What literary devices are used in Chapter 3 of Frankenstein?

Victor discusses what it felt like to think so intensely on the same subject for an extended period of time.  He says that in "the midst of this darkness a sudden light broke in upon [him] -- a light so brilliant and wondrous, yet so simply, that [he] became dizzy with the immensity of the prospect which it illustrated [...]."  Light has often been connected to knowledge in the novel, and thus it functions as a symbol.  Victor describes an intellectual breakthrough as though it were a light pouring over him.  Importantly, though, light can be both life-giving as well as dangerous, just as knowledge can be.

The motif of knowledge returns again in the chapter when Victor tells Captain Walton to "Learn from [him] [...] how dangerous is the acquirement of knowledge, and how much happier that man is who believes his native town to be the world [...]."  A motif is a recurring symbol that is often connected to theme.  Certainly one theme of this novel is that knowledge can be both a positive force as well as a destructive one.  The light motif is furthered by Victor's assertion that, with his knowledge, he will "pour a torrent of light into [their] dark world."  He believes that he will be able to render humans invulnerable to disease with his discoveries. 

Victor also employs a metaphor when he says that his "eyes swim with the remembrance" of what he thought at the time.  His eyes, of course, don't really swim, but he is describing the tears produced by remembering how naive he was, back before he created a monster (literally).  There are so many tears now, that he compares the quantity of water to a deep pool or a flood.  In other words, he feels great remorse in this moment.

As he worked on his experiment, Victor says that his "eyes were insensible to the charms of nature."  This is an example of metonymy; he does not mean that he literally could not see nature's beauty but that he couldn't recognize it or its value.  Metonymy is the use of a detail associated with something for the thing itself.  In this case, his eyes and his physical sight stand in for his mind, his figurative ability to see truth, or to see what's important.

Victor also uses allusions when he refers to the histories of various countries in the world (Greece, America, Peru, etc.) and the ethical failures of people who failed to realize that we should not apply ourselves to pursuits that "[have] a tendency to weaken [our] affections, and to destroy [our] taste for [...] simple pleasures [...]."