At the violet hour, when the eyes and back Turn upward from the desk, when the human engine waits Like a taxi throbbing waiting
The Fire Sermon moves through London's river and its history of pollution. Tiresias, the blind prophet who has lived as both man and woman, now witnesses the modern world's loveless encounters. The violet hour marks the transition into the typist-and-clerk scene.
The transition from day to night as mechanical routine — the "human engine" reduced to the rhythm of a taxi meter.