Fig. 5. 
displacement which 
they undergo is too 
small to be shown in 
the figure, and is 
altogether unimport- 
ant. 
Second : the ex- 
treme rays from each 
pencil cross each oth- 
er in the borders of 
the objective. 
Third : the rays is- 
sue from the pos- 
terior combination 
slightly over-correct- 
ed for color, so that 
if no other lens in- 
tervened a blue im- 
age would be formed 
at B B, and a red 
image at K K, wliile 
other images, with 
intermediate colors, 
would fill up all the 
space between B B 
and K E. 
In a single convex 
lens, as we have seen 
in § 10, the blue im- 
age is formed nearer 
to the lens than the 
red. 
This slight over- 
correction of the ob- 
ject-glass,really much 
less than shown in the 
Note, — T he course of 
rays shown is not strictly 
accurate, but such as to 
show correctly the princi- 
ples referred to in the de- 
scription. 
