Such a fact, which is implicitly included in the general law we have laid down for the origin of myth, will also as I think throw further light on the origin of many hallucinations, both in normal conditions of mind and in the abnormal state of nervous disorders.  The different appearances of objects, animals, and men, the voices, words, songs, and conversations seen and heard in these hallucinations, are produced, by an internal impulse as well as by a stimulus from without; they are internal in the images and sensation already unconsciously impressed upon the memory, and they are external in the accidentally modified form in which they occur in sensible objects, so that they act reciprocally as an incentive and impulse to each other.

If in normal hallucinations the vividness of the internal image is in certain physiological conditions projected outwardly, the configuration and accidental form of the external objects contribute to complete the composition in accordance with the nature and design of this internal image.  Sometimes the physiological conditions of hallucination are so powerful that it is at once produced by the appearance of an object which has some analogy with the mental image.  Whatever may be the genesis and primitive character of the idea of space, and its psychical and physiological relations to actual space—­a question which has been the theme of so much discussion in our time—­it is certain that first habit and then hereditary influence cause us to have the sensation and apprehension of a psychical space, which may be termed artificial and congenital, and upon which the various impressions of the senses are spontaneously projected.  Of this there is an evident proof in the fact that if we look at the sun or any bright object, such as the windows of a room in the day time, and then close our eyes, so as to make the vision of external space impossible, the image of the sun, sometimes of a different colour, or of the window, is projected into the darkness at some distance from us, and moves about this psychical space.  This phenomenon also occurs in the subjective sensations of hearing, since the sounds do not appear to be close to the ear, but at a distance.  We are not here called upon to discuss the causes which generate the appearance of this psychical space, but the fact is indisputable; so that conversely it becomes intelligible how the internal image may be projected in the same way, or may at least appear to be externally projected in hallucinations.  This surprising phenomenon is only a modification of the ordinary exercise of the psychical and physiological faculties in the projection of images; of which, after the idea of space has been formed by primitive experience, habit and education are the chief factors.