Many people will object - some have already objected - to the subject of this book. It is an offence to some to take a ghost too seriously; to others it is a still greater offence not to take ghosts seriously enough. One set of objections can be played off against the other; neither objection has a very solid foundation. The time has surely come when the fair claim of ghosts to the impartial attention and careful observation of mankind should no longer be ignored. In earlier times people believed in them so much that they sought their acquaintance; in later times people believe in them so little that they will not even admit their existence. Thus these mysterious visitants have hitherto failed to enter into that friendly relation with mankind which many of them seem sincerely to desire.