THE PERCEPTION OF SPACE. 163 



faint of tlie wliole Hue on which they lie. In other words, 

 no ray of light can fall on any retinal spot without the lo- 

 cal sign of that spot revealing to us, by recalling the line 

 of its most habitual associates, its direction and distance 

 from the centre of the field. The fovea acts thus as the 

 origin of a system of polar co-ordinates, in relation to which 

 each and every retinal point has through an incessantly-re- 

 peated process of association its distance and direction de- 

 termined. Were P alone illumined and all the rest of the 

 field dark we should still, even with motionless eyes, know 

 whether P lay high or low, right or left, through the ideal 

 streak, diiferent from all other streaks, which P alone 

 has the power of awakening.* 



* So far all has been plain sailing, but our course begins to be so tortu- 

 ous when we descend into minuter detail that I will treat of the more pre- 

 cise determination of locality in a long note. When P recalls an ideal line 

 leadiug to the fovea the line is felt in its entirety and but vaguely ; whilst 

 P, which we supposed to be a single star of actual light, stands out in strong 

 distinction from it. The ground of the distinction between P and the 

 ideal line which it terminates is manifest — P being vivid while the line is 

 faint ; but why should P hold the particular position it does, at the end of the 

 line, rather than anywhere else— for example, in its middle? That seems 

 something not at all manifest. 



To clear up our thoughts about this latter mystery, let us take the case 

 of an actual line of light, none of whose parts is ideal. The feeling of 

 the line is produced, as we know, when a multitude of retinal points are 

 excited together, each of which when excited separately would give rise to 

 one of the feelings called local signs. Each of these signs is the feeling of 

 a small space. From their simultaneous arousal we might well suppose a 

 feeliug of larger space to result. But why is it necessary that in this 

 larger spaciousness the sign a should appear always at one end of the line, 

 z at the other, and m in the middle ? For though the line be a unitary 

 streak of light, its several constituent points can nevertheless break out 

 from it, and become alive, each for itself, under the selective eye of atten- 

 tion. 



The uncritical reader, giving his tirst careless glance at the subject, will 

 say that there is no mystery in this, and that 'of course ' local signs must 

 appear alongside of each other, each in its own place; — there is no other 

 way possible. But the more philosophic student, whose business it is to 

 discover difficulties quite as much as to get rid of them, will reflect that it 

 is conceivable that the partial factors might fuse into a larger space, and 

 yet not each be located within it any more than a voice is located in a 

 chorus. He will wonder how, after combining into the line, the points 

 can become severally alive again : the separate puffs of a ' sirene ' no longer 

 strike the ear after they have fused into a certain pitch of sound. He will 

 recall the fact that when, after looking at things with one eye closed, we 



