1920. A few of these poems may be difficult to understand, perhaps more difficult than Yeats knew. After the first few poems, Yeats came into possession of Michael Robartes' exposition of the 'Speculum Angelorum et Hominum' of Geraldus, and in the excitement of arranging and editing could no more keep out philosophy than could Goethe himself at certain periods of his life. Yeats has tried to make understanding easy by a couple of notes.