Historical Account Of The Origin And Progress Of Astronomy

Preface

THE object of the Work now submitted to tlie public is to indicate the probable origin, and to trace the pi ogress, of astronomical science. Setting out with a view of the heavens, the sentiments which that view may be supposed to excite are dcscnbed, and the purposes to which the most obvious phenomena might be made subservient arc stated In the next place, the manner in which the ancients endeavoured to explain the constitution of the universe, and account for the movements observed in the heavenly bodies, is shewn. The successive changes made in the celestial mechanism, in proportion as the phenomena were more attentively considered, aae then detailed, an4 the Work terminates with an outline of the system founded on the received hypothesis of gravitation.

From the relations transmitted by some of the ancient writers, and from those delivered by modem navigators, we find that men, in the lowest grade of civilisation, have always entertained nearly the same ideas concerning the forms of the earth and heavens, and that they have drawn those ideas immediately from the mfoimation afforded by the senses alone. It is certain, also, that from the time at which the proper movements of the sun, moon and planets were first detected, till the hypothesis of the earth's motion was recognised, in the days of Copernicus and Kepler, the opinion that each of those celestial bodies was attached to the surface of a revolving sphere was universally held. But the faint and dubious hints to be found in the existing works of the ancients being insufficient to guide us to a knowledge of the manner in which the penochcal revolutions of the planets were originally observed, this is, necessarily, m part,

IV PREFACE

supplied by conjecture. In the following pages, however, caie has been taken to suppose, in the discoveier, no previous information, except such as might be furnished by those phenomena which are manifest to an unassisted eye, and which could not have escaped an attentive observer , and it will, probably, be admitted that the notions imagined to arise on contemplating the moving bodies in the fiimament aie precisely those which would occur to the mmcl of an intelligent spectator, if placed in such circumstances

It has been attempted, in the piesent Work, to connect the history with the fiist elements of astionomy, in older that they who seek to obtain a knowledge of the science may derive assistance at the commencement of their enquiries, when any difficulty which the student may happen to encounter is most likely to deter him from the pursuit , and when, also, to keep alive his interest in the subject, there is need of some such allurement as may be found m a relation of the steps accomplished by the celebrated men of past ages Nor can it be doubted that the generous desire of participating in the renown acquired by the ancient masters in astronomy must, to those who have arrived at its principles by thus tracing the succession of discovenes, present an inducement, under favourable opportunities, to join their efforts for the improvement of the science to those by which it has been brought to its actual state. The obscure pcuod during which astronomy was in its infancy, and in which the fiist notions must have been obtained from a mere view of the heavens, has been dwelt on at some length, and the probable nature of the earliest observations has been descubed. Some mention has, next, been made of the distribution of the fixed stars into clusters , of the dispositions of the principal circles imagined to be described on the smface of the celestial sphere for the purpose of marking with some precision the places of the sun, the moon and the erratic stars ; and of the nature of the observations by which the periodical revolutions and, consequently, the mean motions of these may have been discovered before their places in the heavens could have been directly determined by instruments. An endeavour has, subsequently, been made to shew the natuie of those assemblages of

PREFACE.

spheres which were invented to exhibit some of the principal movements of the heavenly bodies, and to enable the astronomer to anticipate the more remarkable phenomena with tolerable accuracy. Then, after explaining from what causes the first systems ceased to answer the purposes for \\lnch they were imagined, some account has been rendered of the struggles between ancient prejudices and the evidence of newly discovered facts, the efforts made to accommodate the original hypotheses to the complex variations of the planetary motions have boon noticed, and the historical sketch has, finally, been extended to the epoch at which the persevenng spirit of man succeeded in detecting the laws which govern the movements of the great bodies m the universe Occasionally, the sentiments of the ancients on the principal points in the philosophy of the heavens have been introduced , and it will, no doubt, be agreeable to the reader to see those opinions collected which aie thinly scattered in woiks not readily accessible to his enquiries. The contemplation of these subjects affoids the satisfaction of observing how, from the first rude notions of unenlightened men, and through many slowly advancing improvements, the modem science has gradually attained its present eminence , and even a review ol the false steps which have been taken, and by which its progress has been retaidcd, cannot be uninteresting to those who would' minutely trace the operations of the human mind m the career of discovery.

