ANIMAL MECHANISM. 123 



in a greater distance than most quadrupeds. There are 

 many curious observations illustrative of what we have just 

 said. He says, he threw, at a considerable distance from 

 a throstle or mavis ( Turdus musicus) a few small beetles, 

 of a pale gray color, which the unassisted human eye 

 could not discover, yet the throstle observed them imme- 

 diately, and devoured them. The long tail titmouse 

 (Parus Cordatus) flits with great quickness among the 

 branches of trees, and finds on the very smooth bark its 

 particular food. When we examine the spots where it 

 stops for food, nothing is perceived by the naked eye, 

 although minute insects are visible by means of the 

 magnifying glass. A very tame redbreast (Sylvia rebecula) 

 discovered from the height of the branch where it usually 

 sat, at the distance of eighteen feet, small crumbs of 

 bread spread out on the ground, the instant they were 

 thrown down ; and this, by bending its head to one side, 

 and therefore using only one eye. A quail, at the same 

 distance, discovered, by the use of only one eye, some 

 poppy seeds. 



A REASON WHY PERSONS IN ADVANCED LIFE, REQUIRE 

 CONVEX GLASSES. 



Age gradually relaxes the tension of the whole system ; 

 the eye, therefore, suffers in a corresponding ratio. The 

 cornea becomes less prominent : the convexity of the 

 lens is also diminished, and the rays of light are conse- 

 quently less convergent than formerly. The picture of 

 the object is faint, because the rays have a tendency, by 

 their divergency, to impinge at a supposable plane, be- 

 yond the retina. 



FIG. 11. 



Explanation of Figure 11. 



In this figure is represented the effect of old age on the 



humors: without the intervention of the glass A, the rays have 



