of one another, on the same screen, and elicited a resultant face which resembled no one of the components in particular, but included all. Whatever was common to all the portraits became intensified by combination; whatever was peculiar to each portrait was relatively too faint to attract attention, and virtually disappeared. I made a great variety of experiments; in some I optically superimposed images by arrangements of lenses, mirrors, stereoscopes, or doubly refracting crystals; in others I combined separate photographic impressions upon a single sensitized plate. The result was that I invariably found it possible to make a generalized picture, having a remarkable appearance of individuality, out of a collection of separate portraits, so long as the latter bore a moderate resemblance to one another, and were taken from the same point of view, and were of the same size.
I argue that the mind of a man whose visualizing faculty is free in its action forms these generalized images of its own accord out of its past experiences. It readily reduces images to the same scale, through its constant practice in watching objects as they approach or recede, and consequently grow or diminish in size. It readily shifts images to any desired point of the field of view, through its habit of following bodies in motion to the right or left, upward or downward. It selects images that present the same aspect, either by a simple act of memory or by a feat of imagination that forces them into the desired position, and it has little or no difficulty in reversing them from right to left, as if seen in a looking-glass. In illustration of these generalized mental images let us recur to the boat, and suppose the speaker to continue as follows: "The boat was a four-oared racing boat; it was passing quickly just in front of me, and the men were bending forward to take a fresh stroke." Now, at this point of the story the listener ought to have a picture well before his eye. It ought to have the distinctness of a real four-oar going either to the right or the left, at the moment when many of its details still remained unheeded, such as the dresses of the men and their individual features. It would be the generic image of a four-oar formed by the combination into a single picture of a great many sight-memories of those boats.
In the highest minds a descriptive word is sufficient to evoke crowds of shadowy associations, each striving to manifest itself. When they differ so much from one another as to be unfit to combine into a single idea, there will be a conflict between them, each being prevented by the rest from obtaining sole possession of the field of consciousness. There would, therefore, be no definite imagery so long as the aggregate of all the pictures that the word could reasonably suggest, of objects presenting similar aspects, reduced to the same size, and accurately superposed, resulted in a mere blur; but a picture would gradually evolve as qualifications were added to the word, and it would attain to the distinctness and vividness of a generic image long before the word had been so restricted as to be individualized. If the intellect be slow,