Posidonius, 6545.The correct figure is 11,726. It will be seen that these estimates continually improved (that of
Ptolemy, however, showed a retrogression); that of Posidonius * is about half the correct figure.
On the whole, their picture of the solar system was not so very far from the truth.Greek astronomy was geometrical, not dynamic. The ancients thought of the motions of the
heavenly bodies as uniform and circular, or compounded of circular motions. They had not the
conception of force. There were spheres which moved as a whole, and on which the various
heavenly bodies were fixed. With Newton and gravitation a new point of view, less geometrical,
was introduced. It is curious to observe that there is a reversion to the geometrical point____________________* Posidonius was Cicero's teacher. He flourished in the latter half of the second century. B.C.-216-of view in Einstein's General Theory of Relativity, from which the conception of force, in the
Newtonian sense, has been banished.
The problem for the astronomer is this: given the apparent motions of the heavenly bodies on the
celestial sphere, to introduce, by hypothesis, a third co-ordinate, depth, in such a way as to make
the description of the phenomena as simple as possible. The merit of the Copernican hypothesis is
not truth, but simplicity; in view of the relativity of motion, no question of truth is involved. The
Greeks, in their search for hypotheses which would "save the phenomena," were in effect, though
not altogether in intention, tackling the problem in the scientifically correct way. A comparison
with their predecessors, and with their successors until Copernicus, must convince every student
of their truly astonishing genius.
Two very great men, Archimedes and Apollonius, in the third century B.C., complete the list of
first-class Greek mathematicians. Archimedes was a friend, probably a cousin, of the king of
Syracuse, and was killed when that city was captured by the Romans in 212 B.C. Apollonius,
from his youth, lived at Alexandria. Archimedes was not only a mathematician, but also a
physicist and student of hydrostatics. Apollonius is chiefly noted for his work on conic sections. I
shall say no more about them, as they came too late to influence philosophy.
After these two men, though respectable work continued to be done in Alexandria, the great age
was ended. Under the Roman domination, the Greeks lost the self-confidence that belongs to
political liberty, and in losing it acquired a paralysing respect for their predecessors. The Roman
soldier who killed Archimedes was a symbol of the death of original thought that Rome caused
throughout the Hellenic world.