_Turning now to the author of the following pages, everyone must recognise the industry he has shown and the fairness of spirit he has endeavoured to maintain. With different groups of phenomena, the evidential value varies enormously. The testimony of honest and even careful witnesses requires to be received with caution, owing to the intrusion of two sources of error to which untrained observers are very liable. These are unconscious_ mal-observation _and unintentional_ mis-description. _I cannot here enter into the proof of this statement, but it is fully established. Oddly enough, not only a credulous observer but a cynical or ferocious sceptic is singularly prone to these errors when, for the first time, he is induced to investigate psychical phenomena which, in the pride of his superior intelligence, he has hitherto scorned. I could give some amusing illustrations of this within my own knowledge. For instance, a clever but critical friend who had frequently scoffed at the evidence for thought-transference published in the "Proceedings of the Society for Psychical Research," one day seriously informed me he had been converted to a belief in thought-transference by some conclusive experiments he had witnessed. Upon inquiring where these experiments took place I found it was at a public performance of a very inferior Zancig who was then touring through the provinces!_ _Mr Beckles Willson frankly tells us that "the light heart and open mind" with which he set forth on his inquiry deserted him before he drew his labours to a close. For, entering upon the subject as a novice, he found himself unexpectedly confronted by the mass of evidence and the numerous and profoundly difficult problems which the Psychical Society have had to face. His conclusions are derived from a study of the available evidence, and this study has convinced him--as it has convinced, so far as I know, every other painstaking and honest inquirer--that no theories based on fraud, illusion, nor even on telepathy, are adequate to account for the whole of the phenomena he has reviewed. Contrary to his prepossessions, Mr Willson tells us that he has been led to the conclusion that the only satisfactory explanation of these phenomena is the action of discarnate human beings--that is to say, the Spiritualistic hypothesis._