That astronomy had been cultivated m the East to such an extent and in such ancient times as to permit, at an epoch more remote than that of the Noachian Deluge, the attainment of a very correct knowledge of the mean movements and places of the sun, moon, and planets, is an opinion which, during the last century, had several distinguished partisans, but which is, now, perhaps, nearly abandoned. Yet, as the idea is too remarkable and interesting to deserve entire neglect, it Las been thought proper to notice it, m the following history, so far as to point out the circumstances on which it has been supported and the arguments by which it haw been dwpiovod. Some attempt lias, also, been made to shew that, withmthe interval of two thousand years which elapsed between the establishment of the Chaldean marchy and the age of Aristotle, it was possible, fiom obsertion, to discover all those elements of the celestial movements iich aie contained in the Hindu Tables , and to foim those lar periods which, soon after the tune of the above philosocr, were known to the Gieeks and which were, perhaps then, st determined from the registeis of observed phenomena, kept Babylon or in Egypt during the said interval. All the evidence which we now possess favoms the belief that e country between the Nile and the Euphrates is the birthace of astionomy, the cradle in which it was nursed, and the urce from whence it extended to other regions , and, though » written monument remains of the state of the science among e fiist inhabitants of that part of the world, the reputation aich they had acquired, and which, long after then nation Ld ceased to exist, procuied for those who piofesscd to follow eir doctrines the esteem and confidence of mankind is, in the >sence of such monuments, the best pioof that can be offeied of en early devotion to the study of the heavens.

One of the objects proposed m this Woik is to give a distinct scount of the methods devised by the ancients for* explaining .e observed inequalities m the celestial movements; and, as the 3velopment of the planetary systems is ceitainly due to the -iceks, who first adjusted the positions of the spheres, their tagmtudes and times of revolution, to the visible phenomena of ic heavens, the description of those systems is introduced in le account of the Greek astronomy : no doubt, however, can last that, at laast, the hypothesis of concentric spheres, which ears the marks of being almost the earliest conception foimcd om the apparent revolutions of the stars about the earth, was iventcd by the Chaldeans , and it is even probable that this eople did more than merely suggest the idea of such a mahmery It is natural that some curiosity should be felt to know iiy the results and computations founded on the ancient sysjms, now known to be erroneous in every respect, should, necrtheless, have approached, in many cases, so near the truth , nd it has, therefore, been thought convenient to enter so far ito the explanation of those systems as to shew, from the acount delivered by Ptolemy, how the dimensions of the Dclbi-

PREFACE. vii

ents and Epicycles, and the values of the equations arising from them, were determined. But the entire neglect into which the systems have fallen seems lo render needless any more extensive development of the subject, which, however, is treated at length m the Almagest, and with considerable perspicuity in Delambre's History a.

The astronomy of the ancients was founded on the practice of remaiking the periodical returns of like phenomena, which, from their general regularity, in some measure supplied the place of theory ; and, as the lengths of the intervals compensated the inaccuracies of the observations, it is evident that the mean motions of the sun, moon, and planets might be, thus, very precisely determined. Then, since the dimensions and motions of the spheres were so determined, by computation, as to represent the discoveied inequalities when these weie in a maximum or minimum state, it may be easily imagined that the differences between the observed and calculated places of the erratic bodies would never bo gieat, and would often be incapable of detection by the instruments m use The correct values of those inequalities, m the intermediate states, and several others now known to exist, by all of which the fallacy of the ancient hypotheses would have been demonstrated, were not till later ages discovered.

The Writer has attempted to trace with care the pro gi ess of astronomy among the Greeks. This people began the cultivation of the science with a knowledge of the elements obtained from the ancient observations made by the Chaldeans or Egyptians ; and to them must be attiibutcd the honour of having, first, applied the thcoiems of pme mathematics in the investigation of astionomical propositions. In fact, we perceive, in their writings, precisely that advance towards the discovery of the true laws of Natme which might bo expected fiom men of lofty intellect, who seem to have been letaidcd in their career only by adhering with too much tenacity to a metaphysical notion concerning the perfection of the universe. The planetary systems of t]i$ Greek philosophers piesent an admirable display of ingenuity and address m their adaptation to the chfFcicnt movements which, clown to the time of Ilippaichus, had been ascertained , but the

* Hist, do PAbtion Tom II.

