This sentence compares books to magnets, which highlights the attraction of books. The rhetorical device of metaphor is actually the attraction of books, comparing books to magnets in sentences. From this sentence, we can only see the rhetorical devices of metaphor. There is the word like in the sentence, and all of them use metaphors. For example, the leaves of Indus are like palms, and the curved moon is like a boat. So this sentence compares the book to a magnet, which highlights the attraction of the book.