[4] Mr. Triplett went through a similar performance with a ball in the presence of school children; and of 165 children, 78 described how they saw the ball go up and disappear; of those who were thus hallucinated 40 per cent. were boys and 60 per cent. were girls. Hallucinations of perfumes in children were obtained by another experimenter when water was sprayed from bottles labeled as perfumes; 76 per cent. of 381 pupils saw a toy camel move when a crank attached to the camel by a string was turned, although the camel remained quite motionless. The experimental tests, though rather cold and lifeless when compared with the dramatic stage deceptions, illustrate the same process, and make possible a comparative study of the degree of deception in different individuals and under different circumstances. [5] "Again, a mere tap with the wand on any spot, at the same time looking at it attentively, will infallibly draw the eyes of a whole company in the same direction."--_Houdin._ Robert Houdin, often termed "the king of the conjurers," was a man of remarkable ingenuity and insight. His autobiography is throughout interesting and psychologically valuable, and his conjuring precepts abound in points of importance to the psychologist. THE PSYCHOLOGY OF SPIRITUALISM I In 1848, from the town of Hydeville, New York, came the somewhat startling announcement that certain knockings, the source of which had mystified the household of one of its residents, seemed to be intelligently guided and ready to appear at call. Somewhat later, communication was established by agreeing that one rap should mean _no_, and three raps _yes_; to which was afterwards added the device of calling off the alphabet and noting at which letters the raps occurred. In this way, the rapper revealed himself as the spirit of a murdered peddler. Within a short period the news of this simple and childish invention had called into existence thousands of spirit-circles; had developed wonderful "mediums" to whose special gifts the manifestations were ascribed; had amassed a vast store of strange testimony; had added to the rappings such performances as moving tables, causing objects to be mysteriously thrown about, playing on instruments by unseen hands, materializing spirit flowers, producing spirit forms and faces, gathering messages from spirits on sealed slates, and so on. In brief, the movement became an epidemic; and that despite the fact that from the beginning and continuously satisfactory and rational explanations were offered of what really occurred, and that mediums were constantly detected in the grossest fraud. So early as 1851 the peculiar rappings occurring in the presence of the Fox sisters, the originators of the movement, were conclusively traced to the partial dislocation and resetting of a joint of the knee or foot; and the raps failed to occur when the girls were placed in a position in which the leverage necessary for this action was denied them.