All of us are familiar with the appearance of a microscope ready adjusted for use, with its little lamp, its mirror and illuminating apparatus under the stage, with a specimen on the stage under the object-glass, its object-glass and its eye-piece. Any one who understands the working of a microscope finds this a most suggestive spectacle. He follows in his imagination the light as it comes from the lamp to the mirror, through the illuminating lenses, through the transparent specimen, through perhaps a dozen lenses arranged as an object-glass within an inch of distance, through the eye-piece and into the observer’s eye. Give him the parts, lenses, prisms, and mirrors into his hands, and he will test them all, and tell you exactly how they work. This {16} scientific onlooker may be compared to the psychologist looking at another man’s mind. He sees it as a thing among other things, a working system of parts. But there is one thing that the mere onlooker cannot see. He cannot see the object. That can only be seen by looking through the tube. And every one has felt, I should think, the magical transformation, suggestive of looking through another man’s eye and mind, which occurs when you put your eye to the eye-piece of an optical instrument. The outside world of other objects, the tube, the stage, the mirror, the bystanders, the external light, all disappear, and you see nothing but the field of vision and whatever distinctly pictured structure may be displayed within it. The observer who looks through the tube may be compared with each one of us as he contemplates his own world of knowledge and perception. This is a thing that no one else can ever do. The metaphor, indeed, breaks down, in so far as each of us is able to observe the history and character of his own mind as an object within the field of presentation which is before his mind. Of course such a metaphor must break down at some point. But it remains true that the mind, while directly observing its field of objects, cannot observe its own peculiarities, and when turned, as we say, upon itself, is still observing only a part of itself. It remains true that my mind contains the whole presented world for me and is merely one among thousands of similar mind-things for you.