40 NOTICES OF THE. MEETINGS [March 14, 
the movement is spontaneous and not willed. For instance, a ray of 
light falling on the sensitive surface at the bottom of the eye (retina) 
produces a contraction of the pupil, a movement of which we are en- 
tirely unconscious. Irritation of the lining of the nostril is followed by 
an irresistible tendency to motion for removing it (sneezing). Ina 
still higher series, we have the mechanism brought out by conditions 
more complex than mere sensations. The emotions, anger, joy, 
sorrow, though based upon the psychical constitution, yet have a 
mechanical expression independent of the will; the contraction of the 
muscles of the face varying precisely according to the kind and de- 
gree of the emotion, and thus forming a language which we instantly 
read, a language which is unchangeable and universal, and without 
compact or imitation. 
From this substratum of natural actions, we pass to such as 
are voluntary, over which we feel we have power. These, as we have 
previously seen, are also related to external impressions. It has been 
stated that the elements of the motor mechanism are not directly 
submitted to the will, and that we require an objective impression 
or an objective design to guide us. If the objective impressions 
are confused, our volitional power is for the time disturbed ; hence, the 
unsteadiness which follows upon looking at a moving object, as a 
railway carriage in rapid motion, when we are so near to it that it ex- 
cludes objects at rest ; hence also much of the unsteadiness which fol- 
lows upon ordinary giddiness. The office of sensation as a guide to 
our voluntary movements and as suggestive of them is also well illus- 
trated in the teaching of deaf-mutes. The muscular system of the 
organs of voice in these persons readily obeys the stimulus of phy- 
sical or emotional impulses, for they cry and shout; but it lies 
unused as an instrument of volition, until through the suggestion of 
the sense of touch its vibrations are excited, afterwards to be vocalized 
into speech by the imitative teaching of the eye. Although by the 
aid of these two senses mutes may be taught to use the muscles for 
speech, yet their voice never fails to show a want of delicate direction, 
which the ear can alone supply; hence the monotony of their ex- 
pression so characteristic of this deficiency. 
As the rays of light by which we acquire a knowledge of external 
objects are inverted in the eye, so that images are painted reversed, 
it has been a problem of difficult solution to account for the corre- 
spondence of the impressions received through the eye, with those 
received through the touch; for it is obvious, that any want of cor- 
respondence must of necessity lead to confusion. There are some 
circumstances connected with the subject of voluntary movement 
now under consideration, which bear upon the explanation of this 
seeming contradiction. The eye presents us with two sensitive 
surfaces — the anterior and exposed part having sensation common 
to that of the surface generally, and the posterior and deeply seated 
part for the reception of luminous rays (the retina), having its own 
special reaction. By the rotation of the globe upon its axis, these 
