predecessor of Kepler and Newton, did not come from a noble family,
as certain other early astronomers have done, for his father was a
tradesman. Chroniclers are, however, careful to tell us that one of
his uncles was a bishop. We are not acquainted with any of those
details of his childhood or youth which are often of such interest in
other cases where men have risen to exalted fame. It would appear
that the young Nicolaus, for such was his Christian name, received
his education at home until such time as he was deemed sufficiently
advanced to be sent to the University at Cracow. The education that
he there obtained must have been in those days of a very primitive
description, but Copernicus seems to have availed himself of it to
the utmost. He devoted himself more particularly to the study of
medicine, with the view of adopting its practice as the profession of
his life. The tendencies of the future astronomer were, however,
revealed in the fact that he worked hard at mathematics, and, like
one of his illustrious successors, Galileo, the practice of the art
of painting had for him a very great interest, and in it he obtained
some measure of success.
By the time he was twenty-seven years old, it would seem that
Copernicus had given up the notion of becoming a medical
practitioner, and had resolved to devote himself to science. He was
engaged in teaching mathematics, and appears to have acquired some
reputation. His growing fame attracted the notice of his uncle the
bishop, at whose suggestion Copernicus took holy orders, and he was
presently appointed to a canonry in the cathedral of Frauenburg, near
the mouth of the Vistula.
To Frauenburg, accordingly, this man of varied gifts retired.
Possessing somewhat of the ascetic spirit, he resolved to devote his
life to work of the most serious description. He eschewed all
ordinary society, restricting his intimacies to very grave and
learned companions, and refusing to engage in conversation of any
useless kind. It would seem as if his gifts for painting were
condemned as frivolous; at all events, we do not learn that he
continued to practise them. In addition to the discharge of his
theological duties, his life was occupied partly in ministering
medically to the wants of the poor, and partly with his researches in
astronomy and mathematics. His equipment in the matter of
instruments for the study of the heavens seems to have been of a very
meagre description. He arranged apertures in the walls of his house
at Allenstein, so that he could observe in some fashion the passage
of the stars across the meridian. That he possessed some talent for
practical mechanics is proved by his construction of a contrivance
for raising water from a stream, for the use of the inhabitants of
Frauenburg. Relics of this machine are still to be seen.
[PLATE: COPERNICUS.]
The intellectual slumber of the Middle Ages was destined to be
awakened by the revolutionary doctrines of Copernicus. It may be
noted, as an interesting circumstance, that the time at which he
discovered the scheme of the solar system has coincided with a
remarkable epoch in the world's history. The great astronomer had
just reached manhood at the time when Columbus discovered the new
world.
Before the publication of the researches of Copernicus, the orthodox
scientific creed averred that the earth was stationary, and that the
apparent movements of the heavenly bodies were indeed real
movements. Ptolemy had laid down this doctrine 1,400 years before.
In his theory this huge error was associated with so much important
truth, and the whole presented such a coherent scheme for the
explanation of the heavenly movements, that the Ptolemaic theory was
not seriously questioned until the great work of Copernicus
appeared. No doubt others, before Copernicus, had from time to time
in some vague fashion surmised, with more or less plausibility, that
the sun, and not the earth, was the centre about which the system
really revolved. It is, however, one thing to state a scientific
fact; it is quite another thing to be in possession of the train of
reasoning, founded on observation or experiment, by which that fact
may be established. Pythagoras, it appears, had indeed told his
disciples that it was the sun, and not the earth, which was the
centre of movement, but it does not seem at all certain that
Pythagoras had any grounds which science could recognise for the
belief which is attributed to him. So far as information is
available to us, it would seem that Pythagoras associated his scheme
of things celestial with a number of preposterous notions in natural
philosophy. He may certainly have made a correct statement as to
which was the most important body in the solar system, but he
certainly did not provide any rational demonstration of the fact.
