Great Astronomers | Page 8

same from all
stations if the earth were flat. When Ptolemy, therefore, demonstrated
that the time of sunset was not the same at various places, he showed
conclusively that the earth was not flat.
As the same arguments applied to all parts of the earth where Ptolemy
had either been himself, or from which he could gain the necessary
information, it followed that the earth, instead of being the flat plain,
girdled with an illimitable ocean, as was generally supposed, must be in
reality globular. This led at once to a startling consequence. It was
obvious that there could be no supports of any kind by which this globe
was sustained; it therefore followed that the mighty object must be
simply poised in space. This is indeed an astonishing doctrine to
anyone who relies on what merely seems the evidence of the senses,
without giving to that evidence its due intellectual interpretation.
According to our ordinary experience, the very idea of an object poised
without support in space, appears preposterous. Would it not fall? we
are immediately asked. Yes, doubtless it could not remain poised in any
way in which we try the experiment. We must, however, observe that
there are no such ideas as upwards or downwards in relation to open
space. To say that a body falls downwards, merely means that it tries to
fall as nearly as possible towards the centre of the earth. There is no
one direction along which a body will tend to move in space, in
preference to any other. This may be illustrated by the fact that a stone
let fall at New Zealand will, in its approach towards the earth's centre,
be actually moving upwards as far as any locality in our hemisphere is
concerned. Why, then, argued Ptolemy, may not the earth remain
poised in space, for as all directions are equally upward or equally
downward, there seems no reason why the earth should require any
support? By this reasoning he arrives at the fundamental conclusion
that the earth is a globular body freely lying in space, and surrounded
above, below, and on all sides by the glittering stars of heaven.
The perception of this sublime truth marks a notable epoch in the
history of the gradual development of the human intellect. No doubt,

other philosophers, in groping after knowledge, may have set forth
certain assertions that are more or less equivalent to this fundamental
truth. It is to Ptolemy we must give credit, however, not only for
announcing this doctrine, but for demonstrating it by clear and logical
argument. We cannot easily project our minds back to the conception
of an intellectual state in which this truth was unfamiliar. It may,
however, be well imagined that, to one who thought the earth was a flat
plain of indefinite extent, it would be nothing less than an intellectual
convulsion for him to be forced to believe that he stood upon a
spherical earth, forming merely a particle relatively to the immense
sphere of the heavens.
What Ptolemy saw in the movements of the stars led him to the
conclusion that they were bright points attached to the inside of a
tremendous globe. The movements of this globe which carried the stars
were only compatible with the supposition that the earth occupied its
centre. The imperceptible effect produced by a change in the locality of
the observer on the apparent brightness of the stars made it plain that
the dimensions of the terrestrial globe must be quite insignificant in
comparison with those of the celestial sphere. The earth might, in fact,
be regarded as a grain of sand while the stars lay upon a globe many
yards in diameter.
So tremendous was the revolution in human knowledge implied by this
discovery, that we can well imagine how Ptolemy, dazzled as it were
by the fame which had so justly accrued to him, failed to make one
further step. Had he made that step, it would have emancipated the
human intellect from the bondage of fourteen centuries of servitude to a
wholly monstrous notion of this earth's importance in the scheme of the
heavens. The obvious fact that the sun, the moon, and the stars rose day
by day, moved across the sky in a glorious never-ending procession,
and duly set when their appointed courses had been run, demanded
some explanation. The circumstance that the fixed stars preserved their
mutual distances from year to year, and from age to age, appeared to
Ptolemy to prove that the sphere which contained those stars, and on
whose surface they were believed by him to be fixed, revolved
completely around the earth once every day. He would thus account for

all the phenomena of rising and setting consistently with the
supposition that our globe was stationary. Probably