These are the principal phenomena of Dream and the study of them cannot fail to throw a flood of light upon mental physiology and psychology. In them we are enabled to view the operations of the mind and the relationship of soul and body under conditions that reveal to us parts of the mechanism of man that are wholly concealed from us in the normal state of that relationship. The strange neglect of such an obvious means of knowledge is doubtless due to the fundamental error that has excluded Mind and Soul from the category of physical sciences and consigned them to the hopeless region of metaphysics, persisting in their pursuit by abstractions, argument and conjecture, and refusing to them investigation by _facts_, as the other sciences are now investigated. If the phenomena of dream were strange and rare as are those of somnambulism, they would as much excite our curiosity and strike us with amazement. But they are not wondered at only because they are so familiar. If dream, instead of being common to us all, were developed only in a few, the persons subject to it would certainly be denounced as impostors and prosecuted as rogues and vagabonds by the High Priests of Science. But the very facility for examination of the mental condition of dream should induce those who really desire to promote the most important of all knowledge—the knowledge of ourselves, our constitution, our mechanism, and our destiny—to seek where we may most reasonably expect to find it—in the condition in which the Mind is every night practically severed from its connection with the body and works by its own impulses, without the aid or incumbrance of the senses, and without the directing power of the intelligence and its _Will_. CHAPTER IX. THE PSYCHOLOGY OF DREAM. Dream is essentially a psychological condition and therefore an important study for the Psychologist, for in dream we learn, not only what is the mechanism of the Mind, but also much of the manner in which its operations are performed. Dream teaches us what recent physiologists have by their experiments confirmed—that the mind is not structured as one homogeneous entity, the whole of which is employed in every mental act; but that it is a machine composed of parts, each of which has its own special function, exhibited in the various expressions which we call ideas, sentiments and emotions. For convenience we have given to the entity, of which these various faculties are parts, the collective name of “Mind.” But it may well be questioned if such an entity exists. Certainly we cannot find it, whether we observe the action of our own minds or that of others. All that we can discover by help of our senses and by reasoning upon their information is the existence of a wonderful piece of Mechanism—the brain—by which the functions of Mind are performed and whose structure regulates the entire character of the Mind.