Copernicus, by a strict train of reasoning, convinced those who would
listen to him that the sun was the centre of the system. It is
useful for us to consider the arguments which he urged, and by which
he effected that intellectual revolution which is always connected
with his name.
The first of the great discoveries which Copernicus made relates to
the rotation of the earth on its axis. That general diurnal
movement, by which the stars and all other celestial bodies appear to
be carried completely round the heavens once every twenty-four hours,
had been accounted for by Ptolemy on the supposition that the
apparent movements were the real movements. As we have already seen,
Ptolemy himself felt the extraordinary difficulty involved in the
supposition that so stupendous a fabric as the celestial sphere
should spin in the way supposed. Such movements required that many
of the stars should travel with almost inconceivable velocity.
Copernicus also saw that the daily rising and setting of the heavenly
bodies could be accounted for either by the supposition that the
celestial sphere moved round and that the earth remained at rest, or
by the supposition that the celestial sphere was at rest while the
earth turned round in the opposite direction. He weighed the
arguments on both sides as Ptolemy had done, and, as the result of
his deliberations, Copernicus came to an opposite conclusion from
Ptolemy. To Copernicus it appeared that the difficulties attending
the supposition that the celestial sphere revolved, were vastly
greater than those which appeared so weighty to Ptolemy as to force
him to deny the earth's rotation.
Copernicus shows clearly how the observed phenomena could be
accounted for just as completely by a rotation of the earth as by a
rotation of the heavens. He alludes to the fact that, to those on
board a vessel which is moving through smooth water, the vessel
itself appears to be at rest, while the objects on shore seem to be
moving past. If, therefore, the earth were rotating uniformly, we
dwellers upon the earth, oblivious of our own movement, would wrongly
attribute to the stars the displacement which was actually the
consequence of our own motion.
Copernicus saw the futility of the arguments by which Ptolemy had
endeavoured to demonstrate that a revolution of the earth was
impossible. It was plain to him that there was nothing whatever to
warrant refusal to believe in the rotation of the earth. In his
clear-sightedness on this matter we have specially to admire the
sagacity of Copernicus as a natural philosopher. It had been urged
that, if the earth moved round, its motion would not be imparted to
the air, and that therefore the earth would be uninhabitable by the
terrific winds which would be the result of our being carried through
the air. Copernicus convinced himself that this deduction was
preposterous. He proved that the air must accompany the earth, just
as his coat remains round him, notwithstanding the fact that he is
walking down the street. In this way he was able to show that all a
priori objections to the earth's movements were absurd, and therefore
he was able to compare together the plausibilities of the two rival
schemes for explaining the diurnal movement.
[PLATE: FRAUENBURG, FROM AN OLD PRINT.]
Once the issue had been placed in this form, the result could not be
long in doubt. Here is the question: Which is it more likely--that
the earth, like a grain of sand at the centre of a mighty globe,
should turn round once in twenty-four hours, or that the whole of
that vast globe should complete a rotation in the opposite direction
in the same time? Obviously, the former is far the more simple
supposition. But the case is really much stronger than this. Ptolemy
had supposed that all the stars were attached to the surface of a
sphere. He had no ground whatever for this supposition, except that
otherwise it would have been well-nigh impossible to have devised a
scheme by which the rotation of the heavens around a fixed earth
could have been arranged. Copernicus, however, with the just
instinct of a philosopher, considered that the celestial sphere,
however convenient from a geometrical point of view, as a means of
representing apparent phenomena, could not actually have a material
existence. In the first place, the existence of a material celestial
sphere would require that all the myriad stars should be at exactly
the same distances from the earth. Of course, no one will say that
this or any other arbitrary disposition of the stars is actually
impossible, but as there was no conceivable physical reason why the
distances of all the stars from the earth should be identical, it
seemed in the very highest degree improbable that the stars should be
so placed.
