Irony is an insult conveyed in the form of a compliment.
In Lectures on Subjects Connected with Literature and Life (1859), Lecture III : Wit and Humor, p. 102
From the hour of the invention of printing, books, and not kings, were to rule the world. Weapons forged in the mind, keen-edged, and brighter than a sunbeam, were to supplant the sword and battle-axe. Books! lighthouses built on the sea of time! Books! by whose sorcery the whole pageantry of the world's history moves in solemn procession before our eyes. From their pages great souls look down in all their grandeur, undimmed by the faults and follies of earthly existence, consecrated by time.
Reported in Josiah Hotchkiss Gilbert, Dictionary of Burning Words of Brilliant Writers (1895), p. 386.