40 MAMMALIA—MAN. 
as I now sce things, I could not at that time recognize and distinguish from 
each other. ‘This was shocking to look at; and besides, it made me feel 
anxious and uneasy; because it appeared to me, as if my window had been 
closed up with this party-colored shutter, in order to prevent me from looking 
out into the open air. That what I then saw, were fields, hills, and houses ; 
that many things, which at that time appeared to me much larger, were, in 
fact, much smaller; while many other things that appeared smaller, were, 
in reality, larger than other things, 1s a fact, of which I was afterwards con- 
vinced, by the experience gained during my walks; at length I no longer 
saw any thing more of the shutter.” He stated that in the beginning, he 
could not distinguish between what was really round or triangular, and what 
was only painted as round or triangular. The men and horses represented 
on paper, appeared to him precisely like those that were carved in wood, 
but that in the packing and unpacking of them, he had soon found the 
difference. 
We judge of distance only by experience, otherwise, when experience dues 
not set us right, the more distant an object is, the smaller it appears. 
When, from particular circumstances, we cannot form a just idea of dis- 
tance, and when we cannot judge of objects but by the angle, or rather the 
image, which they form in our eyes, we are then necessarily deceived as to 
the size of such objects. Every man has experienced how liable we are, in 
travelling by night, to mistake a bush which is at hand, for a tree which is 
at a distance, or indeed a tree which is at a distance, for a bush which is 
at hand. In the same manner, if we do not distinguish objects by their 
form, and if thereby we cannot judge of distance, the same fallacy will still 
remain: in this case, a fly which is passing rapidly, close before our eyes, 
will appear to be a bird at a considerable distance ; and a horse which may 
be in the middle of a plain, without motion, and in an attitude similar, for 
example, to that of a sheep, will appear no larger than a sheep, till we have 
once discovered that it is a horse. 
Whenever, therefore, we find ourselves benighted in an unknown place, 
where no judgment is to be formed of distance, we are every moment liable 
to deceptions of vision; hence originate, in part, the dreadful anecdotes of 
spectres, and of those strange, hideous, and gigantic figures, which so 
many persons tell us they have seen. Though such appearances, it is com- 
monly asserted, exist solely in the imagination, yet it is highly possible that 
they might appear literally to the eye, and be in every respect seen as 
described to us. 
The deception arising from the eye misjudging of magnitudes and dis- 
tances, is not, however, the only source of spectral illusions. Disease, 
particularly of the head, and violent excitement of the nervous system, often 
produce the most singular and vivid phantasms. Of this kind, many cases 
are on record in the annals of medicine. One of the first that was brought 
to public notice, and one of the most remarkable, is that of M. Nicolai, the 
