Cloudless, and pierced by one solitary star, a copper-green sky gleamed through the windows. He read on by its wan light till he could read no more."
Wilde makes this passage an exemplary portrayal of the terrible hold Lord Henry has on Dorian by using a symbol, hyperboles, metaphors, appropriate diction, rhythmic syntax, and vivid imagery.
The book is a symbol for Lord Henry. He was the one who gave it to Dorian, and the reader notices their respective effects on Dorian are similar. Both touch his mind.
Instead of writing, "the book had a poisonous effect," Wilde exaggerates and writes, "it was a poisonous book," in order to highlight the extent of Henry's influence, and instead of writing, "he read on... until it got dark," Wilde writes, "he read on... till he could read no more," in order to portray the hypnotic effects Henry has on Wilde. Wilde also writes, "the heavy odor of incense seemed to cling about its [the book's] pages and to trouble the brain." This hyperbole intimates that the book is like a drug to Dorian; the incensed air keeps him from thinking straight.
Wilde's metaphor furthers support this idea. He compares the lines of the book to a piece of music, and complements the metaphors with appropriate musical diction. He gives the text rhythm, melody, and structure, but chooses the words, "cadence," "subtle monotony of their music," and "complex refrains and movements elaborately repeated." The purpose of using these words instead of the former, is to connote the mesmerizing effect the text is having on Gray.
Wilde also uses connotative words like "reverie," "dreaming, " and "unconscious." The airy diction gives us that same idea of hypnosis.
On top of the metaphors and the diction, Wilde also chooses a rhythmic syntax to further accentuate the hypnotic theme of the passage. He structures hypnosis-themed line in that same repeated refrains and cadence-like way he had described the text as having. "The mere cadence of the sentences, the subtle monotony of their music, so full as it was of complex refrains and movements elaborately repeated, produced in the mind of the lad, as he passed from chapter to chapter, a form of reverie, a malady of dreaming, that made him unconscious of the falling day and the creeping shadows." He use of commas is very liberal and the clauses/phrases in between are about of the same medium length.
And Wilde's use of imagery, I believe, is truly amazing. The passage is first colorless. The reader only sees the black and white letters of the book, the black of unconsciousness and falling shadows, and gray in monotones and heavy odors. Then in the next paragraph he introduces color, but in the most gorgeous way. He writes, "Cloudless (white), and pierced by one solitary star (white), a copper-green sky gleamed through the windows." A copper-green sky is something I'd like to see very much. The absurdity and fantasticality of a copper-green sky just adds to the weird, airy, poisoned, druggy mood of the passage which, in turn demonstrate Henry's influence.