Frank J. Wilstach, comp. A Dictionary of Similes. 1916.

Tranquil

Tranquil as night.
—Anonymous

Tranquil as a star.
—Alfred Austin

As tranquil and unmoved as Fate.
—Ambrose Bierce

Tranquil like a summer cloud
Which, having rained itself to a tardy peace,
Stands still in heaven as if it ruled the day.
—Elizabeth Barrett Browning

Tranquil as a child who goes to gather flowers.
—Fernán Caballero

Tranquil as a marble statue.
—Theodore S. Fay

Tranquil as the clear moonlight, that woos the palms on Orient shores.
—Paul Hamilton Hayne

More tranquil than a musk-rose blowing in a green island.
—John Keats

Tranquil as a summer sea.
—William Wordsworth

Tranquil as a dreamless sleep.
—William Wordsworth