404 



A YEAR IN SCIENCE 



must be done in a different way. It is brought about 

 by a change in the shape of the lens. The lens is elastic, 

 and if left to itself it tends to become more convex. 

 It is fastened to the choroid coat by a ligament, known 



Fig-. 185. Diagram of the eye showing- the convex lens forming 

 an image by converging the rays on the retina. 



as the suspensory ligament. This is ordinarily 

 stretched tight and exerts a constant pull on the lens, 

 tending to make it thinner. By means of ciliary mus- 

 cles the choroid coat can be drawn forward. This 

 loosens the suspensory ligament and the lens becomes 

 more convex. This power of the eye to change the 

 curvature of the lens is called accommodation. 



The more convex the lens is, the more 

 it bends the rays of light. When an 

 object is near, the light rays from any 

 point of it spread out or diverge rapidly. 

 To bring these to a focus they must be 

 bent very decidedly. This can be done 

 when the lens is convex. Light from a 

 distant object comes to us almost paral- 



Fig. 186. Dia- 



frate changes^ lel ancl nence a flattened lens can bring 



the lens in ac- . 



commodation. it to a IOCUS. 