Doubtless, also, Copernicus felt a considerable difficulty as to the
nature of the materials from which Ptolemy's wonderful sphere was to
be constructed. Nor could a philosopher of his penetration have
failed to observe that, unless that sphere were infinitely large,
there must have been space outside it, a consideration which would
open up other difficult questions. Whether infinite or not, it was
obvious that the celestial sphere must have a diameter at least many
thousands of times as great as that of the earth. From these
considerations Copernicus deduced the important fact that the stars
and the other celestial bodies must all be vast objects. He was thus
enabled to put the question in such a form that it could hardly
receive any answer but the correct one. Which is it more rational to
suppose, that the earth should turn round on its axis once in
twenty-four hours, or that thousands of mighty stars should circle
round the earth in the same time, many of them having to describe
circles many thousands of times greater in circumference than the
circuit of the earth at the equator? The obvious answer pressed upon
Copernicus with so much force that he was compelled to reject
Ptolemy's theory of the stationary earth, and to attribute the
diurnal rotation of the heavens to the revolution of the earth on its
axis.
Once this tremendous step had been taken, the great difficulties
which beset the monstrous conception of the celestial sphere
vanished, for the stars need no longer be regarded as situated at
equal distances from the earth. Copernicus saw that they might lie
at the most varied degrees of remoteness, some being hundreds or
thousands of times farther away than others. The complicated
structure of the celestial sphere as a material object disappeared
altogether; it remained only as a geometrical conception, whereon we
find it convenient to indicate the places of the stars. Once the
Copernican doctrine had been fully set forth, it was impossible for
anyone, who had both the inclination and the capacity to understand
it, to withhold acceptance of its truth. The doctrine of a
stationary earth had gone for ever.
Copernicus having established a theory of the celestial movements
which deliberately set aside the stability of the earth, it seemed
natural that he should inquire whether the doctrine of a moving earth
might not remove the difficulties presented in other celestial
phenomena. It had been universally admitted that the earth lay
unsupported in space. Copernicus had further shown that it possessed
a movement of rotation. Its want of stability being thus recognised,
it seemed reasonable to suppose that the earth might also have some
other kinds of movements as well. In this, Copernicus essayed to
solve a problem far more difficult than that which had hitherto
occupied his attention. It was a comparatively easy task to show how
the diurnal rising and setting could be accounted for by the rotation
of the earth. It was a much more difficult undertaking to
demonstrate that the planetary movements, which Ptolemy had
represented with so much success, could be completely explained by
the supposition that each of those planets revolved uniformly round
the sun, and that the earth was also a planet, accomplishing a
complete circuit of the sun once in the course of a year.
[PLATE: EXPLANATION OF PLANETARY MOVEMENTS.]
It would be impossible in a sketch like the present to enter into any
detail as to the geometrical propositions on which this beautiful
investigation of Copernicus depended. We can only mention a few of
the leading principles. It may be laid down in general that, if an
observer is in movement, he will, if unconscious of the fact,
attribute to the fixed objects around him a movement equal and
opposite to that which he actually possesses. A passenger on a
canal-boat sees the objects on the banks apparently moving backward
with a speed equal to that by which he is himself advancing
forwards. By an application of this principle, we can account for
all the phenomena of the movements of the planets, which Ptolemy had
so ingeniously represented by his circles. Let us take, for
instance, the most characteristic feature in the irregularities of
the outer planets. We have already remarked that Mars, though
generally advancing from west to east among the stars, occasionally
pauses, retraces his steps for awhile, again pauses, and then resumes
his ordinary onward progress. Copernicus showed clearly how this
effect was produced by the real motion of the earth, combined with
the real motion of Mars. In the adjoining figure we represent a
portion of the circular tracks in which the earth and Mars move in
accordance with the Copernican doctrine. I show particularly the
case where the earth comes directly between the planet and the sun,
because it is on such occasions that the retrograde movement (for so
this backward movement of Mars is termed) is at its highest. Mars is
then advancing in the direction shown by the arrow-head, and the
earth is also advancing in the same direction. We, on the earth,
however, being unconscious of our own motion, attribute, by the
principle I have already explained, an equal and opposite motion to
Mars. The visible effect upon the planet is, that Mars has two
movements, a real onward movement in one direction, and an apparent
movement in the opposite direction. If it so happened that the earth
was moving with the same speed as Mars, then the apparent movement
would exactly neutralise the real movement, and Mars would seem to be
at rest relatively to the surrounding stars. Under the actual
circumstances represented, however, the earth is moving faster than
Mars, and the consequence is, that the apparent movement of the
planet backwards exceeds the real movement forwards, the net result
being an apparent retrograde movement.
