Dagny Taggart hears Brakeman whistling the theme of a concerto. Whe she asks him what piece it's from, he says Halley's Fifth Concerto. When Dagny points out that Richard Halley only wrote four concertos, Brakeman claims he made a mistake and he doesn't recall where he heard the piece.
Later, after Dagny instructs the train crew how to proceed, he asks a co-worker who she is, and learns she is the one who runs Taggart Transcontinental.
Part 1, Chapter 1, section 2 Section112 Part 1, Chapter 1, section 3 Section113