What does Gatsby's formal gesture of waving farewell remind us of?
At the end of Chapter Two, Nick sees Gatsby across the lake: "But I didn't call to him for he gave a sudden intimation that he was content to be alone -- he stretched out his arms toward the dark water in a curious way, and far as I was from him I could have sworn he was trembling. Involuntarily I glanced seaward -- and distinguished nothing except a single green light...When I looked once more for Gatsby he had vanished, and I was alone again in the unquiet darkness."
Ch. 3 echoes this sense of isolation even among people and "unquiet darkness" as Gatsby's house and the man himself are enveloped in a "sudden emptiness" which "seemed to flow from the now from the windows and the great doors, endowing with complete isolation the figure of the host who stood on the proch, his hand up in a formal gesture of farewell."