Here's a list of works recommended in the introduction -
Joseph Conrad - Heart of Darkness
T. S. Eliot - The Waste Land
Henry Adams - The Education of Henry Adams
Max Weber - The Protestant Ethic and the Spirit of Capitalism
Machiavelli - The Prince
Robert Graves - The White Goddess
Goethe - Faust
Norbert Wiener - The Human Use of Human Beings
Rilke - Duino Elegies, Sonnets to Orpheus
Wagner - Tannhauser, Tristan & Isolde, the Ring operas
Alfred North Whitehead - Process and Reality