J 12 ^h€ Art (//Farriery 



its Caufe is, there is a manifeft Advantage in the 



TheAdvan- Optick Nerves being inferted on the Infide of the 



O^tick^^^ Optick Axes; for if they had pierced the Eye, 



Nerves be- ^^'^^'^ ^^^ middle Point of every Obje6l had been 



jrginferced invifible. And where all Things conduce to make 



nn the in- us fee bell, there we had not feen at all . We muft 



oitkk ^^^ likewife have loft fome Part of an Objeft, if the 



Axes Optick Nerves had been placed on the Outfide of 



the Optick Jxes't becauie an Objedt may be fo 



placed as that all the Rays, which come from one 



Point, may fall upon the Outfide of both Eyes ; 



but it is impoffibie they fhould fall upon the Infide 



of both Eyes ; and therefore that Point which is loft 



in one Eye is vifible by the other. 



Hew Vifion All Rays of Light which come from one Point of 



is perforin- an Objed, are by the Cornea and Humours of the 



' Eye united in a Point of the Retina, which is in a 



ftraight Line drav/n from the fame Point of the 



Objeft through the Center of the Eye, and con- 



fequently all the Rays which come from all the 



Points of an Objeft are united on the Retina 



in the fame Order and Proportion as the Points 



of the Objeft are from whence thofe Rays come. 



Therefore the Interpofition which thefe Rays make 



upon the Retina muft be the Image of the Obje6l : 



And thus Vifion in general is performed. But to 



know what the feveral and diftin<51: Parts of the 



Globe of the Eye contribute hereunto, it is need- 



fill to obferve, that the Cornea is more Convex 



than any other Part of tlie Eye, by which Means 



all the Rays are gathered, fo that they may pafs 



through the Pupil or Sight of the Eye, and none of 



them be loft upon the Uvea. 



The Aqueous Humour being thinneft and moft 

 liquid eafily changes its Figure, when either the 

 Ligamentum Ciliure contradb, or both the oblique 

 TbeRealbn Mufcles fqueeze the Middle of the Bulb of the 

 ofthe.Con- £ j.^ ^^^^^^^ it oblonff, when Objeds are tco 

 tractionand ^ i-m n ■ i iV-i r ^ tt j-i 



Dilatation "^^^ "S- The ftraight fibres of trie Uvea dilate 

 of the Pupil, the Pupilla or Sight of the Eye, a$ it is commonly 



called^ 



