PTOLEMY. 
pritalogiie of the fixed stars; and formed 
tiiljles, by which the motions of tlie sun, 
moon, and planets might be calculated and 
regulated. He was, indeed, the first who 
collected the scattered and detached obser- 
vations of the ancients, and digested them 
into a system, which he set forth in his 
“ Mfyatifi XuvraliK, aive Magna Constructio,’’ 
divided into thirteen books. He adopts and 
exhibits here the ancient system of the 
woiid, which placed the earth in'the centre 
of the universe ; and this has been called, 
tVom him, the Ptolemaic System, to distin- 
guish it from those of Copernicus and Tycho 
ISrahe, 
About the year 827, this work was trans- 
lated by the Arabians into their language, 
in which it was called “ Almagestum,” by 
order of one of their kings ; and from Ara- 
bic into Latin, about 1230, by the encou- 
ragement of the Emperor Frederic 11. 
There were also other versions from the 
Arabic into Latin ; and a manuscript of one 
done by Girardus Cremonensis, who flou- 
rished about the middle of the fourteenth 
century,. Fabricins 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 the fifteenth century, and 
was first published by Simon Grynaeus, at 
Basil, 1538, in folio, with the eleven books 
of Commentaries by Theon, who flourished 
at Alexandria in the reign of the elder Theo- 
dosius. 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 Caraerarius. 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 partictilar account. In general 
it may 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 mo- 
tions are all directed by one, which Pto- 
lemy calls the priinum mobile, or First 
Mover, of which he discourses at large. 
But, to be more particular, this great work 
is divided into thirteen books. 
In the first book, Ptolemy shows that the 
earth is in the centre of those orbs, and of 
the universe itself, as he understood it ; he 
represents the earth as of a spherical figure, 
and but as a point in comparison of the rest 
of the heavejily bodies : he treats concern- 
ing the several circles of the earth, and 
their distances from the equator ; as also of 
the right and oblique ascension of the hea- 
venly bodies in a right sphere. 
In the second book he treats of the habi- 
table parts of the earth ; of the elevation 
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 depend- 
ing on the same. 
In the third book he treats of the quan- 
tity ot the year, and of the unequal motion 
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 inequality of days and 
nights. 
In the fourth book he treats of the lunar 
motions, and their various phenomena ; he 
gives tables for finding the moon’s mean 
motions, with her latitude and longitude ; 
he discourses largely concerning lunar epi- 
cycles ; and by comparing the times of a 
great number of eclipses mentioned by Hip- 
parchus, Calippus, and others, he has com- 
puted the places of the sun and moon, ac- 
cording to their mean motions, from the first 
year of Nabonazar, 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 accord- 
ing to her distance from the sun ; he also 
gives tables, and an universal canon for the 
inequality of the lunar motions : he theq 
treats of the different aspects or phases of 
the moon, and gives a computation of the 
diameter of the sun and moon, with the 
magnitude of the sun, moon, and earth com- 
pared together ; he states also the different 
measures of the distance of the sun and 
moon, according as they are determined by 
ancient mathematicians 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 parti- 
culars. 
In the seventh book he treats of the fixed 
stars, and shows the methods of describing 
them, ill their various constellations, on the 
surface of an artifidal sphere or globe ; he 
rectifies the places of the stars to his ow'n 
