Unfortunately, we know very little as to the personal history of
Ptolemy. He was a native of Egypt, and though it has been sometimes
conjectured that he belonged to the royal families of the same name,
yet there is nothing to support such a belief. The name, Ptolemy,
appears to have been a common one in Egypt in those days. The time
at which he lived is fixed by the fact that his first recorded
observation was made in 127 AD, and his last in 151 AD. When we add
that he seems to have lived in or near Alexandria, or to use his own
words, "on the parallel of Alexandria," we have said everything that
can be said so far as his individuality is concerned.

Ptolemy is, without doubt, the greatest figure in ancient astronomy.
He gathered up the wisdom of the philosophers who had preceded him.
He incorporated this with the results of his own observations, and
illumined it with his theories. His speculations, even when they
were, as we now know, quite erroneous, had such an astonishing
verisimilitude to the actual facts of nature that they commanded
universal assent. Even in these modern days we not unfrequently find
lovers of paradox who maintain that Ptolemy's doctrines not only seem
true, but actually are true.

In the absence of any accurate knowledge of the science of mechanics,
philosophers in early times were forced to fall back on certain
principles of more or less validity, which they derived from their
imagination as to what the natural fitness of things ought to be.
There was no geometrical figure so simple and so symmetrical as a
circle, and as it was apparent that the heavenly bodies pursued
tracks which were not straight lines, the conclusion obviously
followed that their movements ought to be circular. There was no