so definitely limited calls out of itself a reflex movement of the eye toward it, as truly spontaneous as the impulse toward the object of intrinsic interest.  But what is ‘the expenditure of attention’ in physiological terms?  It is nothing more than the measure of the motor impulses directed to the object of attention.  And whether the motor impulse appears as the tendency to fixate an object or as the tendency to follow out the suggestions of motion in the object, they reduce to the same physiological basis.  It may here be objected that our motor impulses are, nevertheless, still heterogeneous, inasmuch as some are toward the object of interest, and some along the line of movement.  But it must be said, first, that these are not felt in the body, but transferred as values of weight to points in the picture—­it is the amount and not the direction of excitement that is counted; and secondly, that even if it were not so, the suggested movement along a line is felt as ‘weight’ at a particular point.

From this point of view the justification of the metaphor of mechanical balance is quite clear.  Given two lines, the most pleasing arrangement makes the larger near the center, and the smaller far from it.  This is balanced because the spontaneous impulse of attention to the near, large line, equals in amount the involuntary expenditure of attention to apprehend the small farther one.  And this expenditure of motor impulses is pleasing, because it is the type of motor impulses most in harmony with our own physical organism.

We may thus think of a space to be composed as a kind of target, in which certain spots or territories count more or less, both according to their distance from the center and according to what fills them.  Every element of a picture, in whatever way it gains power to excite motor impulses, is felt as expressing that power in the flat pattern.  A noble vista is understood and enjoyed as a vista, but it is counted in the motor equation, our ‘balance,’ as a spot of so much intrinsic value at such and such a distance from the center.  The skilful artist will fill his target in the way to give the maximum of motor impulses with the perfection of balance between them.

IV.  SYMMETRY IN PICTURES.

A.  The Balancing Factors.

The experimental treatment of suggestions as to the elements in pictorial composition has furnished an hypothesis for the basis of our pleasure in a well-composed picture, and for the particular function of each of the several elements.  This hypothesis may be expressed as follows:  (1) The basis of aesthetic pleasure in composition is a balance of motor impulses on the part of the spectator; (2) this balance of motor impulses is brought about by means of the elements, through the power which they possess of drawing the attention with more or less strength towards a certain field.  But to the experimental working out of