R. S. Ball, Great Astronomers.pdf

Great Astronomers

R. S. Ball

● Preface

● Introduction

● PTOLEMY.

● COPERNICUS.

● TYCHO BRAHE.

● GALILEO.

● KEPLER.

● ISAAC NEWTON.

● FLAMSTEED.

● HALLEY.

● BRADLEY.

● WILLIAM HERSCHEL.

● LAPLACE.

● BRINKLEY.

● JOHN HERSCHEL.

● THE EARL OF ROSSE.

● AIRY.

● HAMILTON.

● LE VERRIER.

● ADAMS.

PREFACE.

It has been my object in these pages to present the life of each astronomer in such detail as

to enable the reader to realise in some degree the man's character and surroundings; and I

have endeavoured to indicate as clearly as circumstances would permit the main features of

the discoveries by which he has become known.

There are many types of astronomers--from the stargazer who merely watches the heavens,

to the abstract mathematician who merely works at his desk; it has, consequently, been

necessary in the case of some lives to adopt a very different treatment from that which

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seemed suitable for others.

While the work was in progress, some of the sketches appeared in "Good Words." The chapter

on Brinkley has been chiefly derived from an article on the "History of Dunsink Observatory,"

which was published on the occasion of the tercentenary celebration of the University of

Dublin in 1892, and the life of Sir William Rowan Hamilton is taken, with a few alterations and

omissions, from an article contributed to the "Quarterly Review" on Graves' life of the great

mathematician. The remaining chapters now appear for the first time. For many of the facts

contained in the sketch of the late Professor Adams, I am indebted to the obituary notice

written by my friend Dr. J.W.L. Glaisher, for the Royal Astronomical Society; while with regard

to the late Sir George Airy, I have a similar acknowledgment to make to Professor H.H.

Turner. To my friend Dr. Arthur A. Rambaut I owe my hearty thanks for his kindness in aiding

me in the revision of the work.

R.S.B. The Observatory, Cambridge. October, 1895

INTRODUCTION.

Of all the natural sciences there is not one which offers such sublime objects to the attention

of the inquirer as does the science of astronomy. From the earliest ages the study of the stars

has exercised the same fascination as it possesses at the present day. Among the most

primitive peoples, the movements of the sun, the moon, and the stars commanded attention

from their supposed influence on human affairs.

The practical utilities of astronomy were also obvious in primeval times. Maxims of extreme

antiquity show how the avocations of the husbandman are to be guided by the movements of

the heavenly bodies. The positions of the stars indicated the time to plough, and the time to

sow. To the mariner who was seeking a way across the trackless ocean, the heavenly bodies

offered the only reliable marks by which his path could be guided. There was, accordingly, a

stimulus both from intellectual curiosity and from practical necessity to follow the movements

of the stars. Thus began a search for the causes of the ever-varying phenomena which the

heavens display.

Many of the earliest discoveries are indeed prehistoric. The great diurnal movement of the

heavens, and the annual revolution of the sun, seem to have been known in times far more

ancient than those to which any human monuments can be referred. The acuteness of the

early observers enabled them to single out the more important of the wanderers which we

now call planets. They saw that the star-like objects, Jupiter, Saturn, and Mars, with the more

conspicuous Venus, constituted a class of bodies wholly distinct from the fixed stars among

which their movements lay, and to which they bear such a superficial resemblance. But the

penetration of the early astronomers went even further, for they recognized that Mercury also

belongs to the same group, though this particular object is seen so rarely. It would seem that

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eclipses and other phenomena were observed at Babylon from a very remote period, while the

most ancient records of celestial observations that we possess are to be found in the Chinese

annals.

The study of astronomy, in the sense in which we understand the word, may be said to have

commenced under the reign of the Ptolemies at Alexandria. The most famous name in the

science of this period is that of Hipparchus who lived and worked at Rhodes about the year

160BC. It was his splendid investigations that first wrought the observed facts into a coherent

branch of knowledge. He recognized the primary obligation which lies on the student of the

heavens to compile as complete an inventory as possible of the objects which are there to be

found. Hipparchus accordingly commenced by undertaking, on a small scale, a task exactly

similar to that on which modern astronomers, with all available appliances of meridian circles,

and photographic telescopes, are constantly engaged at the present day. He compiled a

catalogue of the principal fixed stars, which is of special value to astronomers, as being the

earliest work of its kind which has been handed down. He also studied the movements of the

sun and the moon, and framed theories to account for the incessant changes which he saw in

progress. He found a much more difficult problem in his attempt to interpret satisfactorily the

complicated movements of the planets. With the view of constructing a theory which should

give some coherent account of the subject, he made many observations of the places of these

wandering stars. How great were the advances which Hipparchus accomplished may be

appreciated if we reflect that, as a preliminary task to his more purely astronomical labours, he

had to invent that branch of mathematical science by which alone the problems he proposed

could be solved. It was for this purpose that he devised the indispensable method of

calculation which we now know so well as trigonometry. Without the aid rendered by this

beautiful art it would have been impossible for any really important advance in astronomical

calculation to have been effected.

But the discovery which shows, beyond all others, that Hipparchus possessed one of the

master-minds of all time was the detection of that remarkable celestial movement known as

the precession of the equinoxes. The inquiry which conducted to this discovery involved a

most profound investigation, especially when it is remembered that in the days of Hipparchus

the means of observation of the heavenly bodies were only of the rudest description, and the

available observations of earlier dates were extremely scanty. We can but look with

astonishment on the genius of the man who, in spite of such difficulties, was able to detect

such a phenomenon as the precession, and to exhibit its actual magnitude. I shall endeavour

to explain the nature of this singular celestial movement, for it may be said to offer the first

instance in the history of science in which we find that combination of accurate observation

with skilful interpretation, of which, in the subsequent development of astronomy, we have so

many splendid examples.

