Running underneath all the observations of the above-mentioned writers, one dominant idea can be read as if in palimpsest; namely, the imperious necessity the experimenters are constantly under of suspecting tricks in this medium (Mme. Paladino). But all mediums, men and women, have to be watched. During a period of more than forty years I believe that I have received at my home nearly all of them, men and women of divers nationalities and from every quarter of the globe. One may lay it down as a principle that all professional mediums cheat. But they do not always cheat; and they possess real, undeniable psychic powers. Their case is nearly that of the hysterical folk under observation at the Salpetriere or elsewhere. I have seen some of them outwit with their profound craft not only Dr. Charcot, but especially Dr. Luys, and all the physicians who were making a study of their case. But, because hysteriacs deceive and simulate, it would be a gross error to conclude that hysteria does not exist. And, because mediums frequently descend to the most brazen-faced imposture, it would not be less absurd to conclude that mediumship has no existence. Disreputable somnambulists do not forbid the existence of magnetism, hypnotism, and genuine somnambulism. This necessity of being constantly on our guard has discouraged more than one investigator, as the illustrious astronomer Schiaparelli, director of the Observatory of Milan, specially wrote me, in a letter which will appear farther on. Still, we have got to endure this evil. The words "fraud" (_supercherie_) and "trickery" (_tricherie_) have in this connection a sense a little different from their ordinary meaning. Sometimes the mediums deceive purposely, knowing well what they are doing, and enjoying the fun. But oftener they unconsciously deceive, impelled by the desire to produce the phenomena that people are expecting. They help on the success of the experiment when that success is slow in its appearance. Mediums who deal with objective phenomena are gifted with the power of causing objects at a distance to move, of lifting tables, etc. But they usually appear to apply this power at the ends of their fingers, and the objects to be moved have to be within reach of their hands or feet, a very regrettable thing, and one which furnishes fine sport for the prejudiced sceptics. Sometimes the mediums act like the billiard player, who continues for an instant the gesture of hand and arm, holding his cue pointed at the rolling ivory ball, and leaning forward as if by his will he could push it to a carom. He knows very well that he has no further power over the fate of the ball, which his initial stroke alone impels; but he guides its course by his thought and his gesture.