With consummate skill, Copernicus showed how the applications of the
same principles could account for the characteristic movements of the
planets. His reasoning in due time bore down all opposition. The
supreme importance of the earth in the system vanished. It had now
merely to take rank as one of the planets.
The same great astronomer now, for the first time, rendered something
like a rational account of the changes of the seasons. Nor did
certain of the more obscure astronomical phenomena escape his
attention.
He delayed publishing his wonderful discoveries to the world until he
was quite an old man. He had a well-founded apprehension of the
storm of opposition which they would arouse. However, he yielded at
last to the entreaties of his friends, and his book was sent to the
press. But ere it made its appearance to the world, Copernicus was
seized by mortal illness. A copy of the book was brought to him on
May 23, 1543. We are told that he was able to see it and to touch
it, but no more, and he died a few hours afterwards. He was buried
in that Cathedral of Frauenburg, with which his life had been so
closely associated.
TYCHO BRAHE.
The most picturesque figure in the history of astronomy is
undoubtedly that of the famous old Danish astronomer whose name
stands at the head of this chapter. Tycho Brahe was alike notable
for his astronomical genius and for the extraordinary vehemence of a
character which was by no means perfect. His romantic career as a
philosopher, and his taste for splendour as a Danish noble, his
ardent friendships and his furious quarrels, make him an ideal
subject for a biographer, while the magnificent astronomical work
which he accomplished, has given him imperishable fame.
The history of Tycho Brahe has been admirably told by Dr. Dreyer, the
accomplished astronomer who now directs the observatory at Armagh,
though himself a countryman of Tycho. Every student of the career of
the great Dane must necessarily look on Dr. Dreyer's work as the
chief authority on the subject. Tycho sprang from an illustrious
stock. His family had flourished for centuries, both in Sweden and
in Denmark, where his descendants are to be met with at the present
day. The astronomer's father was a privy councillor, and having
filled important positions in the Danish government, he was
ultimately promoted to be governor of Helsingborg Castle, where he
spent the last years of his life. His illustrious son Tycho was born
in 1546, and was the second child and eldest boy in a family of ten.
It appears that Otto, the father of Tycho, had a brother named
George, who was childless. George, however, desired to adopt a boy
on whom he could lavish his affection and to whom he could bequeath
his wealth. A somewhat singular arrangement was accordingly entered
into by the brothers at the time when Otto was married. It was
agreed that the first son who might be born to Otto should be
forthwith handed over by the parents to George to be reared and
adopted by him. In due time little Tycho appeared, and was
immediately claimed by George in pursuance of the compact. But it
was not unnatural that the parental instinct, which had been dormant
when the agreement was made, should here interpose. Tycho's father
and mother receded from the bargain, and refused to part with their
son. George thought he was badly treated. However, he took no
violent steps until a year later, when a brother was born to Tycho.
The uncle then felt no scruple in asserting what he believed to be
his rights by the simple process of stealing the first-born nephew,
which the original bargain had promised him. After a little time it
would seem that the parents acquiesced in the loss, and thus it was
in Uncle George's home that the future astronomer passed his
childhood.
