665 



ASTRONOMY. 



ASTRONOMY. 



6?6 



Arabs the Almagest [ALMAGEST ; SYNTAXIS] is the work from which we 

 derive most of our knowledge of the Greek astronomy. We find there 

 a full account of the observations and discoveries of Hipparchus ; those 

 of Ptolemy himself ; the reasons and elements of his system ; various 

 mechanical arguments against the motion of the earth, which show 

 that the first principles of dynamics were utterly unknown ; a descrip- 

 tion of the heavens and the Milky Way, and a catalogue of stars, which 

 we may be nearly certain was that of Hipparchus, reduced to his own 

 time by an assumed value for the precession, but which has been 

 asserted to have been corrected by new observations ; a theory of the 

 planetary motions ; the length of the year ; the instruments he 

 employed, &c. 



The Ptolemaic system [for more detail of which see PTOLEMAIC 

 SYSTEM] was an attempt to represent the motions of the planets by 

 supposing them to move uniformly in circles, the centres of which 

 circles themselves moved uniformly in circles round the earth. The 

 angular motions of the planets, as then known, were sufficiently well 

 represented by this system ; not so their changes of distance from the 

 earth, as seen in their apparent diameters. This was the universal 

 system of after-times till Copernicus. 



The principal discovery of Ptolemy is that of the LUNAR EVECTION 

 (which see), an inequality such as would be caused by an alternate 

 increase and diminution of the eccentricity of the moon's orbit. He 

 alo discovered the REFRACTION (which see), and made some tolerably 

 correct experiments to determine its law. He explained the apparent 

 enlargement of the discs of the sun and moon when near the horizon. 

 He extended the projection of the sphere of Hipparchus. He entered 

 into the investigation of every point which Hipparchus had touched ; 

 in some instances finding more correct values; in others, altering 

 without amending. He was not an astronomer only, but wrote on geo- 

 graphy, music, chronology, mechanics, and, unfortunately, on astrology. 



With Ptolemy the originality of the Greek school ends. We must 

 come to the Arabs before we find anything worth particular notice. 



Sextui Empirlcui, A.D. 173, described and wrote against the Chaldean 

 astrology. 



Cenmtrinus, A.D. 238, wrote an astrological work on the day of nativity, 

 containing historical information with regard to astronomy. 



Julius Firmicttit Maternut, A.D. 370, wrote on astronomy. 



Pappus of Alexandria, A.D. 383. His commentary on Ptolemy is 

 nearly all lost. 



Them of Alexandria, A.D. 385, the most celebrated commentator on 

 Ptolemy. He was a good mathematician, but no great astronomer. 

 He has however left some tables, and a method of constructing 

 almanacs. 



f/<,/iatia (his daughter), murdered A.D. 415, the first female on 

 record celebrated for her scientific talents. She wrote one book of her 

 father's commentary, and constructed some tables. 



ifartiana* Capclla, A.D. 470, in his ' Satyricon,' has some astrono- 

 mical notions, among which is the following : that Mercury and Venus 

 move round the sun. Cicero and Macrobius give the same idea ; but the 

 passage of Martianus is remarkable as being reported to have turned 

 the attention of Copernicus to the system which bears his name. 



Tfo'tw of Athens, A.D. 500, has left six observations of lunar occul- 

 tations and solstices : the only obserration* recorded between Ptolemy and 

 the Arabt. 



/Jiciia, A.D. 546, has left a commentary on, and description of, 

 the astronomical work of Aristotle, which we have mentioned as lost. 



Procliu Diadochv* (the commentator of Euclid), A.D. 550, wrote a 

 commentary on the astrology of Aristotle, and a description of astrono- 

 mical phenomena. 



Isidore, archbishop of Hispalis (Seville), A.D. 636, wrote a theological 

 work on astronomy. 



Bede, A.D. 720, and Barlaam the monk, A.D. 1330, are attached to the 

 preceding by Delambre. Both wrote astronomical works of little dis- 

 tinct merit. The last Greek writer on astronomy of the least note is 

 Michel PteUw, A.D. 1050. 



It is remarkable that, excepting his own commentators, few of the 

 authors who flourished during the period immediately succeeding ever 

 quote Ptolemy. Had it not been for the Arabs, the writings of the 

 latter must have been lost. 



The Alexandrian school was destroyed by the Saracens under Omar, 

 A.D. 640 ; and the rise of astronomy among the eastern Saracens dates 

 from the building of Bagdad by the Caliph Al Mansur, in the year 762. 

 In the reign of this prince translations of the Greek writers were begun ; 

 and, with nearly the same instruments and the same theory as Ptolemy, 

 a career of four centuries of observation commenced, during which 

 many astronomical elements, and in particular the obliquity of the 

 ecliptic, and the precession of the equinoxes, were more accurately 

 determined. 



In the reign of Al Mamoum, son of Harun al Rashid, himself a diligent 

 observer, great encouragement was given to astronomy. A degree of 

 th meridian was measured, but with what accuracy cannot be known, 

 from our ignorance of the measure employed. 



AUiateyniut, or Al-Batani, A.D. 880, discovered the motion of the 

 solar apogee, corrected the value of the precession, the solar eccentricity, 

 and the obliquity of the ecliptic, and published tables. He is the first 

 who made use of sines (instead of chords) and versed sines. He found 

 the length of the year, more accurately. He is, beyond all doubt, the 



only distinguished observer of whom we know anything between 

 Hipparchus and Tycho Brand. 



