66 On Seeing at a Distance. 



cede quadi-upeds of similar magnitude, are inferior to them in 

 distant vision, and that man agrees with birds in this respect. 

 Thus the great owl (Strix bubo) ostrich, and golden eagle, ex- 

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

 &c. The chamoi and the lynx, and many other animals, 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 con- 

 sidered 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 

 in a 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 al- 

 so on the relation of the object and the eye to the neighbour- 

 hood. But it is quite otherwise with birds which look from 

 above downwards ox 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 re- 

 marks, " 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 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 {Lestri), and petrels, fly from all sides to a par- 

 ticular point, where an object is seen floating on water ; he pre- 

 sents 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 shew, that birds, 

 although in general their power of distant vision is not very great. 



