1851.] OF THE ROYAL INSTITUTION. 41 
surfaces are necessarily moved at the same time in opposite direc- 
tions as regards superior and inferior. This inversion of movement 
produces a correspondence between impressions made upon the 
surface of the body and those which result from the stimulus of 
light upon the retina; for the same movement which directs the 
transparent and exposed surface upwards, also brings the retina 
downwards into those rays of light, which, coming from above have 
undergone inversion in the eye by refraction.— But if the same 
voluntary movement places both sensitive surfaces in the same 
relation to the object, there can be no want of correspondence. 
In no instance in the body is the connexion between sensitive 
surface and muscular movement more exact, than in the necessary 
convergence of the optical axes of the two eyes upon the same 
object, in order that we may receive a single impression. This 
necessary consensual movement seems to lie at the foundation of a 
curious and hitherto unexplained arrangement in the nervous system. 
It is well known that the right hemisphere of the brain presides 
over the movements of the left side of the body, and the left hemi- 
sphere over the right side of the body. It is equally determined 
that the left optic centre (optic lobe) is in relation with the right 
eye and vice versd: so that blindness of the opposite eye follows 
upon disease or injury of either optic lobe. By means of this 
crossed relation (the third pair of nerves being an exception) the 
eyes are by the action of one hemisphere made to converge upon 
an object when it is situated either to the right or left side with 
the same facility as when the object lies directly in front of the two 
eyes and affects both hemispheres. 
The relation of objective impressions to animal movements seems 
to be an essential one. In the lower series of such phenomena (the 
physical, aisthesical, and emotional,) external impressions are sufh- 
cient, without any implication of the will, to bring out their naturally 
associated results; but in the exercise of volition, though sensation 
takes a subordinate position as a cause, it has an essential office as 
guiding us to the instinctive use of that complicated arrangement 
of parts, of whose existence we are naturally ignorant, and which 
rightly to know challenges our highest efforts.— And not only does 
sensation thus guide us in the beginning, but when our voluntary 
actions have been often repeated, it stands in a yet closer relation, 
and forms the basis of habit, so far as it depends upon mechanical 
skill. By habit, the suggestions of sense call forth the most com- 
plex movements, and so spontaneously that they seem the expressions 
of a natural law requiring only the assent of the will for their per- 
formance. W. W. G. 
In the Library, were exhibited : — 
A Chinese Sun-dial and model of a Chain-pump; and Chinese 
and Hindu playing-Cards; Chinese Document, with’ the Em- 
