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render for the soul the clue, by following which it transposes the same red, now to one, now to another spot, or simultaneously to different spots in the space intuited by it.

In order, however, that this may take place in a methodical way, these accessory impressions must be completely different from the main impressions, the colors, and must not disturb the latter. They must be, however, not merely of the same kind among themselves, but wholly definite members of a series or system of series; so that for every impression "r" there may be assigned, by the aid of this adjoined "local sign," not merely a particular, but a quite definite spot among all the rest of the impressions. The foregoing is the theory of "Local Signs."

The best anatomical and physiological researches fail to reveal spatial order as inherent in sensation; and, even if this ignorance be due to the impossibility of following up the evolutionary regress, it is a real difficulty. Lotze therefore concluded that "localization in space belongs to the unconscious product of the soul's action through the mechanism of its internal states." We gain a field of vision from an ensemble of local signs, and, as concerns tactile sense, the same thing happens, the functions of the corpuscles of touch being like those of the cones and rods of the retina in sight. As a result, our notion of the extended originates in a perception of qualitative differences, from which the mind, by its own power of transformation, constructs extensive relations. Later researches into the structure of the peripheral nerve terminations seem to confirm, rather than undermine, the hypothesis. That it is a typical example of the limitations of hypothesis Lotze acknowledged quite frankly. But he claimed, with justice, that it explained the actual phenomena better than any other theory. As a consequence, even if modified, it has been incorporated in physiological psychology, and, especially as regards vision and touch, must be reckoned with still. To sum up—the point is this: Lotze held that every sensation, say, of color, was accompanied by an "accessory impression" of locality. The facts made it necessary to assume this "accessory impression." Now, just because it happens to be an assumption, it lies open to several interpretations. In other words, the principle of the hypothesis may stand, but opinions as to the way in which it may be read can differ widely. However this may be, more than any other psychologist, he has laid bare the numerous pitfalls surrounding the explanation of a psychological fact so obvious and common as space perception.

Nascent sciences present a certain family likeness in their life