included between the two poles, and is therefore spherical in form. Let us add that the inhabitants of the East do not observe the eclipse of the sun or of the moon which occurs in the evening, and the inhabitants of the West those which occur in the morning, while those who dwell between see those later and these earlier. That the water also has the same form can be observed from ships, in that the land which cannot be seen from the deck, is visible from the mast-tree. And conversely if a light be placed at the mast-head it seems to those who remain on the shores gradually to sink and at last still sinking to disappear. It is clear that the water also according to its nature continually presses like the earth downward, and does not rise above its banks higher than its convexity permits. So the land extends above the ocean as much as the land happens to be higher.

WHETHER THE EARTH HAS A CIRCULAR MOTION, AND CONCERNING THE LOCATION OF
THE EARTH

As it has been already shown that the earth has the form of a sphere, we must consider whether a movement also coincides with this form, and what place the earth holds in the universe. Without this there will be no secure results to be obtained in regard to the heavenly phenomena. The great majority of authors of course agree that the earth stands still in the center of the universe, and consider it inconceivable and ridiculous to suppose the opposite. But if the matter is carefully weighed it will be seen that the question is not yet settled and therefore by no means to be regarded lightly. Every change of place which is observed is due, namely, to a movement of the observed object or of the observer, or to movements of both, naturally in different directions, for if the observed object and the observer move in the same manner and in the same direction no movement will be seen. Now it is from the earth that the revolution of the heavens is observed and it is produced for our eyes. Therefore if the earth undergoes no movement this movement must take place in everything outside of the earth, but in the opposite direction than if everything on the earth moved, and of this kind is the daily revolution. So this appears to affect the whole universe, that is, everything outside the earth with the single exception of the earth itself. If, however, one should admit that this movement was not peculiar to the heavens, but that the earth revolved from west to east, and if this was carefully considered in regard to the apparent rising and setting of the sun, the moon and the stars, it would be discovered that this was the real situation. Since the sky, which contains and shelters all things, is the common seat of all things, it is not easy to understand why motion should not be ascribed rather to the thing contained than to the containing, to the located rather than to the location. From this supposition follows another question of no less importance, concerning the place of the earth, although it has been accepted and believed by almost all, that the earth occupies the middle of the universe. But if one should suppose that the earth is not at the center of the universe, that, however, the distance between the two is not great enough to be measured on the orbits of the fixed stars, but would be noticeable and perceptible on the orbit of the sun or of the planets: and if one was further of the opinion that the movements of the planets appeared to be irregular as if they were governed by a center other than the earth, then such an one could perhaps have given the true reasons for the apparently irregular movement. For since the planets appear now nearer and now farther from the earth, this shows necessarily that the center of their revolutions is not the center of the earth: although it does not settle whether the earth increases and decreases the distance from them or they their distance from the earth.

REFUTATION OF THE ARGUMENT OF THE ANCIENTS THAT THE EARTH REMAINS STILL
IN THE MIDDLE OF THE UNIVERSE, AS IF IT WERE ITS CENTER

From this and similar reasons it is supposed that the earth rests at the center of the universe and that there is no doubt of the fact. But if one believed that the earth revolved, he would certainly be of the opinion that this movement was natural and not arbitrary. For whatever is in accord with nature produces results which are the opposite of those produced by force. Things upon which force or an outside power has acted, must be injured and cannot long endure: what happens by nature, however, preserves itself well and exists in the best condition. So Ptolemy feared without good reason that the earth and all earthly objects subject to the revolution would be destroyed by the act of nature, since this latter is opposed to artificial acts, or to what is produced by the human spirit. But why did not he fear the same, and in a much higher degree, of the universe, whose motion must be as much more rapid as the heavens are greater than the earth? Or has the heaven become so immense because it has been driven outward from the center by the inconceivable power of the revolution; while if it stood still, on the contrary, it would collapse and fall together? But surely if this is the case the extent of the heavens would increase infinitely. For the more it is driven higher by the outward force of the movement, so much the more rapid will the movement become, because of the ever increasing circle which must be traversed in 24 hours; and conversely if the movement grows the immensity of the heavens grows. So the velocity would increase the size and the size would increase the velocity unendingly. According to the physical law that the endless cannot wear away nor in any way move, the heavens must necessarily stand still.

