10 OBSERVATIONS 



arriving at the eye of a fish, as at O, is sufficient 

 to produce very great indistinctness and distortion 

 of the image of M P formed in his eye. 



(Perhaps indistinctness of vision may, on other 

 accounts, take place in the eye of a fish looking 

 through air. The crystalline and perhaps other 

 humours may not be capable of such comprehen- 

 sive adjustment as would enable him to see so 

 distinctly through air as he can through water). 



But long before a pencil of light, as NEL, 

 becomes horizontal it will not enter the water at 

 all ; consequently, although the fish at O may see 

 the upper part of the man situated at M P, he 

 will do so very indistinctly, and in a new position, 

 because the pencil NEOFM will be very much 

 refracted ; he will not see the part, N L, of the man 

 at all, because the pencil, NEL, does not enter 

 the water at all ; and he will see probably his 

 legs, LP, (in the clear water), because there is 

 neither refraction nor obstruction to prevent him. 

 So that the figure M P will, in the eye of the fish, 

 be cut up into two portions separated from each 

 other by a long unsubstantial interval. The appli- 

 cation of these two little theorems to the use of the 

 fisherman is too obvious to need pointing out here.* 



* This diagram is constructed on two well-known optical laws, viz. 

 first, the sine a. b. of the angle of incidence, A E f, of a ray of light 

 passing out of air into water, is always to the sine, c. d, of the angle 

 of refraction, C E e, as about four to three : and, secondly, light will 



