Nicholas Copernicus was born February 19, 1473, in Poland. He entered the
University of Krakow in 1491, then in 1495 went to Padua and studied medicine. In 1500 he
was called to Rome and took the chair of mathematics there. He began to believe that the
earth went round the sun about 1507 and from that time until his death worked, more or
less intermittently, on his exposition of his theory. He delayed the publication of this
exposition because of fear of being accused of heresy. Copernicus died May 24, 1543, just
as his book was published. The knowledge of the time was not sufficient to prove his
theory; his great argument for it was from its simplicity as compared to the epicycle
hypothesis.
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 Canopus 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 the 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 masthead 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 arguments 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 he not 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
twenty-four 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 rising
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 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 more noble and 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 clement 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.
