Fig. 36. 
Fig. 37. 
OPTICAL IMAGES. 
-4- 
CHAPTEE III. 
63. Experimental illustration.— 64. Dispersive powers.— 65. Dispersive 
power does not necessarily increase with refractive power.—66. 
. . Example of the diamond.— 67. Achromatic lens.— 68. Achromatic 
combination of flint and crown-glass.—69. Form of the compound 
lens. 
63. To make this, which is a circumstance of the highest 
importance, more clear, let Li, fig. 32, and x/ l', fig. 33, be two 
lenses, the former of diamond, and the latter of glass, and let o o 
and o' o' be a white object placed at the same distance before them. 
Let v be the violet, and n the red image, produced by the lens 
L l, the images of the intermediate colours being between v and r 
according to what has been explained above. Now let us suppose 
that such a convexity is given to the lens l' i/, which is evidently 
always possible, that the distance of the, violet image v' of o' o' 
from the lens l' l' shall be equal to that of the violet image v of o o 
Lardner’s Museum op Science. i 113 
No. 84. 
