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and has n ° connexion of itself with i the opposite extremities , where the I Kody which is the object of vision is situated . Philosophers have heuce ' been led to suspect that there existed
pome intermediate agent , serving : to connect the impressions produced by the rays which bodies send to the eye , with the modifications of those bodies themselves . They imagine that touch , or the sense of feeiing is in some way
or other instrumental in instructing the eye and enabling us to correct r | ie errors into which we should be led hv this organ , when left to itself . This has been explained after the following manner , by M . Condillac , in his ? ' Traite des Sensations . ' *
Our first lessons , are derived from the various motions which the hand makes that has its own image in the bottom of the eye , While in turns it approaches nearer to or withdraws farther from this organ , it teaches us
to refer to a greater or less distance to one place than to another , the impression that is produced on the retina , from the knowledge we have of the position of the hand , arjd of the direction and extent of every irjovement which it makes . While one hand
passes over the other , it conveys , in a manner , over its surface , the colour of which the impression is in the eye ; it circumscribes this colour within its limits , and excites in tjie mind the representation of a body shaped in such a manner . Afterwards when
we touch different objects the hand directs the eye over the several parts of each of them , and renders tire arrangement and respective positions sensible to it . It acts incessantly with
regard to the eye , by means of the fays of light , as if it held one extremtyof agtick , of which the other end touched the bottom of the eye , and s ^ ded this stick in succession over
ey ery part of the object . It seems e ? en to inform tjie eye that the point rt touches is the extremity of the ray w wh strikes that organ ; and thus wpile it runs over the surface of the otyect , it seems to pronounce its true orm . When once the eves are inructed
s , the experience they have ^ qui red enables them to do without &e help of touch , and the presence oftlf ° ° * i € ets -occasions the return be sam e sensations , whea the rays Mmif *^ frottl tuti se ob 3 *** ' mafcc Uar ^ pressious on the organ , JVLl
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At the same time that the sense of feeling instructs the eye with regar 4 to the images of objects , it exercises it also in the art of estimating their
position in space , their size , and their distance ; and when this distance exceeds that to which the motion of the hand extends , we supply the defect by another exercise , which consists
in approaching towards the object till we touch it , and then receding froin it again ; and by the extent of these contrary movements we ascertain its . distance with a degree of accuracy quite sufficient for all common pur ? poses . When the object exceeds the
compass of our ordinary movements , the proportions we are accustomed to remark serve as rules by which to apply to more remote objects the im ? pressions that are made upon us ; but as the distance increases , circumstances
become less favourable to such appli ^ cations , and beyond a certain limit objects present themselves more or less under a deceitful appearance , and we are led into that kind of errors calle 4 optical delusions .
Having given this brief account of the manner , or supposed manner of vision , we shall proceed to observe , that we cannot contemplate the struct tyre and uses of this organ without admiration of the power , the wisdom ,
and the goodness of the Creator , e& ? pecially when we consider the prodi * gious exactness , and exquisite skill employed in every part , administering to this noble and necessary oFgane To pass over the arteries and veins , and other parts that are common to the
rest of the body let us reflect on its , several muscles , which are placed , so as to be adapted not only to every possible motion of the eye , but each is . endowed with such an exact degree of strength , as to cause the most perfect equilibration * by which all
contortions of the eye are prevented , and it can with the utmost readiness apply itself to every object . Again , tjie tu ^ nics or coats are so admirably seated ^ and of so firm a texture , as to fit every place , to answer every occasion , and to be proof against all common
inconveniences and annoyances . In the humours also , we find all the requisite clearness and transparency , fbr an easy admission of the rays of light ^ well placed for refracting them , ami farmed , by the uicest laws of optics to collect the wandering rays into a
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Natural Theology . No . Ill * —On the Eye * jftj
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T Jk r y
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Citation
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Monthly Repository (1806-1838) and Unitarian Chronicle (1832-1833), March 2, 1815, page 161, in the Nineteenth-Century Serials Edition (2008; 2018) ncse.ac.uk/periodicals/mruc/issues/vm2-ncseproduct1758/page/33/
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