ON SENSORIAL VISION. 407 



equally so with the eyes open or closed, and it appeared 

 to advance slowly from out of the corner till it spread all 

 over the visual area, and passed across to the right side, 

 where it disappeared. I cannot say how long it lasted, 

 but it must have been a minute or two. I was a little 

 alarmed, looking on it as the precursor of some disorder of 

 the eyes, but no ill consequence followed. Several years 

 afterward:: the same thing again occurred, and I recog- 

 nized, not indeed the same precise form, but the same 

 general character -the fortification outline, the dark and 

 bright lines, and the steady progressive advance from left 

 to right. I have mentioned this to several persons, but 

 have only met with one to whom it has occurred. This 

 was a lady of my acquaintance, who assured me that she 

 had often experienced a similar affection, and that it was 

 always followed by a violent headache, which was not 

 the case with me. In this case the regularity of the pat- 

 tern was not great, but the lines were quite straight and 

 the angles sharp and well defined. Had it remained 

 stationary, it might be assumed that the retina had a 

 structure corresponding to tlie figure ; and that some 

 undue pressure might render that structure visible. But 

 such an hypothesis is precluded by the gradual transit of 

 tlie lines over every part of the visual area. 



(10.) I come now to cases of perfect symmetry, and geo- 

 metrical regularity. The most ordinary class of patterns 

 of this sort I find to be formed only in darkness, and if 

 the darkness be complete, equally with open as with 

 closed eyes. The forms are not modified by slight pres- 

 sure, but their degree of visibility is much and caprici- 



