Brewer's: Music of the Spheres
Pythagoras was the first who suggested the notion so beautifully expressed by Shakespeare-
There's not the smallest orb which thou beholdst But in his motion like an angel sings, Still quiring to the young-eyed cherubims.
Merchant of Venice. v. l.
Plato says that a siren sits on each planet, who carols a most sweet song, agreeing to the motion of her own particular planet, but harmonising with all the others. Hence Milton speaks of the “celestial syrens' harmony, that sit upon the nine enfolded spheres.” (Arcades. (See Nine Spheres.)
Maximus Tyrius says that the mere proper motion of the planets must create sounds, and as the planets move at regular intervals the sounds must harmonise.