(Those are pearls that were his eyes. Look!)
Shakespeare's The Tempest tells of the sorcerer Prospero, who along with his daughter has been exiled on a remote island for many years. Prospero engineers a shipwreck to reclaim his usurped position as the Duke of Milan. Among the shipwrecked is Ferdinand, prince of Naples and soon-to-be suitor to Proper's daughter, Miranda.
The lines quoted by Eliot are part of song by the spirit Ariel, servant to Prospero, telling Ferdinand that his father died in the shipwreck. Unbeknownst to Ferdinand, the spirit is lying.
From Act 1, Scene 2:
Where should this music be? i' the air or the earth?
It sounds no more: and sure, it waits upon
Some god o' the island. Sitting on a bank,
Weeping again the king my father's wreck,
This music crept by me upon the waters,
Allaying both their fury and my passion
With its sweet air: thence I have follow'd it,
Or it hath drawn me rather. But 'tis gone.
No, it begins again.
Full fathom five thy father lies;
Of his bones are coral made;
Those are pearls that were his eyes:
Nothing of him that doth fade
But doth suffer a sea-change
Into something rich and strange.
Later, in the note to line 218, Eliot links Ferdinand to both the Phoenician sailor and Fisher King. He returns to this passage throughout The Waste Land:
Those are pearls that were his eyes.
Musing upon the king my brother's wreck
And on the king my father's death before him.
“This music crept by me upon the waters”