Great Astronomers - Robert Stawell Ball (the little red hen ebook .TXT) 📗
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movements they performed by the supposition that each planet had
perfect rotation in a circle of its own, which circle itself had
perfect movement around the earth in the centre.
It is somewhat strange that Ptolemy did not advance one step
further, as by so doing he would have given great simplicity to
his system. He might, for instance, have represented the
movements of Venus equally well by putting the centre of the
moving circle at the sun itself, and correspondingly enlarging the
circle in which Venus revolved. He might, too, have arranged that
the several circles which the outer planets traversed should also
have had their centres at the sun. The planetary system would
then have consisted of an earth fixed at the centre, of a sun
revolving uniformly around it, and of a system of planets each
describing its own circle around a moving centre placed in the
sun. Perhaps Ptolemy had not thought of this, or perhaps he may
have seen arguments against it. This important step was, however,
taken by Tycho. He considered that all the planets revolved
around the sun in circles, and that the sun itself, bearing all
these orbits, described a mighty circle around the earth. This
point having been reached, only one more step would have been
necessary to reach the glorious truths that revealed the structure
of the solar system. That last step was taken by Copernicus.
COPERNICUS
[PLATE: THORN, FROM AN OLD PRINT.]
The quaint town of Thorn, on the Vistula, was more than two
centuries old when Copernicus was born there on the 19th of
February, 1473. The situation of this town on the frontier
between Prussia and Poland, with the commodious waterway offered
by the river, made it a place of considerable trade. A view of
the town, as it was at the time of the birth of Copernicus, is
here given. The walls, with their watch-towers, will be noted,
and the strategic importance which the situation of Thorn gave to
it in the fifteenth century still belongs thereto, so much so
that the German Government recently constituted the town a
fortress of the first class.
Copernicus, the astronomer, whose discoveries make him the great
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
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