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Great Astronomers

Great Astronomers
Title: Great Astronomers
Release Date: 2000-08-01
Type book: Text
Copyright Status: Public domain in the USA.
Date added: 24 March 2019
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Lowndean Professor of Astronomy and Geometry in theUniversity of Cambridge
Author of "In Starry Realms" "In the High Heavens" etc.



It has been my object in these pages to present the life of eachastronomer in such detail as to enable the reader to realise insome degree the man's character and surroundings; and I haveendeavoured to indicate as clearly as circumstances would permitthe main features of the discoveries by which he has become known.

There are many types of astronomers—from the stargazer who merelywatches the heavens, to the abstract mathematician who merelyworks at his desk; it has, consequently, been necessary in thecase of some lives to adopt a very different treatment from thatwhich 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 froman article on the "History of Dunsink Observatory," which waspublished on the occasion of the tercentenary celebration of theUniversity of Dublin in 1892, and the life of Sir William RowanHamilton is taken, with a few alterations and omissions, from anarticle contributed to the "Quarterly Review" on Graves' life ofthe great mathematician. The remaining chapters now appear forthe first time. For many of the facts contained in the sketch ofthe late Professor Adams, I am indebted to the obituary noticewritten by my friend Dr. J. W. L. Glaisher, for the Royal AstronomicalSociety; while with regard to the late Sir George Airy, I have asimilar acknowledgment to make to Professor H. H. Turner. To myfriend Dr. Arthur A. Rambaut I owe my hearty thanks for hiskindness in aiding me in the revision of the work.


The Observatory, Cambridge.
October, 1895




[Note of etext transcriber: The illustrations by be seen enlarged by clicking on them.]


Of all the natural sciences there is not one which offers suchsublime objects to the attention of the inquirer as does the scienceof astronomy. From the earliest ages the study of the stars hasexercised 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 onhuman affairs.

The practical utilities of astronomy were also obvious in primevaltimes. Maxims of extreme antiquity show how the avocations of thehusbandman are to be guided by the movements of the heavenly bodies.The positions of the stars indicated the time to plough, and the timeto sow. To the mariner who was seeking a way across the tracklessocean, the heavenly bodies offered the only reliable marks by whichhis path could be guided. There was, accordingly, a stimulus bothfrom intellectual curiosity and from practical necessity to followthe movements of the stars. Thus began a search for the causes ofthe ever-varying phenomena which the heavens display.

Many of the earliest discoveries are indeed prehistoric. The greatdiurnal movement of the heavens, and the annual revolution of thesun, seem to have been known in times far more ancient than those towhich any human monuments can be referred. The acuteness of theearly observers enabled them to single out the more important of thewanderers which we now call planets. They saw that the star-likeobjects, Jupiter, Saturn, and Mars, with the more conspicuous Venus,constituted a class of bodies wholly distinct from the fixed starsamong which their movements lay, and to which they bear such asuperficial resemblance. But the penetration of the earlyastronomers went even further, for they recognized that Mercury alsobelongs to the same group, though this particular object is seen sorarely. It would seem that eclipses and other phenomena wereobserved at Babylon from a very remote period, while the most ancientrecords of celestial observations that we possess are to be found inthe 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 atAlexandria. The most famous name in the science of this period isthat of Hipparchus who lived and worked at Rhodes about the year160BC. It was his splendid investigations that first wrought theobserved facts into a coherent branch of knowledge. He recognizedthe primary obligation which lies on the student of the heavens tocompile as complete an inventory as possible of the objects which arethere to be found. Hipparchus accordingly commenced by undertaking,on a small scale, a task exactly similar to that on which modernastronomers, with all available appliances of meridian circles, andphotographic telescopes, are constantly engaged at the present day.He compiled a catalogue of the principal fixed stars, which is ofspecial value to astronomers, as being the earliest work of its kindwhich has been handed down. He also studied the movements of the sunand the moon, and framed theories to account for the incessantchanges which he saw in progress. He found a much more difficultproblem in his attempt to interpret satisfactorily the complicatedmovements of the planets. With the view of constructing a theorywhich should give some coherent account of the subject, he made manyobservations of the places of these wandering stars. How great werethe advances which Hipparchus accomplished may be appreciated if wereflect that, as a preliminary task to his more purely astronomicallabours, he had to invent that branch of mathematical science bywhich alone the problems he proposed could be solved. It was forthis purpose that he devised the indispensable method of calculationwhich we now know so well as trigonometry. Without the aid renderedby this beautiful art it would have been impossible for any reallyimportant advance in astronomical calculation to have been effected.