PREFACE.

attempt to represent the inequalities which more perfect observations afterward brought to light, necessarily gave use to such modifications that the complexity of the machmeiy, at length, destroyed its utility. Some enlightened minds certainly entertained the idea that the revolutions of the celestial bodies wcic, in reality, very different from those which appeared , and even suggested, concerning those revolutions, an hypothesis comprehending the movement of the earth. But it requited many centuries to vanquish the strong prejudices in favour of its quiescence, as well as to disabuse mankind concerning the fancied influence exeicised by the stars on terrestrial substances ; if, indeed, even now, it may be said that this last superstition has ceased to exist.

An account of all the processes employed in the modem astronomy, with the details of their discovery, could not be introduced in a work like the present without gieatly increasing its bulk, and without entering into investigations which propeily belong to a tieatise on tlie science itself. But the ancient mechanism of the heavens, and the invention of the fiist rules for dcteiminmg, by computation, the places of the sun, moon, and stars, form subjects differing, m eveiy respect, from those which correspond to them in the actual theory of the universe. The Writer tiusts, therefore, to have done that which will be considered neither uninteresting noi umnstructive, in shewing how the revolutions of a planet m a simple eccentric oibit about the earth were made to exhibit the alternately direct and letrogiadc movements observed in the foimer , and how its supposed revolution in an epicycle, about its mean place, produced the apparent changes of direction, and the principal variations of its velocity

Between the time of Ptolemy and the establishment of the Mohammedan power in Asia, astronomy appears to have been but little cultivated; a few commcntatois on the works of the Greek mathematicians and philosophers alone kept alive the science, which, moreover, was, during sevcial ages, afiected with errois perhaps before unknown, and arising cither from great inaccuracies m the then observed longitudes of the fixed stars, or, which is moic probable, fiom mistakes lespccting the longi-

PREFACE. IX

tudes assigned to them by the astronomers of some earlier age.

The Arabs, in their deserts, had always preserved a rude astionomy in connection with their worship of the " heavenly host/' and it is probable that, when they attained political impoitance, they only prosecuted with moie vigour, and rnoie extensive means, a study, in which they had ever been interested. The duration of their science was limited by that of their empire; we aie, however, indebted to them for pieseiving the knowledge acquired by the Greeks , foi increasing it by a number of observations made with superior instruments, and for communicating it to the inhabitants of Western Em ope.

The ancient Hindus, apparently, had claims to the character of a scientific people , part of their astronomy bears the maiks of originality, and its foundations were, peihaps, laid 111 or near the times at which the Chaldeans and Egyptians aie believed to have instituted the first measuies foi the cultivation of the science. It was, however, while the Arabian Khahfs occupied the throne of Bagdad that the first communication between the learned men of India and Syna, of which we have any distinct infoimation, took place , though there is no reason to doubt that, after the conquests of Alexander had made India known to the Greeks, and during the reigns of that prince's successors, a constant mtei course subsisted between the same countries. The discoveries of Hipparchus at Hhodes 01 Alexandria might have been, then, conveyed to the banks of the Ganges, and, by the Hindu astronomers, mcorpoiated with the elements of tho science previously founded on the obseivations of their own predecessors • the results of Ptolemy's icsearchcs, also, if not immediately on their publication, were, at a subsequent time, probably along with the paiticular cletciminations of the Arabians, received and adopted by the same people.

No proof exists that the ancient Chinese cultivated astronomy as a science , the only inonurncnts of the attention paid to the subject by the natives of the " celestial empire" being limited to a catalogue of phenomena obseivcd by the eye, and to a few simple elements determined by means of the gnomon, the whole scaicely serving any other pmpobe than to shew that, in

PREFACE.

