44 MAMMALIA—MAN. 
“This was performed on the 20th of April, at eleven o’clock in the fove- 
noon. I was alone with the surgeon, but during the operation the room 
swarmed with human forms of every description, which crowded fast one 
on another; this continued till half past four o’clock, exactly the time when 
the digestion commences. I then observed that the figures began to move 
more slowly ; soon afterwards the colors became gradually paler, and every 
seven minctes they lost more and more of their intensity, without any 
alteration in the distinct figure of the apparitions. At about half past six 
o’clock, all the figures were entirely white, and moved very little; yet the 
forms appeared perfectly distinct ; by degrees they became visibly less plain, 
without decreasing in number, as had often formerly been the case. The 
ficures did not move off, neither did ‘they vanish, which also had usually 
happened un other occasions. In this instance they dissolved immediately 
into air; of some, even whole pieces remained for a length of time, which 
also by degrees were lost to the eye. At about eight o’clock, there did not 
remain a vestige of any of them, and I never since experienced any appear- 
ance of the same kind. Twice or thrice since that time, I have felt a pro- 
pensity, if I may be so allowed to express myself, of a sensation, as if I saw 
something which in a moment again was gone. I was even surprised by 
this sensation, whilst writing the present account, having, in order to render 
it more accurate, perused the papers of 1791, and recalled to my memory 
all the circumstances of that time. So little are we sometimes, even in the 
greatest composure of mind, masters of our imagination.” 
As the sense of sight is the effect of the action of light upon the eye, it is 
well known that too much light as well as too little, is extremely prejudi- 
cial. Travellers, who cross countries covered with snow, are obliged to 
wear a crape before their eyes. Persons, therefore, who read or write much, 
should accustom themselves to a moderate light. 
There are many reasons to induce us to suppose, that such persons as are 
short-sighted, would see objects larger than others; and yet it is a certain 
truth that they see them smaller. 
Error is however not confined to any one sense; and that of HEARING is 
liable to similar mistakes with that of sight. This sense conveys no distinct 
. intelligence of the distance whence a sounding body is heard: a great noise 
far off, and a small one very near, produce the same sensation; and, unless 
we receive information from some other sense, we can never distinctly tell 
whether the sound bea great ora small one. It is not till we have, by 
experience, become acquainted with any particular sound, that we can judge 
of the distance when we hear it. When, for example, we know the tone 
of a bell, we are then at no great loss to determine how far it is from us. 
The air is the principal means of conveying the sound.* Sound is in 
SS eee 
* The strokes of a bell give no sound, when it is placed under the receiver of an ait 
pump, which is exhausted of its air. 
