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" and very often both tliefe colours are found in the fame eye. It has 

 " been obferved, that in general, thofe, whofe hair and complexion 

 " are light coloured, have the iris blue or grey ; and on the contrary, 

 " thole whofe hair and complexion are dark, have the iris of a deep 

 " brown: whether this occafions any difference in tlie fenfe of vifion, 

 " is not difcoverable. Thofe eyes which are called black, when jiar- 

 " rowly infpe6led, are only of a dark hazel colour, appearing black, 

 *' becaufe they are contraftcd with the white of the eye. The black 

 " and the blue are the molt beautiful colours, and give mod fire and 

 " vivacity of expreflion to the eye. In black eyes there is more 

 " force and impetuofity ; but tlie blue excel in fweetnefs and delicacy. 



" The pupil of the eye has no determinate fize, being greater or 

 " fmaller, according to the quantity of light that falls upon the eye. 

 " Wiien the light is ftrong, or the vifual objedl too luminous, we con- 

 " tra6l the pupil, in order to intercept a part of the light, which 

 '• would otherwife hurt or dazzle our eyes ; but when the light is weak, 

 " we enlarge the pupil, that a greater quantity may enter the eye, 

 " and thus make a ftrongcr impreflion upon it. This aperture dilates 

 *' alfo for viewing diftant obje6ts, and becomes narrower for fuch as 

 " are near. The contraction of the pupil is a ftate of violence, 

 " effected by an exertion of the will : the dilatation is a remiffion of 

 " power, or rather an intermiffion of volition. The latitude of con- 

 " tra6lion and dilatation of the pupil is very confiderable ; and it is 

 " very admirable, that while the pupil changes its magnitude, it pre- 

 " ferves its figure. 



" Anatomills are not agreed, whether the iris be compofed of two 

 " fets of fibres, the orbicular and radial, or of either. Haller fays, 

 " he could never difcover the orbicular fibres, even with a microfcope ; 

 " the radial i'eem vifible to the naked eye, and are fufficicnt to an- 

 " fwer all the purpofes required in the motion of the iris : when the 

 " pupil is contracted the radial fibres are Ilrait, when it is dilated, 

 " they are drawn mto Terpentine folds. 



