The literary technique of personification is sparsely used in Shelley's Frankenstein. I might speculate that this is to underscore the rational qualities that seem to both lead to the creature's creation and condemn his creation. This would provide an additional instance of the theme of duality that is so important in Frankenstein. One instance of personification occurs in Chapter 22 while Victor is exclaiming to his father that he is in fact culpable for the deaths of his wife and sons.
Justine, poor unhappy Justine, was as innocent as I, and she suffered the same charge; she died for it; and I am the cause of this—I murdered her. William, Justine, and Henry—they all died by my hands."
Victor's father begs for an explanation to these wild assertions and yet Victor can tell him nothing as anything he could say would reveal his dreadful experimentation and his creation of the monster creature. Victor is bound for all his life to keep the strictest secrecy no matter how deeply he longs for sympathy and comfort from another living soul--he knows it is doubtful that he would receive sympathy or comfort.
His father implores him and Victor replies. It is in the reply that we find the personification [there is an interesting distinction between personification and pathetic fallacy, a subcategory of personification].
"My dearest Victor, what infatuation is this? My dear son, I entreat you never to make such an assertion again."
"I am not mad," I cried energetically; "the sun and the heavens, who have viewed my operations, can bear witness of my truth."
Personification is the literary technique that gives human qualities to that which is nonhuman. Victor is saying that the nonhuman Sun and Moon have watched what he did--watching is a human characteristic--and can bear witness to the truth of his words. Bearing witness to or attesting the truth of a statement is an exclusively human characteristic (as far as we know yet at any rate!). By giving the Sun and Moon the ability to discerningly watch, then attest that Victor's statements match the truth of what they watched, Victor has personified the Sun and Moon.