So evident is this celestial harmony that men, seeking to account for it by what was most harmonious in themselves or in their experience, supposed an actual Music of the Spheres inaudible to mortals; Plato (who learned of Pythagoras) inventing his Octave of Sirens, spinning in the whorls of the great planets and intoning as they spin; Chaucer (who learned of Dante and makes the spheres nine) in his Parliament of Foules telling, out of Cicero’s Somnium Scipionis, how the great Scipio Africanus visited his descendant in a dream and—­

Shewed he him the litel erthe, that heer is, In regard of the hevenes quantite:  And after shewed he him the nyne speres, And after that the melodye herde he That cometh of thilke speres thryes-three That welle is of musicke and melodye In this world heer, and cause of armonye.

While Shakespeare in the last Act of The Merchant of Venice makes all the stars vocal, and not the planets only: 

There’s not the smallest orb which thou beholdest
But in his motion like an angel sings,
Still quiring to the young-eyed cherubims...

And Milton in Arcades goes straight back to Plato (save that his spheres are nine, as with Chaucer): 

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

From the greater poets let us turn to a lesser one, whom we shall have occasion to quote again by and by:  to the Orchestra of Sir John Davies (1596), who sees this whole Universe treading the harmonious measures of a dance; and let us select one stanza, of the tides: 

For lo, the sea that fleets about the land, And like a girdle clips her solid waist, Music and Measure both doth understand; For his great Crystal Eye is always cast Up to the Moon, and on her fixed fast; And as she daunceth in her pallid sphere, So daunceth he about the centre here.

This may be fantastic.  As the late Professor Skeat informed the world solemnly in a footnote, “Modern astronomy has exploded the singular notion of revolving hollow concentric spheres....” (The Professor wrote “singular” when he meant “curious.”—­The notion was never “singular.”) “These ‘spheres,’” he adds, “have disappeared, and their music with them, except in poetry.”  Nevertheless the fable presents a truth, and one of the two most important truths in the world.  This Universe is not a Chaos. (If it were, by the way, we should be unable to reason about it at all.) It stands and is continually renewed upon an ascertained harmony:  and what Plato called “Necessity” is the duty in all things of obedience to that harmony, the Duty of which Wordsworth sings in his noble Ode,