167 
Mr. Bell on the motions of the eye, &c. 
sion in the human face. But this admiration is in part 
misplaced, if given to the optic nerve and ball of the eye 
exclusively ; since these high endowments belong to the 
exercise of the whole eye, its exterior apparatus as much as 
to that nerve which is sensible to the impressions of light. It 
is to the muscular apparatus, and to the conclusions we are 
enabled to draw from the consciousness of muscular effort, 
that we owe that geometrical sense, by which we become 
acquainted with the form, and magnitude, and distance of 
objects. We might as well expect to understand the uses of 
a theodolite, or any complicated instrument for observations, 
by estimating the optical powers of the glasses, without con- 
sidering the quadrant, level, or plumb-line, as expect to learn 
the whole powers of the eye by confining our study to the 
naked ball. I propose to show, that we must distinguish 
the motions of the eye, according to their objects or uses, 
whether for the direct purpose of vision, or for the preserva- 
tion of the organ that the eye undergoes a revolving mo- 
tion not hitherto noticed ; that it is subject to a state of rest 
and activity, and that the different conditions of the retina are 
accompanied by appropriate conditions of the surrounding 
muscles ; that these muscles are to be distinguished into two 
natural classes ; and that in sleep, faintness, and insensibility, 
the eye-ball is given up to the one, and in watchfulness, and 
the full exercise of the organ, it is given up to the influence of 
the other class of muscles : and finally, that the consideration 
of these natural conditions of the eye explains its changes as 
symptomatic of disease, or as expressive of passion. 