But it is said that beyond the sky no body, no place, no vacant space, in fact nothing at all exists; then it is strange that some thing should be enclosed by nothing. But if the heaven is endless and is bounded only by the inner hollow, perhaps this establishes all the more clearly the fact that there is nothing outside the heavens, because everything is within it, but the heaven must then remain unmoved. The highest proof on which one supports the finite character of the universe is its movement. But whether the universe is endless or limited we will leave to the physiologues; this remains sure for us that the earth enclosed between the poles, is bounded by a spherical surface. Why therefore should we not take the position of ascribing to a movement conformable to its nature and corresponding to its form, rather than suppose that the whole universe whose limits are not and cannot be known moves? and why will we not recognize that the appearance of a daily revolution belongs to the heavens, but the actuality to the earth; and that the relation is similar to that of which one says: “We run out of the harbor, the lands and cities retreat from us.” Because if a ship sails along quietly, everything outside of it appears to those on board as if it moved with the motion of the boat, and the boatman thinks that the boat with all on board is standing still, this same thing may hold without doubt of the motion of the earth, and it may seem as if the whole universe revolved. What shall we say, however, of the clouds and other things floating, falling or raising in the air--except that not only does the earth move with the watery elements belonging with it, but also a large part of the atmosphere, and whatever else is in any way connected with the earth; whether it is because the air immediately touching the earth has the same nature as the earth, or that the motion has become imparted to the atmosphere. A like astonishment must be felt if that highest region of the air be supposed to follow the heavenly motion, as shown by those suddenly appearing stars which the Greeks call comets or bearded stars, which belong to that region and which rise and set like other stars. We may suppose that part of the atmosphere, because of its great distance from the earth, has become free from the earthly motion. So the atmosphere which lies close to the earth and all things floating in it would appear to remain still, unless driven here and there by the wind or some other outside force, which chance may bring into play; for how is the wind in the air different from the current in the sea? We must admit that the motion of things rising and falling in the air is in relation to the universe a double one, being always made up of a rectilinear and a circular movement. Since that which seeks of its own weight to fall is essentially earthy, so there is no doubt that these follow the same natural law as their whole; and it results from the same principle that those things which pertain to fire are forcibly driven on high. Earthly fire is nourished with earthly stuff, and it is said that the flame is only burning smoke. But the peculiarity of the fire consists in this that it expands whatever it seizes upon, and it carries this out so consistently that it can in no way and by no machinery be prevented from breaking its bonds and completing its work. The expanding motion, however, is directed from the center outward; therefore if any earthly material is ignited it moves upward. So to each single body belongs a single motion, and this is evinced preferably in a circular direction as long as the single body remains in its natural place and its entirety. In this position the movement is the circular movement which as far as the body itself is concerned is as if it did not occur. The rectilinear motion, however, seizes upon those bodies which have wandered or have been driven from their natural position or have been in any way disturbed. Nothing is so much opposed to the order and form of the world as the displacement of one of its parts. Rectilinear motion takes place only when objects are not properly related, and are not complete according to their nature because they have separated from their whole and have lost their unity. Moreover, objects which have been driven outward or away, leaving out of consideration the circular motion, do not obey a single, simple and regular motion, since they cannot be controlled simply by their lightness or by the force of their weight, and if in falling they have at first a slow movement the rapidity of the motion increases as they fall, while in the case of earthly fire which is forced upwards--and we have no means of knowing any other kind of fire--we will see that its motion is slow as if its earthly origin thereby showed itself. The circular motion, on the other hand, is always regular, because it is not subject to an intermittent cause. Those other objects, however, would cease to be either light or heavy in respect to their natural movement if they reached their own place, and thus they would fit into that movement. Therefore if the circular movement is to be ascribed to the universe as a whole and the rectilinear to the parts, we might say that the revolution is to the straight line as the natural state is to sickness. That Aristotle divided motion into three sorts, that from the center out, that inward toward the center, and that around about the center, appears to be merely a logical convenience, just as we distinguish point, line and surface, although one cannot exist without the others, and none of them are found apart from bodies. This fact is also to be considered, that the condition of immovability is held to be nobler and more divine than that of change and inconstancy, which latter therefore should be ascribed rather to the earth than to the universe, and I would add also that it seems inconsistent to attribute motion to the containing and locating element rather than to the contained and located object, which the earth is. Finally since the planets plainly are at one time nearer and at another time farther from the earth, it would follow, on the theory that the universe revolves, that the movement of the one and same body which is known to take place about a center, that is the center of the earth, must also be directed toward the center from without and from the center outward. The movement about the center must therefore be made more general, and it suffices if that single movement be about its own center. So it appears from all these considerations that the movement of the earth is more probable than its fixity, especially in regard to the daily revolution, which is most peculiar to the earth.

