apostrophe

Definition 
A figure of speech in which a speaker turns from the audience to address an absent person or abstract idea. It differs from a soliloquy in that the speaker of an apostrophe need not be alone on the stage. An example occurs in the second act of Hamlet, when the Prince turns from a conversation with Rosencrantz and Guildenstern to declare:

What a piece of work is a man, how noble in reason, how infinite in faculties, in form and moving how express and admirable, in action how like an angel, in apprehension how like a god: the beauty of the world, the paragon of animals—and yet, to me, what is this quintessence of dust?

Tyger, tyger, burning bright

In the forest of the night,

What immortal hand or eye

Could frame thy fearful symmetry?