Clairvoyance means literally nothing more than "clear-seeing," and it is a word which has been sorely misused, and even degraded so far as to be employed to describe the trickery of a mountebank in a variety show. Even in its more restricted sense it covers a wide range of phenomena, differing so greatly in character that it is not easy to give a definition of the word which shall be at once succinct and accurate. It has been called "spiritual vision," but no rendering could well be more misleading than that, for in the vast majority of cases there is no faculty connected with it which has the slightest claim to be honoured by so lofty a name.
For the purpose of this treatise we may, perhaps, define it as the power to see what is hidden from ordinary physical sight. It will be as well to premise that it is very frequently (though by no means always) accompanied by what is called clairaudience, or the power to hear what would be inaudible to the ordinary physical ear; and we will for the nonce take our title as covering this faculty also, in order to avoid the clumsiness of perpetually using two long words where one will suffice. Let me make two points clear before I begin.
First, I am not writing for those who do not believe that there is such a thing as clairvoyance, nor am I seeking to convince those who are in doubt about the matter. In so small a work as this I have no space for that; such people must study the many books containing lists of cases, or make experiments for themselves along mesmeric lines. I am addressing myself to the better-instructed class who know that clairvoyance exists, and are sufficiently interested in the subject to be glad of information as to its methods and possibilities; and I would assure them that what I write is the result of much careful study and experiment, and that though some of the powers which I shall have to describe may seem new and wonderful to them, I mention no single one of which I have not myself seen examples.