Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . projectedon a sheet of paper. * [Volkmann instituted many very ableexperiments upon the condition of retinalimages, and from this inferred the focal experiment easily performed is the fol-lowing :—Upon an horizontal table let a num-ber of straight lines (fig. 39) a a, b b, &c.,he drawn, all of which intersect at the pointc; upon this point, c, let a prepared whiterabbits eye, E, Y, E, be so placed, that theaxis of the eye coinci
Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . projectedon a sheet of paper. * [Volkmann instituted many very ableexperiments upon the condition of retinalimages, and from this inferred the focal experiment easily performed is the fol-lowing :—Upon an horizontal table let a num-ber of straight lines (fig. 39) a a, b b, &c.,he drawn, all of which intersect at the pointc; upon this point, c, let a prepared whiterabbits eye, E, Y, E, be so placed, that theaxis of the eye coincides with the line a7, the anterior part of the cornea, Y. stand atthe due distance from c, then will objects ata, &, d, e, /, form their appropriate retinalimages at a, 6, d, e, /. The chamberbeing darkened, let tapers be placed at «, 6,d, e, /, and the spectator look successively ata, from a, at 6, from b, at d, from d\ cVc.,and it will be found that the line of visionwill cut the retinal image of a, at a, of b, at&, &c. The retinal images of the whole ofthe tapers lie in straight lines, which intersectat the focal point, or SIGHT. 63 dioptrical media of the eye are appreciated, but all are notseen with equal distinctness. Images appear by so much themore indistinct, as they are formed more remotely from thepoint upon which the optic axis of the eye falls. This pointcorresponds very accurately to the foramen of the peculiar distinctness of vision at this point de-pends on the structure of the retina there, or is to be ascribedto this, that in the usual position of the eyes their axes are sodirected towards objects, that the principal rays from thesestrike through the centres of the lenses, remains latter view is, however, the more probable. For as thoserays of a pencil of light that strike through the edges of thelens must be differently refracted from those that pass throughits centre ; in consequence of the difference of density
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1870
