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 

 glass 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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