The poetical impression of any object is that uneasy, exquisite sense of beauty or power that cannot be contained within itself; that is impatient of all limit; that (as flame bends to flame) strives to link itself to some other image of kindred beauty or grandeur; to enshrine itself, as it were, in the highest forms of fancy, and to relieve the aching sense of pleasure by expressing it in the boldest manner, and by the most striking examples of the same quality in other instances.

Lectures on the English Poets (1818) - Lecture I, "On Poetry in General"