These, for our purposes, are hallucinatory appearances occurring in the experience of people healthy and sane.

The difficulty begins when we ask whether these appearances ever have any provoking mental cause outside the minds of the people who experience them--any cause arising in the minds of others, alive or dead.

This is a question which orthodox psychology does not approach, standing aside from any evidence which may be produced.
This book does not pretend to be a convincing, but merely an illustrative collection of evidence.

It may, or may not, suggest to some readers the desirableness of further inquiry; the author certainly does not hope to do more, if as much.
It may be urged that many of the stories here narrated come from remote times, and, as the testimony for these cannot be rigidly studied, that the old unauthenticated stories clash with the analogous tales current on better authority in our own day.

But these ancient legends are given, not as evidence, but for three reasons: first, because of their merit as mere stories; next, because several of them are now perhaps for the first time offered with a critical discussion of their historical sources; lastly, because the old legends seem to show how the fancy of periods less critical than ours dealt with such facts as are now reported in a dull undramatic manner.