EYES OF DIFFERENT ANIMALS. 89 



which, therefore, does not allow any reflection of light 

 from one part of the interior of the eye to another. 

 The eyes of night animals are, on the other hand, with- 

 out this, or have it light-coloured, by which means 

 lights are reflected within the eye. Each of these 

 adapts the animal to the time at which it is abroad : 

 the owl cannot see in the bright sun, because the image 

 of the object, to which its eye is turned, is confused by 

 the reflection, from the inner surface of the eye, of all 

 the images of surrounding objects ; and the eagle can- 

 not see in the dark, because of the deficiency of light, 

 in consequence of none of the side lights being reflected. 

 Each, however, can see more perfectly in its own 

 element than if it had the opposite contrivance. Be- 

 tween animals that live in the air, and those that live in 

 the water, there are differences equally curious. The 

 contrivance, by which the light that enters at the fore- 

 part of the eye is so managed as to produce vision, is 

 similar to that by which the sight is improved when we 

 use spectacles or telescopes. There are certain trans- 

 parent parts of the eye which are thinned off toward 

 the sides, and left thick in the middle, as is the case 

 with those glasses or lenses, of which telescopes and 

 other optical instruments are composed. Those natural 

 lenses, by making the rays or points of light that come 

 from the outsides of objects more rapidly approach 

 each other within the eye, make the object appear to 

 occupy a much greater space than it otherwise would. 

 Thus they magnify it, and of course make all the parts 

 more distinct; as, if in looking at any surface, that 

 of the moon, for instance, the rays from the extremities 

 be made to contract twice as much, the surface will 



