THE OBJECTIVE. 29 



We obtain from the above, for the combination of botli lenses, 



,o=-l=|,'=-l -_|,,. ,-*- + ;!: 



further 



g = vPf + 1 .. | X I ' + 1 '- + . , 



55 25 



i = r + i = _ | x | + i = + | , 



bo ,3 



5 31 3 13 



*"* + "' ' 6 X 25 + 6" -SO' 



For the cardinal points of the double-lens, therefore, 



30 



= ^ + 1 ' 8173 ' 



25 _ jg_ 30 . 180 



1O OK 1 Q ~ QOK 



Ad 10 fjZO 



" 30 

 ! 4 -*. + ! 53846, 



on 



= = 2-3077. 



Second double-lens. Let r = 4, d = , rf r = r ; 



o 3 



then 



e = ^ 3 + ~ , i" = ^ 4 , e' = JV 2 



From this 



# = d + 1-01803 = J^-+ 1-43469 

 /' = ^ + -6193 = N 5 + -1487 

 = 8-77347. 



