Hallucinations, in the cases observed above, are due to an external impulse; and this is especially the case in madness and other nervous disorders; since a critical observation and clear discernment of things is wanting, some object of vision, a voice, phrases, or sounds are much more apt to act as a stimulus to a vast field of visual hallucinations, or to a long succession of sentences and speeches.  It is not, therefore, wonderful that in an ecstasy, for instance, in which all the faculties are concentrated on very few ideas and images, or perhaps on one only, every external sign, whether obvious to sight or hearing, combined with the mnemonic effort already explained, is modified to correspond with these vivid and exalted images; thus constituting the wonderful phenomenon of ecstasy.  In such a case the ecstatic phenomenon in persons subject to these nervous affections is often invested with fresh wonders by the additional sensations of light and subjective colours; this is not uncommon even in persons of a sane mind and body, but undoubtedly it is more frequently the case in those whose mental and physical conditions are abnormal.  It is not rare to hear an ecstatic person recount divine visions, suffused with extraordinary light and glory.

In order to contribute to the researches of others into the nature of this phenomenon, I must be permitted—­not from vanity, but from a desire that my own imperfections may serve the cause of science however slightly—­to relate some facts, personal to myself, which bear upon the question, facts of very general experience.  From my childhood I have had, both by day and night, various subjective sensations of light which I was, as a person of perfectly sane mind, able to observe dispassionately.  After reading for a long while, or when fatigued by sleeplessness, mental excitement, or some temporary gastric derangement, I see clear flames circling before my eyes.  These are in a small, oblong form, arranged at brief intervals in concentric curves, and composing a moving garland projected upon space, tinged with a yellowish light, shading into vivid blue.  Sometimes this figure is changed for stars, twinkling in a vast and remote space, as in a firmament.  In addition to this phenomenon, I have about twenty times in the course of my life experienced other subjective and more extraordinary sensations of light, not unknown to others.  This phenomenon occurs when I am in a normal condition of health, and always begins with a confusion of sight, so that I am unable to see objects and the faces of people distinctly; after which everything within the range of vision becomes mobile and tremulous.  This state continues for ten minutes, and then clear and distinct vision returns.  Next a lucid circle, zig-zagged in acute angles, appears close to the eyes, now on the right, now on the left.  It moves in a somewhat serpentine course, and is broken in the centre of the lower half.  It withdraws from the eye into subjective space, and the shining band of which it is composed gradually loses its sharp angles, and becomes wider and undulated, while still in motion.