the study of the heavens, the couise pursued among this lemote people was similar to that pursued by the western nations in corresponding circumstances. That such should be the fact cannot cause any surprise if we consider that the book of Nature is open to all, and that, therefore, all must, to a certain extent, read and reason alike. It is, however, woithy of remark that, besides an agreement in sentiment, among men in diffeicnt ages and countries, concerning the visible phenomena of the tiniverse, the principle of general attraction so extensively developed by Newton, was, two thousand years before his time, proposed as an hypothesis by the philosophers of Greece, and is found in the allegorical poems of the Hindus. Moreover, and the circumstance is equally worthy of observation, the metaphysical opinion of Beikclcy concerning what is called material substance, that its essence consists ^n being perceived, is known to have been a fundamental tenet of the Vedanta school a. We may, therefoie, allow, though it can by no means be positively affiimed, that both the Hindus and Chinese ariived at their astronomical elements independently, of any other people; but, be this as it may, the want of authentic documents relating to their caily histories and the gieat probability that much of then learning was drawn fiom foreign sources will, certainly, justify us m placing their astronomy after that of the Greeks

We are brought, next, to the times in which the writings of Ptolemy and his commentators were studied m Europe; audit will be seen that although, with general litciature, astronomy began then to be assiduously cultivated m this part of the world, the authonty of the Gieek school of philosophy still held the minds of men m bondage, and that repeated effoits were made to represent the phenomena of the heavens by modifications of the ancient hypothesis even after the fallacy of the latter must have been manifest. Copernicus himself, who entirely changed the face of the science by considering the sun as the fixed centre of the oibits of the earth and planets, was not able to vanquish some of the ancient prejudices, and the planctaiy system pioposed by him differs materially fiom that which is aSu William Jones'b D i scouises, Disc XL

PREFACE. XI now, usually, called by his name The persevering labours of Keplei conspnmg with the foitimate invention of the telescope, at length succeeded, however, in annihilating every impediment, and prepared the way for the present thcoiy of the universe.

It will, also, be seen that the discoveries of the above astronomcis were, by Newton, proved to be necessary consequences of a principle of nature which exists, identically, m the fall of a stone to the ground, in the tendency of the moon to the eaith, and m those of the planets to the sun , and it is to be observed that from reseaichcs, founded on this principle alone, which were begun by our gieat philosopher, and extended alter his death by the mathematicians of the continent, lesult the modern tables of the celestial movements. These exhibit, chiefly, the mean or uniform velocity which each planet would have if it moved in an undistmbed circular oibit, the first inequality of velocity, commonly called the equation of the centre, which expresses the variation arising from the movement in a supposed elliptical oibit; and the effects of the several perturbations produced by the attractions of othei planets, by which the motion of each, both in longitude and latitude, is rendered still further vanable , besides these, the tables contain the vaiiable distances of the earth and planets from the sun, the movements of the apsides and nodes of their orbits, and all the corresponding elements of the satellites

Hitherto the improvements m analysis, by which the foimulse relating to the lunar and planetary motions were investigated, have been accompanied by corresponding amelioiations in the instruments of observation , and thus, the constant coefficients of the variable terms which enter into the foimulse have been obtained with considerable accuracy. But, that instruments more capable than those already in use, of determining accurately the places of celestial bodies by observation, should hereafter be constructed, seems very uncertain Instruments of great magnitude, though they afford superior optical poweis, and are susceptible of more minute graduations than those of smallci size, are moie than the lattei subject to partial expansions or contractions, fiom inequalities in the material, and to derangements, from the stiams produced by changing their

PREFACE.

directions during the observation , and these evils, necessarily, place a limit to their useful dimensions. But we may acid that the enors in the obseived places of stars, arising from imperfection of vision and from inappreciable variations in the state of the atmosphere, too often render useless the skill displayed in the design, and the accuracy attained in the execution of the magnificent mstiuments produced by modern ait

A history of the progress of astronomy would, probably, be thought incomplete if the actual state of the science were not descnbcd. Therefore, after exhibiting an outline of the lesearches of Kepler and of the planetaiy theory of Newton, the last, in all probability, to be recoided, some account has been given of the recent discoveries made in the heavens, of the operations undertaken to ascertain the figure of the earth, and of the nature of the instruments employed in observation and a chapter has been added, containing a statement of the subjects to which the modern analysis has been applied in investigating, by the theoiy of gravitation, the formulae for representing the celestial movements

