THE PERCEPTION OF SPACE. 239 



are foresliortened ; and the transitions from one to another 

 of these altering forms are infinite and continuah Out of 

 the flux, however, one phase always stands prominent. It 

 is the form the object has when we see it easiest and best : 

 and that is when our eyes and the object both are in what 

 may be called the normal position. In this position our 

 head is upright and our optic axes either parallel or sym- 

 metrically convergent ; the plane of the object is j^erpen- 

 dicular to the visual plane ; and if the object is one containing 

 many lines it is turned so as to make them, as far as possible, 

 either parallel or perpendicular to the visual plane. In this 

 situation it is that we compare all shapes with each other ; 

 here every exact measurement and decision is made.* 



It is very easy to see ivliy the normal situation should have 

 this extraordinary pre-eminence. First, it is the position in 

 which we easiest hold anything we are examining in our 

 hands ; second, it is a turning-j^oint between all right- and 

 all left-hand perspective views of a given object ; third, it 

 is the only position in which symmetrical figures seem sym- 

 metrical and equal angles seem equal ; fourth, it is often 

 that starting-point of movements from which the eye is 

 least troubled by axial rotations, by which superposition f of 

 the retinal images of different lines and diflerent parts of 

 the same line is easiest produced, and consequently by 

 which the eye can make the best comparative measure- 

 ments in its sweeps. All these merits single the normal 

 position out to be chosen. No other point of view offers 

 so many aesthetic and i:)ractical advantages. Here we be- 

 lieve we see the object as it is ; elsewhere, only as it seems. 

 ExjDerience and custom soon teach us, however, that the 

 seeming appearance passes into the real one by continuous 

 gradations. They teach us, moreover, that seeming and 

 being may be strangely interchanged. Now a real circle 

 may slide into a seeming ellipse ; now an ellipse may, by 

 sliding in the same direction, become a seeming circle ; now 



* Tlie only exception seems to be when we expressly wish to abstract from 

 particulars, and to judge of the general 'effect.' Witness ladies trying on 

 new dresses with their heads inclined and their eyes askance ; or painters in 

 the same attitude judging of the ' values ' in their pictures. 



f The importance of Superposition will appear later on. 



