37^ '' Mr Charles Bell on the Motions c^the Eye. 
tions of the eye. Principally from respect to that learned body^ 
I did not enter into all the details necessary to complete the 
subject incidentally stated. Dr Brewster^ in a paper read in the 
Boyai Society of Edinburgh, has made his remarks on these 
papers very freely, and has persuaded himself, that, by rendering 
suspicious some of the illustrations of my system, he has under- 
mined the whole. In proceeding to ^how how inapplicable his 
criticisms are, I shall, at the same time, expose the inaccuracy 
of his alleged scientific facts.” 
I am not a little startled to find- myself unexpectedly opposed 
to a man of Dr BrewstePs philosophical habits, and I am very 
reluctant to go into an element where he is so familiar. But I 
have sometimes found very little meaning invested with scienti- 
fic form, and I think I shall show, in the present instance, that 
the truth is more obscured than illustrated by phrases and dia- 
grams, which deter the general reader from entering on the sub- 
ject. 
It will be necessary, in the first place, to assign due import- 
ance to the sense of muscular exertion; a subject which Dr 
Brewster treats, not only with inaccuracy, but with such chasms in 
the course of his argument, as to throw obscurity over the whole 
matter. I shall then examine the optical phenomena ; where 
the inaccuracies are such, that were I interested in the discus- 
sions in which this gentleman is engaged, I should hold it to be 
a duty not to leave one of his positions, however wrapt up in 
the form of mathematical reasoning, without a thorough exami- 
nation. 
My original statement was to this effect : That not only are 
our ideas formed by a comparison of the different signs present- 
ed to us through the senses, but that there is a power in the 
body, which, though not called a sense, is superior to all the 
senses, in the precision which it gives to our perception ; bestow- 
ing on us accurate ideas of distance, of space, of form, and sub- 
stance : That the muscular frame, and that sense which we pos- 
sess of the muscular frame in action, gives us this power : That 
the sense of vision in the eye is imperfect, until aided by mus- 
cular motion, as the sense of touch in the hand would inform us 
of nothing without the motions of the hand : That hardness, 
and softness, and smoothness, and angularity, are properties 
