Transactions . ic eye. The possibilities as to size of a circle of diffusion when projected,would be any diameter between 5 nun. and 125 cm., since, if the twowires were made to cross at the anterior focus of Bonders eye 15mm., their distant points would be apart 125 cm. and the two pointswithin the eye would be apart 5 mm. ; the similarity of the largeand small angles being assumed as the basis for these hypotheses. The apparent enlargement of a small distant point of light to anametrope metaphorically resembles the separation of the two wiresanterior to the eye, whilst the divergence at the
Transactions . ic eye. The possibilities as to size of a circle of diffusion when projected,would be any diameter between 5 nun. and 125 cm., since, if the twowires were made to cross at the anterior focus of Bonders eye 15mm., their distant points would be apart 125 cm. and the two pointswithin the eye would be apart 5 mm. ; the similarity of the largeand small angles being assumed as the basis for these hypotheses. The apparent enlargement of a small distant point of light to anametrope metaphorically resembles the separation of the two wiresanterior to the eye, whilst the divergence at the points within the eyeis like the circle of diffusion which falls on the ametropes directions of the anterior wires, whether they diverge from thecornea and if continued backwards would meet behind the retina, orconverge in front and cross at some point, give us the direction ofthe rays of light in H. or M., and the distance from the eye to such])oints of junction would be the piiiu-tiiin The convergence of the wires at a distance of 15 mm., the anteriorfocus of Donders eye, resembles a M. of that degree, and wouldrender parallel the jaws within, separate the ends 5 mm., and beattended by a separation of the anterior extremities of 125 cm., vide fig. 2. Assuming that a small light at 5 ni. is focussed on the retina ofBonders eye, let us reason upon the results of a condition of produced by a + glass giving a pnnctiim remotum of 25cm. : the image of the light would now be a circle of diffusion, whichwould diminish as the light point was l)rought near, and come to a 46o focus when it reached a distance of 25 cm. or about 10, and therays had become divergent. We may now say as 250 mm. thelength of the induced radius : 5000 mm. the length of the largeradius :: 5 mm., the arc of small angle : the answer, being 100 mm. ;and hence we find by calculation that the circle of diffiision shouldappear by projection to be 100 mm., or 4 in diameter. It w
Size: 2252px × 1110px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1860, booksubjectophthalmology, bookye
