20 



The Astronomer Royal on Hemiopsy. 



given which present themselves when the principal obscuration 

 appears to be on the right side. (In my own experience, I believe 

 it is an even chance whether the obscuration is to the right or to 

 the left.) The bounding circle shows roughly the extent to 

 which the eye is sensible of vision more or less vivid. Only one 

 arch is seen at onetime: the arch is small at first, and gradually 

 increases in dimensions. 



A, the beginning of the disease. 



Bb, Cc, Dd, Ee, successive appearances, as the arch gradually enlarges. 



The zigzags nearly resemble those in the ornaments of a 

 Norman arch, but are somewhat sharper. Those near the let- 

 ters B, C, D, E are much deeper than those near b, c, d, e. The 

 zigzags do not change their relative arrangement during the di- 

 latation of the arch, but they tremble strongly : the trembling 

 near B, C, D, E is much greater than that near b, c } d, e. There 

 is a slight appearance of scarlet colour on one edge, the external 

 edge, I believe, of the zigzags. As the arch enlarges, vision 

 becomes distinct in the centre of the field. The strongly- 

 trembling extremity of the arch rises at the same time that it 

 passes to the left, and finally passes from the visible field, and 

 the whole phenomenon disappears. 



I have never been able to decide with certainty whether the 

 disease really affects both eyes. The first impression on the mind 

 is that only one eye is affected (in the instance depicted above, 



