In lines 57-60 of Juliet's speech, the literary device used is personification. Juliet is giving human qualities to inanimate objects, such as her heart, eyes, and earth. She is asking her heart to break, her eyes to go to prison and never see liberty, and the earth to resign its motion and become one with Romeo. By giving human characteristics to non-human things, Juliet is emphasizing the depth of her emotion and the overwhelming sadness she feels. This use of personification allows the reader to better understand the intensity of her feelings and the extent to which they are affecting her.