The Writer has not attempted, in the Work, to trespass on the domain of natural theology; and he only solicits the readei's indulgence while he remarks that astionomy affoids the most striking evidences of the infinite power and intelligence of the Deity. The former is manifested in the incalculable number and vast magnitudes of the bodies in the universe, and the distances to which their attractive influences extend; the latter, m the proportion established between the intensities of the moving forces acting on each, by which, while in constant oscillation between opposing attractions, the planets constitute systems capable of an endless diuation. That inconceivable tendency of all the particles of matter to approach each other, can only be considered as the result of a principle originally communicated to them purposely to be the bond by which the different parts of the universe might be held together. But, because this tendency, if it acted alone, would have caused all the particles to unite m one mass, the Divine Power, which gave existence and a law of attraction to matter, must, also, have been exerted m causing the unions of portions of that matter in many distinct masses constituting suns and planets, in establishing the former as centres of particulai systems, and in applying to each of the latter an impulsive force by which it is enabled to revolve about the common centre of the system to which it was made to belong. Here, then, are several independent actions which, since they are combined together to work out certain useful ends, necessanly exclude the possibility of a fortuitous occuirence. And though the piofound geometer may determine tlie direction of the impelling foice and the position of the point of application by which, for any planet, the particular motion in the orbit and the obsetved obliquity in the axis of rotation might be obtained, he is as incapable as the rudest peasant of shewing, fiora natural causes, what communicated the force, 01 why, among the infinite number of possible directions and intensities, those should have been given which, alone, are capable of pioducing the phenomena of smnmei and winter, of day and night, m unceasing alternation

It is evident that the science of astronomy may be treated in two very different ways. The observed circumstances, in respect of time and place, which attend the recuirence of celestial phenomena, by affoidmg data for anticipating the repetition of the like phenomena in times to come, permit the laws which regulate the movements of the sun, moon and planets to be determined : or the existence of a law of nature, according to which material bodies may act on each other, being assumed ; from this may be deduced formulse expressing both the mean and variable movements, and agreeing with those obtained from a comparison of observations An astronomy formed from observation of the heavens is the subject of many excellent and well known English woiks , but the other, or that which is properly denominated Physical Astronomy, though now, perhaps, gaining ground, has, hitherto been but little studied in this country, If the first work of the kind, the " Prmcipia" of the illustrious Newton, and the essays of Simpson and Robison, be exccptcd, icfcrence can only be made to the treatises of the late Mr. Woodhouse, the learned researches of Ivory, Herschell, Airy, and Lubbock ; and the valuable but, as yet, unfinished transla-

XIV PREFACE.

tions of 'the M^cantque Celesfe, by Bowclitcli and Mis. Someiville

To a treatise on astronomy founded on either of the two principles above mentioned the following Wpik will, it is hoped, seive as a convenient intioduction , it may be considered as holding an intermediate place with respect to the voluminous histories of M.M Bailly and Delambre and, be it said, while acknowledging the merits of such as the elegant essay of Dr. Adam Smith, or that recently published in the Libraiy of Useful Knowledge, the very general outlines which have, occasionally, been given of the origin and progress of the science,

Royal Military College, Sandhurst^ May 20, 1833.

Contents

Chapter

I. Causes vdnch led to the Contemplation of the Heavens 1

II. The first Notices concerning Astronomy 20

Chapter I. Causes Which Led To The Contemplation

OF THE HEAVENS.

Sentiments excited by a view of the Fumament —The worship of the celestial bodies was general, in the first ages of the World. — The positions «of the celestial bodies were supposed to be Indicative of physical and moral effects on the Earth. — Cucunutances leading to the study of the heavens. — The probable origin of Astrology.— Agiicultuie and Navigation anciently regulated by observations on the phenomena of the heavens — The necessity of anticipating the returns of the seasons.— Opinion concerning the existence of a very ancient Astronomy. — Alleged antiquity of Astronomy in, the East. - Prejudice in favour of the antiquity of Eastern science.

THE brilliant spectacle which the celestial hemisphere exhibits when the Sun is pursuing his daily course within it, and when, fiom tlie same canopy, adorned with innumerable glittering points, the Moon displays her milder radiance, has always excited mingled emotions of pleasure and surprise in the mind of man. Nor do these affections alone appear to have attended the contemplation of the heavens. It is probable that man had ftoxn the first boen instructed by express revelation, that the Universe is the work, and is subject to th6 government of a4 Being possessing infinite power and intelligence, but wanting a ju$t conception of the true nature and attributes of the Creator, and being seduced by the splendour of the celestial host, he was soon led to regard, with reverential feelings, the Sun, Moon, and Stars, as appropriate symbols of that First Cause Which he could only imagine to be supremely great and

glorious.

