PTOLEMY 



PTOMAINES 



479 



authority on ancient astronomy, the system they 

 expound is called the Ptolemaic System, after the 

 author. 



As a geographer Ptolemy is the corrector and 

 improver of the works of a predecessor, Marinus 

 of Tyre, about whom, except from Ptolemy's 

 writings, little is known. Ptolemy's improve- 

 ments and suggestions are at once more valu- 

 able and correct ; but it is sometimes difficult 

 to separate his data from those of Mariuus. 

 His geography is divided into eight books, all 

 of which, with the exception of the first, eighth, 

 and a portion of the seventh, are nothing more 

 than a catalogue of places, with their latitude 

 and longitude (to 12ths of a degree), with a 

 brief general description prefixed to each continent 

 and country or tribe, and interspersed here and 

 there with remarks of a miscellaneous character 

 on any point of interest. The rest of the work con- 

 tains details regarding his mode of noting the posi- 

 tions of places by latitude (melcos) and longitude 

 (platos) with the calculation of the size of the 

 sphere of the earth, and of the extent of surface 

 then known. The latitudes were calculated from 

 Ferro (q.v. ) in the Canaries, chosen as the western- 

 most part of the world ; but lie counted it only 

 2J degrees W. of Cape St Vincent, instead of the 

 real distance, 9 20'. He took the parallel of 

 Khodi-s for his chief line of latitude, thinking it 

 occupied the mean position in the zone of climate 

 into which he divided the earth. He descril>es the 

 mode adopted by him of projecting the surface of a 

 hemisphere on a flat surface, and shows its superior- 

 ity over the projections of Eratosthenes, Hippar- 

 chtiH, and Marinus. He also constructed a series 

 of twenty-six maps, together with a general map 

 of the world, in illustration of his work. See MAP. 



The PTOLEMAIC SYSTEM of astronomy, so called 

 from Ptolemy, its chief expounder, was really 

 originated long before his time, and was, in 

 fact, merely an attempt to reduce to a scientific 

 form the common and primitive notions concern- 

 ing the motions of the heavenly bodies. It was 

 implicitly adopted by Plato, Aristotle, Hipparchus, 

 ana ( with the exception of the Pythagoreans, and 

 probably of Pythagoras himself) all the eminent 

 physicists and philosophers of ancient times ; pass- 

 ing from them to the Byzantines and Arabs, who, 

 especially the latter, were the means of dissem- 

 inating it through western Europe, where it con- 

 tinued to be the universally established doctrine 

 till the 16th century. The primary and funda- 

 mental doctrines of this system are that the earth 

 is the centre of the universe, and that the heavenly 

 bodies revolve round it in circles, and at a uniform 

 rate. These notions, which are naturally suggested 

 by the first general aspect of things, having, pre- 

 vious to any accurate observation, established 

 themselves as unquestionable axioms, phenomena 

 which were found on closer examination to be 

 inconsistent with them, were explained by the 

 introduction of additional hypotheses. The belief 

 that the earth is the centre of the universe was 

 supported by its accordance with the relation 

 of the primary elements of which the material 

 world was supposed to be composed. Thus, 

 earth, the most stable of the elements, held the 

 lowest place, and supported water, the second in 

 order; above water was placed air, and then fire, 

 ether being supposed to extend indefinitely above 

 the others. In or lieyond the ether element were 

 certain zones or heavens, each heaven containing 

 an immense crystalline spherical shell, the smallest 

 enclosing the earth and its superincumbent ele- 

 ments, and the larger spheres enclosing the smaller. 

 To each of these spheres was attached a heavenly 

 body, which, by the revolution of the crystalline, 

 was made to move round the earth. The first or 



innermost sphere was that of the moon, and after 

 it in order came those of Mercury, Venus, the 

 Sun, Mars, Jupiter, Saturn and the fixed stars, 

 eight in all. To this system later astronomers 

 added a ninth sphere, the motion of which should 

 produce the Precession of the Equinoxes (q.v.), and 

 a tenth to cause the alternation of day and night. 

 This tenth sphere, or primum mobile, was supposed 

 to revolve from east to west in twenty-four hours, 

 and to carry the others along with it in its motion ; 

 but the Ptolemaic astronomers do not venture to 

 explain how this was done, although, since the axis 

 of motion of the primum mobile was that of the 

 equator, its extremities being the poles of the 

 heavens, while that of the ninth sphere was the 

 axis of the ecliptic, some explanation was certainly 

 necessary. As observations of the heavens in- 

 creased in accuracy it was found that the heavenly 

 motions were apparently not uniform, and this 

 was explained as follows : The acceleration of the 

 sun on one side, and retardation on the other 

 side of his orbit is only apparent, and results 

 from the earth not being in the centre of the sun's 

 sphere, C (see fig.), but at E, and consequently 

 his motion appears to be slowest at P and quickest 

 at R. The alter- 

 nate progression 

 and regression of 

 the planets was 

 accounted for by 

 supposing them to 

 move, not directly 

 with their crystal- 

 lines, but in a 

 small circle, whose 

 centre was a fixed 

 point in the crys- 

 talline, and which 

 revolved on its axis 



as it was carried round with the latter ; thus (fig.) 

 the planet was carried round the small circle ABD, 

 as that circle was carried round PQR (now sup- 

 posed to represent the planetary crystalline). The 

 planet while in the outer portion of .its small circle 

 would thus have a forward, and in the inner por- 

 tion a backward motion. The larger circle was 

 called an eccentric, and the smaller an epicycle. 

 This theory of eccentrics and epicycles satisfied 

 the early astronomers ; but further investigation 

 showed its incompleteness, and in later times it 

 was found necessary to explain newly-discovered 

 discrepancies by heaping epicycle upon epicycle 

 till a most complex entanglement resulted. As 

 soon as astronomers came to understand and test 

 the Copernican Theory (see COPERNICUS), this 

 venerable and disorderly pile of hypotheses, which 

 had received the papal seal of infallibility, and 

 had in various forms held supreme sway over the 

 minds of men for twenty centuries, at once 

 crumbled to atoms and sunk into oblivion. See 

 ASTRONOMY. 



The Almagett and the Geography were the standard 

 text-books to succeeding ages, the first till the time of 

 Copernicus, the second till the great maritime discoveries 

 of the 15th century showed its deficiencies. They have 

 passed through numerous editions, the best of which are, 

 for the Almofiest and the most of Ptolemy's minor works, 

 that by Halma ( Paris, 4 vols. 1813-28) ; and for the Geo- 

 graphy, the Latin versions of 1482 and 1490, published 

 at Rome, the editio princeps of the Greek text by Erasmus 

 (1533), the Elzevir edition (1619), those of Wilberg and 

 Grashof (1K44), Nobbe (1845), Muller (Paris, 1883), and 

 the photographic reproduction of the MS. in the monas- 

 tery of Mount Atlios by Langlois (Paris, 1866). The 

 catalogue of stars has been frequently reprinted separately, 

 the best edition being that of Francis Baily, in vol. xiii. 

 of the Memoirs of the Royal Astronomical Society (1843). 



Ptomaines. It has been known for a very 

 long time that food which has undergone putra- 