FOOTNOTES:

[Footnote 4: Selections from the Introduction to _De Orbium Caelestium Revolutionibus_.]

III

JOHANN KEPLER

1571-1630

_Tycho Brahe (1546-1601), nobleman of Denmark, studied law at the University of Copenhagen and became attracted to astronomical studies by the occurrence of a predicted eclipse. Constructing his own instruments, he made observations of the stars at Augsburg and Wittenberg, and in 1576 established the first observatory at Huen, where he continued his work for twenty years. Banished from Germany, he was invited by Emperor Rudolph to Prague, where he began his compilation of the Rudolphin Tables which listed many of his observations on the locations of the planets. Hearing of Kepler’s interest in astronomy, he secured the young German’s assistance and assigned to him the study of the planet Mars, which study Kepler continued after Tycho Brahe’s death in 1601._

_Johann Kepler, the son of an innkeeper, was born December 27, 1571, in Württemberg and sent to a local school, from which he was removed when he was nine years old because of his father’s impoverishment. After three years of work in the tavern, he was sent to a monastic school and thence to the University of Tübingen. Although he was very frail in physique, he was a good student and attained high scholarly standing. Becoming interested in the Copernican theory, in 1599 he was invited by Tycho Brahe to become his assistant at Prague._

_Kepler found his master’s tables sufficiently accurate in his efforts to discover some recognizable motion of the planet Mars which would account for its apparent positions. In the course of this work he corrected some of the Ptolemaic ideas which Copernicus had not completely abandoned. The latter retained the epicycle motion of the planets within their larger revolutions in cycles. In comparing this theory with his tables, Kepler found that it would not satisfactorily account for the positions of Mars; and he was therefore led to the long studies and mathematical computations which finally resulted in his discovery of the orbit of Mars, and to the establishment of the first two of his three famous laws: “1. the planet describes an ellipse, the sun being in one focus; 2. the straight line joining the planet to the sun sweeps out equal areas in equal intervals of time.” (Sedgwick and Tyler, pp. 211-213). He published these laws in 1609 in his “Commentaries on the Motions of Mars.”_

_In 1611, when his patron, Emperor Rudolph, was compelled to abdicate, Kepler was left penniless, but he moved to Linz where he was appointed to a professorship. In 1619 he published his “Harmony of the World,” which contained his third law: “The squares of the times of revolution of any two planets (including the earth) about the sun are proportional to the cubes of their mean distances from the sun.” (Sedgwick and Tyler, p. 213). This was the triumph about which he wrote in the year of its discovery, 1618: “What I prophesied twenty-two years ago, as soon as I found the heavenly orbits were of the same number as the five (regular) solids, what I fully believed long before I had seen Ptolemy’s Harmonies, what I promised my friends in the name of this book, which I christened before I was sixteen years old, I urged as an end to be sought, that for which I joined Tycho Brahe, for which I settled at Prague, for which I have spent most of my life at astronomical calculations--at last I have brought to light, and seen to be true beyond my fondest hopes. It is not eighteen months since I saw the first ray of light, three months since the unclouded sun-glorious sight! burst upon me. Let nothing confine me: I will indulge my sacred ecstasy. I will triumph over mankind by the honest confession that I have stolen the golden vases of the Egyptians to raise a tabernacle for my God far away from the lands of Egypt. If you forgive me, I rejoice; if you are angry, I cannot help it. The book is written; the die is cast. Let it be read now or by posterity, I care not which. It may well wait a century for a reader, as God had waited six thousand years for an observer.” Kepler died at Ratisbon, November 15, 1630._

ON THE PRINCIPLES OF ASTRONOMY[5]

What is _astronomy_? It is the science of treating of the causes of those celestial appearances which we who live on the earth observe and which mark the changes of times and seasons; by the studying of which we are able to predict for the future the face of the heavens, that is, the stellar phenomena, and to assign fixed dates for those which have occurred in the past.

