340 



GREEK SCIENCE. 



the stars. 



Ptolemy. 

 A. c. 120. 



cities, as we do those of the stars, by circles drawn through the poles 

 perpendicularly to the equator; that is, by latitudes and by circles 

 parallel to the equator, corresponding to our longitudes. From his 

 projection it is, that our maps and nautical charts are now principally 

 constructed, and his method, by means of eclipses, was for a long 

 time the only one by which the longitude could be determined. 

 Catalogue of Another most important work of Hipparchus, was his formation of 

 a catalogue of the stars* The appearance of a new star in his time, 

 caused him to form the grand project of enabling future astronomers 

 to ascertain whether the general picture of the heavens were always 

 the same. This he aimed to effect, by attempting the actual enume- 

 ration of the stars. The magnitude and difficulty of the undertaking 

 did not deter this indefatigable astronomer ; he prepared and arranged 

 an extensive catalogue of the fixed stars, which subsequently served as 

 the basis of that of Ptolemy. So great, indeed, is the merit of this 

 prince of Grecian astronomy, that the enthusiastic language in which 

 Pliny speaks of him in his Hist. Nat. (lib. ii. cap. 26) may rather be 

 admired than censured. 



After Hipparchus, we meet with no astronomer of eminence amongst 

 the Greeks till the time of Ptolemy, who flourished between the years 

 125 and 140 of the Christian era; a space of nearly three hundred 

 years. There were, however, some astronomical writers, both Greeks 

 and Romans in the course of this time, whom it may not be amiss to 

 enumerate, although the little progress that the science made in their 

 hands will exempt us from the necessity of entering minutely into an 

 analysis of their several works : these were, Geminus, who lived about 

 70 years B. c., whose book is entitled * Introduction to the Phenomena;' 

 Achilles Tatius, of about the same period ; Cleomedes, who lived in 

 the time of Augustus; Theodosius, Menelaus, and Hypsicles, who 

 are supposed to have written about the year 50 B. c. ; Manilius, Strabo, 

 Posidonius, and Cicero, who were about half a century later; after 

 which, we meet with no one to whom it is at all necessary even to 

 refer, till we come to Ptolemy, who was born in the year of Christ 70; 

 and who made, as we have stated above, most of his observations 

 between the years 125 and 140 of our era. 



Ptolemy has rendered all succeeding astronomers indebted to him, 

 both for his own observations, which were very numerous, and his 

 construction of various tables, but most of all for the important collec- 

 tion which he made of all astronomical knowledge prior to his time, 

 and which he entitled, MeyaX?/ Zvvraic, or Great Collection. 1 Of 

 his own labours, we may mention his theory and calculation of tables 

 of the planets, and his determination, with a precision little to be 

 expected in his time, of the ratio of their epicycles to their mean dis- 

 tances; that is to say, in other terms, the ratio of their mean distances 

 to the distance of the earth from the sun. This theory, imperfect as 



1 Called by the Arabs, who translated it, the Almagest (from the Arabic art. al, 

 and the Greek superlative megistos, greatest). 



Various 

 labours of 

 Ptolemy. 



