60 Dr Gillies (M a peculiar modification of Vision. 
on different occasions varied Considerably in point of intensity, 
my vision continued for a longer or shorter length of time, and 
then the affection disappeared in the same gradual manner as on 
its accession, till at length it became so very slight as to be 
with difficulty distinguished from my natural vision. 
Such was the ordinary succession of phenomena, as they oc- 
curred in my vision, on those occasions to which I have alluded. 
There are, however, several other circumstances which re- 
quire to be mentioned more in detail : These, for the sake of 
brevity and arrangement, I shall state under separate heads. 
The duration of this affection varied considerably, from a 
few minutes to seven or eight hours ; in ordinary cases, how- 
ever, it only continued from half an hour to an hour. In fre- 
quency of recurrence it varied also exceedingly. During the 
summer of 1816, when these phenomena first made their ap- 
pearance, it usually came on about once every two or three 
weeks, but these attacks became much less frequent during the 
succeeding autumnal months. However, in the months of No- 
vember, December, and the early part of January 1817, they 
became much more frequent and troublesome, recurring every 
eight or ten days ; sometimes appearing daily for several days 
in succession. It appeared to have reached its maximum de- 
gree of frequency about the commencement of the year 1817 ; 
for, during the 31st December, the 1st, 2d, and 3d of January, 
it came on in such rapid succession, that I seldom enjoyed 
my natural vision longer than two or three hours at a time, 
often indeed only for a few minutes ; but I may here observe, 
that although its recurrence was so very frequent, yet it seemed 
gradually to diminish in duration each time. 
In degree^ this affection likewise varied very much, and 
occurred in every variety from the slightest deviation from 
the natural vision to its most intense degree, which I find 
much difficulty in estimating with tolerable precision, as I had 
no standard to judge by, or any other guide, except my own 
sensations ; but, from the observations I was enabled to make, 
I am inclined to think, tliat on some occasions the surrounding 
objects appeared to my eye as if removed to six or eight times 
their real distance. These sensations were neither confined to 
objects near me, nor to those at a distance, but were equally par- 
