Rtfrangibility of Light. 149 



water, you will find that the shilling will be ren- 

 dered perfectly visible, though in fact neither you 

 nor it have changed places in the slightest degree. 

 Let it be remembered, that it is only the rays 

 which fall obliquely that are thus refracted; for a 

 ray which falls perpendicularly is equally attract- 

 ed on all sides, and therefore suffers no refrac- 

 tion at all. To illustrate this by the experiment 

 which has just been mentioned. You must know 

 that it is by light reflected from it to your eye 

 that any object is rendered visible : you see the 

 shilling in the bason, therefore, by rays of light 

 which are reflected from its surface. Now the 

 angle of incidence and the angle of reflection are 

 equal ; and as you stand in an oblique direction 

 to the shilling, you see it, while the bason is 

 empty, by rays of light which fall upon it in a 

 direction exactly as oblique as that in which your 

 eye is situated towards it. The shilling, then, 

 which before was hid from your sight, is ren- 

 dered visible by pouring in the water, because the 

 rays of light, which serve to render it then visi- 

 ble, are bent out of their course. Thus the ray 

 of light, AC, pi. XII. (fig. 48), which passes ob- 

 liquely from the air into water at C, instead of 

 continuing its course to B, takes the direction 

 4, .and consequently an object at a would be 

 Tendered visible by rays proceeding in that direc- 

 tion, when they would not have touched it, had 

 .they proceeded in their direct course, 



