The chief purpose of this book is, if fortune helps, to entertain people interested in the kind of narratives here collected.

For the sake of orderly arrangement, the stories are classed in different grades, as they advance from the normal and familiar to the undeniably startling.

At the same time an account of the current theories of Apparitions is offered, in language as free from technicalities as possible.

According to modern opinion every "ghost" is a "hallucination," a false perception, the perception of something which is not present.
It has not been thought necessary to discuss the psychological and physiological processes involved in perception, real or false.

Every "hallucination" is a perception, "as good and true a sensation as if there were a real object there.