How does the setting of this passage have referential function (concerning heat) in The Great Gatsby?
The next day was broiling, almost the last, certainly the warmest, of the summer. As my train emerged from the tunnel into sunlight, only the hot whistles of the National Biscuit Company broke the simmering hush at noon. The straw seats of the car hovered on the edge of combustion; the woman next to me perspired delicately for a while into her white shirtwaist, and then, as her newspaper dampened under her fingers, lapsed despairingly into deep heat with a desolate cry. Her pocket-book slapped to the floor.
The passage indirectly reflects the heat of the passions building between Gatsby and Daisy and the affair between Tom Buchanan and Myrtle Wilson. Chapter 7, which includes this passage, also records Tom's realization that Daisy is having an affair with Gatsby, George Wilson's understanding that Myrtle is being unfaithful (although he doesn't know who her lover is), and the car accident that kills Myrtle.
The woman on the train sitting next to Nick, who "perspired delicately for a while into her white shirtwaist," is described in almost the same terms as Myrtle in the immediate aftermath of the accident - "when they had torn open her shirtwaist, still damp with perspiration..."
The suspicions and accusations and recriminations come to a white-hot climax in the New York City hotel room that afternoon, as Tom confronts Gatsby, Gatsby tries and fails to get Daisy to renounce Tom for him, and Daisy begins her reluctant withdrawal from Gatsby in the face of Tom's revelations. Just as the "train emerged from the tunnel into sunlight," truth begins to shine for the characters.