OPTICAL IMAGES. 
But if, leaving the direction e I, it issue from the surface at I, 
it will be refracted from the perpendicular in in a direction 
such as i E. This is a law of refraction to which there is no 
exception. 
16. Light will enter a transparent body whatever may be the 
obliquity with which it falls upon it; but it must be remembered 
that a certain proportion of it will be reflected. This proportion 
is very small, when the light strikes the body with very little 
obliquity, but it increases as the obliquity is increased, and is very 
Considerable at great obliquities. 
17. This will explain a phenomenon which is familiar to every 
eye. A spectator stationed on the banks of a river or lake, as at 
s, fig. 10, will see the opposite bank and objects such as o upon 
it, reflected in the surface of the water, and will see in the same 
way distant boats or vessels, such as b, reflected, the images being 
inverted according to what has been already explained (6, 7). 
But he will not see any reflection of a near object, such as A, In 
Fig 10. 
the case of distant objects, such as o and b, the rays ob,b e, 
which proceed from them striking the surface of the water very 
obliquely, the part of the light which is reflected in the direction 
E s is so considerable as to make a very sensible impression on the 
eye, although it is far from being as strong as a more complete 
reflection would produce, as is proved by the fact of which every 
one is conscious, that the images of objects thus reflected in water 
are far less intense and vivid than images would be reflected from 
the surface of a looking-glass. 
As for objects, such as a, placed near the spectator, they are 
not seen reflected, because the rays A e', which proceed from them, 
strike the water with but little obliquity, and consequently the 
part of their light which is reflected in the direction E's towards 
the spectator is not sufficiently considerable to produce a sensible 
impression on the eye. 
For this reason, also, a aerson on board a vessel may see 
90 