But the discovery which shows, beyond all others, that Hipparchuspossessed one of the master-minds of all time was the detection ofthat remarkable celestial movement known as the precession of theequinoxes. The inquiry which conducted to this discovery involved amost profound investigation, especially when it is remembered that inthe days of Hipparchus the means of observation of the heavenlybodies were only of the rudest description, and the availableobservations of earlier dates were extremely scanty. We can but lookwith astonishment on the genius of the man who, in spite of suchdifficulties, was able to detect such a phenomenon as the precession,and to exhibit its actual magnitude. I shall endeavour to explainthe nature of this singular celestial movement, for it may be said tooffer the first instance in the history of science in which we findthat combination of accurate observation with skilful interpretation,of which, in the subsequent development of astronomy, we have so manysplendid examples.

The word equinox implies the condition that the night is equal to theday. To a resident on the equator the night is no doubt equal to theday at all times in the year, but to one who lives on any other partof the earth, in either hemisphere, the night and the day are notgenerally equal. There is, however, one occasion in spring, andanother in autumn, on which the day and the night are each twelvehours at all places on the earth. When the night and day are equalin spring, the point which the sun occupies on the heavens is termedthe vernal equinox. There is similarly another point in which thesun is situated at the time of the autumnal equinox. In anyinvestigation of the celestial movements the positions of these twoequinoxes on the heavens are of primary importance, and Hipparchus,with the instinct of genius, perceived their significance, andcommenced to study them. It will be understood that we can alwaysdefine the position of a point on the sky with reference to thesurrounding stars. No doubt we do not see the stars near the sunwhen the sun is shining, but they are there nevertheless. Theingenuity of Hipparchus enabled him to determine the positions ofeach of the two equinoxes relatively to the stars which lie in itsimmediate vicinity. After examination of the celestial places ofthese points at different periods, he was led to the conclusion thateach equinox was moving relatively to the stars, though that movementwas so slow that twenty five thousand years would necessarily elapsebefore a complete circuit of the heavens was accomplished. Hipparchustraced out this phenomenon, and established it on an impregnablebasis, so that all astronomers have ever since recognised theprecession of the equinoxes as one of the fundamental facts ofastronomy. Not until nearly two thousand years after Hipparchus hadmade this splendid discovery was the explanation of its cause givenby Newton.

From the days of Hipparchus down to the present hour the science ofastronomy has steadily grown. One great observer after another hasappeared from time to time, to reveal some new phenomenon with regardto the celestial bodies or their movements, while from time to timeone commanding intellect after another has arisen to explain the trueimport of the facts of observations. The history of astronomy thusbecomes inseparable from the history of the great men to whoselabours its development is due.

In the ensuing chapters we have endeavoured to sketch the lives andthe work of the great philosophers, by whose labours the science ofastronomy 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 theMiddle Ages. We shall next see the mighty revolution in ourconceptions of the universe which are associated with the name ofCopernicus. We then pass to those periods illumined by the genius ofGalileo and Newton, and afterwards we shall trace the careers ofother more recent discoverers, by whose industry and genius theboundaries of human knowledge have been so greatly extended. Ourhistory will be brought down late enough to include some of theillustrious astronomers who laboured in the generation which has justpassed away.



The career of the famous man whose

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