The anterior and posterior surfaces of all organs, by whose aid we exercise our faculties, which surfaces represent their poles and dual factors, the positive and the negative, the material and the spiritual, change places in conformity with whether an object is impressed upon them exteriorly or interiorly, in the present or the past, directly or indirectly, physically or spiritually. Things which are brought to our consciousness from the exterior world and in a direct manner--through our senses--may be said to be of a _material_ nature; while those which come to us indirectly--through our inner consciousness--may be said to be of _spiritual_ origin. The clearness of our visions naturally depends upon the clearness of the impression still remaining upon the tablets of the brain. The more stirring the event in the first instance, the deeper and more lasting, of course, the impression. All this, however, does not throw any light upon the process of abstract thought; nor am I in a position to aid in so doing. Yet it appears to me to be a sister proceeding; and that a nearer approach to an explanation of those more material phenomena may finally assist in arriving at an explanation of the causes of these more recondite and apparently purely spiritual phenomena. The correctness of the preceding remarks will become more apparent when we substitute for the faculty of seeing, that of hearing. We hear the voice of another person through the _anterior_ part of our ear, _entering_, as it does, from _without_. We hear our own voice through the _posterior_ part of our ear, _going out_, as it does, from _within_. No matter how low we may speak, we can always hear our own voice, though inaudible to others; and we can still distinctly hear it at such time, even when we fail to hear a low, though in fact relatively much louder, tone proceeding from the voice of another person. A ventriloquist, on the other hand, with whom these relations are reversed, hears his own voice reflected from without, inwardly, while, if he continues in the same condition while listening to another person's voice, he will hear the latter from within, outwardly. For the purpose of testing the correctness of these observations, please pay attention to the following: In listening to the sounds of another person's speech, you will have no difficulty in noticing that they stream into your ear from without, inwardly. Now, substitute for this other person's voice the sounds of your own voice, _and continue to listen to the same in precisely the same manner in which you did to those of this other person_; that is, let them flow into your ear from without, inwardly. The result will be _that you will not only not hear the sounds of your own voice, but that these sounds themselves will become paralyzed, that you will not be able to produce any sound whatever_.