116 NEW BOOKS. Experiments are then described, using the air-plethysmograph, which show mainly that the more intense and sudden is the stimulus, the more marked are the organic changes, and on the basis of this a theory is stated which refers the changes to the regularity or irregularity of the process of attention. No marked difference was found to distinguish the effects of pleasant and unpleasant stimuli. In a short paper on " Habit and Attention " Prof. Angell gives an account of some reaction-time experiments, which show that there is a tendency for the muscular and sensorial forms of reaction to approach one another with practice. The next paper is by Prof. Angell on the comparison of length as estimated by passive dermal stimulation with visual estimation. The normal underestimation of the former was found to be lessened, or even converted into overestimation by increase of pressure and by using hot or cold stimuli. Each of these factors was only studied on one individual. The last paper is by M. L. Ashley on the significance of intensity of light in visual estimates of depth. The special point was to investigate the influence of change of brightness apart from that of distinctness, although in some of the experiments the latter factor came into play. In the monocular and in some of the binocular experiments, the arrange- ment which was employed excluded any other factor than that of change in brightness and in these increase of brightness led to an appearance of nearness, decrease to one of famess ; the change in brightness was seen as such earlier than the apparent change in distance. In other binocular experiments, the binocular mechanism was allowed to come into play, and even in these experiments alteration of illumination was found to have distinct influence though the results were more uncertain and more individual differences were met with. The author does not say whether he tested his observers for the presence of binocular vision. The paper is an important contribution to the difficult problem of estimation of depth, and adds another to the so-called " experience " factors which have to be excluded in studying the physiological factors in this process. In Dixon and Hillebrand's experiments on this subject the arrangement used was such, however, that the factor in question cannot have had any appreciable influence. W. H. K. B. Mad Humanity : Its Forms, Apparent and Obscure. By L. F. WINSLOW. New York : M. F. Mansfield & Co., 1899. Pp. xix., 451. The title of this book leads us to expect a popular account of insanity, rather than a scientific treatise. And the author's style is for the most part anecdotal and reminiscential, though he appears also to have had his serious purpose in writing. He believes that insanity is on the increase ; that the degeneration of the human race is " in gradual and sad progres- sion " ; and that much of this result is due to indulgence in alcohol. He further urges Lombroso's theory that genius is akin to insanity. But his proof of this position consists merely in a list of geniuses who were more or less deranged : and one is tempted to inquire for the geniuses who were not insane. If genius is a form of madness, all geniuses should have been mad. Dr. Winslow writes from abundant personal experience, and his book may do the good he hopes for in enabling " some to detect the incipient progress of mental diseases ". It is well illustrated.
