Great Astronomers | Page 6

the name of Copernicus. We then
pass to those periods illumined by the genius of Galileo and Newton,
and afterwards we shall trace the careers of other more recent

discoverers, by whose industry and genius the boundaries of human
knowledge have been so greatly extended. Our history will be brought
down late enough to include some of the illustrious astronomers who
laboured in the generation which has just passed away.

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 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 argument in favour of
this notion, other than the merely imaginary reflection that circular
movement, and circular movement alone, was "perfect," whatever
"perfect" may have meant. It was further believed to be impossible that
the heavenly bodies could have any other movements save those which
were perfect. Assuming this, it followed, in Ptolemy's opinion, and in
that of those who came after him for fourteen centuries, that all the
tracks of the heavenly bodies were in some way or other to be reduced
to circles.
Ptolemy succeeded in devising a scheme by which the apparent

changes that take place in the heavens could, so far as he knew them,
be explained by certain combinations of circular movement. This
seemed to reconcile so completely the scheme of things celestial with
the geometrical instincts which pointed to the circle as the type of
perfect movement, that we can hardly wonder Ptolemy's theory met
with the astonishing success that attended it. We shall, therefore, set
forth with sufficient detail the various steps of this famous doctrine.
Ptolemy