As the tale, then, is told by Plato, in the tenth book of “The Republic”, one Er the son of Armenius, a Pamphylian, was slain in battle; and ten days afterwards, when they collected the dead for burial, his body alone showed no taint of corruption.  His relatives, however, bore it off to the funeral pyre; and on the twelfth day, lying there, he returned to life, and he told them what he had seen in the other world.  Many wonders he related concerning the dead, for example, with their rewards and punishments:  but what had impressed him as most wonderful of all was the great spindle of Necessity, reaching up to Heaven, with the planets revolving around it in graduated whorls of width and spread:  yet all concentric and so timed that all complete the full circle punctually together—­’The Spindle turns on the knees of Necessity; and on the rim of each whorl sits perched a Siren who goes round with it, hymning a single note; the eight notes together forming one harmony.’

Now as—­we have the divine word for it—­upon two great commandments hang all the law and the prophets, so all religions, all philosophies, hang upon two steadfast and faithful beliefs; the first of which Plato would show by the above parable.

It is, of course, that the stability of the Universe rests upon ordered motion—­that the ‘firmament’ above, around, beneath, stands firm, continues firm, on a balance of active and tremendous forces somehow harmoniously composed.  Theology asks ‘by What?’ or ‘by Whom?’ Philosophy inclines rather to ask ‘How?’ Natural Science, allowing that for the present these questions are probably unanswerable, contents itself with mapping and measuring what it can of the various forces.  But all agree about the harmony; and when a Galileo or a Newton discovers a single rule of it for us, he but makes our assurance surer.  For uncounted centuries before ever hearing of Gravitation men knew of the sun that he rose and set, of the moon that she waxed and waned, of the tides that they flowed and ebbed, all regularly, at times to be predicted; of the stars that they swung as by clockwork around the pole.  Says the son of Sirach: 

     At the word of the Holy One they will stand in due order,
     And they will not faint in their watches.

So evident is this calculated harmony that men, seeking to interpret it by what was most harmonious in themselves or in their human experience, supposed an actual Music of the Spheres inaudible to mortals:  Plato as we see (who learned of Pythagoras) inventing his Octave of Sirens, perched on the whorls of the great spindle and intoning as they spin.

Dante (Chaucer copying him in “The Parlement of Fowls”) makes the spheres nine:  and so does Milton: 

     then listen I
  To the celestial Sirens harmony,
  That sit upon the nine infolded Sphears,
  And sing to those that hold the vital shears,
  And turn the Adamantine spindle round
  On which the fate of gods and men is wound. 
  Such sweet compulsion doth in musick lie
  To lull the daughters of Necessity,
  And keep unsteady Nature to her law,
  And the low world in measur’d motion draw
  After the heavenly tune....