The word equinox implies the condition that the night is equal to the day. To a resident on the

equator the night is no doubt equal to the day at all times in the year, but to one who lives on

any other part of the earth, in either hemisphere, the night and the day are not generally

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equal. There is, however, one occasion in spring, and another in autumn, on which the day

and the night are each twelve hours at all places on the earth. When the night and day are

equal in spring, the point which the sun occupies on the heavens is termed the vernal

equinox. There is similarly another point in which the sun is situated at the time of the

autumnal equinox. In any investigation of the celestial movements the positions of these two

equinoxes on the heavens are of primary importance, and Hipparchus, with the instinct of

genius, perceived their significance, and commenced to study them. It will be understood that

we can always define the position of a point on the sky with reference to the surrounding

stars. No doubt we do not see the stars near the sun when the sun is shining, but they are

there nevertheless. The ingenuity of Hipparchus enabled him to determine the positions of

each of the two equinoxes relatively to the stars which lie in its immediate vicinity. After

examination of the celestial places of these points at different periods, he was led to the

conclusion that each equinox was moving relatively to the stars, though that movement was

so slow that twenty five thousand years would necessarily elapse before a complete circuit of

the heavens was accomplished. Hipparchus traced out this phenomenon, and established it on

an impregnable basis, so that all astronomers have ever since recognised the precession of the

equinoxes as one of the fundamental facts of astronomy. Not until nearly two thousand years

after Hipparchus had made this splendid discovery was the explanation of its cause given by

Newton.

From the days of Hipparchus down to the present hour the science of astronomy has steadily

grown. One great observer after another has appeared from time to time, to reveal some new

phenomenon with regard to the celestial bodies or their movements, while from time to time

one commanding intellect after another has arisen to explain the true import of the facts of

observations. The history of astronomy thus becomes inseparable from the history of the great

men to whose labours its development is due.

In the ensuing chapters we have endeavoured to sketch the lives and the work of the great

philosophers, by whose labours the science of astronomy has been created. We shall

commence with Ptolemy, who, after the foundations of the science had been laid by

Hipparchus, gave to astronomy the form in which it was taught throughout the Middle Ages.

We shall next see the mighty revolution in our conceptions of the universe which are

associated with the name of Copernicus. We then pass to those periods illumined by the

genius of Galileo and Newton, and afterwards we shall trace the careers of other more recent

discoverers, by whose industry and genius the boundaries of human knowledge have been so

greatly extended. Our history will be brought down late enough to include some of the

illustrious astronomers who laboured in the generation which has just passed away.

PTOLEMY.

The career of the famous man whose name stands at the head of this chapter is one of the

most remarkable in the history of human learning. There may have been other discoverers

who have done more for science than ever Ptolemy accomplished, but there never has been

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any other discoverer whose authority on the subject of the movements of the heavenly bodies

has held sway over the minds of men for so long a period as the fourteen centuries during

which his opinions reigned supreme. The doctrines he laid down in his famous book, "The

Almagest," prevailed throughout those ages. No substantial addition was made in all that time

to the undoubted truths which this work contained. No important correction was made of the

serious errors with which Ptolemy's theories were contaminated. The authority of Ptolemy as

to all things in the heavens, and as to a good many things on the earth (for the same

illustrious man was also a diligent geographer), was invariably final.

Though every child may now know more of the actual truths of the celestial motions than ever

Ptolemy knew, yet the fact that his work exercised such an astonishing effect on the human

intellect for some sixty generations, shows that it must have been an extraordinary

production. We must look into the career of this wonderful man to discover wherein lay the

secret of that marvellous success which made him the unchallenged instructor of the human

race for such a protracted period.

Unfortunately, we know very little as to the personal history of Ptolemy. He was a native of

Egypt, and though it has been sometimes conjectured that he belonged to the royal families of

the same name, yet there is nothing to support such a belief. The name, Ptolemy, appears to

have been a common one in Egypt in those days. The time at which he lived is fixed by the

fact that his first recorded observation was made in 127 AD, and his last in 151 AD. When we

add that he seems to have lived in or near Alexandria, or to use his own words, "on the

parallel of Alexandria," we have said everything that can be said so far as his individuality is

concerned.

Ptolemy is, without doubt, the greatest figure in ancient astronomy. He gathered up the

wisdom of the philosophers who had preceded him. He incorporated this with the results of his

own observations, and illumined it with his theories. His speculations, even when they were,

as we now know, quite erroneous, had such an astonishing verisimilitude to the actual facts of

nature that they commanded universal assent. Even in these modern days we not

unfrequently find lovers of paradox who maintain that Ptolemy's doctrines not only seem true,

but actually are true.

In the absence of any accurate knowledge of the science of mechanics, philosophers in early

times were forced to fall back on certain principles of more or less validity, which they derived

from their imagination as to what the natural fitness of things ought to be. There was no

geometrical figure so simple and so symmetrical as a circle, and as it was apparent that the

heavenly bodies pursued tracks which were not straight lines, the conclusion obviously

followed that their movements ought to be circular. There was no argument in favour of this

notion, other than the merely imaginary reflection that circular movement, and circular

movement alone, was "perfect," whatever "perfect" may have meant. It was further believed

to be impossible that the heavenly bodies could have any other movements save those which

were perfect. Assuming this, it followed, in Ptolemy's opinion, and in that of those who came

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