Alfraganui, or Al-Fergadl, and Thabet ben Korrali, both about 

 A.D. 950. The first has left a work on astronomy ; the second is prin- 

 cipally remarkable by his having revived an old notion of the Greeks 

 (not mentioned by Ptolemy, but by Theon) of a variation in the position 

 of the ecliptic, which has been called a trepidation. (See ' Hist. Ast./ 

 Library of Useful Knowledge, p. 33.) 



Ebn Tunis, and Abul- Wefa, about A.D. 1000. The former, an 

 Egyptian, an observer and mathematician of great merit, has left a 

 work containing tables and observations. He first noted the time of the 

 beginning and end of an eclipse by taking the altitude of a star. His 

 work shows an increasing knowledge of trigonometry. He was the first 

 who employed subsidiary angles. Abul-Wefa first formally used tan- 

 gents, cotangents, and secants, which Albategnius had overlooked. 

 He gave tables of tangents and cotangents. 



Alphetragius of Morocco, 1050, attempted a new explanation of the 

 planetary motions, not worthy of further notice. 



Arsachd, a Spanish Moor, 1080, has left some tables [TOLEDO, 

 TABLES OF] of indifferent accuracy. His contemporary, Alhazen, wrote 

 on refraction. Geber, also a Spaniard (about 1080 ?), made some 

 improvements in spherical trigonometry. He introduced the use of 

 the cosine. 



Abid Hassan, about 1200, has left a catalogue of stars, and some 

 improvements in dialling. 



We have Persian tables (of the 1 1th century ?) translated by George 

 Chrysococca, a Greek physician, in the 1 4th century ; but the best 

 known are those of Nasireddin, published in 1270, under the pro- 

 tection of Hulagu, grandson of Jenghis Khan, and conqueror of 

 Persia. The Persians have a method of intercalating their solar years, 

 which, though complicated, is of surprising accuracy, but when they 

 first began to employ it is unknown. [CALENDAR.] 



Ulug Beg, grandson of Timur, 1433. This prince made a large 

 number of observations at Samarcaud. His catalogue of stars of the 

 date above-mentioned, was, in its day, the most correct ever published. 

 He also gave tables of geographical latitudes and longitudes. The 

 Emperor Akbar (sixth from Timur, died 1605) also encouraged astro- 

 nomy, and caused many Hindoo works to be translated into Persian. 



In China, Cucheoii-King 1280, patronised by Kublai, brother of 

 Hulagu, and fifth successor of Jenghis Khan, in the partial conquest 

 which that prince made of China, made a great number of good obser- 

 vations. He introduced spherical trigonometry, and rejected the 

 ancient chronology. 



Since the loth century, astronomy has declined throughout the 

 East. The Chinese received many methods from the Jesuits, but to 

 little purpose. Among the Hindoos, there are very few who can 

 understand the ancient writings. The Turks and Persians have 

 little besides astrology. We now proceed with the chain of European 

 astronomy. 



Astronomy was introduced again into Europe by means of the Greek 

 writers, mostly through translations from the Arabic. The first trans- 

 lation of the ' Almagest ' was made under the auspices of the Emperor 

 Frederic II., about 1230. 



Sacroboscg (an Englishman named ffoli/wood), 1220, wrote a work 

 on the sphere taken from Ptolemy, &c. It continued for a long time 

 in great repute. He also wrote on the Calendar. About the same 

 time, Jardanut wrote a curious work on the Planisphere. 



Alonso X., king of Castile, 1252, with the assistance of Arabs and 

 Jews, formed the first European tables. They differ little from those 

 of Ptolemy. [ALONSISE TABLES.] 



Jloyer Bacon, 1255, wrote on the phenomena of astronomy. (For 

 writers of this period, not worth naming, see Delambre, ' Hist. Ast. 

 Moy.' pp. 258, 444.) 



The Cardinal Ciwa, 1440, wrote on the correction of the Calendar. 

 He is said to have maintained the motion of the earth. 



George Purbach, 1460, extended trigonometrical tables, and published 

 a theory of the planets based on that of Ptolemy. 



John Miiller, called Reyiomontqnw (died 1476), made an abridgment 

 of the '.Almagest,' published more extensive trigonometrical tables, 

 extended various parts of trigonometry, and was an observer, though 

 not, in this respect, superior to some of the Arabs. His almanacs 

 were the first which were worthy of the name, and were in great repute. 



The two last-mentioned writers deserve some special notice, though 

 it cannot be said that they made any direct advances either in theory 

 or observation. Their writing, and the facilities afforded by their 

 tables, undoubtedly did much to promote a taste for astronomy. 



George of Trebizimd, called Trapezuntius, who died 1486, first trans- 

 lated the ' Almagest ' from the Qreek into Latin. 



Bianchini, 1495, published tables similar to those of Alonso. 



Waltlierus (died 1504), a pupil of Regiomontanus, made numerous 

 observations which were often reprinted. 



The following names are inserted that the reader may know to what 

 names to refer for the astronomy of the time immediately preceding 

 the promulgation of the system of Copernicus. Except in this point 

 of view, there is but little interest attached to their labours : 



Riccius, 1521, wrote a work on astronomy, containing much historical 

 discussion. 



Werner (died 1528), gave a more correct value of the precession. 



