Great Astronomers by Robert Stawell Ball (best ereader for students .txt) 📖

in explaining the

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