OPTICAL IMAGES. 
by a simple and homogeneous red light placed before a convex 
lens A c, fig. 31, and that an image of it is produced at r r\ Let 
Fig. 31. 
R 
the same object be now supposed to be illuminated by simple and 
homogeneous orange light. This light being more refrangible 
than red light, the lens A c will produce an image o o' of the 
object, a little nearer to it than rr\ If the object be next 
illuminated with simple and homogeneous yellow light which is 
still more refrangible, the image y y' will be produced at a still 
less distance from the lens, and in fine if the object be successively 
illuminated with simple green, blue, indigo and violet lights, the 
images will be produced successively at g g' } b b ', % i', and v v% 
nearer and nearer to the lens as the light is more refrangible. 
57. If the object, instead of being illuminated as we have here 
supposed it to be by a simple homogeneous light, be illuminated 
by any light compounded of two or more simple lights, then so 
many distinct images of it will be produced at different distances 
from the lens, as there are simple lights in the compound, and 
these images will differ in colour from the object and from each 
other. Thus, for example, if the object be illuminated by a 
compound light of a green tint, composed of simple yellow and 
blue lights, two images of it will be produced, the nearer blue, 
and the more distant yellow. 
A like consequence will follow if the object be illuminated by 
a compound light made up of three simple lights, when three 
images will be formed, and so on. 
If then an object reflect from its surface the white solar 
light, which is a compound of all the colours, it will follow that 
all the coloured images which have been here produced in succes¬ 
sion, will be produced at one and the same time, and will be 
placed one before the other in a regular series at unequal distances 
from the lens, as already described. 
58. It has been shown* that the colours of natural objects 
generally are more or less compounded. It is only in very rare 
* See Tract on 11 Colour.” 
110 
