Mr Charles the Motion of the Eye. SSt 
for other essential purposes than that of merely lubricating the 
cornea. 
The last observation of mine which Pr Brewster contradicts, is, 
that the eyeball revolves a certain degree upwards when the eyelids 
are shut. Daily experience of things, which, in all probability, 
do not present them selves to that gentleman, authorise my con- 
clusion. ■ I am surprised that he did not sooner notice the; 
fact, and that gentlemen do not understand the subject when it 
is put before them. 
Experiments on this subject require very particular attention. 
If a person, with whom we are conversing, is asked to shut his:. 
eye, the axis of the eye-ball continues to be directed towards you 
i^s long as that person is conscious that you are looking at him, 
or is attentive to your discourse. Even when the eyes are shut, 
if the person has his mind awake, the eye-bail will continue in 
motion, and correspond with the ideas in the mind. This is the 
reason I apprehend that my friend Dr Knox has rather con- 
firmed Dr Brewster in his misconception. 
In the winking motions of the eye-lids, for the purpose of 
brushing the surface of the cornea, the motion of the eye-lid is 
more rapid than thought, and difficult to observe. But the gra- 
dual yielding up of the controul of the eye-ball, on the approach 
of sleep or insensibility, from whatever cause, is a thing so cu- 
rious in itself, and so clear to demonstration, that I must ex- 
press my surprise that ingenious men will rather deny the fact, 
than prosecute it in all its bearings. 
But why should Dr Brewster take the facts of a case as stated 
by me, and which seem, to superficial observation, against my ar- 
gument, and omit to notice that part of the statement which is in 
my favour. Is not this as if he preferred the pride of victory, 
and were more the advocate of liis cause than of philosophy ? In 
the case to which he has drawn the attention of the Society, the 
patient had lost the power of moving the eye-ball, and by far 
the most important circumstance of that case was, that when he 
shut his eyes the red light came through the eye-lid of the eye 
that was imperfect. How is this to be accounted for, unless we 
suppose that the cornea of the sound eye was turned up, whilst 
the other was in its fixed position ? 
Any one can confirm this fact by dosing his eye-lids and 
