Sightings of lights in the sky are often neglected by many ufologists who consider them too ‘simple’, and unworthy of their avant-garde researches. Yet this simplicity is an important factor. Abnormal luminous phenomena can be compared with rather well-known manifestations, such as St Eilmo’s Fire, auroral phenomena or optical refraction phenomena, many examples of which can be found in Corliss’s books. 
Few people today will have heard about the once common phenomenon known generally in the British Isles as ‘Will o’the Wisp’ or ‘Jack o’Lantern’. Prior to the end of the 19th century this rural mystery was a terror familiar to night travellers, especially in the marshy, undrained areas which still remained in many parts of England.
The Japanese spirit world is populated by a strange crew; there are teasing, shape-changing entities known as kitsune or ‘fox spirits’ which delight in deceiving lone travellers; there are bird-faced tengu in the forests, and half-human, half turtle kappa in the deep ponds. And of course there are the ghosts of the departed who cling obsessively to the things left undone or uncorrected in their earthly existence.