VISUAL ANALOGUES 179 
manner. I had been intently looking at a particular 
window, and obtaining the subsequent after-images by 
closing the eye; my attention was concentrated on the 
window, and I saw nothing but the window either as a 
direct or as an after effect. After this had been 
repeated a number of times, I found on one occasion, 
after closing the eye, that, owing to weariness of the 
particular portion of the retina, I could no longer see 
the after-image of the window; instead of this I 
however saw distinctly a circular opening closed with 
class panes, and I noticed even the jagged edges of a 
broken pane. I was not aware of the existence of a 
circular opening higher up in the wall. The image of 
this had impressed itself on the retina without my 
knowledge, and had undoubtedly been producing the 
recurrent images which remained unnoticed because my 
principal field of after-vision was filled up and my atten- 
tion directed towards the recurrent image of the window. 
When this failed to appear, my field of after-vision 
was relatively free from distraction, and I could 
not help seeing what was unnoticed before. It thus 
appears that, in addition to the images impressed in the 
retina of which we are conscious, there are many others 
which are imprinted without our knowledge. We fail 
to notice them because our attention is directed to 
something else. But at a subsequent period, when the 
mind is in a passive state, these impressions may sud- 
denly revive owing to the phenomenon of recurrence. 
This observation may afford an explanation of some of 
the phenomena connected with ocular phantoms and 
hallucinations not traceable to any disease. In these 
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