Siiherical & Chromatic Aberration. By Dr. Houston-Fig ott, 283 
Also the spherical aberration for flint for red ray is proportionate 
to 
_ (1-6277 5)- _ 6-723r,0 
8 (yii - 1)2 ~ 8 (0-62775)2 ~ 8 
or red aberration in flint .. .. = 0-810450 
violet „ „ .. .. = 0-775124 
Difference .. = 0 -005326 
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; V . ': '-^ 
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 
