At a fascinating moment in French intellectual history, an interest in matters occult was not equivalent to a rejection of scientific thought; participants in seances and magic rituals were seekers after experimental data as well as spiritual truth. A young astronomy student wrote of his quest: "I am not in the presence or under the influence of any evil spirit: I study Spiritism as I study mathematics." He did not see himself as an ecstatic visionary but rather as a sober observer. For him, the darkened room of occult practice was as much laboratory as church.

In an evocative...