When we read that Tycho was no more than thirteen years old at the
time he entered the University of Copenhagen, it might be at first
supposed that even in his boyish years he must have exhibited some of
those remarkable talents with which he was afterwards to astonish the
world. Such an inference should not, however, be drawn. The fact is
that in those days it was customary for students to enter the
universities at a much earlier age than is now the case. Not,
indeed, that the boys of thirteen knew more then than the boys of
thirteen know now. But the education imparted in the universities at
that time was of a much more rudimentary kind than that which we
understand by university education at present. In illustration of
this Dr. Dreyer tells us how, in the University of Wittenberg, one of
the professors, in his opening address, was accustomed to point out
that even the processes of multiplication and division in arithmetic
might be learned by any student who possessed the necessary
diligence.
It was the wish and the intention of his uncle that Tycho's education
should be specially directed to those branches of rhetoric and
philosophy which were then supposed to be a necessary preparation for
the career of a statesman. Tycho, however, speedily made it plain to
his teachers that though he was an ardent student, yet the things
which interested him were the movements of the heavenly bodies and
not the subtleties of metaphysics.
[PLATE: TYCHO BRAHE.]
On the 21st October, 1560, an eclipse of the sun occurred, which was
partially visible at Copenhagen. Tycho, boy though he was, took the
utmost interest in this event. His ardour and astonishment in
connection with the circumstance were chiefly excited by the fact
that the time of the occurrence of the phenomenon could be predicted
with so much accuracy. Urged by his desire to understand the matter
thoroughly, Tycho sought to procure some book which might explain
what he so greatly wanted to know. In those days books of any kind
were but few and scarce, and scientific books were especially
unattainable. It so happened, however, that a Latin version of
Ptolemy's astronomical works had appeared a few years before the
eclipse took place, and Tycho managed to buy a copy of this book,
which was then the chief authority on celestial matters. Young as
the boy astronomer was, he studied hard, although perhaps not always
successfully, to understand Ptolemy, and to this day his copy of the
great work, copiously annotated and marked by the schoolboy hand, is
preserved as one of the chief treasures in the library of the
University at Prague.
After Tycho had studied for about three years at the University of
Copenhagen, his uncle thought it would be better to send him, as was
usual in those days, to complete his education by a course of study
in some foreign university. The uncle cherished the hope that in
this way the attention of the young astronomer might be withdrawn
from the study of the stars and directed in what appeared to him a
more useful way. Indeed, to the wise heads of those days, the
pursuit of natural science seemed so much waste of good time which
might otherwise be devoted to logic or rhetoric or some other branch
of study more in vogue at that time. To assist in this attempt to
wean Tycho from his scientific tastes, his uncle chose as a tutor to
accompany him an intelligent and upright young man named Vedel, who
was four years senior to his pupil, and accordingly, in 1562, we find
the pair taking up their abode at the University of Leipzig.
The tutor, however, soon found that he had undertaken a most hopeless
task. He could not succeed in imbuing Tycho with the slightest taste
for the study of the law or the other branches of knowledge which
were then thought so desirable. The stars, and nothing but the
stars, engrossed the attention of his pupil. We are told that all
the money he could obtain was spent secretly in buying astronomical
books and instruments. He learned the name of the stars from a
little globe, which he kept hidden from Vedel, and only ventured to
use during the latter's absence. No little friction was at first
caused by all this, but in after years a fast and enduring friendship
grew up between Tycho and his tutor, each of whom learned to respect
and to love the other.
Before Tycho was seventeen he had commenced the difficult task of
calculating the movements of the planets and the places which they
occupied on the sky from time to time. He was not a little surprised
to find that the actual positions of the planets differed very widely
from those which were assigned to them by calculations from the best
existing works of astronomers. With the insight of genius he saw
that the only true method of investigating the movements of the
heavenly bodies would be to carry on a protracted series of
measurements of their places. This, which now seems to us so
obvious, was then entirely new doctrine. Tycho at once commenced
regular observations in such fashion as he could. His first
instrument was, indeed, a very primitive one, consisting of a simple
pair of compasses, which he used in this way. He placed his eye at
the hinge, and then opened the legs of the compass so that one leg
pointed to one star and the other leg to the other star. The compass
was then brought down to a divided circle, by which means the number
of degrees in the apparent angular distance of the two stars was
determined.