Bīrūnī, Muḥammad ibn Aḥmad, Alberuni's India (v. 2)

(London :  Kegan Paul, Trench, Trübner & Co.,  1910.)



Jump to page:

Table of Contents

  Page 69  

CHAPTER LV.                               69

This theory differs from that on which Ptolemy has Ptoiemy on
based his computation of the distances of the planets tancesof
in the Kitdb-ctlmctnshurdt, and in which he has been page 236. "
followed both by the ancient and the modern astrono¬
mers.    It is their principle that the greatest distance
of a planet is equal to its smallest distance from the
next higher planet, and that between the two globes
there is not a space void of action.

According to this theory, there is between the two
globes a space not occupied by either of them, in which
there is something like an axis around which the rota¬
tion takes place. It seems that they attributed to the
aether a certain gravity, in consequence of which they
felt the necessity of adopting something which keep)s or
holds the inner globe (the planet) in the midst of the
outer globe (the sether).

It is well known among all astronomers that there On occuita-
is no possibility of distinguishing between the higher parallax.
and the lower one of two planets except by means of
the occultation or the increase of ih.e parallctx. However,
the occultation occurs only very seldom, and only the
parallax of a single planet, viz. the moon, can be ob¬
served. Now the Hindus believe that the motions are
equal, but the distances different. The reason why the
higher planet moves more slowly than the lower is the
greater extension of its sphere (or orbit); and the reason
why the lower planet moves more rapidly is that its
sphere or orbit is less extended. Thus, e.g. one minute
in the sphere of Saturn is equal to 262 minutes in the
sphere of the moon. Therefore the times in which
Saturn and the moon traverse the same space are dif¬
ferent, whilst their motions are equal.

I have never found a Hindu treatise on this subject,
but only numbers relating thereto scattered in various
books—numbers which are corrupt. Somebody objected
to Pulisa that he reckoned the circumference of the
sphere of each planet as 21,600, audits radius as 3438,
  Page 69