Authors:

The swan in the pool is singing, And up and down doth he steer, And, singing gently ever, Dips under the water clear.

Heinrich Heine (2016). “Delphi Complete Poetical Works of Heinrich Heine (Illustrated)”, p.159, Delphi Classics
The swan in the pool is singing, And up and down doth he steer, And, singing gently ever, Dips under the water clear.