24:0 BY ROOK AND BY CROOK. 



objects at various distances, a result which is achieved 

 in the telescope by varying the length of the tube, or, in 

 other words, the distance separating the glasses. 



As proof of this, if the eye when employed with a 

 near object be suddenly lifted to another farther off, it 

 will be noted that a moment will be required to 

 correctly focus the new picture. 



It is diflficult to determine the range of a fishes 

 vision as regards submerged objects, for opportunities 

 of observation are of rare occurrence; perhaps that 

 afforded by a bridge is as good as most, as the fish, 

 having become accustomed to the structure and its 

 traffic, behave in a natural manner. 



From such observatories we have remarked that 

 natural or artificial flies do not attract the attention of 

 fish until within the range of a few feet, suggesting the 

 inference that they have no very extensive vision ; like- 

 wise they will remain stationary until the close ap- 

 proach of a boat, but they are easily shifted by a person 

 wading, unless he come upon them from behind. 



When wading up stream to command a particular 

 catch we have accidently waded right over fish, and 

 have only become aware of the fact by their haste to 

 escape ; but fish see very badly any object approaching 

 from the rear, as their eyes are not set for the purpose, 

 and their habit is to watch for objects floating with the 

 stream. 



The facility with which fish discern objects on or 

 above the surface of water is another matter, as doubt- 



