34 Professor Airy on the Spherical Aberration 



1 1 



„ /I iV /I »i+i\ s '^ C s 



+ «-. 7? -1. (- + -).(-+ ) • T -aba: 



Vs x/ Vs nx / I 1 



taking the reciprocal and subtracting it from RM, and substituting as 

 .before for x. 



Mm=S-." 



+ 



( ^ 1 



-1 1X1 iV S "^ g ><1 M + I X 



71' )\7 "*■ 6/ ■ 1 1 Vr "^ fl y 



Now Mm : MS :: sin MSm : sin SmR :: Gg : RG nearly 



1 j_ 



Sa . a -^ 



1 J_ 



1 1 Sa 



«, n— 1 1/1 1\' /I n + l\ /I l\- /I n+l\i 



= z'.i^\r.a'. 



And OT may be considered equal to MS: putting, therefore, for OC its 

 value. 



