Astronomy was ardently studied at Alexandria, and was fortunately
combined with an assiduous study of mathematics. Aristarchus
(about 320-250 B.C.) calculated that the sun was 84,000,000 miles
away; a vast expansion of the solar system and, for the time, a
remarkable approach to the real figure (92,000,000) Eratosthenes
(276-196 B.C.) made an extremely good calculation of the size of
the earth, though he held it to be the centre of a small
universe. He concluded that it was a globe measuring 27,000
(instead of 23,700) miles in circumference. Posidonius (135-51
B.C.) came even nearer with a calculation that the circumference
was between 25,000 and 19,000 miles; and he made a fairly correct
estimate of the diameter, and therefore distance, of the sun.
Hipparchus (190-120 B.C.) made an extremely good calculation of
the distance of the moon.

By the brilliant work of the Alexandrian astronomers the old
world seemed to be approaching the discovery of the universe. Men
were beginning to think in millions, to gaze boldly into deep
abysses of space, to talk of vast fiery globes that made the
earth insignificant But the splendid energy gradually failed, and
the long line was closed by Ptolemaeus, who once more put the
earth in the centre of the system, and so imposed what is called
the Ptolemaic system on Europe. The keen school-life of
Alexandria still ran on, and there might have been a return to
the saner early doctrines, but at last Alexandrian culture was
extinguished in the blood of the aged Hypatia, and the night
fell. Rome had had no genius for science; though Lucretius gave
an immortal expression to the views of Democritus and Epicurus,
and such writers as Cicero and Pliny did great service to a later
age in preserving fragments of the older discoveries. The