_Why is it called astronomy?_ From the law (νουος) or governance of the stars (ἀστρα), that is, of the motions in which the stars move, just as economy is named from the law of domestic affairs (οἰκονουία) and paedonomy (παιδονουία) from the ruling of youths.

_What is the relation of this science to the other sciences?_ 1) It is a branch of physics because it investigates the causes of natural objects and events, and because among its subjects are the motions of the heavenly bodies, and because it has the same end as physics, to inquire into the conformation of the world and its parts.

2) Astronomy is the soul of geography and hydrography, for the various appearances of the sky in various districts and regions of the earth and sea are known only by astronomy.

3) Chronology is dependent upon it, because the movements of the heavenly bodies prescribe seasons and years and date the histories.

4) Meteorology is also its subordinate, for the stars move and influence this sublunary nature and even men themselves.

5) It includes a large part of optics, because it has a subject in common with that; that is, the light of the heavenly bodies, and because it corrects many errors of sight in regard to the character of the earth and its motions.

6) It is, however, subordinate to the general subject of mathematics and uses arithmetic and geometry as its two wings, studying the extent and form of the bodies and motions of the universe and computing the periods, by these means expediting its demonstrations and reducing them to use and practical value.

_How many, then, are the branches of astronomical study?_ The departments of the study of astronomy are five; historical, in the matter of observations, optical as to the hypothesis, physical as to the causes of the hypotheses, arithmetical as to the tables and calculations, mechanical as to its instruments.

* * * * *

_Since we must begin with appearances, explain how the world seems to be made up._ The world is commonly thought, accepting the testimony of the eyes, to be an immense structure consisting of two parts, the earth and the sky.

_What do men imagine concerning the figure of the earth?_ The earth seems to be a broad plane extending in a circle in every direction around the spectator. And from this appearance of a plane bounded by a great circle the appellation, _orbis terrarum_, the circle of the earth, has arisen, and has been taken over by the Scripture and among other nations.

_What do men imagine to be the center of the earth?_ Each nation, unless it has become familiar with the notion of the circle, thinks by the instinct of nature and the error of vision that its country is in the center or middle of this plane circle. So the common people among the Jews believe still that Jerusalem, the earliest home of their race, is situated at the center of the world.

_What do men think about the waters?_ Since men proceeding as far as possible in any direction finally came upon the ocean, some have thought that the earth is like a disc swimming in the waters, and that the waters are held up by the lower part of the sky, whence poets have called the ocean, the father of all things. Others believe that a strip of land surrounds the ocean which keeps the water from flowing away, and these suppose there is land under the water, saying that the water is held up by the earth. Besides these there are still others who, since the ocean seems higher than the land if it is looked at from the edge of the shore, believe that the earth is, as it were, sunk in the waters and supernaturally guarded by the omnipotence of God lest the waters rushing in from the deep should overwhelm it.

_What do men imagine to be under both the land and the waters?_ There has been great discussion among men marveling concerning the foundation which could bear up the great mass of the earth so that it should remain for so many centuries firm and immovable and should not sink; and Heraclitus among the early philosophers, and Lactantius among the ecclesiastics said that it reached down to the lowest root of things.

_How about the other part of the world, the sky and its extent?_ Men have thought that the sky was not much larger than the earth, and indeed was connected with the earth and the ocean at the circumference of the circle, so that it bounded the earth; and that anyone going that far, if it could be done, would run up against the sky, blocking further progress. With this idea of men the Scriptures also agreed.

So also the poets said that Mt. Atlas, a lofty mountain on the farthest shore of Africa, bore up the sky on his shoulders, and Homer placed the Aethiopeans at the extremities of the rising and setting sun, thinking that because of the contiguity of the earth and sky there, the sun was so close to them that it burned their skin.

