A NEW OPHTHALMOSCOPE. 



91 



/'»J2 



nation, but other rays proceed to de, 

 where they are incident on the lens H 

 by which they are refracted, and they 

 would proceed to a focus at the priuci- ^___ 

 pal focal distance of the lens H (viz., at { C 

 P at five inches) but they are again ^,^^:i:^^^Z 

 intercepted at fg by the lens I, which i 

 refracts them to an earlier focus, at h. 

 In the same way rays from i, on E's 

 retina, proceed from the cornea parallel 

 to the axis iTcm and are also refracted 

 by the lenses H and I, and are brought 

 to a focus at o. In like manner all 

 points intermediate between i and a, on 

 E's retina, are reflected from the fundus, 

 andj refracted by the lenses forming an 

 inverted image of ia at oh, which is re- 

 ceived upon the ground glass placed at F. 



t(hhJ» 



Fig. 4. 



ADVANTAGES. 



The advantages I claim for this instrument are : — , 



1st. The simplicity of its construction, taking into consideration 

 its twofold purpose, namely, as an ophthalmoscope and as a phota- 

 graphing instrument. My friend Dr. Noyes, of the New York Eye 

 Infirmary, constructed an instrument for photographing the fundus 

 oculi, and which was, I believe, to a considerable extent successful, 

 but its construction was too complicated and the instrument too ex- 

 pensive to be generally adopted. Dr. Noyes' instrument is constructed 

 somewhat on the principle of the binocular microscope. Any good 

 optician can construct this new instrument. The one I exhibit to the 

 Institute was made by Charles Potter, No. 20, King-street East. 

 They can be had complete for $10. 



2nd. The limited experience necessary in order to use it success- 

 ftiUy. ^he ordinary Ophthalmoscope requires months of practice 

 before it can be used satisfactorily. 



3rd. Being able to see the aerial image free from reflections from 

 the object lens, which reflections are serious obstacles to beginners. 



4th. Being able to receive the image either of a healthy or diseased 

 fundus upon a screen of ground glass, which can be seen by a number 

 of persons at the same time, and can be taken advantage of by gen- 



