IN THE DOUBLE ACHROMATIC OBJECT-GLASS. 557 



then let the radii O, R, = r„ 

 O3 R3 = r^, 

 and R, /', R, /', the tangents at R, and R„ 



R. M., = y„ 

 R3 M, = y,. 

 Distance R, R^ = z^. 



Also let m' = index of refraction. 



Then, as before, the angle of the virtual prism = z / 

 = ^ R, O, M, + ^R^Os M3 



•^- V q,R, 

 ^-1 



also JL- - H i_ 1 , 



And 1 =-J-_ 

 q^R2 q,R^-f, 



At^i \ jU^i 





'^-l 



q.R. n +7^"''-i77r) = 



1 ^-'^^^ . ,,. O'-i) 



4b 2 



t^ i^r^ 



