a subject's arm by the imposition of a tactile hallucination. It is right to point out that these experiments, by the authors' admission, succeed only occasionally, and that many of them have not yet been confirmed by other observers. In fact, according to the evidence collected by the S.P.R., the results of applying such optical tests differ with each individual. Thus Mr. Myers succeeded by post-hypnotic suggestion in inducing two young men to see hallucinatory images in the crystal enlarged by the application of a magnifying glass (_S.P.R._, viii. 462, 463), and Miss X. (_id._, pp. 485, 486) reports that she sees hallucinatory pictures distorted in a spoon, reversed in a mirror, enlarged by a magnifying glass, and doubly refracted by Iceland spar. She believes herself also to have experienced complementary colours as the result of prolonged looking at a hallucinatory picture. But Mrs. Verrall (_id._, p. 474) finds the crystal pictures vanish when the magnifying glass is applied; and Miss A. (_id._, p. 500) finds that the superimposition of a magnifying glass does not affect the picture. In all these cases, it should be noted, the percipients were in their normal condition, and were more or less familiar with the nature of the optical effects following under similar circumstances with real percepts. MM. Binet and Féré suppose that the appropriate reaction of the hallucinatory picture to the various tests described is due to the hallucination being built up round a fragment of actual percept, such as a mark on a card, which would conform to ordinary optical laws. This imaginary nucleus they name the _point de repère_. It is not improbable that in some cases this may be the true explanation. But experience leads us to infer that suggestion would be competent to produce all the observed effects in cases where the subject, either from previous knowledge of the instrument or process, from the behaviour of the investigators, or from his own observations at the time, was aware of the nature of the effect to be expected. And it is not clear that MM. Binet and Féré, and other investigators of this school, have been sufficiently on their guard against the abnormal receptivity of the hypnotised subjects with whom they have for the most part experimented. Miss X., it may be remarked, professes herself uncertain whether or not to ascribe the results which she has recorded to self-suggestion. But to choose between these alternative explanations is not important for our present purpose. To whatever cause we may attribute the results observed, there can be no doubt either of the sense of reality conveyed by the false percept, or of its appropriate behaviour under favourable conditions.