16 Professor Airy on the Spherical Aberration 



If equi-convex, /?= - - ^^ ; ■ If plano-convex, in the other po- 

 sition^ 



m , o 390- 



t)= — 



and R 



3' 108 M^' 



3d. If the second lens be plano-convex, the convex side toward 

 the first lens, v' = m, and ^' = ^ • ;^e • ^f equi-convex. 



If plano-convex in the other position, 



v = -m, andfl= — .■^. 



4th. The most favourable combination of common lenses is the 

 first equi-convex, and the second plano-convex, with its convex side 

 toward the first lens. This gives 



The next best is, the first plano-convex, its plane side toward the 

 object-glass, and the second equi-convex, which gives 



108 31- 



Next are, either two plano-convex lenses with their convexities turned 

 the same way (it is indifferent which way), or two equi-convex lenses, 

 all which give 



3th. When the second lens is plano-convex, its convex side 

 toward the first lens, the distortion will be destroyed if 



14 A^ 42 ,, ., 42 ,. 42 



19 29 



r=— M, s=--^M, or if r=^M, s=^M; 



