IMAGES BY INFRACTION. 
plainly enough the banks or shores reflected in ^the water; but 
if he lean over the bulwark, and look down, he cannot see his 
own image. 
18. In general, the illustrations and imagery of poetry, drawn 
from natural phenomena, are just and true. Yet this is not in^ 
variably the case. Every one will perceive from what has just 
been stated, that the fable of the Dog and the Shadow, which has 
been handed down through so many ages, diffused through so 
many languages, and taught so universally in the nursery and the 
school, is a most gross optical blunder. 
19. If a visible object be placed below a transparent body, as, 
for example, at the bottom of a reservoir of water, or attached to 
the lower surface of a plate of glass, an observer above will see, 
not the object itself, but an optical image of it, which will be 
nearer to the surface, or less deep than the object. A reservoir 
of water, a river, or a lake, or the sea, when not too deep to allow 
the bottom to be visible, will on this account always appear to be 
less deep than it really is, 
because the optical image 
of the bottom, which is in 
fact what the observer 
sees, is less deep than the 
bottom itself. After what 
has been stated above, this 
is easily explained. 
Let R (fig. 11) be a point 
of any object below the 
surface A c of any transpa¬ 
rent body. The rays R D, 
which diverge from r, will, 
after emerging, be deflected from the perpendicular in the direc¬ 
tions i) E, and will enter the eye of an observer as if they came 
from i, a point less deep than R. The point R will, therefore, 
be seen as if it were at I, and the same being true of all the 
points of the object, it follows that an optical image of the object 
will be formed at a certain depth below the surface, less than the 
depth of the object. 
This image will evidently be imaginary, since the rays by which 
it is produced diverge from the surface of the transparent body, 
but not from the points of the image. 
The greater the refracting power of the body is the more the 
•rays D e, emerging from the surface, will be deflected from 
the perpendicular, and consequently the nearer the point I of 
their divergence, or, what is the same, the image, will be to the 
surface. 
Fig. 11. 
M 