B

In process of time these symbols, by withdrawing the attention from, and inducing an oblivion of the original object, usurped the place of that which they were, at first, intended only to represent Thus the Sun, Moon, and Planets began, themselves, to be considered as the real intelligences which govern the world ; consequently, as having claims to the right of receiving divine honours: and they, then, were represented by terjestnal objects denoting their supposed qualities or attributes. Diogenes Laertius <l, asserts that the ancient Egyptians worshipped the Sun and Moon , designating them Osiris and Isis, and representing them by a Scarabeus, a Dragon, a Hawk or some other animal , and Diodorus Siculus b, says that they considered those luminanes as the eternal and first gods : he adds that Osiris signifies many-eyed, and that the name was given in allusion to the lays which proceed from the sun in every direction and enlighten the earth.

The identity of Isis and the Moon is, however, doubtful, since, as Dr. Young observes, the name given by the Egyptians to the latter is masculine, which renders it unlikely that the luminary should have been worshipped as a goddess ; but that a relation was supposed to subsist between Isis and the lunar influence is evident. Diodorus states that the Egyptians gave horns to the goddess, in order to express the cuspid appearance of the moon when she is in the increase and wane , and also, because an ox was consecrated to hoi. In Chaldea and the western parts of Asia, accoi cling to Herodotus0, and Eusebmsd, the sun was worshipped as king of Heaven, under the name of Belus. In Persia e he was adored undei the denomination of Mithras, and considered either as the image, or as the abode of Deity : and Lucianf states that there was in Phoenicia, a great temple dedicated to Astarte, who, as he was informed by one of the priests, was believed to be the same as the moon. In his second book, Diodorus Siculus also informs us that the Chaldeans assigned a Divinity to each of the portions into which they divided the zodiac, or path in the heavens apparently described by the Sun

* In Proocmio »> Bibhotliecae Histoiicze Lib I. sect. 11.

c Clio sect 181. d Praep Evaiig Lib. I.

e Strab. Lib. XI. Plutarch. De Iside et Osinde ' De Syua Dea sect. 4.

in his annual course , and Plutarch, in the tieatise above quoted, says they considered the seven planets as Gods, of which two weie evil, two weie good, and the remaining thiee were in* different. The celestial bodies have, in all succeeding ages, been objects of adoration , and they probably will, in times to come, continue to find votaries, till the knowledge of the tiue religion has enlightened every nation of the eaith The untutored savage still prostrates himself before the rising sun, or, with the observance of some lehgious rite, celcbiates the principal phases of the changing moon.

Almost the first view of the face of nature must have shewn that the sun exerts a most powerful and beneficial effect upon the earth, by producing changes in the tempeiature of the air, in the processes of vegetation, and in the habits of animals . it must also have shewn that these effects depend upon the position of the sun m the heavens By analogy, therefoie, it was not unreasonable to suppose that the moon and stars weie productive of effects similar in kind, though perhaps infenor in degree, which might, like those pioduccd by the sun, be ascribed to their situations m the heavens, and might, with respect to the moon, be conceived to vary with her change of figure These opinions being once entertained, it is probable that it would not be long before a piopcnsity to tiace effects to then causes would lead to an opinion that the celestial bodies weie the powers by whose influence the bodies on the earth were endowed with the piopoitics they are observed to possess, and which could not be accounted for by any discoverable agency. From hence the tiansition was easy to the belief that the sun, moon, and stais weie the causes of, or were influential in developing the physical and moral qualities of man himself. Proofs of the existence of such opinions at an early time, are found in the woiks of several ancient authors • according to Diogenes Laertiusa, Ilccatcus of Miletus, who is supposed to have lived in the sixth centmy before Christ, m his treatise on the Philosophy of the Egyptians, ascribes to that people the opinion that the stars are of fire, and that by their influence all things in the earth are produced Scxtus Empnicus assorts