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This effect (the customary ‘explanation’ of which is, as usual, of no avail to us and so need not concern us here) ranks with phenomena described in optics under the name of ‘apparent optical depth’, a subject we shall discuss more fully in the next chapter. It suffices here to state that it is the higher degree of humidity which, by lending the atmosphere greater optical density (without changing its clarity), makes distant objects seem to be closer to the eye, and vice versa. (If we could substitute for the air a much lighter gas – say, hydrogen – then the things we see through it would look farther off than they ever do in our atmosphere.)

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We may expect by now that our eye is fitted with two modes of seeing activity, polar to each other, and that the way in which they come into operation depends on whether the interplay of positive and negative density outside the eye leads to the appearance of the blue-violet or of the yellow-red side of the colour-scale. Such a polarity in the activity of the eye can indeed be established. Along with it goes a significant functional difference between the two eyes (not unlike that shown of the two hands).

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A fact known to science is that red and blue surface colours, when illumined by light of steadily diminishing intensity, are seen to reverse their normal ratio of brightness. This phenomenon can be seen in nature, if, for instance, one observes a bed of blue and red flowers in the fading evening light and compares the impression with that which the same flowers make in bright daylight. If the phenomenon is reproduced artificially, the actual transition from one state to the other can be clearly observed. The easiest way is to place a red and a blue surface side by side under an electric light whose intensity can be gradually lessened by means of a sliding resistance. Here, as much as in the natural phenomenon, our reason finds it difficult to acknowledge that the surface gleaming in a whitish sheen should be the one which ordinarily appears as darkling blue, and that the one disappearing into darkness should be the surface which normally presents itself as radiant red.

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Observations such as these show us that (a) when external light strikes the retina of our eye, our inner light is stimulated to move out of the eye towards it; (b) in pressing outward, this inner light meets with a certain resistance, and the extent of this determines at what distance from the eye our visual ray comes to rest as the result of a kind of exhaustion. Just as the outer light reaches an inner boundary at our retina, so does the inner light meet with an outer boundary, set by the optical density of the medium spread out before the eye, Outer and inner light interpenetrate each other along the whole tract between these two boundaries, but normally we are not conscious of this process. We first become conscious of it where our active gaze – that is, the inner light sent forth through the eye – reaches the limit of its activity. At that point we become aware of the object of our gaze. So here we find confirmed a fact noted earlier, that consciousness – at least at its present state of evolution – arises where for some reason or other our volition conies to rest.

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To observe this we need simply to compare the two eyes of a person in a photograph by covering alternately the right and the left half of the face. Nearly always it will be found that the right eye looks out clearly into the world with an active expression, and the left eye with a much gentler one, almost held back. Artists are well aware of this asymmetry, as of others in the human countenance, and are careful to depict it. An outstanding example is Raphael’s Sistine Madonna, where in the eyes and whole countenance both of Mother and Child this asymmetry can be studied in a specially impressive way.

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This riddle is readily solved if we apply what we have learnt about the particular shares of lightness and darkness in these two colours, and if we link this up with the respective forms of seeing exercised by our two eyes. To the dim light, clearly, our eyes will respond more with the ‘left-eyed’ than with the ‘right-eyed’ form of vision. Now we know that it is ‘left-eyed’ vision which is roused by the lightness-component in blue and the darkness-component in red. It is only to be expected, therefore, that these elements should become conspicuous when in the dim light our seeing is mainly ‘left-eyed’. This solution of the problem makes us realize further, that the laws which Goethe first found for the coming into appearance of colours freely hovering in space are indeed applicable to the fixed material colours as well.