PTOLEMY. 



called, from him, the Ptolemaic System, 

 to distinguish it from those of Copernicus 

 and Tycho Brahe. 



About the year 82?", this work was 

 translated by the Arabians into their lan- 

 guage, in which it was called "Almages- 

 tum," by order of one of their kings ; and 

 from Arabic into Latin, about 1230, by 

 the encouragement of the Emperor Fre- 

 deric II. There were also other versions 

 from the Arabic into Latin ; and a manu- 

 script of one done by Girardus Cremo- 

 nensis, who flourished about the middle 

 of the fourteeth century, Fabricius says, 

 is still extant in the library of All Souls 

 College, in Oxford. The Greek text of 

 this work began to be read in Europe in 

 Ihe fifteenth century, and was first pub- 

 lished by Simon Grynaeus, at Basil, 1538, 

 in folio, with the eleven books of Com- 

 mentaries by Theon, who flourished at 

 Alexandria in the reign of the elder The- 

 odosius. In 1541, it was reprinted at 

 Basil, with a Latin version by George 

 Trapezond; and again at the same place 

 in 1551, with the addition of other works 

 of Ptolemy, and Latin versions by Came- 

 rarius. We learn from Kepler, that this 

 last edition was used by Tycho. 



Of this principal work of the ancient 

 astronomers, it may not be improper to 

 give here a more particular account. In 

 .general it may be observed, that the work 

 is founded upon the hypothesis of the 

 earth's being at rest in the centre of the 

 universe, and that the heavenly bodies, 

 the stars and planets, all move round it in 

 solid orbs, whose motions are all directed 

 by one, which Ptolemy calls the primum 

 mobile, or First Mover, of which he dis- 

 courses at large. But, to be more parti- 

 cular, this great work is divided into thir- 

 teen books. 



In the first book, Ptolemy shows that, 

 the earth is in the centre of those orbs, 

 and of the universe itself, as he under- 

 stood it ; he represents the earth as of a 

 spherical figure, and but as a point in 

 comparison of the rest of the heavenly 

 bodies : he treats concerning the several 

 circles of the earth, and their distances 

 from the equator ; as also of the right and 

 oblique ascension of the heavenly bodies 

 in a right sphere. 



In the second book he treats of the 

 habitable parts of the earth ; of the ele- 

 vation of the pole in an oblique sphere, 

 and the various angles which the several 

 circles make with the horizon, according 

 to the different latitude of places ; also of 

 the phenomena of the heavenly bodies 

 depending on the same. 



VOL. V. 



In the third book he treats of the quan- 

 tity of the year, and of the unequal mo- 

 tion of the sun through the zodiac : he 

 here gives the method of computing the 

 mean motion of the sun, with tables of 

 the same ; and likewise treats of the in- 

 equality of days and nights. 



In the fourth book he treats of the lu- 

 nar motions, and their various phenome- 

 na ; he gives tables for finding 1 the moon's 

 mean motions, with her latitude and lon- 

 gitude ; he discourses largely concerning 

 lunar epicycles ; and by comparing the 

 times of a great number of eclipses men- 

 tioned by Hipparcus, Calippus, and 

 others, he has computed the places of 

 the sun and moon, according to their 

 mean motions, frcrn the first year of Xa- 

 bonazar, king of Egypt, to his own 

 time. 



In the fifth book he treats of the instru- 

 ment called the astrolabe , he treats also 

 of the eccentricity of the lunar orbit, and 

 the inequality of the moon's motion ac- 

 cording to her distance from the sun ; he 

 also gives tables and an universal canon 

 for the inequality of the lunar motions : 

 he then treats of the different aspects 

 or phases of the moon, and gives a com- 

 putation of the diameter of the sun and 

 moon, with the magnitude of the sun, 

 moon, and earth, compared together ; he 

 states also the different measures of the 

 distance of the sun and moon, according 

 as they are determined by ancient mathe- 

 maticians and philosophers. 



In the sixth book he treats of the con- 

 junctions and oppositions of the sun and 

 moon, with tables for computing the; 

 mean time when they happen ; of the 

 boundaries of solar and lunar eclipses ; of 

 the tables and methods of computing- the 

 eclipses of the sun and moon, with many 

 other particulars. 



In the seventh book he treats of the 

 fixed stars, and shows the methods of de- 

 scribing them, in their various constella- 

 tions, on the surface of an artificial sphere 

 or globe ; he rectifies the places of the 

 stars to his own time, and shows how dif- 

 ferent those places were then,. from -.vliat 

 they had been in the times of Timocharis, 

 Hipparcus, Aristillus, Calippus, and o- 

 thers : he then lays down a catalogue of 

 the stars in each of the northern constel- 

 lations, with their latitude, longitude, and 

 magnitudes. 



In the eighth book he gives a like ca- 

 talogue of the stars in the constellations 

 of the southern hemisphere, and in the 

 twelve signs or constellations of the zo- 

 diac. This is the first catalogue of the 



3S 



