Revolution Of Astronomy By Copernicus

Author:      Ball, Sir Robert Stawell

Revolution Of Astronomy By Copernicus

 

Link: "The Revolutions of the Heavenly Bodies"  A Letter To Pope Paul III

 

 

 

1543

 

     The promulgation of the accepted system of astronomy, called the

Copernican system, which represents the earth as revolving on its axis and

considers the sun as the centre of motion for the earth and other planets,

marked the greatest of scientific revolutions.

 

     Copernicus, whose name, thus Latinized, was Koppernigk or Kopernik, was

born at Thorn, Prussia, February 19, 1473, and died at Frauenburg, Prussia,

May 24, 1543.  The founder of modern astronomy was probably of German descent:

according to some authorities his father was a Germanized Slav, his mother a

German; and the honor of producing him is claimed by both Germany and Poland.

 

     With equal conciseness and lucidity, in the following pages the eminent

British astronomer furnishes important particulars concerning the life of

Copernicus; and he gives an account, no less interesting than instructive, of

the evolution of the Copernican astronomy in its founder's mind.

 

     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 of Cracow.  The education that he there

obtained must have been in those days of 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 for him, as for one of his illustrious successors, Galileo,

the practice of the art of painting had 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.

 

     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 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 real movements.  Ptolemy had laid down

this doctrine fourteen hundred 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 recognize 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.  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 deliberation 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 appear 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

endeavored 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 one's 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.

 

     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 wellnigh impossible to devise 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 other important celestial bodies must all be vast objects.  He

was thus enabled to put the question in such a form that it would 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 that 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 forever.

 

     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 is possessed a movement of rotation.  Its want of stability being

thus recognized, 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 mor difficult that that which 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 these 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.

 

     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 himself is advancing forward.

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.  Mars, though generally advancing

fron west to east among the stars, occasionally pauses, retraces his steps for

a while, 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.  When the earth comes

directly between Mars and the sun, the retrograde movement of Mars is at its

highest.  Mars and the earth are then 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 neutralize the real movement, and Mars

would seem to be at rest relatively to the surrounding stars.  Under the

actual circumstances considered, however, the earth is moving faster than

Mars, and the consequence is that the apparent movement of the planet backward

exceeds the real movement forward, 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 ^1 was sent to the press.  But ere it

made its appearance to the world, Copernicus was seized with 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

afterward.

 

[Footnote 1: De Orbium Caelestium Revolutionibus.]

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