to Memory and Time, to Imitation and Suggestion, to the Æsthetics of Sensations, to the connection of Mind and Body—the latter leading naturally to the final chapter, which discusses the Spiritual Implications of the experimental work.
As the general tenor and guiding spirit of these contributions to knowledge have been here emphasized, it will be pertinent to select, in further presentation of Professor Stratton's purpose, a few specific illustrations of the points above referred to. The chapter on Illusions begins thus: "Our illusions of perception seem contrived for the special purposes of psychology—as if Providence, foreseeing the natural perplexity of the student of mind, had sent them for his comfort. For nothing else reveals as they do the manner of the mind's activity. As long as our mental operation is perfect and does not color or distort the facts, the mind is like some subtle medium that permits us to see all things, while remaining itself unseen. But when once the mind's action becomes troubled so that it tinges and deforms the scene, then our psychic processes themselves come to view and we are enabled to note their form. For psychological purposes, therefore, illusions might perhaps be compared to the delicate artificial stains which are of such help to those who use the microscope; the dyes discolor the aspect and render it in a way untrue, but only to bring out with ten- fold clearness the hidden niceties of its structure." The explanation of even the simplest illusion calls for a complex equipment of psychological principles; for illusion, like habit, like perception, like inference, like attention, like judgment, results from experience, and represents a momentary and interesting concentration-point of these several activities." No sensation has an inviolate inner character which remains unaffected by the larger mental life. The connection, the significance of impressions alters their very essence." It is the comparative uniformity amidst diversity of mental experience that produces alike the "fixity of interpretation" and the exception to it that constitutes an illusion. The illusion that bears the name of Aristotle has remained the classic instance: a small roundish object held between the crossed forefinger and middle finger feels like two objects. This startling tactual duality, in violent contradiction to the visual unity, becomes intelligible when it is made clear that the position of the contacts under ordinary circumstances would naturally be the consequence of two separate objects. To this time-honored illusion Professor Stratton has added a converse: "an impression which is habit- ually due to a single object will be felt as a single object, even when, from the unnatural position of the fingers, it is now produced by two
