ASTRONOMY. 



ASTRONOMY. 



inequality, whose law and approximate magnitude it gives, should 

 be found in the motion of a certain body, if the Newtonian principle be 

 correct. On being looked for in the manner which the nature of the 

 inequality iteelf shows to be most advantageous, it is found accord- 

 ingly, and its e.eact magnitude, as ascertained by observation, is often 

 of use in correcting that ob'tained from theory. For example, had it 

 not been for methods of this kind, our knowledge of the motions of 

 Jupiter's satellites, which is yet far from mature, would have been in a 

 state of the merest infancy. 



If the theory had arrived at a degree of completeness, towards which 

 it has been and is rapidly tending, nothing more would be necessary 

 for the determination of the motions of the solar system than the 

 knowledge of the actual positions, velocities, and directions of the 

 velocities of the bodies composing it, at some one moment, or of any 

 other quantities in which the above were mixed up, and from which 

 they could be obtained by calculation. But up to the present time it 

 has been necessary to use more data of observation than the preceding, 

 and it is only in recent years that tables of the moon, from the first- 

 mentioned data alone, have been published, 



For the details of the actual state of astronomy we must refer the 

 reader to such articles as STABS ; SOLAR SYSTEM ; &c., and the names of 

 the several planets. We shall now proceed to a sketch of the history, 

 or rather the annals, of astronomy, referring for fuller information to 

 the list of works given at the end of this article. 



The real history of written astronomy, that is, of actually recorded 

 and moderately correct observations in sufficient number to constitute 

 a body of science, commences with Hipparchus, about 160 years before 

 our cera. Prior to his time, it is difficult to do more than speculate 

 upon the few facts which are left to us. That astronomical observation 

 of a certain description began in the very earliest ages, there can be no 

 doubt ; but here there could be but one instrument, the horizon, and 

 but one theory, the actual motion of the heavenly bodies round the 

 earth. The earliest observations mentioned are those of the rising and 

 setting of stars, which led to the registration of the different appear- 

 ance* presented by the heavens in the course of a year, to which may 

 be added lunar and solar eclipses and comets. The rapid motion of 

 the moon in the heavens would probably have caused the lunar zodiac 

 to be first marked out, though it is clear that the solar zodiac was of a 

 very early date. Astronomical observation has always been one of the 

 accompaniments of civilisation, both in modern and ancient times ; and 

 however much we may conceive ourselves entitled to look down upon 

 the notions of our predecessors, we must not forget that in speaking of 

 any country which possessed an astronomical theory worth so much as 

 laughing at in modern times, we place that country in the list of 

 exceptions to the rule which prevailed through the greater number. 

 If the Chaldean system appear insufficient or the Ptolemaic compli- 

 cated, these are yet real results of thought, and, to a certain extent, 

 actual representations of fact. Mungo Park mentions an African tribe, 

 whose opinion it was that the inhabitants of the west fried the sun 

 when he got down to them, and after heating him sufficiently for next 

 day's service, took him round by a private passage to the east. If we 

 could collect the astronomy of the whole ancient world, there can be 

 little doubt that the comparatively humble efforts to which we are 

 coming would appear miracles of sense and reflection, among theories 

 not much superior to those of Park's Africans. 



The nations who are known to have cultivated astronomy before the 

 Christian era are the Chinese, Indians, Chaldeans, Egyptians, and 

 Greeks. The first made it a matter of politics, the three next of 

 religious observance, and all four applied it to astrology. Among the 

 Greeks only, the science had no reference either to politics, religion, or 

 soothsaying ; and here it throve with a vigour which permits us to 

 make the astronomy of Hipparchus and Ptolemy a part of the chain 

 which ends with Newton and Laplace. What we know of the four 

 first^mentioned nations is not sufficiently certain or definite to warrant 

 our drawing very positive conclusions as to the time when they began 

 to study the science ; and the question is rendered the more difficult 

 by the pretensions to antiquity which have been advanced in favour of 

 each by well-informed men of modern times. Each nation has its 

 advocates, who maintain that the Chinese, the Indians, the Chaldeans, 

 or the Egyptians, were the first astronomers : which is of itself suffi- 

 cient to prove that the question is doubtful. Fortunately it is of little 

 consequence ; and also the astronomy of the first and two last is of a 

 character and extent which will justify our saying that, be it very 

 ancient or not, there is nothing on the face of it which needs the 

 supposition of any very long time having been expended upon it. The 

 Hindoo astronomy, on the other hand, though certainly more extensive 

 and correct, may have been, for anything that can be shown to the 

 contrary, received from the Arabs of the middle ages. At least such 

 is the opinion of Laplace, Delambre, and several celebrated Anglo- 

 Indians, who have had means of knowing more of the subject than 

 either. But this question is one of difficulty, and ought not to be 

 Considered as finally settled. 



The Chinese have some annals which were translated by De Mailla, 

 a Jesuit missionary at Pekin, 1777-1785. They claim to go back to 

 the year B.C. 2857 ; but of agtronomic.il phenomena they record hardly 

 anything, except eclipses of the sun and the appearance of comets, and 

 of the former nothing but the fact and the day of their happening. 

