But as to whether such hallucinations, among the sane, are ever caused by psychical influences from the minds of others, alive or dead, not communicated through the ordinary channels of sense, my mind is in a balance of doubt.

It is a question of evidence.
In this collection many stories are given without the real names of the witnesses.

In most of the cases the real names, and their owners, are well known to myself.

In not publishing the names I only take the common privilege of writers on medicine and psychology.

In other instances the names are known to the managers of the Society for Psychical Research, who have kindly permitted me to borrow from their collections.
While this book passed through the press, a long correspondence called "On the Trail of a Ghost" appeared in The Times.