Spherical it* Chromatic Aberration. By Dr. Royston-Pigott. 283 
Also the spherical aberration for flint for red ray is proportionate 
to 
_ (1-62775) 2 _ 6-723.i0 
SO-1) 2 S (0‘62775) 2 8 
or red aberration in flint .. .. = 0-840450 
violet „ ,, = 0-775124 
Difference = 0-065326 
If these results be put in plain language, the spherical aber- 
rations of the red and violet rays in crown glass No. 9 are as 
105 to 100; 
and in the flint glass as 
84 to 77, nearly. 
Entirely calculated, be it remarked, from the spherical aberra- 
tion of the extreme red and violet rays in the two cases, which 
thus show the proportions of the chromatic spherical aberration. 
Moreover, the focal lengths of the same equi-convex lens, if of 
crown, are 
For the red and violet rays as 
190 to 183, 
and for the flint as 
159 to 149, very nearly. 
VOL. XIV. 
X 
