ASTRONOMY. 
ciple, who got his sentence of death changed 
into exile. Next after the Ionian school, 
was that of Pythagoras, who was born at 
Samos, about the year 586 before the 
Christian sera, and who, in the celebrity he 
acquired, far exceeded his predecessors. 
Like Thales, he visited Egypt, and after- 
wards the Brachmans of India, from whom 
he is supposed to have obtained many of 
the astronomical truths which he brought 
with him into Italy, to which country he 
was obliged to retire on account of the des- 
potism which then prevailed at Athens. 
Here he first taught the true system of the 
world, which, many centuries after, was 
revived by Copernicus; but hid his doc- 
trines from the vulgar, in imitation of the 
Egyptian priests, who had been his instruc- 
tors. It was even thought, in this school, 
that the planets were inhabited bodies, like 
the earth; and that the stars, which are 
disseminated through infinite space, are 
suns, and the centres of other planetary 
systems. They also considered the comets 
as permanent bodies, moving round the 
sun ; and not as perishing meteors, formed 
in the atmosphere, as they were thought to 
be in after times. From this time to the 
foundation of the school of Alexandria, 
the history of astronomy among the Greeks 
offers nothing remarkable, except some at- 
tempts of Eudoxus to explain the celestial 
phenomena ; and the celebrated cycle of 
19 years, which had been imagined by 
M eton, in order to conciliate the solar and 
lunar motions. This is the most accurate 
period, for a short interval of time, that 
could have been devised for embracing an 
exact number of revolutions of these two 
luminaries ; and is so simple and useful, 
that when Meton proposed it to the Greeks 
assembled at the Olympic games, as the’ 
basis of their calendar, it was received with 
great approbation, and unanimously adopted 
by all their colonies. In the school of 
Alexandria, we see for the first time, a 
combined system of observations, made 
with instruments proper for measuring an- 
gles, and calculated trigonometrically. As- 
tronomy accordingly took a new form, 
which succeeding ages have only brought 
to greater perfection. The position of the 
stars began at this time to be determined ; 
they [traced the course of the planets with 
great care; and the inequalities of the 
solar and lunar motions became better 
known. It was, in short, in this celebrated 
school, that a new system of astronomy 
arose, which embraced the whole of the 
celestial motions; and though inferior to 
that of Pythagoras, and even false in theory, 
it afforded the means, by the numerous ob- 
servations which it furnished, of detecting 
its own fallacy, and of enabling astronomer* 
in later times to discover the true system 
of nature. It was from their observations 
of the principal zodiacal stars, that Hippar- 
chus was led to discover the precession of 
the equinoxes ; and Ptolemy also founded 
upon them his theory of the motions of the 
planets. Next after these w r as Aristarchus 
of Samos, who made the most delicate 
elements of ^he science the objects of his 
research. Among other, things of this kind, 
he attempted to determine the magnitude 
and distance of the sun; and though, as 
may be supposed, the results he obtained 
were considerably wide of tbe truth, the 
methods he employed to resolve these dif- 
ficult problems do great honour to his ge- 
nius. The celebrity of his successor Era- 
tosthenes, arises chiefly from his attempt to 
measure the earth, and his observations on 
the obliquity of the ecliptic. Having re- 
marked at Syene, a well w'hieh was enligh- 
tened to its bottom by the sun, on the day 
of the summer solstice, he observed the 
meridian height of the sun on the same day 
at Alexandria ; and found that the celestial 
arc contained between the two places was 
the 50th part of the whole circumference ; 
and as their distance was estimated at 500 
Stadia, he fixed the length of a great circle 
of the earth at 250,000 ; but as the length 
of the stadium employed by this astronomer 
is not known, we cannot appreciate tbe ex- 
actness of his measurement. Among others 
wiio cultivated and improved this science, 
we may also mention the celebrated Archi- 
medes, who constructed a kind of plane- 
tarium, or orrery, for representing the prin- 
cipal phenomena of heavenly bodies. But 
of all the astronomers of antiquity, Hippar- 
chus of Bitliynia is the one, who, by the 
number and precision of iiis observations, 
as well as by the important result which 
he derived from them, is the most entitled 
to our esteem. He flourished at Alexan- 
dria about the year 162 before the Chris- 
tian sera; and began his astronomical la- 
bours by attempting to determine, with 
more exactness than had hitherto been 
done, the length of the tropical year, which 
he fixed at 365 days, 5 hours, and 55 mi- 
nutes, being nearly 4j minutes too great. 
Like most of his predecessors, he founded 
his .system upon an uniform circular motion 
of the sun ; but instead of placing the earth 
