492 THE OUTGO OF ENERGY 



by placing the appropriate lens before the opening 

 in the mirror. 



As the eye is approached, the details of the 

 fundus will come into view. Find the optic disk. 

 Trace the branches of the central artery and vein 

 which perforate the disk. The image of these 

 parts is virtual, magnified about sixteen times, 

 and erect. 



2. Copy Construction 2, page 485, in which 

 two reduced eyes are placed on the same visual 

 axis facing each other. At the anterior prin- 

 cipal focus of the subject's eye draw a concave 

 mirror of 175 mm. focal distance with an aper- 

 ture of 2 5 mm. through which passes the visual 

 axis. 



The rays converging from the mirror and pass- 

 ing through the pupil are still further converged, 

 and are brought to a focus in the vitreous, 

 whence they diverge to fall in dispersion circles 

 upon the retina, a large area of which is thus 

 illuminated. 



Draw rays reflected from the retina to the 

 pupil of the subject's eye. They must emerge 

 from the eye parallel. Entering the observer's 

 eye, with accommodation relaxed, they will be 

 brought to a focus on the retina. Show by a 

 construction that the image of the optic disk 

 formed in the observer's eye will be inverted but 



