SPECTACLES. 389 



The net-work A B C is called the 

 retina, and the projecting part DEF 

 is called the cor'uea. 



Q. What sort of GLASSES do NEAR-SIGHTED 

 persons wear? 



A. If the cornea be too convex (or 

 projecting), the person must wear double 

 concave glasses, to counteract it. 



Q. What is meant by "DOUBLE CONCATE 



GLASSES ?" 



A. Glasses hollowed in on both sides. 



S 



The figure A is double concave, or concave 

 on both sides. 



Q What is meant by the "IMAGE of objects 

 being reflected BEFORE it reaches the RETINA ?" 



A. If the cornea be too convex, the 

 image of a distant object is reflected (on 

 the vitreous humours of the eye) before it 

 reaches the ret'ina. 



Thus the image is reflected at 

 DE, instead of on ABC (the 

 ret'ina). 



