This text comes from The Poetical Works of John Keats, a historical songbook transcribed on Wikisource and reproduced from the pinned revision linked below.
Byron! how sweetly sad thy melody!
Attuning still the soul to tenderness,
As if soft Pity, with unusual stress,
Had touched her plaintive lute, and thou, being by,
Hadst caught the tones, nor suffered them to die.
O'ershading sorrow doth not make thee less
Delightful: thou thy griefs dost dress
With a bright halo, shining beamily,
As when a cloud the golden moon doth veil,
Its sides are tinged with a resplendent glow,
Through the dark robe oft amber rays prevail,
And like fair veins in sable marble flow;
Still warble, dying swan! still tell the tale,
The enchanting tale, the tale of pleasing woe.