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Great Astronomers

Ptolemy
[PLATE: PTOLEMY.]
The career of the famous man whose name stands at the head of this chapter is one of the
most remarkable in the history of human learning. There may have been other discoverers
who have done more for science than ever Ptolemy accomplished, but there never has
been any other discoverer whose authority on the subject of the movements of the
heavenly bodies has held sway over the minds of men for so long a period as the fourteen
centuries during which his opinions reigned supreme. The doctrines he laid down in his
famous book, "The Almagest," prevailed throughout those ages. No substantial addition
was made in all that time to the undoubted truths which this work contained. No
important correction was made of the serious errors with which Ptolemy's theories were
contaminated. The authority of Ptolemy as to all things in the heavens, and as to a good
many things on the earth (for the same illustrious man was also a diligent geographer),
was invariably final.
Though every child may now know more of the actual truths of the celestial motions than
ever Ptolemy knew, yet the fact that his work exercised such an astonishing effect on the
human intellect for some sixty generations, shows that it must have been an extraordinary
production. We must look into the career of this wonderful man to discover wherein lay
the secret of that marvellous success which made him the unchallenged instructor of the
human race for such a protracted period.
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
 
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