406 ON SENSORIAL VISION. 



casual and irregular patches of unequal darkness, caused 

 by slight local pressure on the retina, the physiognomic 

 exponent of our mental state. Even landscape scenery, 

 to one habitually moved by the aspects of nature in as- 

 sociation with feeling, may be considered as in the same 

 predicament. There is nothing definite or structural in 

 its forms, which are arbitrary to any extent, and composed 

 of parts having no regular or symmetrical relations. It 

 is perfectly conceivable that the imagination may inter- 

 pret forms, in themselves indefinite, as the conventional 

 expressions of realities not limited to precise rules of 

 form. We all know how easy it is to imagine faces in 

 casual blots, or to see pictures in the fire. 



(8.) But no such explanation applies to the class ot 

 phsenomena now in question, which consist in the invol- 

 untary production of visual impressions, into which geo- 

 metrical regularity of form enters as the leading charac- 

 ter, and that, under circumstances which altogether pre- 

 clude any explanation drawn from a possible regularity ot 

 structure in the retina or the optic nerve. 



(9.) I was sitting one morning very quietly at my break- 

 fast-table doing nothing, and thinking of nothing, when 

 I was startled by a singular shadowy appearance at the 

 outside corner of the field of vision of the left eye. It 

 gradually advanced into the field of view, and then ap- 

 peared to be a pattern in straight-lined-angular forms, 

 very much in general aspect like the drawing of a fortifi- 

 cation, with salient and re-entering angles, bastions, and 

 ravelins, with some suspicion of faint lines of colour be- 

 tween the dark lines. The impression was very strong: 



