DR. HUBERT AIRY ON A DISTINCT FORM OF TRANSIENT IIEMIOPSIA. 257 
These three orders of motion, (1) gradual outward spread of the whole, (2) slow 
rolling of parts, (3) rapid tremor of the margin, are especially characteristic of this 
affection. 
As the cloud extends its borders, its central region begins to fade, and clear vision 
begins to return in the concavity of the seething crescent. As fast as the trembling 
rolling jagged margin encroaches on the clear field outside, so fast the power of the 
enemy is waning and the faculty of sight is reasserting itself in the rear of his advance 
(Plate XXV. figs. 4 & 8). 
The sight of both eyes is affected exactly in the same manner and in the same degree 
(though naturally that eye seems most affected which corresponds to the obliterated side 
of the field of view, because the nasal half of the field of view of either eye is more 
limited, and vision there is less distinct than on the temporal side). Whether the 
one eye, or the other, or both, be open, the same strange sight is seen — no mere 
general resemblance, but absolute identity, indubitable, unmistakable. Every angle of 
the outline, every gleam of colour, is still there, in its place, — survives the ordeal of 
alternate closure of the eyes, unaltered except by its own gradual outward spread. 
When the eyes rest on a printed page, the cloud is seen as a faint shade of horseshoe 
shape, with serrated margin, bright-lined in some places, and varied with changing 
gleams of red and blue and yellow and green and orange, in order of frequency, now 
one colour, now another, slowly waxing and waning in harmony with the unrest around. 
All words and letters covered by this strange intruder are completely blotted out ; those 
immediately adjoining the margin seem smeared into it, not cut off sharp ; while inside 
the horseshoe there is gradual transition from the unseen to the seen, again. The 
tremor and rolling are plainly recognized. 
Looking at any surface of uniform colour, as a green wall-paper, or a red table-cover, 
or a mahogany table, the cloud is scarcely to be seen at all : it partakes of the general 
hue of the field on which it lies, and only reveals itself by the bright lines and gleams 
of colour at the margin, by the tremor and rolling that belong to them, and by the obli- 
teration of the grain of the wood and minor markings. 
Looking at the bright sky, the affected portion of the field of view appears as a faint 
shadowy curved cloud. The bright lines at its margin are not conspicuous, except when 
they show gleams of gay colours. The boiling and tremor are well seen. 
Looking at a white ceiling in shade, the display is seen perhaps most favourably. The 
bright lines of the margin contrast with dark lines behind them ; the space immediately 
within the margin is seen to be partly broken up into wedges and angular figures of faint 
light and shade, especially towards the larger end of the curved cloud, which is receding 
from the centre of sight and shows a larger pattern in every respect, — larger zigzags, 
larger wedges, larger boiling, and stronger tremor. Any gleams of colour are well seen. 
When the eyes are so directed that part of the cloud is seen against the sky, and part 
against the dark wall, it may be noticed that the jagged arch appears faintly dark 
against the sky, and faintly light against the wall ; but the part seen against sky is de- 
