. Quarterly journal of microscopical science . From which it is manifest, that however well defined anobject may be, and however assured we may feel t!iat its imagis actually portrayed on the bottom of the eye, it is not recog-nised unless the contiguous surfaces are oppositely affected withrespect to light and shade. The second experiment is the converse of tle last, and goesto prove that an image is visible onh/ whe)i the retina of the ci/eand the object are unequalhj illuminated. Let that portion of acommon sewing-needle which contains the eye be mounted ona slip of glass as if for the micr
. Quarterly journal of microscopical science . From which it is manifest, that however well defined anobject may be, and however assured we may feel t!iat its imagis actually portrayed on the bottom of the eye, it is not recog-nised unless the contiguous surfaces are oppositely affected withrespect to light and shade. The second experiment is the converse of tle last, and goesto prove that an image is visible onh/ whe)i the retina of the ci/eand the object are unequalhj illuminated. Let that portion of acommon sewing-needle which contains the eye be mounted ona slip of glass as if for the microscope; and let the j)aperwith which it is covered, have a very small circular aperturethrough which to examine it, thus (fig. 6) : Fig. ( On holding the object close to the naked eye, it is foundto be altogetlier invisible. Nothing is seen but vacant is matter of certainty, however, that the front ravs are in-tercepted, and that a shadow of the needle is tlierefore reallvformed, l)ut before reaching its destination, lateral rays streaminto the eye? in all directions, which neutralise the shndow,and so nothing is seen (fig. 7). VOL. IV. P 34 GORHAM, ON THE MAGNIFYING But when tliese lateral superfluous rays are excluded byusing a divergent pencil of light only, as in the diascope, theshadow becomes visible ; and not only is the exposed portionof the body of the needle seen, but its eye is well defined, andboth appear considerably magnified (fig. 8). Fig. 7.
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