_What form do they ascribe to the sky?_ The eyes ascribe to the sky the shape of a tent, extending over our heads and beyond the sun, moon and stars, or rather the shape of an arch overspanning the terrestrial plane, with a long curve, so that the part of the sky just over the head of the spectator is much nearer to him than the part that touches the mountains.

_What have men conceived in regard to the motion of the sky?_ Whether the sky moves or stands still is not apparent to the sight because the tenuity of its substance escapes the eyes, unless indeed those things appear to stand still in which the eye can perceive no variation. But the changing positions of the sun, moon and stars in relation to the ends of the earth was apparent to the eyes. For the sun seems to emerge from an opening between the sky and the immovable mountains and ocean, as if coming out of a chamber, and having traversed the vault of the sky seems to sink again in the opposite region; so also the moon, and the planets, and the whole host of stars proceed as if strictly marshalled and drawn up in line, first one and then the other marching along, each in his order and place.

And so, since the ocean lies beyond the extreme lands, the mass of men have thought that the sun plunges into the ocean and is extinguished, and from the opposite region a new sun issues forth daily from the ocean. The poets have used this figure in their creations. But, indeed, there have been even philosophers who have declared that on the farthest shores of Lusitania could be heard the roar of the ocean extinguishing the flames of the sun, as Strabo recounts.

* * * * *

_I understand the forms of the sky and the earth and the atmosphere surrounding the earth, also the place of the earth in the universe; now I would ask what causes the stars to seem to rise daily from the one part of the horizon and to sink in the opposite part; the motion of the sky or of the earth?_ The astronomy of Copernicus shows that our sight has led us astray in regard to this motion; for the stars do not actually come up from beyond the mountains and climb toward the zenith, but rather the mountains which surround us and which are a part of the surface of the earth are revolved along with the whole globe about its axis from west to east and by this revolution the immovable stars of the east are disclosed to us one after the other, and those of the west are obscured, so the stars are not passing over us, but the vertical point is moving through the fixed stars.

_You say that by this marvelous hypothesis may be explained satisfactorily all the phenomena of the first motion and the spherical theory._ Just so, and that is the scope of this section, to demonstrate in fact what has been suggested in words.

_How do you expect to be able to prove this absurd hypothesis, and by what arguments?_ It is possible to demonstrate that this first motion results from the revolution of the earth about its axis, while the heavenly bodies are at rest (as far as this first motion is concerned), by seven kinds of arguments: 1) from the subject of the motion; 2) from the velocity of the motion; 3) from the equableness of the motion; 4) from the cause of the motion, or the moving principle; 5) from the motive instruments, that is, the axis and the poles; 6) from the object of the first motion; and 7) from the indications or results.

_Demonstrate it then from the subject of the motion._ Nature does not seek difficult means when she can use simple ones. Now, by the rotation of the earth, a very small body, about its axis, toward the east, the same thing is accomplished as by the rotation of the immense universe about its axis toward the west. Just as it is more likely that a man’s head turns in the auditorium than that the auditorium is turned about his head, so it is more credible that the earth is rotating from west to east, than that the rest of the machine of the universe is revolved from east to west, since in both cases the same thing results.

If the first motion is in the heavenly bodies, then they are subject to two motions, one common to the whole universe, the other particular to each sphere; but it is much more probable that the two motions should be distinct in regard to their subjects, so that the second set of motions, which is multifold, should belong to each sphere, and the first, which is single, should belong to the single body of the earth, and to it alone.

_Why cannot the whole machinery of the universe be moved?_ The universe is either infinite or finite. Suppose it to be the former, according to the opinion of William Gilbert, who thinks that the omnipotence of God is illustrated in this that the universe extends outward infinitely, so that the infinite power of the creator would be recognized from the infinite extent of the creation. Although this may be refuted by metaphysical arguments, no argument on either side can be drawn from astronomy, in which trust is placed rather in the evidence of the senses than in abstract reasonings not dependent on observation. But supposing this universe to be infinite, Aristotle has shown that the whole universe should not be moved about in a revolution since it is the whole.

