788 THE POPULAR SCIENCE MONTHLY. 



taneous retinal impression. A word or two will perhaps make this 

 clearer. 



The substitution of simultaneous retinal perception of form for 

 successive perception has the effect of bringing together the terms of 

 the relations of variety and contrast, unity and similarity, under what 

 is approximately one act of attention. If we watch the movements 

 of a painter's hand as he draws the outline of a human figure on a 

 canvas, our eye may attain a rough perception of the successive direc- 

 tions and distances ; but how vague will this perception be as com- 

 pared with that which we instantaneously obtain when the artist moves 

 away from his canvas, and shows us these as parts of a permanent co- 

 existent whole ! In the former case we had to bring together by the 

 aid of memory a number of impressions occupying some appreciable 

 time : in the latter these were presented to us in one and the same 

 instant. It must follow, then, that the perception of all relations, 

 whether of dissimilarity or similarity, will under the circumstances 

 become more definite and more exact. 



Nor is this all the gain. The addition of simultaneous retinal ap- 

 preciation introduces a new and finer standard in estimating the ele- 

 ments of form themselves. In the case of two lines, for example, 

 which are nearly equal, or of two lines which are neai'ly parallel, the 

 discrimination of magnitude and direction is finer when the lines are 

 brought together and simultaneously perceived by help of the retinal 

 impressions than when they are so situated that they (or their dis- 

 tances from one another) have to be successively estimated by the 

 moving eye. It may be thought that these more delicate estimates 

 are of more importance in science than in art ; yet even in the latter 

 the less obtrusive charms of form, more particularly that of the human 

 face, involve this finer retinal appreciation. It may be added that, 

 even when the former is too large to be easily taken in by the eye at 

 rest, the retinal capability of simultaneous perception greatly assists 

 m the clearer and more exact appreciation of relations. In estimating, 

 for example, the symmetry of a tapering column, of a pyramid or of a 

 human figure, the eye need not pass over the whole of the contour. It 

 is sufiicient if it describe a path answering to the axis of the figure ; 

 for in this case the perfect equality of any two opposed parts will be 

 estimated by retinal perception, and the whole intuition of form will 

 then consist of a series of simultaneous perceptions. 



