. The refraction of the eye; including a complete treatise on ophthalmometry; . ; 3 mm. InFig. II is shown an enlargedview of the cornea, with themires reflected on it, as seenthrough the telescope. Now, if the distance be-tween the right-hand edge of the primary image of the stepped mire A, and the right-hand edgeof its secondary image A, is exactly 3 mm., and if the right-hand edge of the secondary image A i^ exactly in contact with theleft-hand edge of the primary image B, of the other mire, it is at. Fig. II. 4j4 THE KEFRACTIOX OF THE EYE once CTident that the distance between tlie inner e
. The refraction of the eye; including a complete treatise on ophthalmometry; . ; 3 mm. InFig. II is shown an enlargedview of the cornea, with themires reflected on it, as seenthrough the telescope. Now, if the distance be-tween the right-hand edge of the primary image of the stepped mire A, and the right-hand edgeof its secondary image A, is exactly 3 mm., and if the right-hand edge of the secondary image A i^ exactly in contact with theleft-hand edge of the primary image B, of the other mire, it is at. Fig. II. 4j4 THE KEFRACTIOX OF THE EYE once CTident that the distance between tlie inner edges of the twomires on the arcs is equal to the size of the object which will giveon the cornea a reflected image 3 mTn. in diameter. Consequently,we have here all the means of calculati::i ureied to give as riieradial? cf curvature of the Qpmeal surface. • TIt mires are made movable on the arcs, one of them having azi-i z . _: :n cE. Fig- I i:r ^r \ -zient, so that the Of>er-::;:. ~_:^t : zinr fhroTigli zhe teles::^e. c:.ii slide the mires awayr: 11 :z -.:— : ^. r i. cTier. Tintil their two central images on the cor-- - ^ : : - 7- arcs are graduated on their inner edges:^ 1 ;:: r _l~ji^ : ^ iTi:i:rive power in diopters and quarters of apiano lens having rhe same curve as the corneal curve indicated bythe position of the mires. A scale is also provided on the otheredge of the arc. giving the zadins of the cornea. But, as the instm-niriir is i-ifzj isri ior diagnc^ing astigziarisni. ine li
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