But let the universe be finite; then there is nothing outside the universe which would locate the universe but should remain quiet itself. Where there is nothing that rests there is no motion. For 1) motion is the separation of a movable thing from its place and its transfer to another place: 2) the motion of a machine about an axis and quiescent poles cannot be grasped by the mind where there is nothing in respect to which the poles remain still.

FOOTNOTES:

[Footnote 5: From _The Epitome of Astronomy_.]

IV

GALILEO GALILEI

1564-1642

_Galileo Galilei, born at Pisa, February 15, 1564, was the son of a mathematician who, seeing no future in that profession, had him educated for the practice of medicine. But when Galileo was about eighteen years of age, while observing a large lamp swinging in the Pisa cathedral, he noticed that, regardless of the length of the oscillation, the time did not vary. In spite of his father’s discouragements, therefore, he became absorbed in mathematics and abandoned the study of medicine. Applying himself to the study of motion, he performed his famous experiment of letting bodies of different weights fall from the leaning tower of Pisa, proving that things of unequal weight, if heavier than the resistance of air, fall with the same speed. The doctrine of inertia which he deduced from this and similar experiments decisively answered the opponents of Copernicus; for the principle stated that bodies would continue to move in the same direction forever unless their course was disturbed or opposed by another force, and that the motion of bodies resulted from independent forces operating upon them. His treatise on the center of gravity in solids earned him a lectureship at the University of Pisa._

_Meeting malignant opposition at Pisa, he secured the chair of mathematics at Padua (which he held from 1592 to 1610) and there continued his observations and experiments in physics and chemistry. He succeeded in making a crude thermometer in 1600. In 1609 he learned that Hans Lippershey, an optician of Middleburg, had succeeded in making a telescope. He thereupon made one of his own and improved it until it had a power of magnifying thirty-two times, enabling him to discover the mountainous surface of the moon, the moons of the planet Jupiter, the fact that Venus showed different sides like the moon, and that many small stars made up the Milky Way._

_In 1610 he left Padua for Florence, and by 1613 openly declared his acceptance of Copernican ideas. Immediately he was opposed by theologians, and after being given an opportunity to renounce his adherence to the new system of astronomy, was sentenced in 1616 not to hold, teach, or defend it. In 1623, when his friend Maffeo was made Pope Urban VIII, he wrote his dialogues on the system of the world. He had much difficulty in getting them published and succeeded only when he assured the authorities that they were not heretical. It was quite evident, however, that the dialogues were slightly concealed arguments for the acceptance of the Copernican system and consequently in 1633 he was summoned before the Inquisition and compelled to renounce his heresy. In 1637, a few months after he had discovered the librations of the moon, he lost his sight. He died five years later, January 8, 1642._

THE COPERNICAN VERSUS THE PTOLEMAIC ASTRONOMIES[6]

Formerly I used frequently to visit the marvelous city of Venice and to meet there Signore Giovan Francesco Sagredo, a man of most distinguished ancestry and remarkable intelligence. Thither also came from Florence, Signore Filippo Salviati, whose least claim to renown was his noble blood and great wealth; a noble mind, that held no enjoyment of greater price than that of study and thought. With both of these men I often discussed these questions, in the presence of a Peripatetic philosopher, who apparently valued the acquisition of knowledge in no way in so high a degree, as he did the renown which his interpretations of Aristotle had gained for him.

Now that cruel death has robbed the cities of Venice and Florence of these two enlightened men in the bloom of their years, I have endeavored, as far as my weak powers may permit, to perpetuate their fame in these pages by making them the speakers in this dialogue. The valiant Peripatetic also shall not fail to appear; because of his over-weaning love for the commentary of Simplicius, it seemed permissible to omit his own name and let him pass under that of his favorite author. May the souls of these two great men accept this public testimony of my undying love; may the recollection of their eloquence aid me in setting down for posterity the spoken discussions.

SECOND DAY

SALVIATI: We departed yesterday so often and so far from the direct path of our discussion, that I can scarcely return to the right point and proceed without your help.