 They state that the astronomers by profession were obliged, on pain of 



death, to predict every eclipse that occurred, and that, even after such 

 phenomena were found capable of prediction, it was the practice to 

 shout, beat drums, &c., during every eclipse, to frighten away the 

 monster which they supposed to be devouring the sun. The mathe- 

 maticians, in spite of their responsibility, were forbidden to make any 

 alteration in their theories or methods, without the consent of the 

 emperor. The loss of many methods, asserted to have been formerly 

 practised, is attributed to the burning of all scientific books by one of 

 their princes, B.C. 221. But perhaps the loss was not great ; for 

 Gaubil, who recalculated their asserted eclipses, could not verify more 

 than oue of a date anterior to the time of Ptolemy ; and even that one 

 is doubtful The fact of the motions of the planets was known to the 

 Chinese, but not the precession of the equinoxes, till about A.D. 400. 

 They had also the Metonic and Calippic periods. 



The question with regard to the Hindoos is not whether their 

 astronomy is sufficiently high in its pretensions to make it worth while 

 to inquire into its antiquity, but whether an astronomical system of a 

 very advanced character, which certainly was found among them, is or 

 is not as old as they assert it to be. This system is found in certain 

 tables, called the tables of Tirvalore, which have been brought into 

 Europe by Le Gentil, and in an original work, the ' Surya Siddhanta,' 

 of which an account will be found under VIOA GANITA, in the 

 BIOG. Drv.; and it may be fairly considered as about equal to the 

 European system of the 12th century. The epoch claimed by the 

 tables is B.C. 3102, the beginning of the Cali-yug, or iron age of 

 Hindoo mythology, at which time a conjunction of all the planets is 

 asserted. But this has too figurative a character ; and moreover, the 

 elements of the tables are hardly such as would have been derived 

 from observations actually made at that period. That the epoch is 

 fictitious may be readily believed; but the question is, was this 

 fictitious epoch formed by Hindoos from their own observations before 

 the Christian era, or was their system introduced by the Arabs, or 

 by direct communication with the Greeks ? On the one hand it is 

 argued that the Indian tables, being in many respects a mean between 

 those of Ptolemy and Albategnius, may have been derived from those 

 two ; on the other hand, the remarkable correctness of several points, 

 and the known character of the people in question, whose advances in 

 mathematics cannot be doubted, and whose habits have, throughout 

 recorded history, induced them to repel all connection with foreigners, 

 are urged in favour of the originality of their system. Those who are 

 curious may consult Bailly's ' Hist, de 1' Astronomic Indieune,' on the 

 oue hand, or Delambre, on the other ; but this question has unfortu- 

 nately been treated with considerable spirit of system on both 

 sides. 



The Chaldeans, according to Diodorus, had long observed the risings 

 and settings of the heavenly bodies, as well as eclipses. They had the 

 celebrated Metonic period of nineteen years, and it is supposed that 

 Melon obtained it from them, though this point is doubtful. They had 

 also other periods, the meaning of which has caused discussion. [SAROS, 

 NEROS, Sosos.] Simplicius, a commentator on Aristotle, and also 

 Porphyry relate that a series of eclipses preserved at Babylon was trans- 

 mitted by Alexander to Aristotle, and contained the observations of 

 1903 years preceding the conquest of Babylon by the Macedonians. But 

 Ptolemy gives only a few of them, the earliest of these not reaching 

 higher than B.C. 720. They are of the roughest kind, the times being 

 given only in hours, and the part of the diameter eclipsed within a 

 quarter ; but nevertheless they are the earliest trustworthy observa- 

 tions we possess, and led, in the hands of Halley, to the discovery of 

 the acceleration of the moon's mean motion. We find also among the 

 Chaldeans the use of the clepsydra as a clock, of the gnomon as an 

 instrument for measuring solstices, and of the hemispherical dial called 

 by the Greeks irxd^ri, for ascertaining the positions of the sun. "By the 

 clepsydra they were enabled to divide the ecliptic nearly into twelve 

 .equal parts, and are thus said to have invented the zodiac. 



The Egyptians have left us no observations, and few astronomical 

 relics, the meaning of which can be made very clear, though it is 

 probable that they were the first instructors of the Greeks. Their 

 year was of 365 days : for their method of correcting it, see SOTHIAC 

 PERIOD. They observed eclipses, but none have come to us ; they 

 foretold comets, according to Diodorus ; but as this author also 

 mentions at the same time that they foretold future events, it becomes 

 doubtful whether we are to understand that their predictions were 

 successful. The idea attributed to them that Mercury and Venus 

 moved round the sun is not mentioned by Ptolemy ; whose silence on 

 this and many other points, writing as he did in Egypt, is remarkable, 

 unless it be admitted at once as a proof of exaggeration in the pre- 

 ceding accounts. The correct manner in which some of the pyramids 

 are said to be placed north and south has always been quoted as a 

 ground of suspicion, that these buildings had some astronomical use. 

 The zodiac has also been attributed to the Egyptians. [DENDERAH, 

 ZODIAC OF.] The only attempt at a measure which we have remain- 

 ing is one of the diameter of the sun, the meaning of which is obscure; 

 but if what Delambre mentions (without citing his authority) be true, 

 that they measured time by the distance run l/y a horse, as well as by 

 the clepsydra, we need not be surprised that Ptolemy found no 

 assistance from their ancient observations. The story of Thales 

 teaching the Egyptians how to find the height of the pyramids by the 

 shadow, and that in Herodotus, of his being told by them that the sun 



