122 ANIMAL MECHANISM. 



first point ; in the latter are inferior to the ox, elephant, 

 &-c. The chamoi and the Lynx, and many other ani- 

 mals, have a wider power of vision than man, in which 

 the radius of the sphere of distinct vision is much smaller 

 than in him. 



This conclusion is contrary to the -generally received 

 opinion on the subject. Birds, and particularly rapacious 

 birds, are considered as having a much greater power of 

 distant vision than most quadrupeds ; and many will be 

 disposed to challenge the fact, that the ox possesses this 

 power in an equally high, or even higher degree. But 

 when we consider fairly the experience on this subject, 

 we shall find that it is not in opposition to what has just 

 been stated. Mayer found in his experiments on the 

 acuteness of vision, that, in seeing, it depends not only 

 on the illumination of the object, and its distance from 

 the eye, but also on the relation of the object and the eye 

 to the neighborhood. But it is quite otherwise with birds 

 which look from above, downwards, or with quadrupeds, 

 whose vision is directed upwards or forwards. No one 

 has measured the great distance at which a far-seeing bird 

 perceives its prey ; and indeed it will always be difficult 

 to do this with accuracy. But Treviranus remarks, ' I 

 doubt not, if we possessed certain observation on this 

 point, that the greatest distance would not exceed that of 

 a far-seeing man. 



When, for example, Faber, in proof of the sharpness 

 of the sight of birds, remarks, ' the high flying eagle or the 

 kite perceive the motions of small animals on the ground ; 

 the solan sees a very small fish from a considerable 

 height ; and gulls, terns, rapacious gulls, '(Lcftri,) and 

 petrels, fly from all sides to a particular point, where 

 an object is seen floating on water ; he presents us with 

 data which are far from being satisfactory. When, on 

 the contrary, Ross affirms, in his voyage to Baffin's Bay, 

 that he obtained certain data, proving that the power of 

 vision of man over the surface of the sea extended to 150 

 English miles, it is conceivable that the farthest seeing 

 bird could not exceed this. But experience would seem to 

 show, that birds, although in general their power of distant 

 vision is not very great, that they possess a very sharp sight 