SAGREDO: I find it quite intelligible that you are somewhat at a loss, since you have had your head so full of both the things already brought forward and things still to be discussed. I, however, who as merely a listener have in mind only the things already discussed, may I hope set our investigation straight by a brief summary of what has been gone over. So, if my memory fails not, the chief result of our yesterday’s conversation was that we tested thoroughly which of the two theories was the more probable and better grounded; that according to which the substance of the heavenly bodies is unproducible, indestructible, unchangeable, intangible, in brief not subject to any variation aside from change of location, and so presents a fifth element which is entirely distinct from our elementary, producible, destructible, changeable bodies; or the other view, according to which an incongruity between parts of the universe is rejected, our earth rather enjoys the same privileges as the rest of the constituent bodies of the universe, in a word, is a freely moving ball just as the moon, Jupiter, Venus, or any other planet. Finally we noticed the many similarities in particular between the earth and the moon, and of course with the moon more than any other planet because of the closer and more definite knowledge which we possess of it by reason of its less distance. Since we agreed that this second opinion possessed the greater probability, the logical consequence, it seems to me, is that we should investigate the question whether we should hold the world immovable, as has been formerly believed in general, or movable as some ancient philosophers believed and as some recent ones suppose: and if movable, how its movement could have been produced.

SALV.: Let us begin our discussion with the admission that whatever sort of motion may be ascribed the earth, we, as its inhabitants and therefore partakers in the movement, would be unconscious of it, as if it did not occur, since we can only take into consideration earthly things. Therefore it is necessary that this movement should seem to belong to all the other bodies and visible objects in common which, separated from the earth, have no share in its movement. The correct method of determining whether movement is to be attributed to the earth, and what movement, is that one should inquire and observe whether an apparent movement can be ascribed to the bodies outside of the earth, which belongs to all of them in the same degree. So a movement which, for example, can be supposed of the moon, and not of Venus or Jupiter or other stars, cannot be peculiar to the earth. Now there is such a general movement governing all other objects, namely that which the sun, moon, planets, fixed stars, in a word the whole universe with the single exception of the earth, seems to follow from east to west within the space of twenty-four hours. This, at least at first glance, may be just as well attributed to the earth alone, as to the rest of the entire universe except the earth.

SAGR.: I understand clearly that your suggestion is correct. An objection, however, forces itself upon me that I cannot solve. That is, since Copernicus ascribes to the earth a further movement aside from the daily one, according to the above mentioned principle this should be apparently un-noticeable on the earth, but should be visible in the rest of the universe. I come then to the conclusion that either he plainly erred when he ascribed to the earth a movement to which no counterpart is apparent in the firmament, or else such a movement exists, and then Ptolemaus is guilty of a second error in that he did not refute with arguments this movement as well as that daily rotation.

SALV.: Your objection is very just. If we take up this other movement, you shall see how much superior in intelligence was Copernicus to Ptolemaus, in that he saw what this one did not, namely how wonderfully this second motion is reflected in the rest of the heavenly bodies. For the present, however, we will leave this aside and return to our first consideration. Proceeding from the most general suppositions, I will present the arguments which seem to favor the motion of the earth, in order then to hear the opposing arguments of Signore Simplicio. First, then, when we consider the immense circumference of the stellar sphere in comparison with the smallness of the earth, which is contained in that several million times, and therefore regard the velocity of motion which would be necessary for an entire revolution in the course of a day and night, I am unable to understand how any one could hold it more reasonable and credible that it is this whole stellar sphere that moves and that the earth remains still.

SAGR.: Even if universal phenomena which depend upon these movements could be explained as readily by the one hypothesis as by the other, yet by the first general impression I would regard as more unreasonable the view that the whole universe moves; just as if any one should climb to the top of your dome for the purpose of getting a view of the city and its environs and then should demand that the whole region be made to move around him to save him the trouble of turning his head. In any event, there would have to be great advantages connected with this theory, which were lacking in the other, in order that such an absurdity should be balanced and outweighed and should appear more credible than the opposite opinion. But Aristotle, Ptolemaus, and Signore Simplicio must find such advantages in their theory, and I should be glad if we might hear these advantages if they exist, or if they do not, that some one would explain to me why they do not and cannot exist.